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Water deficit influences leaf transpiration rate and photosynthetic activity. The genotype-dependent response of the latter has not been assessed in sunflower (Helianthus annuus L.), particularly during the reproductive period when grain filling and lipogenesis depend greatly on photosynthate availability. To evaluate genotypic responses to water deficit before and after flowering, two greenhouse experiments were performed. Four genotypes—two inbred lines (PSC8, XRQ) and two cultivars (Inedi, Melody)—were subjected to progressive water deficit. Non-linear regression was used to calculate the soil water deficit threshold (FTSWt) at which processes (transpiration and photosynthetic activity) were affected by water deficit. In the vegetative growth stage, photosynthetic activity was affected at a lower mean value of FTSWt (0.39) than transpiration (0.55). However, in the reproductive stage, photosynthetic activity was more sensitive to soil water deficit (FTSWt = 0.45). We found a significant (P = 0.02) effect of plant growth stage on the difference between photosynthesis and transpiration rate thresholds and, a significant (P = 0.03) effect of leaf age on transpiration. Such results will improve phenotyping methods and provide paths for integrating genotypic variability into crop models. [ABSTRACT FROM AUTHOR]

We evaluated tolerances to salinity (10-2000mM NaCl) in three halophytic succulent Tecticornia species that are differentially distributed along a salinity gradient at an ephemeral salt lake. The three species showed similar relative shoot and root growth rates at 10-1200mM NaCl; at 2000mM NaCl, T. indica subsp. bidens (Nees) K.A.Sheph and P.G.Wilson died, but T. medusa (K.A.Sheph and S.J.van Leeuwen) and T. auriculata (P.G.Wilson) K.A.Sheph and P.G.Wilson survived but showed highly diminished growth rates and were at incipient water stress. The mechanisms of salinity tolerance did not differ among the three species and involved the osmotic adjustment of succulent shoot tissues by the accumulation of Na+, Cl- and the compatible solute glycinebetaine, and the maintenance of high net K+ to Na+ selectivity to the shoot. Growth at extreme salinity was presumably limited by the capacity for vacuolar Na+ and Cl- uptake to provide sufficiently low tissue osmotic potentials for turgor-driven growth. Tissue sugar concentrations were not reduced at high salinity, suggesting that declines in growth would not have been caused by inadequate photosynthesis and substrate limitation compared with plants at low salinity. Equable salt tolerance among the three species up to 1200mMNaCl means that other factors are likely to contribute to species composition at sites with salinities below this level. The lower NaCl tolerance threshold for survival in T. indica suggests that this species would be competitively inferior to T. medusa and T. auriculata in extremely saline soils. [ABSTRACT FROM AUTHOR]

We measured a diverse range of foliar characteristics in shrub and tree species in temperate rainforest communities along a soil chronosequence (six sites from 8 to 120 000 years) and used multilevel model analysis to attribute the proportion of variance for each trait into genetic (G, here meaning species-level), environmental (E) and residual error components. We hypothesised that differences in leaf traits would be driven primarily by changes in soil nutrient availability during ecosystem progression and retrogression. Several leaf structural, chemical and gas-exchange traits were more strongly driven by G than E effects. For leaf mass per unit area (MA), foliar [N], net CO2 assimilation and dark respiration rates and foliar carbohydrate concentration, the G component accounted for 60-87% of the total variance, with the variability associated with plot, the E effect, much less important. Other traits, such as foliar [P] and N: P, displayed strong E and residual effects. Analyses revealed significant reductions in the slopes of G-only bivariate relationships when compared with raw relationships, indicating that a large proportion of trait-trait relationships is species based, and not a response to environment per se. This should be accounted for when assessing the mechanistic basis for using such relationships in order to make predictions of responses of plants to short-term environmental change. [ABSTRACT FROM AUTHOR]

Resurrection plants can withstand extreme dehydration to an air-dry state and then recover upon receiving water. Tripogon loliiformis (F.Muell.) C.E.Hubb. is a largely uncharacterised native Australian desiccation-tolerant grass that resurrects from the desiccated state within 72 h. Using a combination of structural and physiological techniques the structural and physiological features that enable T. loliiformis to tolerate desiccation were investigated. These features include: (i) a myriad of structural changes such as leaf folding, cell wall folding and vacuole fragmentation that mitigate desiccation stress, (ii) potential role of sclerenchymatous tissue within leaf folding and radiation protection, (iii) retention of ~70% chlorophyll in the desiccated state, (iv) early response of photosynthesis to dehydration by 50% reduction and ceasing completely at 80 and 70% relative water content, respectively, (v) a sharp increase in electrolyte leakage during dehydration, and (vi) confirmation of membrane integrity throughout desiccation and rehydration. Taken together, these results demonstrate that T. loliiformis implements a range of structural and physiological mechanisms that minimise mechanical, oxidative and irradiation stress. These results provide powerful insights into tolerance mechanisms for potential utilisation in the enhancement of stress-tolerance in crop plants. [ABSTRACT FROM AUTHOR]

Photosynthesis, stomatal conductance, electron transport, internal CO2 and sugar levels were determined in the leaves of Yellow Canopy Syndrome (YCS) symptomatic sugarcane (Saccharum spp.) plants. Two varieties from two different geographic regions in Australia, KQ228 and Q200 were used. Although visual yellowing was only evident in the lower leaves of the canopy (older than Leaf 5), photosynthesis and stomatal conductance were lower in both the yellowing leaves and those not yet showing any visible symptoms. On a canopy basis, photosynthesis was reduced by 14% and 36% in YCS symptomatic KQ228 and Q200 plants, respectively. Sucrose levels increased significantly in the leaves, reflecting some of the earliest changes induced in YCS symptomatic plants. The electron transport characteristics of dark-adapted leaves showed disruptions on both the electron acceptor and donor side of PSII. Some of these changes are characteristic of a degree of disruption to the protein structure associated with the electron transport chain. Based on the results, we propose that the first change in metabolism in the YCS symptomatic plants was an increase in sucrose in the leaves and that all the other changes are secondary effects modulated by the increased sugar levels. [ABSTRACT FROM AUTHOR]

Partitioning of light energy into several pathways and its relation to photosynthesis were examined in a shade-demanding species Panax notoginseng (Burkill) F.H.Chen ex C.Y.Wu & K.M.Feng grown along a light gradient. In fully light-induced leaves, the actual efficiency of PSII photochemistry (ΔF/Fm'), electron transport rate (ETR), non-photochemical quenching (NPQ) and photochemical quenching (qP) were lower in low-light-grown plants; this was also the case in fully dark-adapted leaves under a simulated sunfleck. In response to varied light intensity, high-light-grown plants showed greater quantum yields of light-dependent non-photochemical quenching (ΦNPQ) and PSII photochemistry (ΦPSII) and smaller quantum yields of fluorescence and constitutive thermal dissipation (Φf,d). Under the simulated sunfleck, high-light-grown plants showed greater ΦPSII and smaller Φf,d. There were positive relationships between net photosynthesis (Anet) and ΦNPQ+f,d and negative relationships between Anet and ΦPSII in fully light-induced leaves; negative correlations of Anet with ΦNPQ+f,d and positive correlations of Anet with ΦPSII were observed in fully dark-adapted leaves. In addition, more nitrogen was partitioned to light-harvesting components in low-light-grown plants, whereas leaf morphology and anatomy facilitate reducing light capture in high-light-grown plants. The pool of xanthophyll pigments and the de-epoxidation state was greater in high-light-grown plants. Antioxidant defence was elevated by increased growth irradiance. Overall, the evidences from P. notoginseng suggest that in high-light-grown shade-demanding plants irradiated by high light more electrons were consumed by non-net carboxylative processes that activate the component of NPQ, that low-light-grown plants correspondingly protect the photosynthetic apparatus against photodamage by reducing the efficiency of PSII photochemistry under high light illumination, and that during the photosynthetic induction, the ΔpH-dependent (qE) component of NPQ might dominate photoprotection, but the NPQ also depresses the enhancement of photosynthesis via competition for light energy. [ABSTRACT FROM AUTHOR]

Drought stress is one of the most important environmental factors that adversely affect the productivity and quality of crops. Most studies focus on elucidating plant responses to this stress but the reversibility of these effects is less known. The aim of this work was to evaluate whether drought-stressed peanut (Arachis hypogaea L.) plants were capable of recovering their metabolism upon rehydration, with a focus on their antioxidant system. Peanut plants in the flowering phase (30 days after sowing) were exposed to drought stress by withholding irrigation during 14 days and subsequent rehydration during 3 days. Under these conditions, physiological status indicators, reactive oxygen species production and antioxidant system activity were evaluated. Under drought stress, the stomatal conductance, photosynthetic quantum yield and 13C: 12C ratio of the peanut plants were negatively affected, and also they accumulated reactive oxygen species. The antioxidant system of peanut plants showed increases in superoxide dismutase-, ascorbate peroxidase- and glutathione reductasespecific activities, as well as the total ascorbate content. All of these responses were reversed upon rehydration at 3 days. The efficient and dynamic regulation of variables related to photosynthesis and the antioxidant system during a drought and rehydration cycle in peanut plants was demonstrated. It is suggested that the activation of the antioxidant system could mediate the signalling of drought stress responses that enable the plant to survive and recover completely within 3 days of rehydration. [ABSTRACT FROM AUTHOR]

High concentrations of ozone (O3) can have significant impacts on the health and productivity of agricultural and forest ecosystems, leading to significant economic losses. In order to estimate this impact under a wide range of environmental conditions, the mechanisms of O3 impacts on physiological and biochemical processes have been intensively investigated. This includes the impact on stomatal conductance, the formation of reactive oxygen species and their effects on enzymes and membranes, as well as several induced and constitutive defence responses. This review summarises these processes, discusses their importance for O3 damage scenarios and assesses to which degree this knowledge is currently used in ecosystem models which are applied for impact analyses. We found that even in highly sophisticated models, feedbacks affecting regulation, detoxification capacity and vulnerability are generally not considered. This implies that O3 inflicted alterations in carbon and water balances cannot be sufficiently well described to cover immediate plant responses under changing environmental conditions. Therefore, we suggest conceptual models that link the depicted feedbacks to available process-based descriptions of stomatal conductance, photosynthesis and isoprenoid formation, particularly the linkage to isoprenoid models opens up new options for describing biosphereatmosphere interactions. [ABSTRACT FROM AUTHOR]

Many plant species or cultivars form variegated leaves in which blades are made of green and white sectors. On the one hand, there is little photosynthetic CO2 assimilation in white tissue simply because of the lack of functional chloroplasts and thus, leaf white tissue is heterotrophic and fed by photosynthates exported by leaf green tissue. On the other hand, it has been previously shown that the white tissue is enriched in nitrogenous compounds such as amino acids and polyamines, which can, in turn, be remobilised upon nitrogen deficiency. However, the origin of organic nitrogen in leaf white tissue, including the possible requirement for N-reduction in leaf green tissue before export to white tissue, has not been examined. Here, we took advantage of isotopic methods to investigate the source of nitrogen in the white tissue. A survey of natural isotope abundance (δ15N) and elemental composition (%N) in various variegated species shows no visible difference between white and green tissues, suggesting a common N source. However, there is a tendency for N-rich white tissue to be naturally 15N-enriched whereas in the model species Pelargonium × hortorum, white sectors are naturally 15N-depleted, indicating that changes in metabolic composition and/or N-partitioning may occur. Isotopic labelling with 15N-nitrate on illuminated leaf discs clearly shows that the white tissue assimilates little nitrogen and thus relies on nitrate reduction and metabolism in the green tissue. The N-sink represented by the white tissue is considerable, accounting for nearly 50% of total assimilated nitrate. [ABSTRACT FROM AUTHOR]

We measured proline and glycine betaine levels and photosynthetic performance (net-photosynthetic rate (Pn), stomatal conductance (gs), maximum quantum yield of PSII (Fv/Fm) and non-photochemical quenching (NPQ)) in relation to Na+ and Cl- accumulation in Melilotus siculus (Turra) B.D.Jacks. (Fabaceae), Tecticornia pergranulata (J.M.Black) K.A.Sheph. & Paul G.Wilson (Amaranthaceae: Salicornioideae) and Thinopyrum ponticum (Podp.) Z.-W. Liu & R.-C. Wang (Poaceae) grown under saline conditions in the greenhouse. These plants were selected in this study because of their known salt-tolerance capacity and value as forage plants. Moreover, the pasture legume M. siculus is considered to have particular potential for saline land remediation because of its salinity and waterlogging tolerance. Maximum Na+ and Cl- accumulation occurred in Te. pergranulata shoots. Minimum was in Th. ponticum shoots. Maximum Na+ accumulation occurred in the roots of Te. pergranulata, whereas that of Cl- occurred in the roots of Th. ponticum. Accumulation of both Na+ and Cl- was the least in M. siculus roots. Te. pergranulata metabolized high levels of glycine betaine (110 mmol g-1 DW). M. siculus metabolized high levels of proline (6 mmol g-1 DW). Th. ponticum accumulated intermediate levels of these organic osmolytes. No significant change occurred in Fv/Fmvalues. Pn value increased and NPQ value decreased in Te. pergranulata with increasing salinity and the reverse occurred in both M. siculus and Th. ponticum. A negative significant correlation occurred between Pn and glycine betaine in M. siculus and Th. ponticum. A positive significant correlation occurred between NPQ and glycine betaine in M. siculus. No correlation occurred between proline and Pn, proline and NPQ in the tested three plants. Te. pergranulata could maintain cell-osmotic balance by synthesising high levels of organic osmolytes especially glycine betaine and concurrently showing the most efficient photosynthetic performance. Compared with the levels of osmolytes in Te. pergranulata, the levels of osmolytes that occur in M. siculus and Th. ponticum were insufficient to maintain cell-osmotic balance and also that M. siculus and Th. ponticum showed a lower level of photosynthetic performance. We conclude that glycine betaine is potentially the vital organic osmolyte for Te. pergranulata and Th. ponticum enabling salinity stress tolerance. However, in M. siculus, proline appears to be the potential organic osmolyte in salinity stress tolerance. In terms of the potential of these species for stabilising saline soils in central-western New South Wales, Te. pergranulata would be the candidate of choice; however, for greater pasture value Th. ponticum would be the next. [ABSTRACT FROM AUTHOR]

Although plant salt tolerance has been improved by soil inoculation with rhizobacteria containing the enzyme 1-aminocyclopropane-l-carboxylate (ACC) deaminase (which metabolises ACC, the immediate precursor of the phytohormone ethylene), it is not always clear whether ion homeostasis and plant water relations are affected. When pea (Pisum sativum L. cv. Alderman) was grown with 70 and 130 mM NaCl, the ACC-deaminase containing rhizobacterium Variovorax paradoxus 5C-2 increased total biomass by 25 and 54% respectively. Nutrient flow modelling showed that V. paradoxus 5C-2 increased K uptake and root to shoot K flow, but decreased Na flow and increased Na deposition in roots. Thus, shoot K[sup +]: Na[sup +] ratio increased following V.paradoxus 5C-2 inoculation. At 70 and 130 mMNaCl, rhizobacterial inoculation decreased stomatal resistance by 14 and 31 % and decreased xylem balancing pressure by 7 and 21 % respectively. Furthermore, rhizobacterial inoculation improved photo synthetic efficiency (F[sub v]F[sub m]) by 12 and 19% and increased maximal electron transport rate (ETR) by 18 and 22% at 70 and 130mM NaCl respectively. Thus V. paradoxus 5C-2 mitigates salt stress by improving water relations, ion homeostasis and photosynthesis of pea plants, and may provide an economic means of promoting growth of plants exposed to salt stress. [ABSTRACT FROM AUTHOR]

Limited rainfall is the main constraint to agriculture, making agricultural research to understand plant behaviour that leads to avoidance of soil water deficit a matter of priority. One focus has screened for crop varieties that decrease stomatal conductance under high vapour pressure deficit (VPD), a proxy for the leaf evaporative gradient. However, the link between stomatal closure and physiological consequences in field environments is not yet clear. A field experiment on soybeans demonstrated that considerable variation in leaf temperature relative to air temperature occurred, leading to evaporative gradients differing substantially from VPD. Thus, transpiration is decreased by stomatal closure at high VPD, but to compensate, transpiration is somewhat increased due to higher leaf temperatures. Soil water deficit led to lower stomatal conductance, particularly under low evaporative conditions, not just under hot conditions. Non-stomatal photosynthetic limitations were observed due to combined occurrence of stomatal closure and high temperature under high VPD. Although leaves reached temperatures higher than the threshold for a decrease in maximum photochemical efficiency, and displayed non-stomatal photosynthetic limitations, no photoinhibition or damage was observed by night-time. The results demonstrate that more understanding of physiological strategies for achieving altered water use is needed to avoid trade-offs and heat stress. [ABSTRACT FROM AUTHOR]

Plants infected with hemiparasites often have lowered rates of photosynthesis, which could make them more susceptible to photodamage. However, it is also possible that infected plants increase their photoprotective capacity by changing their pigment content and/or engagement of the xanthophyll cycle. There are no published studies investigating infection effects on host pigment dynamics and how this relates to host susceptibility to photodamage whether in high(HL) or low light (LL). A glasshouse experiment was conducted where Leptospermum myrsinoides Schltdl. either uninfected or infected with Cassytha pubescens R.Br. was grown in HL or LL and pigment content of both host and parasite were assessed. Infection with C. pubescens significantly decreased all foliar pigment concentrations (except chlorophyll b) in L. myrsinoides in both HL and LL. Xanthophyll cycle (violaxanthin, antheraxanthin, zeaxanthin; VAZ) and chlorophyll (Chl) pigments decreased in parallel in response to infection, hence, VAZ/Chl of the host was unaffected by C. pubescens in either HL or LL. Pre-dawn and midday de-epoxidation state [(A+Z)/(V + A +Z)] of L. myrsinoides was also unaffected by infection in both HL and LL. Thus, L. myrsinoides infected with C. pubescens maintained similar photoprotective capacity per unit chlorophyll and engagement of the xanthophyll cycle as uninfected plants. Even though midday quantum yield (F[sub PSII]) of HL plants was affected by infection, pre-dawn maximum quantum yields (F[sub v]/F[sub m]) of hosts were the same as uninfected plants whether in HL or LL. This ability of L. myrsinoides to maintain photoprotective capacity/engagement when infected by C. pubescens thereby preventing photodamage could explain this host's tolerance to hemiparasite infection. [ABSTRACT FROM AUTHOR]

The Farquhar–von Caemmerer–Berry (FvCB) model of photosynthesis has been widely used to estimate the photosynthetic C flux of plants under different growth conditions. However, the seasonal fluctuation of some photosynthesis parameters (e.g. the maximum carboxylation rate of Rubisco (Vcmax), the maximum electron transport rate (Jmax) and internal mesophyll conductance to CO2 transport (gm)) is not considered in the FvCB model. In this study, we investigated the patterns of the FvCB parameters during flag leaf development based on measured photosynthesis–intercellular CO2 curves in two cultivars of winter wheat (Triticum aestivum L.). Parameterised seasonal patterns of photosynthesis parameters in the FvCB model have subsequently been applied in order to predict the photosynthesis of flag leaves. The results indicate that the Gaussian curve characterises the dynamic patterns of Vcmax, Jmax and gm well. Compared with the model with fixed photosynthesis parameter values, updating the FvCB model by considering seasonal changes in Vcmax and Jmax during flag leaf development slightly improved predictions of photosynthesis. However, if the updated FvCB model incorporated the seasonal patterns of Vcmax and Jmax, and also of gm, predictions of photosynthesis was improved a lot, matching well with the measurements (R2 = 0.87, P < 0.0001). This suggests that the dynamics of photosynthesis parameters, particularly gm, play an important role in estimating the photosynthesis rate of winter wheat. [ABSTRACT FROM AUTHOR]

Many short-term experiments have been conducted under increasing CO[sub 2] but results have been varied and have not yet led to a conclusive quantitative understanding of the CO[sub 2] response of plant growth. This may have been partly due to a lack of explicit consideration of the positive feedback inherent in plant growth during periods of exponential growth. This feedback can increase an initial physiological enhancement of relative growth rate (RGR) into a much larger biomass enhancement. To overcome this problem, we re-analysed existing experimental data from 78 publications. We calculated the RGRs of C[sub 3] plants and their relative enhancement under elevated CO[sub 2] and derived response indices that were independent of the duration of experiments and the RGR at normal atmospheric CO[sub 2]. The RGR of unstressed plants increased by 14 ± 2% under doubled CO[sub 2], with observed RGR enhancement linearly correlated with calculated photosynthetic enhancements (based on the Farquhar-von Caemmerer-Berry photosynthesis model), but at only half their numeric values. Calculated RGR enhancements did not change significantly for temperatures from 12 to 40°C, but were reduced under nutrient limitation, and were increased under water stress or low irradiance. We concluded that short-term experiments can offer simple and cost-effective insights into plant CO[sub 2] responses, provided they are analysed by calculating relative changes in RGR during the strictly exponential initial growth phase. [ABSTRACT FROM AUTHOR]

Drought is one of the most important abiotic stresses constraining crop productivity worldwide. The objective of the present study was to investigate the differences in drought tolerance at leaf and stomatal level of black gram (genotypes: T9, KU 301, PU 19, USJD 113) and green gram (genotypes: Pratap, SG 21-5, SGC 16, TMB 37). Drought was applied for fifteen consecutive days at flowering stage (35 days after sowing). Mid-day leaf water potential (Ψ[sub L]), leaf area, photosynthesis rate (P[sub N]), leaf chlorophyll, stomatal conductance (gs) and seed yield of drought- treated plants were calculated relative to those of well watered plants. Stomatal characteristics were observed in terms of stomatal frequency (SF) and stomatal aperture size (SA). Among the studied genotypes, T9 (black gram) and Pratap (green gram) proved their better tolerance capacity to drought by maintaining higher leaf area, Ψ[sub L], P[sub N], leaf chlorophyll, g[sub s] and SA which contributed to better seed yield. Between the two crops, green gram appeared to be affected to a greater extent, as it experienced higher reduction in yield than black gram. A highly significant positive correlation (level 0.01) of seed yield was obtained with leaf area, Ψ[sub L], P[sub N], leaf chlorophyll, g[sub s] and SA, whereas SF was found to be poorly correlated with seed yield. [ABSTRACT FROM AUTHOR]

Increasing fructokinase (FRK) activity in cotton (Gossypium hirsutum L.) plants may reduce fructose inhibition of sucrose synthase (Sus) and lead to improved fibre yield and quality. Cotton was transformed with a tomato (Solanum lycopersicum L.) fructokinase gene (LeFRK1) under the control of the CMV 35S promoter. In a greenhouse, the LeFRK1 plants had increased fibre and leaf FRK activity over nonexpressing nulls, but not improved fibre length and strength. Compared with the nulls, LeFRK1 plants yielded 13-100% more seed-cotton mass per boll and more bolls per plant, and therefore more seed cotton and fibre yield per plant. The enhanced yield was related to a greater seed number per boll for LeFRK1 plants. Photosynthetic rates were not appreciably different among genotypes. However, more area per leaf and leaf number (in some instances) for LeFRK1 plants than for nulls enhanced the capacity for C gain. Larger leaf areas for LeFRK1 plants were associated with larger stem diameters. Lower sucrose levels in developing leaves of LeFRK1 plants suggest that LeFRK1 overexpression leads to improved in vivo Sus activity in developing leaves and possibly in developing seeds. The improvement in yield for LeFRK1 plants may also be the result of improvements in photosynthate supply as a consequence of greater leaf area. [ABSTRACT FROM AUTHOR]

Rising atmospheric [CO[sub 2]] is associated with increased air temperature, and this warming may drive many rare plant species to extinction. However, to date, studies on the interactive effects of rising [CO[sub 2]] and warming have focussed on just a few widely distributed plant species. Wollemi pine (Wollemia nobilis W.G.Jones, K.D.Hill, & J.M.Allen), formerly widespread in Australia, was reduced to a remnant population of fewer than 100 genetically indistinguishable individuals. Here, we examined the interactive effects of three [CO[sub 2]] (290, 400 and 650 ppm) and two temperature (ambient, ambient+ 4°C) treatments on clonally-propagated Wollemi pine grown for 17 months in glasshouses under well-watered and fertilised conditions. In general, the effects of rising [CO[sub 2]] and temperature on growth and physiology were not interactive. Rising [CO[sub 2]] increased shoot growth, light-saturated net photosynthetic rates (A[sub sat]) andnet carbon gain. Higher net carbon gain was due to increased maximum apparent quantum yield and reduced non-photorespiratory respiration in the light, which also reduced the light compensation point. In contrast, increasing temperature reduced stem growth and A[sub sat]. Compensatory changes in mesophyll conductance and stomatal regulation suggest a narrow functional range of optimal water and CO[sub 2] flux co-regulation. These results suggest A[sub sat] and growth of the surviving genotype of Wollemi pine may continue to increase with rising [CO[sub 2]], but increasing temperatures may offset these effects, and challenges to physiological and morphological controls over water and carbon trade-offs may push the remnant wild population of Wollemi pine towards extinction. [ABSTRACT FROM AUTHOR]

Chlorophyll molecules absorb photosynthetic active radiation (PAR). The resulting excitation energy is dissipated by three competing pathways at the level of photosystem: (i) photochemistry (and, by extension, photosynthesis); (ii) regulated and constitutive thermal energy dissipation; and (iii) chlorophyll-a fluorescence (ChlF). Because the dynamics of photosynthesis modulate the regulated component of thermal energy dissipation (widely addressed as non-photochemical quenching (NPQ)), the relationship between photosynthesis, NPQ and ChlF changes with water, nutrient and light availability. In this study we characterised the relationship between photosynthesis, NPQ and ChlF when conducting light-response curves of photosynthesis in plants growing under different water, nutrient and ambient light conditions. Our goals were to test whether ChlF and photosynthesis correlate in response to water and nutrient deficiency, and determine the optimum PAR level at which the correlation is maximal. Concurrent gas exchange and ChlF light-response curves were measured for Camelina sativa (L.) Crantz and Triticum durum (L.) Desf plants grown under (i) intermediate light growth chamber conditions, and (ii) high light environment field conditions respectively. Plant stress was induced by withdrawing water in the chamber experiment, and applying different nitrogen levels in the field experiment. Our study demonstrated that ChlF was able to track the variations in photosynthetic capacity in both experiments, and that the light level at which plants were grown was optimum for detecting both water and nutrient deficiency with ChlF. The decrease in photosynthesis was found to modulate ChlF via different mechanisms depending on the treatment: through the action of NPQ in response to water stress, or through the action of changes in leaf chlorophyll concentration in response to nitrogen deficiency. This study provides support for the use of remotely sensed ChlF as a proxy to monitor plant stress dynamics from space. [ABSTRACT FROM AUTHOR]

The process of photosynthesis depends on the light, and is modulated by leaf temperature and their interaction is important to understand how climate affects photosynthesis. Photosynthetic and PSII light responses at a range of leaf temperatures were measured on leaves of apple (MalusdomesticaBorkh. cv. Red Gala)trees growing in field conditions. The objective was to assess the interaction between photon flux density (PFD) and temperature on these processes. Results showed leaf temperature strongly modulated the PFD-dependent response of photosynthesis and PSII performance. An interaction on photosynthesis occurred, with temperature affecting saturated rates as well as PFDs saturating photosynthesis. The efficiency of PSII electron transport (operating and maximum in light) universally declined with increasing PFD but temperature strongly influenced the response. Rates of PSII electron transport at saturating PFDs were affected by temperatures. Both photochemical quenching and non-photochemical quenching also responded strongly to temperature but at high PFDs, photochemical quenching increased linearly with decreasing temperatures while non-photochemical quenching increased curvilinearly with increasing temperatures. Modelling revealed changes in photosynthesis were positively correlated with rates of electron transport. These results greatly enhance our understanding of photosynthesis and the underpinning processes and their responses to temperature and PFD. [ABSTRACT FROM AUTHOR]

Local burning of a leaf induces a unique electrical signal in plants: variation potential (VP), which can cause numerous functional responses, including changes in photosynthesis. The influences of VP on damage to photosynthetic machinery and thermal resistance of whole plant with heating were investigated in pea (Pisum sativum L.). Under high external temperature (53°C), VP induction was found to cause accelerated initial lowering of photosynthetic parameters, reduced transpiration rate, decreased PSI damage, and increased PSII damage. Increased PSI resistance was in good accordance with our previous data, but VP-induced stimulation of PSII damage under heating required further analysis. The magnitudes of leaf heating in experiments and controls were found to be different (~46-48°C after VP and ~44-45°C without it) under identical external temperatures and were connected with different transpiration rates under these conditions. Also PSII damage and the magnitude of leaf heating were strongly correlated. As a result, it was supposed that leaf temperature contributed to VP-induced stimulation of PSII damage with heating. Investigation of VP's influence on pea growth after heating showed that the electrical signal decreased plant growth suppression after heating (i.e. VP-induced increases in PSII damage did not noticeably influence thermal resistance in the whole plant). [ABSTRACT FROM AUTHOR]

Jatropha curcas L. is a drought-tolerant shrub or small tree that is a candidate bioenergy feedstock. It is a member of the family Euphorbiaceae in which both CAM and C[sub 4] photosynthesis have evolved. Here, we report that J. curcas exhibits features diagnostic of low-level CAM. Small increases in nocturnal acid content were consistently observed in photosynthetic stems and occasionally in leaves. Acidification was associated with transient contractions in CO[sub 2] loss at night rather than with net CO[sub 2] dark fixation. Although the CAM-type nocturnal CO[sub 2] uptake signal was masked by background respiration, estimates of dark CO[sub 2] fixation based upon the 2:1 stoichiometric relationship between H[sup +] accumulated and CO[sub 2] fixed indicated substantial carbon retention in the stems via the CAM cycle. It is proposed that under conditions of drought, low-level CAM in J. curcas stems serves primarily to conserve carbon rather than water. [ABSTRACT FROM AUTHOR]

The viral disease caused by tobacco mosaic virus (TMV) is the most prevalent viral disease in many tobacco production areas. A breeding strategy based on resistance genes is an effective method for improving TMV resistance in tobacco. Also, the physiological status of plants is also critical to disease resistance improvement. Potassium ion is one of the most abundant inorganic nutrients in plant cells, and mediates plant responses to abiotic and biotic stresses. Improving K+ content in soil by fertilising can enhance diseases resistance of crops. However, the K+ absorption in plants depends mostly on K+ transporters located in cytoplasmic membrane. Therefore, the encoding genes for K+ transporters are putative candidates to target for improving tobacco mosaic virus resistance. In this work, the synergistic effect of a N-like resistance gene CN and a tobacco putative potassium transporter gene HAK1 was studied. The results showed that TMV-resistance in CN-HAK1-containing tobaccos was significantly enhanced though a of strengthening leaf thickness and reduction in the size of necrotic spots compared with only CN-containing plants, indicating the improvement of potassium nutrition in plant cells could increase the tobacco resistance to TMV by reducing the spread of the virus. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis for TMV-CP expression in the inoculated leaf of the transgenic and wild-type plants also supported the conclusion. Further, the results of defence-related determination including antioxidative enzymes (AOEs) activity, salicylic acid (SA) content and the expression of resistance-related genes demonstrated CN with HAK1 synergistically enhanced TMV-resistance in transgenic tobaccos. Additionally, the HAK1- overexpression significantly improved the photosynthesis and K+-enriching ability in trans-CN-HAK1 tobaccos, compared with other counterparts. Finally, this work provides a method for screening new varieties of marker-free and safe transgenic antiviral tobacco. [ABSTRACT FROM AUTHOR]

Increasing leaf photosynthesis rate (A) is considered an important strategy to increase C3 crop yields. Leaf A is usually represented by point measurements, but A varies within each leaf, especially within large leaves. However, little is known about the effect of heterogeneity of A within leaves on rice performance. Here we investigated the changes in gas-exchange parameters and leaf structural and chemical features along leaf blades in two rice cultivars. Stomatal and mesophyll conductance as well as leaf nitrogen (N), Rubisco and chlorophyll contents increased from base to apex; consequently, A increased along leaves in both cultivars. The variation in A, leaf N content and Rubisco content within leaves was similar to the variations among cultivars, and the extent of A heterogeneity within leaves varied between cultivars, leading to different efficiencies of biomass accumulation. Furthermore, variation of A within leaves was closely associated with leaf structural and chemical features. Our findings emphasise that functional changes along leaf blades are associated with structural and chemical trait variation and that variation of A within leaves should be considered to achieve progress in future breeding programs. [ABSTRACT FROM AUTHOR]

Organs of C3 plants differ in their C isotopic signature (δ13C). In general, leaves are 13C-depleted relative to other organs. To investigate the development of spatial δ13C patterns, we induced different C allocation strategies by reducing light and nutrient availability for 12 months in the Mediterranean shrub Halimium halimifolium L. We measured morphological and physiological traits and the spatial δ13C variation among seven tissue classes during the experiment. A reduction of light (Low-L treatment) increased aboveground C allocation, plant height and specific leaf area. Reduced nutrient availability (Low-N treatment) enhanced C allocation into fine roots and reduced the spatial δ13C variation. In contrast, control and Low-L plants with high C allocation in new leaves showed a high δ13C variation within the plant (up to 2.5‰). The spatial δ13C variation was significantly correlated with the proportion of second-generation leaves from whole-plant biomass (r2 = 0.46). According to our results, isotope fractionation in dark respiration can influence the C isotope composition of plant tissues but cannot explain the entire spatial pattern seen. Our study indicates a foliar depletion in 13C during leaf development combined with export of relatively 13C-enriched C by mature source leaves as an important reason for the observed spatial δ13C pattern. [ABSTRACT FROM AUTHOR]

In order to reveal the mechanism of succession in subtropical forest along a light gradient, we investigated photosynthetic physiological responses to three light environments in five tree species including a pioneer species Pinus massoniana Lamb., two mid-successional species Schima superba Gardn. et Champ. and Castanopsis fissa (Champ. ex Benth.) Rehd. et Wils., and two late-successional species Cryptocarya concinna Hance. and Acmena acuminatissima (BI.) Merr et Perry) that were selected from Dinghu Mountain subtropical forest, South China. Results showed that,amongthe three kinds of species in all light conditions (100%,30%and 12% of full sunlight), the pioneer species had the highest photosynthetic capacity (Amax), light saturation point (LSP), carboxylation efficiency (CE) and maximum utilisation rate of triose phosphate (TPU) that characterised a strong photosynthetic capacity and high carbon dioxide uptake efficiency. However, a higher light compensation point (LCP) and dark respiration (Rd) as well as lower apparent quantum yield (AQY) indicated that the pioneer specie cannot adapt to low light conditions. Mid-successional species had photosynthetic characteristics in between pioneer and late-successional species, but had the greatest effective quantum yield of PSII (ΦPSII) and light use efficiency (LUE, expressed in terms of photosynthesis). In contrast to pioneer and mid-successional species, late-successional species had lower photosynthetic capacity and carbon uptake efficiency, but higher shade tolerance and high-light heat dissipation capacity, as characterised by higher levels of total xanthophylls cycle pigments (VAZ) and de-epoxidation state of xanthophyll cycle (DEPs). These results indicate that photosynthetic capacity decreases along the successional axis and that late-successional species have more responsive heat dissipation capability to compensate for their inferior photosynthetic capacity. [ABSTRACT FROM AUTHOR]

Chlorophyll d and chlorophyll f are red-shifted chlorophylls, because their Qy absorption bands are significantly red-shifted compared with chlorophyll a. The red-shifted chlorophylls broaden the light absorption region further into far red light. The presence of red-shifted chlorophylls in photosynthetic systems has opened up new possibilities of research on photosystem energetics and challenged the unique status of chlorophyll a in oxygenic photosynthesis. In this review, we report on the chemistry and function of red-shifted chlorophylls in photosynthesis and summarise the unique adaptations that have allowed the proliferation of chlorophyll d- and chlorophyll f-containing organisms in diverse ecological niches around the world. [ABSTRACT FROM AUTHOR]

Understanding the response of sub-Antarctic plants to a warming climate requires an understanding of the relationship of carbon gain and loss to temperature. In a field study on Heard Island, we investigated the responses of photosynthesis and respiration of the sub-Antarctic megaherb Pringlea antiscorbutica R. Br. to temperature. This was done by instantaneously manipulating leaf temperature in a gas exchange cuvette on plants adapted to natural temperature variation along an altitudinal gradient. There was little altitudinal variation in the temperature response of photosynthesis. Photosynthesis was much less responsive to temperature than electron transport, suggesting that Rubisco activity was generally the rate-limiting process. The temperature response of leaf respiration rates was greater in cold-grown (high altitude) plants compared with warm-grown (low altitude) plants. This thermal acclimation would enable plants to maintain a positive carbon budget over a greater temperature range. [ABSTRACT FROM AUTHOR]

The rate of shoot growth (vigour) in grapevines tends to decrease as the number of shoots per plant increases. Because the underlying causes of this relationship remain unclear, they were studied by variable pruning of field-grown, deficit-irrigated Merlot grapevines (Vitis vinifera L.). Shoot number ranged from 11 to 124 per vine and was inversely correlated with shoot growth rate, leaf appearance rate, axillary bud outgrowth, internode length, leaf size, shoot leaf area, carbon partitioned to the fruit (C[sub fruit]) per shoot, average daily maximum photosynthesis (A[sub max]), stomatal conductance (g[sub max]), and leaf-specific hydraulic conductance (K[sub l]). Shoot number was positively correlated with canopy leaf area, whole-vine C[sub fruit], whole-plant hydraulic conductance (K[sub v]), and canopy conductance (K[sub c]). Higher shoot vigour was associated with higher A[sub max], g[sub max], predawn leaf water potential (Ψ[sub pd]), shoot hydraulic conductance (K[sub s]), K[sub l], and K[sub v]. Vigorous shoots supported both more vegetative growth and more reproductive growth; thus fruit growth did not compete with shoot growth for photosynthates. These results indicate that the hydraulic capacity of grapevines adapts to varying shoot numbers to support leaf physiology, growth, and carbon partitioning, but adaptation may belimited, putting upper bounds on the growth of individual shoots and fruit. [ABSTRACT FROM AUTHOR]

Plant functional traits are closely associated with plant habitats. In this study, we investigated the interspecific variations in stem and leaf hydraulics, xylem and leaf anatomy, gas-exchange rates and leaf pressure-volume relationships among three Syzygium tree species in early, mid- and late successional tropical forests. The objective was to understand the response and adaptation of congeneric species, in terms of branch and leaf functional traits, to different environments. A consistent pattern of decline with succession was evident in leaf and sapwood specific hydraulic conductivity (k[sub s]), maximum leaf hydraulic conductance (K[sub leaf]), and photosynthetic rates for the three Syzygium species. Variations of k[sub s] and K[sub leaf] were correlated with changes in vessel anatomy (i.e. vessel density and diameter) and leaf flux-related structure (i.e. stomatal pore index and vein density) respectively. However, specific leaf area and leaf to sapwood area ratio did not significantly differ among the three species. In addition, the mid-successional species had the lowest values of leaf water potential at full turgor and turgor loss point and 50% loss of K[sub leaf], but the greatest value of xylem water potential at 50% loss of k[sub s]. Our results demonstrate that leaf and branch traits associated with photosynthesis and/or hydraulic conductance, rather than those associated with drought tolerance, are the key factors underlying the response and adaptation of the three Syzygium tree species along the tropical forest succession. [ABSTRACT FROM AUTHOR]

The purpose of our study is to explore the acclimation of Neptune seagrass (Posidonia oceanica (L.) Delile) to depth by characterising the histo-anatomical leaf modifications. P. oceanica is the dominant seagrass and main habitat constructor of seagrass meadows in the Mediterranean Sea. Meadows play an important biological and ecological role in marine ecosystems, serving as a habitat for a large diversity of species and an efficient erosion protection system for our coasts. Seagrasses are very sensitive to change in light availability and small changes can have significant effects on growth, abundance and distribution. In this study, we analyse changes in P. oceanica leaves collected at -5 m, -15 m and -25 m depth in the Cirella meadow (Tyrrhenian coast, Southern Italy) in order to determine their depth-related histo-anatomical variation. Two main changes were observed at depth: (1) photo synthetic epidermal cells showed smaller chloroplasts but in the same number; and (2) leaves showed smaller epidermal cells and in greater number. Hence, the photosynthetic surface of P. oceanica leaves remains the same at different depths but pigment absorption efficiency can be significantly enhanced with depth. This response supports the differential photoacclimatory response of seagrasses with respect to terrestrial plants previously documented. Mesophyll cells are smaller with depth and more numerous, with a consequent increase in leaf density. The number of vascular bundles also increases, which allows improved functional efficiency of the transport system and solute exchange. Our study is a new contribution to the morpho-functional implications of the histo-anatomy of P. oceanica. [ABSTRACT FROM AUTHOR]

Changes in the photosynthetic responses of Malus domestica cv. 'Red Gala' leaves to internal CO2 concentrations at leaf temperatures from 15°C to 40°C were followed across the growing season in field-grown trees exposed to a high temperature event in late summer. Light and CO2-saturated photosynthesis (Amax), maximum rates of ribulose 1,5-bisphosphate (RuBP) carboxylation (V cmax) and maximum rates of electron transport (Jmax) were all highest in spring, althoughAmax was maximal at 30°C, and Vcmax andJmax were maximal at 40°C. All attributes declined in late summer and reached minima that coincided with the occurrence of the high temperature event. Modelling suggested many of the changes were correlated with the seasonal climate, although the measurement or current temperature had an overriding effect, especially on stomatal conductance. Marked changes in the temperature-dependency of Vcmax and Jmax occurred across the season and appeared to relate to the seasonal changes in climate, especially temperature. The reduction in photosynthesis at high temperatures was, however, partly attributable to a stomatal limitation of up to 60% at the high temperatures. Non-stomatal reductions in photosynthesis during the heat event could be attributed to detrimental effect on RuBP carboxylation and on RuBP regeneration. [ABSTRACT FROM AUTHOR]

The south-central Rocky Mountains, USA, are characterised by a dry, continental mesoclimate with typical convective cloud formation during the afternoon. Little is known about the specific influence of such predictable cloud patterns on the microclimate and ecophysiology of associated species. During the summer of 2012, days with afternoon clouds were most common (50% of all days) compared with completely clear (24%) or cloudy days (6.5%). In two representative alpine species, Caltha leptosepala DC. and Arnica parryi A. Gray, fully overcast days reduced mean daily photosynthesis (A) by nearly 50% relative to fully clear days. Mean afternoon A was significantly lower on fully cloudy days relative to days with afternoon clouds only or no clouds in both species. Notably, A did not differ during afternoon cloud days relative to clear afternoons. Afternoon clouds significantly reduced transpiration (E) in C. leptosepala relative to clear days, and both species showed mean reductions in plant water stress (i.e. higher Ψ), though this difference was not significant. Water use efficiency (WUE) (A/E) decreased from morning to afternoon, especially on cloudy days, and the presence of clouds had a positive effect on the light reactions of photosynthesis based on fluorescence measurements (Fv'/Fm'), in both species. Cloudy days were characterised by higher F[sub v]/F[sub m] than afternoon clouds and clear days during both the morning and the afternoon (especially for A. parryi) and recovery to near pre-dawn values for cloudy and afternoon cloud day types, but not clear days. Overall, similar ecophysiological advantages of this typical afternoon cloud pattern was apparent in both species, although their spatial microsite differences related to winter snow accumulation may also play an important role. Natural cloud regimes across the globe are expected to change with continued global warming. Yet, little is known about the impacts on plants, except for a few studies showing potentially strong effects on photosynthetic carbon gain and transpirational water loss. We found that these changes to the natural cloud regime had substantial impacts on photosynthesis, transpiration and water use efficiency. [ABSTRACT FROM AUTHOR]

European mistletoe (Viscum album L.) is a hemiparasitic plant with perennial leaves and photosynthetic stems easily discernible according to their age. These properties make V. album the perfect species to (i) compare the mechanisms of seasonal acclimation of photosynthetic stems with those of leaves, and (ii) evaluate the influence of ageing in the efficiency of photosynthetic tissues. To achieve these general objectives, photosynthetic pigments, maximal photochemical efficiency of PSII (Fv/Fm), recovery kinetics and key thylakoidal proteins were analysed during winter and spring in leaves and at different age stems. During winter, some woody species are able to maintain photosynthetic activity, but at lower rates than during spring. In the case of V. album, photosynthetic relevance of green stems appears equal to leaves in terms of total area. Besides, mistletoe stems are able to maintain higher Fv/Fm and lower level of antioxidants than leaves, especially during winter season. The recovery from winter photoinhibition is also faster in stems than in leaves. Thylakoidal protein composition (mainly high levels of D1) also supports the idea of stems as main photosynthetic organs in V. album during winter. Further, in winter, the level of photoinhibition of V. album stems decreased concomitantly with ageing. This work highlights the importance of stem photosynthesis in plant carbon balance and demonstrates that ageing does not necessarily imply a loss of vitality in stems. European mistletoe (Viscum album) is an evergreen hemiparasitic plant characterised by a continuous photosynthetic surface composed of leaves and stems. We have taken advantage of these traits and used this species as a perfect model plant to study the interactive effect of age and winter on photosynthetic regulation. Winter, as in other temperate evergreens, induces a downregulation of photosynthesis, which in stems is compensated by an ageing-dependent stimulatory effect. Overall, this case study supports the theory of negative senescence. [ABSTRACT FROM AUTHOR]

In woody plants, oxygen transport and delivery via the xylem sap are well described, but the contribution of bark and woody tissue photosynthesis to oxygen delivery in stems is poorly understood. Here, we combined stem chlorophyll fluorescence measurements with microsensor quantifications of bark O[sub 2] levels and oxygen gas exchange measurements of isolated current-year stem tissues of beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.) to investigate how bark and woody tissue photosynthesis impairs the oxygen status of stems. Measurements were made before bud break, when the axial path of oxygen supply via the xylem sap is impeded. At that time, bark O[sub 2] levels showed O[sub 2] concentrations below the atmospheric concentration, indicating hypoxic conditions or O[sub 2] deficiency within the inner bark, but the values were always far a way from anoxic. Under illumination bark and woody tissue photosynthesis rapidly increased internal oxygen concentrations compared with plants in the dark, and thereby counteracted against localised hypoxia. The highest photosynthetic activity and oxygen release rates were found in the outermost cortex tissues. By contrast, rates of woody tissue photosynthesis were considerably lower, due to the high light attenuation of the bark and cortex tissues, as well as resistances in radial oxygen diffusion. Therefore, our results confirm that bark and woody tissue photosynthesis not only play a role in plant carbon economy, but may also be important for preventing low oxygen-limitations of respiration in these dense and metabolically active tissues. [ABSTRACT FROM AUTHOR]

Yield potential is the genome-encoded capacity of a crop species to generate yield in an optimal grow environment. Ninety per cent of plant biomass is derived from the photosynthetic reduction of carbon dioxide to organ carbon (photoassimilates -- primarily sucrose). Thus, development of yield components (organ numbers and individu organ masses) can be limited by photoassimilate supply (photosynthesis arranged in series with phloem transport) or their inherent capacity to utilise imported photoassimilates for growth or storage. To this end, photoassimilate suppl utilisation of crop yield has been quantitatively re-evaluated using published responses of yield components to elevat carbon dioxide concentrations across a selection of key crop species including cereal and pulse grains, fleshy fruits, tube and sugar storing stems and tap roots. The analysis demonstrates that development of harvested organ numbers is strong limited by photoassimilate supply. Vegetative branching and, to a lesser extent, flower/pod/fleshy fruit abortion, are t major yield components contributing to sensitivity of organ numbers to photoassimilate supply. In contrast, harvested org size is partially dependent (eudicots), or completely independent (cereals), of photoassimilate supply. Processes limiti photoassimilate utilisation by harvested organs include membrane transport of soluble sugars and their allocation in polymeric storage products. [ABSTRACT FROM AUTHOR]

In Agave angustifolia Haw., a leaf-succulent constitutive crassulacean acid metabolism (CAM) plant of tropical Panama, we tested whether nocturnal CO2 uptake and growth were reduced at night temperatures above 20°C. Unlike some CAM model species from habitats with pronounced day-night temperature variations, in A. angustifolia temperature affected little the relative contributions of CAM and C3 photosynthesis to growth. In plants grown under 12 h light/dark regimes of 25/17, 30/22 and 35/27°C, biomass increased with temperature. Maintaining day temperature at 35°C and reducing night temperature from 27 to 17°C markedly lowered growth, a reduction partially reversed when roots were heated to 27°C. Across all treatments, whole-shoot δ13C values ranged between -14.6 and -13.2 %, indicating a stable proportion of CO2 was fixed at night, between 75 and 83%. Nocturnal acidification reflected growth, varying between 339 and 393 mol H+g-1 fresh mass and 63-87 µmol H+cm-2. In outdoor open-top chambers, warming the air 3°C above ambient at night did not reduce biomass accumulation. The persistence of a high capacity for nocturnal CO2 fixation at the expense of a limited capacity for switching between C3 and CAM probably makes this Agave, and others like it, potential species for biomass production in seasonally-dry landscapes. [ABSTRACT FROM AUTHOR]

Fruit presence often positively and seldom negatively affects leaf carbon assimilation rate in fruit-trees. In almond (Prunus dulcis (Mill.) DA Webb) the presence of fruit often results in the death of the fruit bearing spurs. The mechanism of this effect is unclear, but may be a consequence of diminished carbon assimilation rate in leaves adjacent to fruit and the subsequent depletion of nutrient and carbohydrates reserves. This study evaluated the influence of fruit on leaf carbon assimilation rate and leaf nitrogen throughout the season. Carbon assimilation rate (A[sub a]), rubisco carboxylation capacity at leaf temperature (V[sub cmax@Tleaf]), maximum rate of RubP regeneration at leaf temperature (J[sub max@Tleaf]), leaf nitrogen on a mass basis (N%) and area basis (N[sub a]), and specific leaf weight data were recorded. Fruit presence negatively affected leaf nitrogen concentration by a reduction in specific leaf weight and leaf nitrogen content. The impact of fruit presence on carbon assimilation rate was predominantly associated with the negative effect of fruit on N[sub a] and resulted in a significant reduction in J[sub max@Tleaf] and therefore in A[sub a], especially after full leaf and fruit expansion. The reduction in leaf area, leaf nitrogen, reduced J[sub max@Tleaf] and decreased carbon assimilation rate in the presence of fruit explains the negative effects of fruit presence on spur vitality. [ABSTRACT FROM AUTHOR]

A relationship exists between the two-dimensional shape of leaves and their venation architecture, such that broad or broad-lobed leaves can have leaf tissue far from major veins, potentially creating stronger gradients in water potential -- and associated photosynthetic function -- than found across narrow counterparts. We examined the spatial patterns of photosynthetic efficiency (ΔF/F[sub m]') and non-photochemical quenching (NPQ) in response to increased vapour pressure deficit (VPD) using two morphs of Lomatia tinctoria (Labill.) R.Br: those with broad-lobed and those with narrow-lobed leaves. Stomatal conductance (g[sub s]), instantaneous water use efficiency (WUE), stomatal and minor veins density also were measured. ΔF/F[sub m]' decreased with stress but was higher and less spatially heterogeneous across broad than narrow lobes. The strongest depression in ΔF/F[sub m]' in broad lobes was at the edges and in narrow lobes, the tips. Non-photochemical quenching was spatially more varied in broad lobes, increasing at the edges and tips. Variation in photosynthetic function could not be explained by g[sub s], WUE or minor vein density, whereas proximity to major veins appeared to mitigate water stress at the tips only for broad lobes. Our findings indicate that the relationship between venation architecture and water delivery alone can partially explain the spatial pattern of photosynthetic function. [ABSTRACT FROM AUTHOR]

Tropical soils are often characterised by low phosphorus availability and tropical forest trees typically exhibit lower area-based rates of photosynthesis (A[sub a]) for a given area-based leaf nitrogen concentration ([N][sub a]) compared with plants growing in higher-latitude, N-limited ecosystems. Nevertheless, to date, very few studies have assessed the effects of P deprivation per se on A[sub a] ↔ [N][sub a] relationships in tropical trees. Our study investigated the effect of reduced soil P availability on light-saturated A[sub a] and related leaf traits of seven Australian tropical tree species. We addressed the following questions: (1) Do contrasting species exhibit inherent differences in nutrient partitioning and morphology? (2) Does P deprivation lead to a change in the nature of the A[sub a] ↔ [N][sub a] relationship? (3) Does P deprivation lead to an alteration in leaf nitrogen levels or N allocation within the leaf? Applying a mixed effects model, we found that for these Australian tropical tree species, removal of P from the nutrient solution decreased area-based photosynthetic capacity (A[sub max,a]) by 18% and reduced the slope of the A[sub max,a] ↔ [N][sub a] relationship and differences among species accounted for around 30% of response variation. Despite greater N allocation to chlorophyll, photosynthetic N use efficiency was significantly reduced in low-P plants. Collectively, our results support the view that low soil P availability can alter photosynthesis-nitrogen relationships in tropical trees. [ABSTRACT FROM AUTHOR]

To clarify the photoprotective mechanisms of cotton leaves under water deficit in the field, leaf gas exchange, chlorophyll a fluorescence as well as the corresponding physiological responses were examined in cotton (Gossypium hirsutum L.) to evaluate electron flux distribution. With increasing water deficit, net photosynthetic rate (P[sub n]) significantly decreased, the total electron flux through PSII [Je(PSII)] gradually decreased and the fraction of electron flux required to sustain CO[sub 2] assimilation [Je(PCR)] markedly declined. Simultaneously, the ratio of quantum efficiency of PSII [Φ(PSII)] to the quantum efficiency of CO[sub 2] fixation [Φ(CO[sub 2])] increased, accompanied by an increase in the alternative electron flux (Ja). The enhanced alternative electronflux of O[sub 2]-dependentJa(O[sub 2]-dependent) indicated that electrons had been transported to O[sub 2] in the Mehler-peroxide reaction (MPR) and that the remaining alternative electron flux Ja(O[sub 2]-independent) had been used for nitrate reduction, as indicated by an increase in nitrate reductase (NR) and glutathinone reductase (GR) activities. In addition, mild water deficit increased the proportion of electron flux for the photorespiratory carbon oxidation [Je(PCO)]. Water deficit significantly increased surperoxide radical production rate (O[sub 2][sup -]*) and hydrogen peroxide content (H[sub 2]O[sub 2]), and the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POD) and catalase (CAT) in cotton leaves also increased under water deficit. Therefore, the Mehler-peroxidation reaction, photorespiration and nitrate reduction helped to dissipated excess light energy, being important photoprotective mechanisms for adapting the photosynthetic apparatus to mild and moderate water deficit in cotton. [ABSTRACT FROM AUTHOR]

A hydrocooling system applied to Semillon (Vitis vinifera L.) grapevines as a means of protecting the vines from recurrent high temperatures. This system was assessed for impacts on vegetative and reproductive growth and development as well as for carbon economy of vines growing in vineyard conditions. The system maintained canopy temperatures at 35°C over the growing season. Leaf and bunch biomass and yield were all higher in the hydrocooled compared with control vines: the major effect was on dynamics of leaf and berry expansion. Leaf expansion was delayed and occurred over a longer duration whereas berry expansion was advanced and occurred over a longer duration than in control vines. Berry ripening was also faster in the hydrocooled vines and berries had accumulated more sugar at harvest. Leaf photosynthesis along the shoot was also higher in hydrocooled than control vines and there was a significant effect of leaf position on rates of photosynthesis of the hydrocooled vines but not with control vines. However, no differences were observed in the net shoot carbon budget. Lowered canopy temperatures were beneficial for yield and berry composition and, therefore, the cooling system warrants adoption in vineyards at risk from high temperature events during the growing season. Heat events are a natural summer occurrence in Australian vineyards but costly in lost production, thus, protecting vines during these events is an economically important issue. We have assessed spraying water onto vines for brief periods as a means of reducing canopy temperatures. The canopies were nearly 10°C cooler during the heat events and both yields and berry composition were improved, suggesting spraying water onto vines is an effective means of reducing impacts of high temperatures. [ABSTRACT FROM AUTHOR]

A better physiological and productive performance of cv. Montepulciano versus cv. Sangiovese under well-watered conditions has been recently assessed. The objective of this study was to verify that this behaviour is maintained when a pre-veraison deficit irrigation (vines held at 40% pot capacity from fruit-set to veraison) followed by re-watering (pot capacity reported at 90%). Single leaf assimilation rate and stomatal conductance, diurnal and seasonal whole-canopy net CO2 exchange (NCER) and water use efficiency were always higher in Sangiovese under deficit irrigation. Due to water shortage Montepulciano displayed a more compact growing habit due to decreased shoot and internode length. Sangiovese showed excellent recovery upon re-watering as NCER resulted to be higher than the pre-stress period; however, this might also relate to early and severe basal leaf yellowing and shedding. Early deficit irrigation affected xylem characteristics of Montepulciano more than in Sangiovese; vessel density increased (37 vs 29%, respectively, compared with well-watered vines) and the hydraulic conductance decreased more (-13 vs -3% respectively) compared with well-watered vines. Yield components and technological maturity were similar in the two cultivars, whereas Montepulciano grapes had lower anthocyanins and phenolics. Higher physiological and productive efficiency under non-limiting water conditions showed by Montepulciano compared with Sangiovese was basically reversed when both cultivars were subjected to an early deficit irrigation. The intraspecific diversity of Sangiovese and Montepulciano grapevine varieties is accentuated under early water deficit. Higher physiological and productive efficiency under non-limiting water supply noted by the near-isohydric Montepulciano compared with the near-anisohydric Sangiovese was reversed when both cultivars were subjected to a pre-veraison water deficit. Sangiovese had excellent net CO2 exchange (NCER) recovery upon re-watering and is confirmed to be better adapted to dry/hot conditions. [ABSTRACT FROM AUTHOR]

An understanding of processes regulating wheat floret and grain number at higher temperatures is required to better exploit genetic variation. In this study we tested the hypothesis that at higher temperatures, a reduction in floret fertility is associated with a decrease in soluble sugars and this response is exacerbated in genotypes low in water soluble carbohydrates (WSC). Four recombinant inbred lines contrasting for stemWSCwere grown at 20/10°C and 11 h photoperiod until terminal spikelet, and then continued in a factorial combination of 20/10°C or 28/14°C with 11 h or 16 h photoperiod until anthesis. Across environments, High WSC lines had more grains per spike associated with more florets per spike. The number of fertile florets was associated with spike biomass at booting and, by extension, with glucose amount, both higher in High WSC lines. At booting, High WSC lines had higher fixed 13C and higher levels of expression of genes involved in photosynthesis and sucrose transport and lower in sucrose degradation compared with Low WSC lines. At higher temperature, the intrinsic rate of floret development rate before booting was slower in High WSC lines. Grain set declined with the intrinsic rate of floret development before booting, with an advantage for High WSC lines at 28/14°C and 16 h. Genotypic and environmental action on floret fertility and grain set was summarised in a model. [ABSTRACT FROM AUTHOR]

Diatoms dominate nearly half of current oceanic productivity, so their responses to ocean acidification are of general concern regarding future oceanic carbon sequestration. Community, mesocosm and laboratory studies show a range of diatom growth and photophysiological responses to increasing pCO2. Nearly 20 studies on effects of elevated pCO2 on diatoms have shown stimulations, no effects or inhibitions of growth rates. These differential responses could result from differences in experimental setups, cell densities, levels of light and temperature, but also from taxon-specific physiology. Generally, ocean acidification treatments of lowered pH with elevated CO2 stimulate diatom growth under low to moderate levels of light, but lead to growth inhibition when combined with excess light. Additionally, diatom cell sizes and their covarying metabolic rates can influence responses to increasing pCO2 and decreasing pH, although cell size effects are confounded with taxonomic specificities in cell structures and metabolism. Here we summarise known diatom growth and photophysiological responses to increasing pCO2 and decreasing pH, and discuss some reasons for the diverse responses observed across studies. [ABSTRACT FROM AUTHOR]

Legumes such as alfalfa (Medicago sativa L.) are vital N[sub 2]-fixing crops accounting for a global N[sub 2] fixation of ~35 Mt N year[sup -1]. Although enzymatic and molecular mechanisms of nodule N[sub 2] fixation are now well documented, some uncertainty remains as to whether N[sub 2] fixation is strictly coupled with photosynthetic carbon fixation. That is, the metabolic origin and redistribution of carbon skeletons used to incorporate nitrogen are still relatively undefined. Here, we conducted isotopic labelling with both [sup 15]N[sub 2] and [sup 13]C-depleted CO[sub 2] on alfalfa plants grown under controlled conditions and took advantage of isotope ratio mass spectrometry to investigate the relationship between carbon and nitrogen turn-over in respired CO[sub 2], total organic matter and amino acids. Our results indicate that CO[sub 2] evolved by respiration had an isotopic composition similar to that in organic matter regardless of the organ considered, suggesting that the turn-over of respiratory pools strictly followed photosynthetic input. However, carbon turn-over was nearly three times greater than N turn-over in total organic matter, suggesting that new organic material synthesised was less N-rich than pre-existing organic material (due to progressive nitrogen elemental dilution) or that N remobilisation occurred to sustain growth. This pattern was not consistent with the total commitment into free amino acids where the input of new C and N appeared to be stoichiometric. The labelling pattern in Asn was complex, with contrasted C and N commitments in different organs, suggesting that neosynthesis and redistribution of new Asn molecules required metabolic remobilisation. We conclude that the production of new organic material during alfalfa growth depends on both C and N remobilisation in different organs. At the plant level, this remobilisation is complicated by allocation and metabolism in the different organs. The combination of double C[sup 13] and N[sup 15] labelling and subsequent compound-specific analysis in amino acids showed the imbalance observed between CO[sub 2] and N[sub 2] fixation in nodulated alfalfa plants. It provided a novel conclusion about the use and importance of pre-existing reserves in the production of new organic matter during growth. [ABSTRACT FROM AUTHOR]

The responses to mild root zone salinity stress were investigated in two co-occurring Mediterranean woody evergreens, Quercus ilex L. and Arbutus unedo L., which differ in morpho-anatomical traits and strategies to cope with water deficit. The aim was to explore their strategies to allocate potentially toxic ions at organism level, and the consequential physiological and biochemical adjustments. Water and ionic relations, gas exchange and PSII performance, the concentration of photosynthetic pigments, and the activity of antioxidant defences, were measured. Q. ilex displayed a greater capacity to exclude Na[sup +] and Cl[sup -] from the leaf than A. unedo, in part as a consequence of greater reductions in transpiration rates. Salt-induced reductions in CO[sub 2] assimilation resulted in Q. ilex suffering from excess of light to a greater extent than A. unedo. Consistently, in Q. ilex effective mechanisms of nonphotochemical quenching, also sustained by the lutein epoxide-lutein cycle, operated in response to salinity stress. Q. ilex also displayed a superior capacity to detoxify reactive oxygen species (ROS) than A. unedo. Our data suggest that the ability to exclude salt from actively growing shoot organs depends on the metabolic cost of sustaining leaf construction, i.e. species-specific leaf life-span, and the relative strategies to cope with salt-induced water stress. We discuss how contrasting abilities to restrict the entry and transport of salt in sensitive organs relates with species-specific salt tolerance. Plants inhabiting Mediterranean coastal areas display contrasting strategies to cope with a wide range of stresses. Also, Mediterranean areas display a high level of biodiversity. Here we explored strategies adopted by two co-occurring woody evergreens when suffering from an excess of soil salinity. Species-specific leaf life-span and drought-tolerance strategies are tightly related with salt-exclusion mechanisms, which, in turn, greatly impacts upon salt-induced metabolic adjustments. [ABSTRACT FROM AUTHOR]

Direct measurements of foliar carbon exchange through the growing season in Arctic species are limited, despite the need for accurate estimates of photosynthesis and respiration to characterise carbon cycling in the tundra. We examined seasonal variation in foliar photosynthesis and respiration (measured at 20°C) in two field-grown tundra species, Betula nana L. and Eriophorum vaginatum L., under ambient and long-term warming (LTW) conditions (+5°C), and the relationship of these fluxes to intraseasonal temperature variability. Species and seasonal timing drove most of the variation in photosynthetic parameters (e.g. gross photosynthesis (A[sub gross])), respiration in the dark (R[sub dark]) and light (R[sub light]), and foliar nitrogen concentration. LTW did not consistently influence fluxes through the season but reduced respiration in both species. Alongside the flatter respiratory response to measurement temperature in LTW leaves, this provided evidence of thermal acclimation. The inhibition of respiration by light increased by ~40%, with R[sub light] : R[sub dark] values of ~0.8 at leaf out decreasing to ~0.4 after 8 weeks. Though LTW had no effect on inhibition, the cross-taxa seasonal decline in R[sub light] : R[sub dark] greatly reduced respiratory carbon loss. Values of R[sub light] : A[sub gross] decreased from ~0.3 in both species to ~0.15 (B. nana) and ~0.05 (E. vaginatum), driven by decreases in respiratory rates, as photosynthetic rates remained stable. The influence of short-term temperature variability did not exhibit predictive trends for leaf gas exchange at a common temperature. These results underscore the influence of temperature on foliar carbon cycling, and the importance of respiration in controlling seasonal carbon exchange. [ABSTRACT FROM AUTHOR]

Genotypic differences in early growth and nitrogen (N) uptake among 24 wheat (Triticum aestivum L.) genotypes were assessed ina field trial. Atlate tillering, large genetic variation was observed for shoot biomass (23-56 g m[sup -2] ground area) and N uptake (1.1-1.8 gm[sup -2] ground area). A strong correlation between aboveground biomass and N uptake was observed. Variation around this relationship was also found, with some genotypes having similar N uptake but large differences in aboveground biomass. A controlled environment experiment was conducted to investigate the underlying mechanisms for this variation in aboveground biomass using three vigorous genotypes (38-19, 92-11 and CV97) and a non-vigorous commercial cultivar (Janz). Vigorous genotypes had lower specific leaf N in the youngest fully expanded leaf than Janz. However, there was no difference in chlorophyll content, maximum Rubisco activity or the rate of electron transport per unit area. This suggests that Janz invested more N in non-photosynthetic components than the vigorous lines, which could explain the higher photosynthetic N use efficiency of the vigorous genotypes. The results suggest that the utilisation of wheat genotypes with high early vigour could improve the efficiency of N use for biomass production in addition to improving N uptake during early growth. [ABSTRACT FROM AUTHOR]

Manganese (Mn[sup 2+]) toxicity or UV-B radiation and their individual effects on plants have been documented previously. However, no study about the combined effect of these stresses is available. We evaluated the individual and combined effects of excess Mn[sup 2+] and UV-B radiation on physiological and biochemical parameters in two highbush blueberry (Vaccinium corymbosum L.) cultivars differing in resistance to Mn toxicity (Brigitta (resistant) and Bluegold (sensitive)). Plants grown in Hoagland nutrient solution were subjected to the following treatments: 2 μM MnCl[sub 2] (control), 500 μMMnCl[sub 2] (toxicMn[sup 2+]),UV-B radiation(a daily dose of 94.4 kJ m[sup -2]), and the combined treatment(toxic Mn[sup 2+] + UV-B) for 30 days. In both cultivars, the Mn[sup 2+] + UV-B treatment caused a more negative effect on net photosynthesis (P[sub n]), stomatal conductance (g[sub s]), the photochemical parameters of PSII and the chl a/b ratio than the treatments with toxic Mn[sup 2+] or UV-B alone. However, Brigitta showed also a better acclimation response in P[sub n] and g[sub s] than Bluegold at the end of the experiment. The Mn[sup 2+] + UV-B treatment inhibited growth, enhanced radical scavenging activity and superoxide dismutase activity, and increased the concentration of total UV-absorbing compounds, phenols and anthocyanins, mainly in Bluegold. In conclusion, Mn-resistant Brigitta showed a better acclimation response and greater resistance to the combined stress of Mn[sup 2+] toxicity and UV-B exposure than the Mn-sensitive Bluegold. An increased concentration of photoprotective compounds and enhanced resistance to oxidative stress in Brigitta could under pin increased resistance to the combined stress. [ABSTRACT FROM AUTHOR]