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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]

The genus Ruscus (Asparagaceæ) consists of evergreen, woody monocot shrubs with modified photosynthetic stems (phylloclades) that occur in dry, shaded woodland areas of the Mediterranean Basin and southern Europe. The combined drought and shade tolerance of Ruscus species challenges the 'trade-off model', which suggests that plants can be either drought or shade adapted, but not both. To clarify the potential mechanisms that enable Ruscus species to survive in shaded environments prone to pronounced soil drought, we studied form-function relations based on a detailed trait survey for Ruscus aculeatus L. and Ruscus microgloβum Bertol., focusing on gas exchange, hydraulics, morphology, anatomy, and nutrient and isotope composition. We then compared these trait values with published data for other species. R. aculeatus and R. microgloβum exhibited numerous traits conferring drought and shade tolerance via reduced demand for resources in general and an ability to survive on stored water. Specific traits include thick phylloclades with low rates of maximum photosynthetic CO[sub 2] aβimilation, low stomatal conductance to water vapour (gs), low respiration rate, low light compensation point, low shoot hydraulic conductance, low cuticular conductance, and substantial water storage tiβue. Ruscus carbon isotope composition values of -33 ‰ were typical of an understory plant, but given the low g[sub s] could be aβociated with internal CO[sub 2] recycling. Ruscus appears to be a model for extreme dual adaptation, both physiologically and morphologically, enabling its occupation of shaded sites within drought prone regions acroβ a wide geographical range, including extremely low resource understory sites. [ABSTRACT FROM AUTHOR]

Diurnal or prolonged exposure to air temperatures above the thermal optimum for a plant can impair physiological performance and reduce crop yields. This study investigated the molecular response to heat streβ of two high-yielding cotton (Goβypium hirsutum L.) cultivars with contrasting heat tolerance. Using global gene profiling, 575 of 21854 genes aβayed were affected by heat streβ, ~60% of which were induced. Genes encoding heat shock proteins, transcription factors and protein cleavage enzymes were induced, whereas genes encoding proteins aβociated with electron flow, photosynthesis, glycolysis, cell wall synthesis and secondary metabolism were generally repreβed under heat streβ. Cultivar differences for the expreβion profiles of a subset of heat-responsive genes analysed using quantitative PCR over a 7-h heat streβ period were aβociated with expreβion level changes rather than the presence or absence of transcripts. Expreβion differences reflected previously determined differences for yield, photosynthesis, electron transport rate, quenching, membrane integrity and enzyme viability under growth cabinet and field-generated heat streβ, and may explain cultivar differences in leaf-level heat tolerance. This study provides a platform for understanding the molecular changes aβociated with the physiological performance and heat tolerance of cotton cultivars that may aid breeding for improved performance in warm and hot field environments. [ABSTRACT FROM AUTHOR]

We tested the hypothesis that an age-dependent reduction in leaf hydraulic conductance (K[sub leaf]) influences the timing of leaf senescence via limitation of the stomatal aperture on xylem compound delivery to leaves of tomato (Solanum lycopersicum L.), the tropical trees Anacardium excelsum Kunth,Pittoniotis trichantha Griseb, and the temperate trees Acer saccharum Marsh. and Quercus rubra L. The onset of leaf senescence was preceded by a decline in K[sub leaf] in tomato and the tropical trees, but not in the temperate trees. Age-dependent changes in K[sub leaf] in tomato were driven by a reduction in leaf vein density without a proportional increase in the xylem hydraulic supply. A decline in stomatal conductance accompanied K[sub leaf] reduction with age in tomato but not in tropical and temperate tree species. Experimental manipulations that reduce the flow of xylem-transported compounds into leaves with open stomata induced early leaf senescence in tomato and A. excelsum, but not in P. trichantha, A. saccharum and Q. rubra leaves. We propose that in tomato, a reduction in K[sub leaf] limits the delivery of xylem-transported compounds into the leaves, thus making them vulnerable to senescence. In the tropical evergreen tree A. excelsum, xylem-transported compounds may play a role in signalling the timing of senescence but are not under leaf hydraulic regulation; leaf senescence in the deciduous trees A. trichanta, A. saccharum and Q. rubrais not influenced by leaf vascular transport. [ABSTRACT FROM AUTHOR]

The hydraulic architecture of leaves represents the final path along which liquid water travels through the plant and comprises a significant resistance for water movement, especially for graβes. We partitioned leaf hydraulic resistance of six genotypes of Sorghum bicolor L. (Moench) into leaf specific hydraulic resistance within the large longitudinal veins (r[sup *][sub LV]) and outside the large veins (r[sup *][sub OLV]), and correlated these resistances with the response of stomatal conductance (g[sub s]) and photosynthesis (A) to drought. Under well-watered conditions, g[sub s] was tightly correlated with r[sup *][sub OLV] (r[sup 2] = 0.95), butaβoil moisture decreased, g[sub s] was more closely correlated withr[sup *][sub L V] (r[sup 2] = 0.97). These results suggest that r[sup *][sub OLV] limits maximum rates of gas exchange, but the ability to efficiently move water long distances (low r[sup *][sub L V]) becomes more important for the maintenance of cell turgor and gas exchange as soil moisture declines. Hydraulic resistance through the leaf was negatively correlated with evapotranspiration (P < 0.001) resulting in more conservative water use in genotypes with large leaf resistance. These results illustrate the functional significance of leaf resistance partitioning to declining soil moisture in a broadly-adapted cereal species. [ABSTRACT FROM AUTHOR]

Olive (Olea europaea L.) production is marked by annual oscillations as trees alternate from high to low crop loads in successive years. Gas exchanges and carbohydrate content of leaves and fruits in olive tree (O. europaea cv. Besbassi) were monitored at pit hardening and fruit ripening. After fruit set, three crop loads were applied (100%, 50% and 25% of the initial fruit load) by manual thinning. Severe fruit thinning reduced photosynthesis, stomatal conductance and intercellular CO[sub 2] concentration. Crop load had no significant effect on chlorophyll fluorescence parameters. The reduction of 75% of the initial crop load favoured the accumulation of starch in leaves and soluble sugars in leaves and fruits. The reduction in initial fruit load had a significant positive effect on the current year's shoot elongation and on inflorescence number the following spring. To increase the fruit size, a strong thinning (75%) was necessary, which coincided with the highest shoot vigour. Moderate thinning (50%) hardly affected leaf carbohydrate content and fruit size, but photosynthetic capacity was only limited at fruit ripening. [ABSTRACT FROM AUTHOR]

Cyclic electron flux (CEF) around PSI is essential for efficient photosynthesis and aids photoprotection, especially in stressful conditions, but the difficulty in quantifying CEF is non-trivial. The total electron flux through PSI (ETR1) and the linear electron flux (LEF[sub O[sub 2] ]) through both photosystems in spinach leaf discs were estimated from the photochemical yield of PSI and the gross oxygen evolution rate, respectively, in CO[sub 2]-enriched air. ΔFlux = ETR1 - LEF[sub O[sub 2] ] is an upper estimate of CEF. Infiltration of leaf discs with 150 μM antimycin A did not affect LEF[sub O[sub 2] ], but decreased ΔFlux 10-fold. ΔFlux was practically negligible below 350 μmol photons m[sup -2] s[sup -1], but increased linearly above it. The following results were obtained at 980 μmol photons m[sup -2] s[sup -1]. ΔFlux increased 3-fold as the temperature increased from 5°C to 40°C. It did not decline at high temperature, even when LEF[sub O[sub 2] ] decreased. ΔFlux increased by 80% as the relative water content of leaf discs decreased from 100 to 40%, when LEF[sub O[sub 2] ] decreased 2-fold. The method of using ΔFlux as a non-intrusive upper estimate of steady-state CEF in leaf tissue appears reasonable when photorespiration is suppressed. In photosynthesis, electrons derived from water are driven uphill in a linear fashion as well as in a loop or cycle, both flows helping to convert CO[sub 2] into sugars. This study estimates the hitherto elusive rate of cyclic flow in leaves in CO[sub 2]-enriched air. Estimates of cyclic flow will help to assess its role and elucidate its regulation in efficient photosynthesis. [ABSTRACT FROM AUTHOR]

Plantlets of Aeluropus lagopoides (Linn.) Trin. Ex Thw. were grown at different NaCl concentrations (26, 167, 373 and 747 mM) for 3, 7 and 15 days; their growth, osmotic adjustment, gas exchange, ion compartmentalisation and expression of various genes related to Na+ flux was studied. Plantlets showed optimal growth in non-saline (control; 26 mM NaCl) solutions, whereas CO[sub 2]/H[sub 2]O gas exchange, leaf water concentration and water use efficiency decreased under all salinity treatments, accompanied by increased leaf senescence, root ash, sodium content and leaf osmolality. A decrease in malondialdehyde (MDA) content with time was correlated with Na+ accumulation in the leaf apoplast and a concomitant increase in Na+ secretion rate. A. lagopoides accumulated a higher concentration of Na+ in root than in leaf vacuoles, corresponding with higher expression of V-NHX and lower expression of PM-NHX in root than leaf tissue. It appears that V-ATPase plays a vital role during Na+ transport by producing an electromotive force, driving ion transport. Leaf calcium increased with increasing salinity, with more rapid accumulation at high salinity than at low salinity, indicating a possible involvement of Ca[sup 2+] in maintaining K+ : Na+ ratio. Our results suggest that A. lagopoides successfully compartmentalised Na+ at salinities up to 373 mM NaCl by upregulating the gene expression of membrane linked transport proteins (V-NHX and PM-NHX). At higher salinity (747 mM NaCl), a reduction in the expression of V-NHX and PM-NHX in leaves without any change in the rate of salt secretion, is a possible cause of the toxicity of NaCl. To investigate the role of compartmentation and secretion rate in the avoidance of Na+ toxicity in the halophyte Aeluropus lagopoides, we report that Na+ was successfully compartmentalised at salinities up to 373 mM NaCl by upregulating the gene expression of membrane linked transport proteins V-NHX and PM-NHX. At higher salinity a reduction in the expression of V-NHX and PM-NHX in leaves without any change in the rate of salt secretion is a possible cause of toxicity of NaCl. [ABSTRACT FROM AUTHOR]

Communities of Tecticornia on the margins of ephemeral salt lakes in Australia often exhibit species zonation, such as at Hannan Lake (Western Australia) where Tecticornia indica subsp. bidens (Nees) K.A.Sheph. and Paul G.Wilson occupies the less saline dune habitat on lake margins and Tecticornia pergranulata (J.M.Black) K.A.Sheph. and Paul G.Wilson subsp. pergranulata occupies both the dunes and the more saline and moist lake playa. Here we tested the hypothesis that these two species differ in tolerance to extreme salinity. Plants were grown in drained sand cultures with treatments of 10-2000 mM NaCl for 85 days. Both species were highly salt tolerant, maintaining growth at treatments of up to 2000 mM NaCl, although the death of two replicates of T. indica at 2000 mM NaCl suggests this salinity is close to the species tolerance limit. Both Tecticornia species maintained a favourable gradient in tissue water potential via osmotic adjustment as external salinity increased, also with reduced tissue water content at very high external salinity. Regulated accumulation of Na+ and Cl[sup -], maintenance of net K+ to Na+ selectivity, high tissue concentrations of glycinebetaine and presumed cellular solute compartmentation, would have contributed to salt tolerance. The growth rate of T. pergranulata was 11-29% higher than T. indica suggesting, in addition to these moderate differences in salinity tolerance, other factors are likely to contribute to species zonation at salt lakes. The higher water use efficiency of the C[sub 4] T. indica compared with the C[sub 3] T. pergranulata may provide an advantage in the drier dune habitat on salt lake margins. An additional experiment confirmed the hypothesis that survival of T. pergranulata seedlings is enhanced by the duration of reduced salinity after germination, as would occur following significant rainfall, as older seedlings maintained higher growth rates during subsequent increases in salinity. Some stem-succulent halophytes inhabit areas of very high salinity, such as inland salt lakes. Tolerance and physiological responses to extreme salinity (2000 mM NaCl) were evaluated for two Tecticornia species; both were highly tolerant. Growth patterns of halophytic species on the margins of salt lakes are likely influenced both by soil salinity and water availability (periodic floods and water deficits). [ABSTRACT FROM AUTHOR]

The successful integration of activity in saline environments requires flexibility of responses at all levels, from genes to life cycles. Because plants are complex systems, there is no 'best' or 'optimal' solution and with respect to salt, glycophytes and halophytes are only the ends of a continuum of responses and possibilities. In this review, I briefly examine seven major aspects of plant function and their responses to salinity including transporters, secondary stresses, carbon acquisition and allocation, water and transpiration, growth and development, reproduction, and cytosolic function and 'integrity'. I conclude that new approaches are needed to move towards understanding either organismal integration or 'salt tolerance', especially cessation of protocols dependent on sudden, often lethal, shock treatments and the embracing of systems level resources. Some of the tools needed to understand the integration of activity and even 'salt stress' are already in hand, such as those for whole-transcriptome analysis. Others, ranging from discovery studies of the nature of the cytosol to expanded tool kits for proteomic, metabolomic and epigenomic studies, still need to be further developed. After resurrecting the distinction between applied stress and the resultant strain and noting that with respect to salinity, the strain is manifest in changes at all -omic levels, I conclude that it should be possible to model and quantify stress responses. Plants have adapted to life in saline environments in a myriad of ways, some more broadly successful than others. These adaptations involve the integration of all activities at levels ranging from genes to physiology to life cycles. With the availability of new '-omic' resources, the tools of systems biology and perhaps forgotten tools of physiology and biophysics, we may now be poised to decipher the complexities of the integration of organismal activities as never before. [ABSTRACT FROM AUTHOR]

The mechanisms of drought resistance in perennial legumes are poorly understood. We explored the diurnal and seasonal variation (May, August, February) in stomatal conductance (g[sub s] ) and paraheliotropism of three tedera accessions (Bituminaria bituminosa (L.) C.H. Stirton var. albomarginata) and lucerne (Medicago sativa L.), both perennial legumes, grown in the field. For the tedera accessions, there was a significant reduction in g[sub s] during the day in May (late autumn) and February (summer), but there was little reduction for lucerne. The peak leaf angle in the tedera accessions ranged from <40° to 70°, whereas for lucerne, the leaf angle was nearly parallel to incident light at 85°. Leaf water-use efficiency, relative leaf water content and leaf retention were higher for the tedera accessions than for lucerne in February. These results highlight the superior drought resistance of tedera compared with lucerne. The reduction in g[sub s] over the day in tedera shows the capacity of this species to reduce water loss quickly when conditions for CO[sub 2] fixation relative to water loss are highly unfavourable. The high retention of leaves in summer by tedera is a valuable trait for a perennial pasture plant in Mediterranean environments. Leaf folding, combined with effective stomatal control in summer, provides tedera with a set of physiological responses that confer high drought resistance. We investigated physiological drought resistance mechanisms under field conditions in mature plants of the perennial herbaceous legume tedera (Bituminaria bituminosa (L.) var. albomarginata). Leaf folding, combined with effective stomatal control, conferred high drought resistance in summer. Measures of leaf water-use efficiency, relative leaf water content, and leaf retention also suggested high drought resistance. Variation among accessions indicates genetic diversity for drought resistance that may be valuable in future breeding programs. Tedera seems good for Western Australia's challenging climate, having survived the arid Canary Islands climate. [ABSTRACT FROM AUTHOR]

Elevated atmospheric CO2 concentrations (ca) will undoubtedly affect the metabolism of tropical forests worldwide; however, critical aspects of how tropical forests will respond remain largely unknown. Here, we review the current state of knowledge about physiological and ecological responses, with the aim of providing a framework that can help to guide future experimental research. Modelling studies have indicated that elevated ca can potentially stimulate photosynthesis more in the tropics than at higher latitudes, because suppression of photorespiration by elevated ca increases with temperature. However, canopy leaves in tropical forests could also potentially reach a high temperature threshold under elevated ca that will moderate the rise in photosynthesis. Belowground responses, including fine root production, nutrient foraging and soil organic matter processing, will be especially important to the integrated ecosystem response to elevated ca. Water use efficiency will increase as ca rises, potentially impacting upon soil moisture status and nutrient availability. Recruitment may be differentially altered for some functional groups, potentially decreasing ecosystem carbon storage. Whole-forest CO2 enrichment experiments are urgently needed to test predictions of tropical forest functioning under elevated ca. Smaller scale experiments in the understorey and in gaps would also be informative, and could provide stepping stones towards stand-scale manipulations. [ABSTRACT FROM AUTHOR]

Productivity of sunflower (Helianthus annuus L.), the fourth most important oilseed crop, is strongly dependent on water availability. To search for genetic variation in the ability of roots to grow into drying soil, 16 sunflower lines were screened in 2 years field experiments by imposing drought stress at flowering stage. The results differentiated RGK 21 and BGK 329 as the most sensitive and tolerant lines respectively. The time course physiological assay of these lines at seedling stage revealed roots as the most affected organ 6 days after imposing drought stress. A proteomics approach was adapted for investigating of differential changes in roots proteome under contrasting moisture regimes. Protein spots with significant changes in protein abundance were identified by nano LC-MS/MS. The results indicated that under drought stress relative abundance of metabolism related proteins were decreased in both sensitive and tolerant lines. Abundance of energy and disease/defence related proteins were decreased in the sensitive but increased in the tolerant line. The results indicate that changes in energy usage, water transport and ROS scavenging are important mechanisms for maintaining root growth as the soil dries. [ABSTRACT FROM AUTHOR]

Xylem-tapping mistletoes are known to have generally higher transpiration rate (T[sub r]), lower CO[sub 2] assimilation rate (A) and therefore lower water-use efficiency (WUE) than their hosts. There are long-standing contradictions in water relations and nitrogen use in photosynthesis. Gas exchange, chlorophyll fluorescence and nutrition components were investigated in a special mistletoe-host pair, Viscum ovalifolium-Sonneratia caseolaris, as the host was a mangrove growing in a saline environment. Our results show that both plants had high foliar N content, therefore it was consistent with the N-parasitism hypothesis, although the mistletoe had a lower T[sub r] than its mangrove host. It was suggested that the mistletoe reduces its T[sub r] under salt stress with N sufficient conditions. The mistletoe had a fundamental limitation of photosynthesis, and was photoinhibited with regard to high salinity, but it developed more photoprotection to thermal radiation. Additionally, both stomatal conductance (g[sub s]) and mesophyll conductance (g[sub m]) limitations on photosynthesis dominated in the mistletoe under salt stress even though it had a high foliar N content similar to the host. [ABSTRACT FROM AUTHOR]

Paris polyphylla Smith var. yunnanensis (Franch.) Hand.-Mazz. is a rhizomatous, herbaceous, perennial plant that is used as a medicinal plant with a variety of pharmacological activities. However, the functions of the green, leafy sepal of this plant are poorly understood. The main objectives of this study were to: (a) test the hypothesis that sepals make measurable contributions to fruit development and rhizome growth; and (b) investigate the allocation and partitioning of photosynthates produced by sepals and leaves to fruit and rhizome. Net photosynthetic rate, photosynthetic pigment composition and δ[sup 13]C values were similar for sepals and leaves. Sepal-darkening and sepal-removal treatments resulted in smaller fruit size and decreased rhizome biomass, whereas fruit removal led to a decrease in calyx size and an increase in rhizome yield and saponin content. Fruit and seed mass were positively and linearly related to calyx size. These results indicate that photosynthates produced by sepals are involved in the fruit growth and seed development and that developing fruit and rhizomes compete for the photosynthates exported by leaves. We propose that the sepals of P. polyphylla function partly as leaves to compensate for reproductive costs. Fruit removal increased carbon partitioning to the rhizome and improved rhizome yield and quality, offering a useful strategy for the domestication of this valuable medicinal plant. [ABSTRACT FROM AUTHOR]

Salicylic acid (SA), a signalling molecule in plant-pathogen interactions induces stomatal closure in intact leaves and it has a direct control over stomatal movement by increasing the levels of reactive oxygen species (ROS) and nitric oxide (NO) in guard cells (GC). Stomatal closure on the abaxial epidermal peels of tomato leaves was induced at 10[sup -7] and 10[sup -3] M SA but stomata remained open at 10[sup -4] M. At concentrations that reduced stomatal aperture, the ROS and NO levels were raised. The accumulation of ROS and NO could be prevented by specific scavengers, which were effective inhibitors of the SA-induced stomatal closure. In contrast with other plant species, the guard cells (GCs) of tomato did not show a long-lasting accumulation of ROS in the presence of 10[sup -4] M SA and their NO content decreased to below the control level, leading to stomatal opening. Increasing SA concentrations resulted in a significant decrease in the maximum and effective quantum yields of PSII photochemistry and in the photochemical quenching parameter of GCs. In the presence of 10[sup -7] and 10[sup -4] M SA, the chloroplasts of GCs sustained a higher electron transport rate than in the presence of 10[sup -3] M, suggesting that the SA-induced inhibition of GC photosynthesis may affect stomatal closure at high SA concentrations. Salicylic acid (SA) is a plant growth regulator and is a central regulator of defence against (hemi-) biotrophic pathogens. We investigated stomatal closure over a range of SA concentrations in tomato leaves and abaxial epidermal peels. SA concentrations of 10[sup -7] or 10[sup -3] M induced stomatal closure, but in epidermal peels 10[sup -4] M SA induced stomatal opening without increasing the level of signalling intermediates. This suggests that a balance exists between the intermediates (reactive oxygen species and nitric oxide) to regulate stomatal aperture. [ABSTRACT FROM AUTHOR]

Different requirements for reproduction between sexes in dioecious plants can lead to gender-specific physiological responses to environmental constraints. Females generally endure higher reproductive investment and costs than males, displaying lower water and nutrient use efficiency and growth. We studied the ecophysiology of the dioecious shrub Corema album L. (D.) Don. to assess how drought impacts physiological responses and gender dimorphism along an aridity gradient within the species' range. Leaf gas exchange, photochemical efficiency (F[sub v]/F[sub m]), water potential (Ψ), vegetative growth (VG) and leaf C isotopic discrimination and nitrogen content were measured in three populations under markedly different climatic conditions. Physiological responses and growth indicated higher level of stress in the drier environments, leading to increased WUE (Δ) and lower VG. Physiological stress increases among plants were related to incremental changes in the degree of gender dimorphism, with significant effects on Ψ and F[sub v]/F[sub m] (P < 0.05); males showed higher VG (P < 0.001). Multivariate analysis of instantaneous and integrated measurements revealed gender-related effects across the climatic gradient (P < 0.01). Reproduction investment has an effect on the physiological performance and growth of C. album. Gender responses are site-specific, being influenced by climate. The increase in physiological stress with aridity could lead to the potential retreat and variation in structure in these populations if genders are affected differently by the predicted climate change. Understanding gender-specific responses of dioecious species to environmental constraints is crucial to assess the effects of reproductive investment in plant performance. The analysis of physiological responses and growth of a dioecious shrub along a climatic gradient revealed gender differences to be site-specific and strong physiological limitations under higher aridity conditions. Results highlight potential effects of climate changes on gender dimorphism and species distribution. [ABSTRACT FROM AUTHOR]

This laboratory experiment tested the ability of the spectral index called 'area under curve normalised to maximal band depth' (ANMB) to track dynamic changes in the xanthophyll cycle of Norway spruce (Picea abies (L.) Karsten) needles. Four-year-old spruce seedlings were gradually acclimated to different photosynthetic photon flux densities (PPFDs) and air temperature regimes. The measurements were conducted at the end of each acclimation period lasting for 11 days. A significant decline in the chlorophylls to carotenoids ratio and the increase of the amount of xanthophyll cycle pigments indicated a higher need for carotenoid-mediated photoprotection in spruce leaves acclimated to high PPFD conditions. Similarly, the photochemical reflectance index (PRI) changed from positive to negative values after changing light conditions from low to high intensity as a consequence of the increase in carotenoid content. Systematic responses of PRI to the de-epoxidation state of xanthophyll cycle pigments (DEPS) were, however, observed only during high temperature treatments and after the exposition of needles to high irradiance. The ANMB index computed from needle reflectance between 507 and 556 nm was able to track dynamic changes in DEPS without any influence induced by changing the content of leaf photosynthetic pigments (chlorophylls, carotenoids). Plant photochemistry includes a photoprotective cycle of xanthophyll pigments. This study introduces a leaf reflectance continuum removal index that can track changes in composition of the xanthophylls induced by increasing light intensity and air temperature independently from an actual content of chlorophylls and carotenoids. If successfully tested at the canopy level, the index may serve as a xanthophyll remote sensing indicator. [ABSTRACT FROM AUTHOR]

Diel (24 h) rhythms are believed to be of great importance to plant growth and carbohydrate metabolism in fluctuating environments. However, it is unclear how plants that have evolved to experience regular day -- night patterns will respond to irregular light environments that disturb diurnally-regulated parameters related to growth. In this study, chrysanthemum plants were exposed to a change in the time-of-day application of light followed by short days or long days with a night interruption of light. We observed a clear shift in the diel cycle of sucrose turnover and relative leaf expansion, indicating a resetting of these activities with a temporal trigger in the early morning. The starch pool was relatively stable in long-day plants and marginally affected by the change in the time-of-day application in light followed by long days with a night interruption. This was in contrast with an onset of a daily starch turnover by a shift to short days. These results confirm findings from model species on the complex relationship between carbohydrate metabolism, source -- sink relations and growth rate and they shed new light on the dynamic processes during acclimation towards altered environmental responses of plants in fluctuating environments. Diurnal leaf carbohydrate turnover patterns are complex and vary in relation to species, developmental stage and environmental conditions. We demonstrate rapid adjustment of carbohydrate turnover and leaf growth to a phase-shift in light conditions in Chrysanthemum. The starch pool confers a high buffer capacity to maintain sugar supply for growth and explains the direct relationship between growth and daily light integral in fluctuating light environments. The results are valuable in describing non-model plant species responses to ever-changing light environments. [ABSTRACT FROM AUTHOR]

Nax1 and Nax2 are two genetic loci that control the removal of Na[sup +] from the xylem and thereby help to exclude Na[sup +] from leaves of plants in saline soil. They originate in the wheat ancestral relative Triticum monococcum L. and are not present in modern durum or bread wheat. The Nax1 and Nax2 loci carry TmHKT1; 4-A2 and TmHKT1; 5-A, respectively, which are the candidate genes for these functions. This paper describes the development of near-isogenic breeding lines suitable for assessing the impact of the Nax loci and their performance in controlled environment and fields of varying salinity. In young plants grown in 150 mM NaCl, Nax1 reduced the leaf Na[sup +] concentration by 3-fold, Nax2 by 2-fold and both Nax1 and Nax2 together by 4-fold. In 250 mM NaCl, Nax1 promoted leaf longevity and greater photosynthesis and stomatal conductance. In the uppermost leaf, the Na[sup +]-excluding effect of the Nax loci was much stronger. In the field, Na[sup +] in the flag leaf was reduced 100-fold by Nax1 and 4-fold by Nax2; however, Nax1 lines yielded 5-10% less than recurrent parent (cv. Tamaroi) in saline soil. In contrast, Nax2 lines had no yield penalty and at high salinity they yielded close to 25% more than Tamaroi, indicating this material is suitable for breeding commercial durum wheat with improved yield on saline soils. Soil salinity is a major limitation on the growth and yield of all crop species, but especially of durum wheat, which lacks the ability to reduce sodium uptake into its leaves. This study describes the development of durum wheat breeding lines containing salt tolerance loci Nax1 and Nax2 and their performance in controlled environment and in fields of varying salinity. Results showed that enhanced sodium exclusion capability associated with Nax2 resulted in improved grain yields of up to 25% in soils with high salinity. [ABSTRACT FROM AUTHOR]

Foliar anthocyanin production is frequently induced by phosphorus deficiency, but the adaptive significance of increased anthocyanin production under P stress, if any, remains unknown. In this study we hypothesised that if anthocyanin expression is an adaptive response to mitigate the stress effects of P deficiency, genotypes with constitutive anthocyanin expression would have greater tolerance to P stress than low anthocyanin-producing genotypes. Four studies were conducted in greenhouse, outdoor chamber and field conditions to compare genetically similar maize and coleus plants with contrasting anthocyanin accumulation (i.e. 'red-leafed' vs 'green-leafed'). In low-P treatments, anthocyanin production did not consistently result in greater photosynthesis or biomass. In coleus, red-leafed phenotypes showed lower chlorophyll a/b ratios suggesting photoprotection by anthocyanins against degradation of light harvesting complex proteins. However, the opposite trend was observed in maize, where red-leafed phenotypes showed greater chlorophyll a/b ratios and lower qP (oxidation state of PSII). Based on results from the various treatments and growth conditions of this study, it could not be concluded that high foliar anthocyanin production confers a general functional advantage under low-P stress. More research comparing inducible vs constitutive production may help elucidate the role of anthocyanin biosynthesis in P deficiency responses. [ABSTRACT FROM AUTHOR]

We investigated the consequences of recurrent winter flooding with saline water on a lemon (Citrus × limon (L.) Burm.f.) orchard, focussing on photosynthesis limitations and emission of secondary metabolites (isoprenoids) from leaves and fruits. Measurements were carried out immediately after flooding (December), at the end of winter (April) and after a dry summer in which plants were irrigated with optimal quality water (September). Photosynthesis was negatively affected by flooding. The effect was still visible at the end of winter, whereas the photosynthetic rate was fully recovered after summer, indicating an unexpected resilience capacity of flooded plants. Photosynthesis inhibition by flooding was not due to diffusive limitations to CO2 entry into the leaf, as indicated by measurements of stomatal conductance and intercellular CO2 concentration. Biochemical and photochemical limitations seemed to play a more important role in limiting the photosynthesis of flooded plants. In young leaves, characterised by high rates of mitochondrial respiration, respiratory rates were enhanced by flooding. Flooding transiently caused large and rapid emission of several volatile isoprenoids. Emission of limonene, the most abundant compound, was stimulated in the leaves, and in young and mature fruits. Flooding changed the blend of emitted isoprenoids, but only few changes were observed in the stored isoprenoids pool. [ABSTRACT FROM AUTHOR]

Morpho-structural and physiological traits of Sangiovese and Montepulciano varieties (Vitis vinifera L. - two red grapes widely cultivated in Italy), grown outside under non-limiting water supply conditions were evaluated in 2007 and 2008 and results were correlated with yield components and grape composition. The 2-year analysis showed intraspecific differences in canopy characteristics, leaf and shoot properties, photosynthetic ability, water use efficiency, vine yield and grape composition. Compared with Sangiovese, Montepulciano was able to assure a higher whole-canopy seasonal net CO2 exchange rate during the season (+38% in mid morning and +49% in mid afternoon). It also had higher water use efficiency (especially early in the morning and in late afternoon) and a higher vine yield (+16%). Furthermore, total soluble solids (+1.7 °Brix), anthocyanins (+0.44 mg cm-2 berry skin) and phenolic compounds (+0.88 mg cm-2 berry skin) were higher in the grapes. To ensure this performance, Montepulciano vines have to support higher costs of growth and maintenance processes, made possible because of the increased respiration activity of the canopy during the night. We confirmed that vine yield and grape composition is strictly dependent on the seasonal photosynthetic capacity of the canopy. Therefore, Montepulciano should be put in a position to fully realise this substantial photosynthetic potential, by avoiding or reducing environmental stress. Sangiovese is structurally and morpho-physiologically better able to withstand any stress during the summer than Montepulciano. Sangiovese xylem tissue had larger mean vessel density and smaller mean vessel diameter and hydraulic conductance than Montepulciano, holding the hypothesis of less susceptibility to conduit damage. [ABSTRACT FROM AUTHOR]

Carotenoids are natural isoprenoid pigments that provide leaves, fruits, vegetables and flowers with distinctive yellow, orange and some reddish colours as well as several aromas in plants. Their bright colours serve as attractants for pollination and seed dispersal. Carotenoids comprise a large family of C40 polyenes and are synthesised by all photosynthetic organisms, aphids, some bacteria and fungi alike. In animals carotenoid derivatives promote health, improve sexual behaviour and are essential for reproduction. As such, carotenoids are commercially important in agriculture, food, health and the cosmetic industries. In plants, carotenoids are essential components required for photosynthesis, photoprotection and the production of carotenoid-derived phytohormones, including ABA and strigolactone. The carotenoid biosynthetic pathway has been extensively studied in a range of organisms providing an almost complete pathway for carotenogenesis. A new wave in carotenoid biology has revealed implications for epigenetic and metabolic feedback control of carotenogenesis. Developmental and environmental signals can regulate carotenoid gene expression thereby affecting carotenoid accumulation. This review highlights mechanisms controlling (1) the first committed step in phytoene biosynthesis, (2) flux through the branch to synthesis of α- and β-carotenes and (3) metabolic feedback signalling within and between the carotenoid, MEP and ABA pathways. [ABSTRACT FROM AUTHOR]

Esca is a destructive disease in grapevines (Vitis vinifera L.) caused by at least three fungi and characterised by two different external symptoms, the apoplectic and leaf stripe form. This latter form can be discerned as soon as symptoms become visible, but the preceding discrete signs during incubation are poorly or not understood. To further understand the development of the leaf stripe form, the period preceding and following the appearance of symptoms was investigated by studying physiological and molecular markers associated with photosynthetic mechanisms and stress response. No perturbation of any targeted metabolism was observed in asymptomatic leaves of asymptomatic canes from vines showing the leaf stripe form of esca. Conversely, drastic alterations of photosynthesis functions were registered in presymptomatic leaves, as revealed by the decrease of gas exchange and chlorophyll fluorescence, and the repression of photosynthesis-related genes. These alterations were amplified during symptom development. Expression of defence-related genes was affected and detected early in presymptomatic leaves and amplified during symptom expression. Our results suggest that grapevines may react precociously by reducing photosynthesis and triggering defence mechanisms in response to the leaf stripe form of esca. [ABSTRACT FROM AUTHOR]

In this report, we investigate the altered APX2 expression 13(alx13) mutation of Arabidopsis thaliana, a mutation in glutamine phosphoribosyl pyrophosphate amidotransferase 2 (ATASE2), the primary isoform of the enzyme mediating the first committed step of purine biosynthesis. Light-dependent leaf variegation was exhibited by alx13plants, with partial shading of alx13rosettes revealing that the development of chlorosis in emerging leaves is influenced by the growth irradiance of established leaves. Chlorotic sectors arose from emerging green alx13leaves during a phase of rapid cell division and expansion, which shows that each new cell’s fate is independent of its progenitor. In conjunction with the variegated phenotype, alx13plants showed altered high light stress responses, including changed expression of genes encoding proteins with antioxidative functions, impaired anthocyanin production and over-accumulation of reactive oxygen species. These characteristics were observed in both photosynthetically-normal green tissues and chlorotic tissues. Chlorotic tissues of alx13leaves accumulated mRNAs of nuclear-encoded photosynthesis genes that are repressed in other variegated mutants of Arabidopsis. Thus, defective purine biosynthesis impairs chloroplast biogenesis in a light-dependent manner and alters the induction of high light stress pathways and nuclear-encoded photosynthesis genes. [ABSTRACT FROM AUTHOR]

Good donors in breeding for salt tolerance are a prerequisite for food security under changing climatic conditions. Horkuch, a farmer-popular salt tolerant rice (Oryza sativaL.) variety from the south-west coast of Bangladesh was characterised up to maturity under NaCl stress, together with a modern variety (BRRI dhan41), a sensitive control (BRRI dhan29) and Pokkali, the salt-tolerant benchmark for rice. Horkuch had low reduction in shoot biomass, a low Na:K ratio in flag leaves, a low percent reduction in yield and good partitioning of Na in the older leaves, and maintained high levels of Ca and Mg in the flag leaves. In order to understand the physiology at the molecular level, the expression of salt-responsive genes was investigated using microarray analysis. Salt-stressed cDNA of Horkuch seedlings were hybridised with cDNA probes synthesised mainly from database sequences of Arabidopsis thaliana(L.) Heynh. The upregulated genes included transcription factors, signal transducers, metabolic enzymes, reactive oxygen species (ROS) scavengers, osmoprotectants and some specific salt-induced transcripts. An increase in expression of photosynthesis-related genes as well ROS scavengers suggested that this could be the reason for the better yield performance of Horkuch. The data therefore indicate Horkuch as a potential donor alternative to Pokkali in breeding programs for salt tolerance. [ABSTRACT FROM AUTHOR]

A leaf gross photosynthesis (A) model for three Mediterranean species from different functional groups (the evergreen sclerophyll Arbutus unedoL., the deciduous tree Quercus frainettoTen. and the semi-deciduous shrub Phlomis fruticosaL.) has been developed through a 3-year seasonal study of gas exchange and plant ecophysiological parameters. The model estimates photosynthesis through four easily measured ecophysiological parameters (chlorophyll content, leaf mass per area (LMA), pre-dawn water potential, leaf temperature) and two meteorological parameters (PAR and average temperature of the 33-day period before measurement (T33)), with a coefficient of determination r2=0.88 (P<0.001). The enhanced accuracy of the presented model may be ascribed to the incorporation of (i) water potential effects on Aand (ii) temperature effects on Anot only in the short term, but also in the long term (acclimation). Water potential and temperature effects may be considered especially important for species of Mediterranean ecosystems, where strong seasonal variation of these parameters often have a major role in plant growth and survival. [ABSTRACT FROM AUTHOR]

In this study, we investigated the potential of the photochemical resistance index (PRI) to track photosynthetic activity under water stress conditions by measuring PRI, leaf fluorescence, the xanthophyll cycle and photosynthetic activity in different forest tree species subjected to progressive drought. The PRI declined with pre-dawn water potential and a significant relationship between PRI and the xanthophyll de-epoxidation state (DEPS) was observed, although with large interspecific variability in the sensitivity of PRI to changes in DEPS. For single tree species, a strong relationship was observed on either PRI light saturated photosynthesis or PRI maximum photochemical efficiency of PSII (ΔF/Fm′); a larger variability in both relationships was apparent when data from different species were pooled together. However, an improved correlation was shown only in the former relationship by plotting the ΔPRI (dawn PRI minus the midday PRI values). Thus, we conclude that PRI is able to provide a good estimate of maximum CO2assimilation at saturating light and ΔF/Fm′ for single tree species, despite the severe drought conditions applied. PRI should be applied more cautiously when dealing with multispecific forests because of confounding factors such as the strong interspecific differences in the initial value of PRI and in the sensitivity of PRI to changes in DEPS in response to drought. [ABSTRACT FROM AUTHOR]

Hibiscus tiliaceusL. is a mangrove associate that occupies the divergent environments of intertidal wetland (L population) and inland (T population). Thus, it is an ideal plant for the study of ecological adaptation and salt tolerance. In this study we compared responses of the two populations to salinity combining a global transcriptional analysis and physiological analysis. Microarray transcript profiling analysis showed both shared and divergent responses to salinity stress in the two populations. A total of 575 unigenes were identified as being salt-responsive in the two populations. Shared responses were exemplified by the regulated genes functioning in confining ribosomal functions, photosynthesis and cellular metabolism. A set of genes functioning in cellular transporting and cell detoxification and a crucial transcription factor AP2 domain-containing protein involved in environmental responsiveness, were differently expressed in the two populations. Physiological analysis showed that the L population was less susceptible to salt stress in photosynthesis and had a stronger capability of K+:Na+regulation than the T population. Both microarray and physiological data showed the L population possess higher fitness under high salinity, probably due to it its long-term adaptation to their native environment. [ABSTRACT FROM AUTHOR]

Present work focussed on improving the description of organogenesis, morphogenesis and metabolism in a biophysical plant model (SUNFLO) applied to sunflower (Helianthus annuusL.). This first version of the model is designed for potential growth conditions without any abiotic or biotic stresses. A greenhouse experiment was conducted to identify and estimate the phenotypic traits involved in plant productivity variability of 26 sunflower genotypes. The ability of SUNFLO to discriminate the genotypes was tested on previous results of a field survey aimed at evaluating the genetic progress since 1960. Plants were phenotyped in four directions; phenology, architecture, photosynthesis and biomass allocation. Twelve genotypic parameters were chosen to account for the phenotypic variability. SUNFLO was built to evaluate their respective contribution to the variability of yield potential. A large phenotypic variability was found for all genotypic parameters. SUNFLO was able to account for 80% of observed variability in yield potential and to analyse the phenotypic variability of complex plant traits such as light interception efficiency or seed yield. It suggested that several ways are possible to reach high yields in sunflower. Unlike classical statistical analysis, this modelling approach highlights some efficient parameter combinations used by the most productive genotypes. The next steps will be to evaluate the genetic determinisms of the genotypic parameters. [ABSTRACT FROM AUTHOR]

A mechanistic model of carbon partitioning, based on the Münch hypothesis of phloem transport and implemented with PIAF-Münch modelling platform (Lacointe and Minchin 2008), was tested for an architecture more complex than any tested previously. Using 11C to label photosynthate, responses in transport of photosynthate within a heavily pruned dwarf bean plant (Phaseolus vulgaris L.) to changes in source and sink activities were compared with model predictions. The observed treatment responses were successfully predicted. However, the observations could not be completely explained if the modelled stem contained only one phloem pathway: tracer from a labelled leaf was always detected in both shoot apex and root, whichever of the two leaves was labelled. This shows that bidirectional flow occurred within the stem, with solute moving simultaneously in both directions. Nevertheless, a model architecture with very little more complexity could incorporate such bidirectional flow. We concluded that the model could explaintheobservations,and that the PIAF-Münch model platform can be expected to describe partitioning in even more complex architectures. [ABSTRACT FROM AUTHOR]

How plastic is hydraulic anatomy with growth temperature, and how does this relate to photosynthesis? These interrelationships were studied in subantarctic Poa foliosaHook. f. and alpine Poa hothamensisVickery grown under 7/4°C and 12/9°C day/night temperatures, reflecting summer temperatures in their respective habitats. Conduit radii were smaller in P. foliosathan in P. hothamensis, consistent with greater avoidance of freeze/thaw-induced embolism. Despite its origins in an environment with relatively little temperature variation, P. foliosaexhibited greater plasticity in hydraulic anatomy than P. hothamensis, increasing the size and density of conduits when grown under the warmer temperature regime. Both species had similar anatomical capacities for water transport when grown at 12/9°C, but stomatal conductance was lower in P. foliosathan P. hothamensis, suggesting hydraulic limitations not explained by leaf vascular anatomy. However, greater photosynthetic capacity and foliar nitrogen contents enabled P. foliosato achieve the same assimilation rate as P. hothamensisunder the 12/9°C growth conditions. Our results showed that nitrogen plays a central role in maintaining assimilation rates when constrained either by enzymatic activity at low temperatures or by hydraulic limitations at high temperatures and evaporative demands. Interspecific differences in nitrogen and water use may influence how subantarctic and alpine vegetation responds to climate warming. [ABSTRACT FROM AUTHOR]

Crassulacean acid metabolism (CAM) is a specialised mode of photosynthesis that improves atmospheric CO2 assimilation in water-limited terrestrial and epiphytic habitats and in CO2-limited aquatic environments. In contrast with C3 and C4 plants, CAM plants take up CO2 from the atmosphere partially or predominantly at night. CAM is taxonomically widespread among vascular plants and is present in many succulent species that occupy semiarid regions, as well as in tropical epiphytes and in some aquatic macrophytes. This water-conserving photosynthetic pathway has evolved multiple times and is found in close to 6% of vascular plant species from at least 35 families. Although many aspects of CAM molecular biology, biochemistry and ecophysiology are well understood, relatively little is known about the evolutionary origins of CAM. This review focuses on five main topics: (1) the permutations and plasticity of CAM, (2) the requirements for CAM evolution, (3) the drivers of CAM evolution, (4) the prevalence and taxonomic distribution of CAM among vascular plants with emphasis on the Orchidaceae and (5) the molecular underpinnings of CAM evolution including circadian clock regulation of gene expression. [ABSTRACT FROM AUTHOR]

Islands of monsoon rainforest and Melaleuca swamp punctuate vast tracts of savanna in monsoonal northern Australia. Seedlings of species from each of these habitat associations were grown in a common garden. Monsoon forest species had higher specific leaf area, lower photosynthetic capacity and lower photosynthetic light compensation points, and required lower irradiance to achieve 50% of light-saturated photosynthesis compared with savanna or swamp species. These traits probably contribute towards greater shade tolerance beneath dense monsoon-forest canopies, whereas savanna and swamp canopies are relatively open. Swamp species, especially two Melaleuca species, had high stomatal conductance and small CO2 drawdown during photosynthesis, and more negative leaf δ13C, compared with monsoon forest and savanna species. Higher stomatal conductance increases carbon uptake during photosynthesis and a high transpiration rate would increase transport of nutrients to absorbing surfaces in the root by mass flow. Thus, a strategy of high transpiration and low water-use efficiency appears to be favoured in swamp species compared with monsoon-forest and savanna species. Instantaneous measurements of the ratio of intercellular to ambient CO2 concentrations (ci/ca) explained 81% of variation in leaf δ13C across 44 species sampled in this and other studies, suggesting that leaf δ13C generally provides a robust proxy for comparisons of ci/ca, even when applied across species. [ABSTRACT FROM AUTHOR]

Root restriction experiments on cotton plants were conducted under conditions where water and nitrogen supplies were not limiting. Xylem sap and leaf tissues were obtained before significant biomass reduction as a result of root restriction. Xylem-derived cytokinins (CTKs) entering a leaf and the CTK levels in the same excised leaf were measured, thus, enabling xylem sap and foliar CTKs to be compared concurrently under root-restrictive and control conditions. Abscisic acid (ABA) was also measured simultaneously in the same xylem sap samples. Root restriction reduced photosynthesis and δ18O of leaf matter showed that leaves of root-restricted plants generally had lower stomatal conductances. Root-restriction significantly decreased (37%) the delivery rate per unit leaf area of CTK bases (dihydrozeatin (DZ) and N6-(2-isopentenyl)adenine (iP)) to the leaf but did not alter the export of CTK O-glucosides and ABA from the roots to leaf 4. Root-restriction also did not alter significantly the levels of total CTK bases in the leaves but increased (54–57% higher) the CTK O-glucosides (especially zeatin O-glucosides). Root restriction also slowed down the apparent CTK turnover rates in the leaves. The slow down in CTK turnover rate can be interpreted as a reduction in leaf CTK metabolism during root restriction. [ABSTRACT FROM AUTHOR]

We examined the relationship between variation in phyllode nerve density and the spatio-temporal response of the photosynthetic apparatus to water-stress in two Acacias.str. species with contrasting nerve patterns: Acacia floribunda(Vent.) Willd and Acacia pycnanthaBenth. A. floribundahad greater primary nerve density than A. pycnanthaand also showed greater spatial homogeneity in photosynthetic function with drought than phyllodes of A. pycnantha. A. pycnanthahad lower maximum quantum efficiency of PSII in phyllode tissue further from primary nerves consistent with its lower primary nerve density. Further, A. floribundaphyllodes maintained function of the photosynthetic apparatus with drought for longer and recovered more swiftly from drought than A. pycnantha. These findings suggest that greater primary nerve density may enhance drought tolerance and are consistent with the observed predominance of acacias with high primary nerve density in areas with lower precipitation. [ABSTRACT FROM AUTHOR]

Age-dependent changes in leaf photosynthetic characteristics (i.e. parameters of the light response curve (maximum photosynthetic rate (Pmax), quantum yield (Φ) and the convexity parameter (θ)), stomatal conductance (gs) and dark respiration rate (Rd)) of an exotic perennial legume, Medicago sativa L. (lucerne), and two potential pasture legumes native to Australia, Cullen australasicum (Schltdl.) J.W. Grime and Cullen pallidum A. Lee, grown in a glasshouse for 5 months at two phosphorus (P) levels (3 (P3) and 30 (P30) mg P kg-1 dry soil) were tested. Leaf appearance rate and leaf area were lower at P3 than at P30 in all species, with M. sativa being the most sensitive to P3. At any leaf age, photosynthetic characteristics did not differ between P treatments. However,Pmax and gs for all the species and Φ for Cullen species increased until full leaf expansion and then decreased. The convexity parameter, θ, did not change with leaf age, whereas Rd decreased. The estimates of leaf net photosynthetic rate (Pleaf) obtained through simulations at variable Pmax and Φ were lower during early and late leaf developmental stages and at lower light intensities than those obtained when Φwas assumed to be constant (e.g. for a horizontally placed leaf, during the 1500°C days developmental period, 3 and 19% reduction of Pleaf at light intensities of 1500 and 500 μmol m-2 s-1, respectively). Therefore, developmental changes in leaf photosynthetic characteristics should be considered when estimating and simulating Pleaf of these pasture species. [ABSTRACT FROM AUTHOR]

To model the impact of grazing on the growth of wheat (Triticum aestivum L.), we measured photosynthesis in the field. Grazing may affect photosynthesis as a consequence of changes to leaf water status, nitrogen content per unit leaf area (Na) or photosynthetic enzyme activity. While light-saturated CO2 assimilation rates (Asat) of field-grown wheat were unchanged during grazing, Asat transiently increased by 33-68% compared with ungrazed leaves over a 2 to 4-week period after grazing ended. Grazing reduced leaf mass per unit area, increased stomatal conductance and increased intercellular CO2 concentrations (Ci) by 36-38%, 88-169% and 17-20%, respectively. Grazing did not alter Na. Using a photosynthesis model, we demonstrated that the increase in Asat after grazing required an increase in Rubisco activity of up to 53%, whereas the increase in Ci could only increase Asat by up to 13%. Increased Rubisco activity was associated with a partial alleviation of leaf water stress. We observed a 68% increase in leaf water potential of grazed plants that could be attributed to reduced leaf area index and canopy evaporative demand, as well as to increased rainfall infiltration into soil. The grazing of rain-fed grain cereals may be tailored to relieve plant water stress and enhance leaf photosynthesis. [ABSTRACT FROM AUTHOR]

Crassula helmsii (T. Kirk) Cockayne is an invasive aquatic plant in Europe that can suppress many native species because it can grow at a large range of dissolved inorganic carbon concentrations and light levels. One reason for its ecological success may be the possession of a regulated Crassulacean Acid Metabolism (CAM), which allows aquatic macrophytes to take up CO2 in the night in addition to the daytime. The effect of light and CO2 on the regulation of CAM and photosynthesis in C. helmsii was investigated to characterise how physiological acclimation may confer this ecological flexibility. After 3 weeks of growth at high light (230 mmol photon m-2 s-1), C. helmsii displayed 2.8 times higher CAM at low compared with high CO2 (22 v. 230 mmol m-3).CAM was absent in plants grown at low light (23 mmol photon m-2 s-1) at both CO2 concentrations. The observed regulation patterns are consistent with CAM acting as a carbon conserving mechanism. For C. helmsii grown at high light and low CO2, mean photosynthetic rates were relatively high at low concentrations of CO2 and were on average 80 and 102 mmol O2 g-1 DW h-1 at CO2 concentrations of 3 and 22 mmolm-3 CO2, which, together with mean final pH values of 9.01 in the pH drift, indicate a low CO2 compensation point (<3 mmolm-3) but do not indicate use of bicarbonate as an additional source of exogenous inorganic carbon. The relatively high photosynthetic rates during the entire daytime were caused by internally derived CAM-CO2 and uptake from the external medium. During decarboxylation, CO2 generated from CAM contributed up to 29% to photosynthesis, whereas over a day the contribution to the carbon balance was ⩽13%. The flexible adjustment of CAM and the ability to maintain photosynthesis at very low external CO2 concentrations, partly by making use of internally generated CO2 via CAM, may contribute to the broad ecological niche of C. helmsii. [ABSTRACT FROM AUTHOR]

This review deals with grapevine responses to water stress by examining perturbations to physiological and molecular processes at the root, shoot, leaf and berry levels. Long-distance signalling among organs is also considered. Isohydric or anisohydric Vitisgenotypes are described in relation to their response to drought, which is linked to stomatal behaviour. Stomatal regulation of grapevine under abscisic acid and hydraulic control (the latter being linked to embolism formation and recovery in water pathways upstream the stomata) is reviewed and linked to impairments of photosynthetic assimilation. We define three stages of photosynthesis regulation in grapevines that are subjected to progressive water stress on the basis of the main causes of assimilation decline. Early and late contributions of aquaporins, which play a fundamental role in water stress control, are discussed. Metabolic mechanisms of dehydration tolerance are rewieved, and variation linked to differences in transcript abundance of genes involved in osmoregulation, photosynthesis, photorespiration, detoxification of free radicals and coping with photoinhibition. Results of these defence strategies accumulated in berries are reviewed, together with perturbations of their molecular pathways. Features observed in different organs show that grapevine fits well as a complex model plant for molecular and physiological studies on plant drought avoidance/tolerance. [ABSTRACT FROM AUTHOR]

Bienertia sinuspersiciAkhani represents one form of C4photosynthesis that occurs without Kranz anatomy in family Chenopodiaceae. Analysis of transcript profiles and proteomics were made to gain information on this single-cell C4photosynthetic mechanism. Chlorenchyma cells were isolated and purified from mature leaves. From these cells, a cDNA library was made from which sequences were obtained on 2385 clones using conventional methods. To obtain a protein profile, the multi dimensional protein identification technique was used, resulting in identification of 322 unique proteins in chlorenchyma cells. After analysing datasets from the EST library and proteomics, genes and proteins were classified into 23 and 17 categories according to types of biological processes, respectively. These include photosynthesis and photorespiration, other biosynthetic and metabolic processes, cell wall modification, defence response, DNA repair, electron transport, other cellular and developmental processes, protein folding, protein targeting, protein modification, proteolysis, redox and ion homeostasis, response to biotic and abiotic stresses, RNA modification, transcription, translation, transport and unknowns. Sequence and phylogenetic analyses were made of C4cycle enzymes to characterise the relationship between homologues found in Bienertiawith public gene sequences from other chenopods and representative C3and C4species from other families. Identified photosynthetic genes and proteins are discussed with respect to the proposed function of an NAD-ME type C4cycle in this single-cell C4system. [ABSTRACT FROM AUTHOR]

Infection with Cassytha pubescensR.Br, an Australian native hemiparasitic plant, can lead to death of the invasive shrub, Cytisus scopariusL. Link (Scotch broom). We examined the influence of C. pubescenson photosynthetic physiology of C. scopariusto determine whether this might contribute to death of infected plants. Infected C. scopariushad significantly lower photosynthetic rates, stomatal conductance and transpiration, and higher Ci(internal [CO2]), than uninfected plants. Rapid light response curves, determined using chlorophyll fluorescence, indicated significantly lower light-saturated electron transport rates and lower quantum yields for infected plants relative to uninfected plants. However, Rubisco content did not differ between infected and uninfected plants, suggesting the lower photosynthetic rates were most likely due to stomatal closure, rather than lower photosynthetic capacity. As a consequence of lower assimilation rates, PSII efficiency was lower in infected plants than uninfected plants across the diurnal cycle. Infected plants also had significantly lower pre-dawn Fv/Fmvalues and slower recovery from exposure to high light than uninfected plants. Our results suggest that infected C. scopariusare more susceptible to photodamage than uninfected plants. Combined with lower carbon fixation rates, this could contribute to the poor performance and even death of infected plants. [ABSTRACT FROM AUTHOR]

Effects of high irradiance and moderate heat on photosynthesis of the tree-fern Dicksonia antarctica(Labill., Dicksoniaceae) were examined in a climate chamber under two contrasting irradiance regimes (900 and 170µmolphotonsm-2s-1) and three sequential temperature treatments (15°C; 35°C; back to 15°C). High irradiance led to decline in predawn quantum yield of photochemistry, Fv/Fm(0.73), maximal Rubisco activity (Vcmax; from 37 to 29µmolm-2s-1), and electron transport capacity (Jmax; from 115 to 67µmolm-2s-1). Temperature increase to 35°C resulted in further decreases in Fv/Fm(0.45) and in chlorophyll bleaching of high irradiance plants, while Vcmaxand Jmaxwere not affected. Critical temperature for thylakoid stability (Tc) of D. antarcticawas comparable with other higher plants (c. 47°C), and increases of Tcwith air temperature were greater in high irradiance plants. Increased Tcwas not associated with accumulation of osmotica or zeaxanthin formation. High irradiance increased the xanthophyll cycle pigment pool (V+A+Z, 91 v. 48mmolmol-1chlorophyll-1), de-epoxidation state (56% v. 4%), and α-tocopherol. Temperature increase to 35°C had no effect on V+A+Z and de-epoxidation state in both light regimes, while lutein, β-carotene and α-tocopherols increased, potentially contributing to increased membrane stability under high irradiance. [ABSTRACT FROM AUTHOR]

Solar ultraviolet radiation (UVR, 280–400nm) is known to negatively affect macroalgal growth and photosynthesis, while phosphorus availability may affect their sensitivity to UVR. Here, we show that UV-A enhanced the growth rate of the red macroalga, Gracilaria lemaneiformisBory de Saint-Vincent under inorganic phosphorus (Pi)-replete but reduced it under Pi-limited conditions. Maximal net photosynthetic rates were significantly reduced by both UV-A and UV-B, but the apparent photosynthetic efficiency was enhanced in the presence of UV-A. The UV-induced inhibition was exacerbated under Pi-limited conditions. The activity of total carbonic anhydrase was enhanced and the photosynthetic affinity for exogenous inorganic carbon (Ci) was raised for thalli grown in the presence of UVR under both Pi-replete and Pi-limited conditions. The relative growth rate was closely related to Ci acquisition capability (Vmax/KDIC), which was enhanced by UVR exposure under Pi-replete but not significantly affected under Pi-limited conditions. [ABSTRACT FROM AUTHOR]

Equations for non-destructive determination of chlorophyll b:aratios in grasses were developed from reflectance spectra of intact leaves of barley (Hordeum vulgareL.) and two barley mutants: clorina f2, which lacks chlorophyll band clorina f104, which has a low chlorophyll bcontent. These plants enabled separation of effects of chlorophyll composition on reflectance spectra due to differential light absorption by chlorophylls aand band to measure the effects of chlorophyll bon the contribution of fluorescence emitted by chlorophyll ato the reflectance spectra. Indices developed from these data were then tested on growth chamber-grown leaves from six C3and 17C4grass species (7 NAD-ME and 10 NADP-ME subtypes). We used the chlorophyll b:aratio because the data were less skewed than the chlorophyll a:bratio. The best index for determination of the chlorophyll b:aratio utilised wavelengths affected by chlorophyll absorbance: [R626– 0.5 (R603+R647)]/[R552– R626]. The chlorophyll b:aratio was significantly lower in the C4than C3grasses, but was not sufficient in itself to separate these two functional groups. However, because of differences in fluorescence characteristics, C3and C4species could be distinguished by an index based on wavelengths affected by chlorophyll fluorescence: [R696 to 709/R545 to 567]. [ABSTRACT FROM AUTHOR]

There is now strong evidence that yield potential in rice (Oryza sativaL.) is becoming limited by ‘source' capacity, i.e. photosynthetic capacity or efficiency, and hence the ability to fill the large number of grain ‘sinks' produced in modern varieties. One solution to this problem is to introduce a more efficient, higher capacity photosynthetic mechanism to rice, the C4pathway. A major challenge is identifying and engineering the genes necessary to install C4photosynthesis in rice. Recently, an international research consortium was established to achieve this aim. Central to the aims of this project is phenotyping large populations of rice and sorghum (Sorghum bicolorL.) mutants for ‘C4-ness' to identify C3plants that have acquired C4characteristics or revertant C4plants that have lost them. This paper describes a variety of plant phenomics approaches to identify these plants and the genes responsible, based on our detailed physiological knowledge of C4photosynthesis. Strategies to asses the physiological effects of the installation of components of the C4pathway in rice are also presented. [ABSTRACT FROM AUTHOR]

Detection of grassland canopy chlorophyll fluorescence (Chl-F) conducted with an imaging spectroradiometer provided evidence of potential remote sensing estimation of steady-state Chl-F(Chl-Fs). Daily near-nadir views of extremely high spatial resolution hyperspectral images were acquired from a distance of 4m for temperate montane grassland in the Czech Republic. Simultaneously, measurements of Chl-Fand total chlorophyll content (Chla+b) were made on a single leaf at ground level were collected. A specifically designed ‘shade removal' experiment revealed the influence of dynamic physiological plant processes on hyperspectral reflectance of three wavelengths: 532, 686 and 740nm. Based on this information, the vegetation indexes R686/R630, R740/R800and PRI calculated as (R532–R570)/(R532+R570) were tested for statistical significance with directly measured Chl-Fparameters (maximum fluorescence yield, Fv/Fm; steady-state chlorophyll fluorescence, Chl-Fsand actual quantum yield, ФII). The grassland species under investigation were: Festuca rubra agg. (L.), Hieraciumsp., Plantagosp., Nardus stricta(L.) and Jacea pseudophrygia(C.A. Meyer). The coefficients of determination (R2) for best-fit relationships between PRI-ФIIand PRI-Chl-Fs, measured in the daily course, show a high variability of 0.23–0.78 and 0.20–0.65, respectively. Similarly, R2for the R686/R630-ФIIand R686/R630-Chl-Fsrelationships varied between 0.20–0.73 and 0.41–0.70, respectively. The highest average R2values were found between PRI and Chla+b(0.63) and R686/R630and Chla+b(0.72). The ratio R740/R800did not yield a statistically significant relation with Chl-Fparameters. [ABSTRACT FROM AUTHOR]

Chlorophyll fluorescence imaging is a non-invasive, non-destructive means with which to examine the impact of fungal pathogens on the photosynthetic metabolism of host plants. As such, it has great potential for screening purposes in high-throughput phenomics environments. However, there is great diversity in the responses of plants to different plant-fungal pathogens and the choice of suitable experimental conditions and protocols and interpretation of the results requires both preliminary laboratory experiments and an understanding of the biology of the specific plant-pathogen interaction. In this review, we examine the interaction between biotrophic, hemi-biotrophic and necrotrophic fungal pathogens and their hosts to illustrate the extent to which chlorophyll fluorescence imaging can be used to detect the presence of disease before the appearance of visible symptoms, distinguish between compatible and incompatible fungal interactions, identify heterogeneity in photosynthetic performance within the infected leaf and provide insights into the underlying mechanisms. The limitations and challenges of using chlorophyll fluorescence imaging in high throughput screens is discussed. [ABSTRACT FROM AUTHOR]

It was previously shown that photosynthetic electron transfer is controlled under low CO2via regulation of the chloroplast ATP synthase. In the current work, we studied the regulation of photosynthesis under feedback limiting conditions, where photosynthesis is limited by the capacity to utilise triose-phosphate for synthesis of end products (starch or sucrose), in a starch-deficient mutant of Nicotiana sylvestrisSpeg. & Comes. At high CO2, we observed feedback control that was progressively reversed by increasing O2levels from 2 to 40%. The activity of the ATP synthase, probed in vivoby the dark-interval relaxation kinetics of the electrochromic shift, was proportional to the O2-induced increases in O2evolution from PSII (JO2), as well as the sum of Rubisco oxygenation (vo) and carboxylation (vc) rates. The altered ATP synthase activity led to changes in the light-driven proton motive force, resulting in regulation of the rate of plastoquinol oxidation at the cytochrome b6fcomplex, quantitatively accounting for the observed control of photosynthetic electron transfer. The ATP content of the cell decreases under feedback limitation, suggesting that the ATP synthesis was downregulated to a larger extent than ATP consumption. This likely resulted in slowing of ribulose bisphosphate regeneration and JO2). Overall, our results indicate that, just as at low CO2, feedback limitations control the light reactions of photosynthesis via regulation of the ATP synthase, and can be reconciled with regulation via stromal Pi, or an unknown allosteric affector. [ABSTRACT FROM AUTHOR]