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Heliotropium thermophilum (Boraginaceae) plants have strong antioxidant properties. This study investigated the effectiveness of the antioxidant system in protecting the photosynthetic machinery of H. thermophilum. Plants were obtained from Kızıldere geothermal area in Buharkent district, Aydın, Turkey. Plants in the geothermal area that grew at 25–35°C were regarded as the low temperature group, while those that grew at 55–65°C were regarded as the high temperature group. We analysed the physiological changes of these plants at the two temperature conditions at stage pre-flowering and flowering. We meaured the effect of high soil temperature on water potential, malondialdehyde, cell membrane stability, and hydrogen peroxide analysis to determine stress levels on leaves and roots. Changes in antioxidant enzyme activities, ascorbate and chlorophyll content, chlorophyll fluorescence, photosynthetic gas exchange parameters, and photosynthetic enzymes (Rubisco and invertase) activities were also determined. Our results showed minimal changes to stress levels, indicating that plants were tolerant to high soil temperatures. In general, an increase in antioxidant enzyme activities, ascorbat levels, and all chlorophyll fluorescence parameters except for non-photochemical quenching (NPQ) and F v/ F m were observed. The pre-flowering and flowering stages were both characterised by decreased NPQ, despite F v/ F m not changing. Additionally, there was a rise in the levels of photosynthetic gas exchange parameters, Rubisco, and invertase activities. High temperature did not affect photosynthetic yield because H. thermophilum was found to stimulate antioxidant capacity, which reduces oxidative damage and maintains its photosynthetic machinery in high temperature conditions and therefore, it is tolerant to high soil temperature. Heliotropium thermophilum did not exhibit significant stress parameters under high soil temperature conditions, and it was a highly tolerant plant to high temperature. In the measurements taken at pre-flowering and flowering, plants in the pre-flowering stage were slightly more tolerant to high temperatures. The protection of PSII function in plants at higher temperatures could be linked to an increase in antioxidant activities. [ABSTRACT FROM AUTHOR]

Low temperature (LT) during the grain-filling stage is an important factor that affects the source–sink relationship and leads to yield loss in maize (Zea mays L). In this study, field and pot trials were conducted to investigate the effects of LT during the grain-filling stage on leaf photosynthesis, antioxidant system, hormones, and grain yield of waxy maize cultivars Suyunuo 5 (S5) and Yunuo 7 (Y7). The results showed that LT treatment inhibited the chlorophyll biosynthesis and reduced the photosynthetic pigment levels during grain-filling stage. Ribulose-1,5-bisphosphate carboxylase and phosphoenolpyruvate carboxylase activities, photosynthetic rate, transpiration rate, and stomatal conductance decreased under LT treatment during the grain-filling stage. Furthermore, LT treatment increased the contents of malondialdehyde and reactive oxygen species, and decreased the activities of catalase, superoxide dismutase, peroxidase, and ascorbate peroxidase in the ear leaves, which accelerated the oxidative damage of leaf. The LT treatment also raised abscisic acid content and reduced indole acetic acid content in the ear leaves during grain-filling stage. The results of field and pot trials were verified by each other, but the field effect was greater than that of pot. Overall, LT treatment reduced the waxy maize dry matter accumulation after silking by affecting the physiological and biochemical processes of leaves, and ultimately decreased grain yield. Low temperature (LT) is an important abiotic stress that seriously affects the production and development of maize (Zea mays L). In this study, two waxy maize hybrids were selected and planted in two experimental environments to determine the dynamic changes in leaf photosynthesis, antioxidant system, hormones, and grain yield under post-silking LT stress. This study can be used as a reference for waxy maize to develop adaptation strategies under future climate conditions. [ABSTRACT FROM AUTHOR]

Manganese (Mn) plays an essential role in plant growth; however, excessive Mn is toxic to plants. Polygonum lapathifolium Linn. was tested as a novel Mn-hyperaccumulating species in our previous study, but the underlying mechanisms of this hyperaccumulation are poorly understood. A hydroponic experiment with (8 mmol L−1) and without additional Mn (CK) was established to explore the possible mechanisms through the effects on photosynthesis-related physiological characteristics and metabolomics. The results showed that additional Mn increased plant biomass, photosynthesis, and stomatal conductance related to increases in the effective photochemical quantum yield of photosystem II and relative electron transport rate (P < 0.05). The results from liquid chromatography–mass spectrometry revealed 56 metabolites differentially accumulated between the plants composing these two groups. Metabolites were enriched in 20 metabolic pathways at three levels (environmental information processing, genetic information processing, and metabolism), of which five metabolic pathways were associated with significant or extremely significant changes (P < 0.05). These five enriched pathways were ABC transporters (environmental information processing), aminoacyl-tRNA biosynthesis (genetic information processing), biosynthesis of amino acids , d-arginine and d-ornithine metabolism , and arginine biosynthesis (metabolism). Flavonoids may play a key role in Mn tolerance, as they accumulated more than 490-fold, and the relationship between flavonoids and Mn tolerance needs to be studied in the future. A hydroponic experiment with (8 mmol L−1) and without manganese was established to explore the mechanisms of manganese tolerance of Polygonum lapathifolium Linn via the effects on photosynthesis and metabolism. The results showed that manganese increased plant biomass, photosynthesis, and stomatal conductance. Moreover, among 1022 metabolites, 56 were significantly differentially accumulated, and flavonoids may be the key to the high tolerance of P. lapathifolium. The increased energy and photosynthates from photosynthesis were not allocated to amino acid synthesis. [ABSTRACT FROM AUTHOR]

Developing seeds of some higher plants are photosynthetically active and contain chlorophylls (Chl), which are typically destroyed at the late stages of seed maturation. However, in some crop plant cultivars, degradation of embryonic Chl remains incomplete, and mature seeds preserve green colour, as it is known for green-seeded cultivars of pea (Pisum sativum L.). The residual Chl compromise seed quality and represent a severe challenge for farmers. Hence, comprehensive understanding of the molecular mechanisms, underlying incomplete Chl degradation is required for maintaining sustainable agriculture. Therefore, here we address dynamics of plastid conversion and photochemical activity alterations, accompanying degradation of Chl in embryos of yellow- and green-seeded cultivars Frisson and Rondo respectively. The yellow-seeded cultivar demonstrated higher rate of Chl degradation at later maturation stage, accompanied with termination of photochemical activity, seed dehydration and conversion of green plastids into amyloplasts. In agreement with this, expression of genes encoding enzymes of Chl degradation was lower in the green seeded cultivar, with the major differences in the levels of Chl b reductase (NYC1) and pheophytinase (PPH) transcripts. Thus, the difference between yellow and green seeds can be attributed to incomplete Chl degradation in the latter at the end of maturation period. Developing seeds of some higher plants are photosynthetically active and contain chlorophylls, which are typically destroyed during seed maturation. However, in some crops, chlorophylls degrade incompletely, which compromises seed quality, and represents a severe challenge for farmers. Here we address dynamics of plastid conversion and photochemical activity alterations, accompanying chlorophylls degradation in maturing embryos of yellow- and green-seeded cultivars of pea (Pisum sativum). Our data enhance the existing knowledge about mechanisms, underlying incomplete chlorophylls degradation during seed maturation. [ABSTRACT FROM AUTHOR]

In China, maize-soybean relay-intercropping system follow the two main planting-patterns: (i) traditional relay-intercropping; maize-soybean equal row planting, where soybean experience severe maize shading on both sides of plants, and (ii) modern relay-intercropping; narrow-wide row planting, in this new planting pattern only one side of soybean leaves suffer from maize shading. Therefore, in this study, changes in morphological traits, cytochrome content, photosynthetic characteristics, carbon status, and the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) were investigated at 30 days after treatment (DAT) in shade-tolerant soybean variety Nandou-12 subjected to three different types of shading conditions; normal light (NL, all trifoliate-leaves of soybean plants were under normal light); unilateral shade (US, all right-side trifoliate-leaves of soybean plants from top to bottom were under shade while all the left-side of trifoliate-leaves from top to bottom were in normal light); bilateral shade (BS, all trifoliate-leaves of soybean plants were under complete shade). Compared with BS, US conditions decreased plant height and increased stem diameter, leaf area, and biomass at 30 DAT. Biomass distribution rates to stem, petiole and leaves, and photosynthetic characteristics were markedly improved by the US at all sampling stages, which proved to be a better growing condition than BS with respect to shade tolerance. The enhanced net photosynthesis and transpiration rates in the left-side leaves (LS) of soybean plants in US, when compared with the LS in BS, allowed them to produce higher total soluble sugar (by 70%) and total soluble protein (by 17%) at 30 DAT which reduce the adverse effects of shading at right-side leaves (RS) of the soybean plants. Similarly, soybean leaves under US accumulated higher proline content in US than the leaves of BS plants. Soybean leaves grown in shading conditions (LS and RS of BS and RS of US) developed antioxidative defence-mechanisms, including the accelerated activities of SOD, POD, APX, and CAT. Comparatively, soybean leaves in US displayed lower activity levels of the antioxidative enzymes than the leaves of BS plants, showing that soybean plants experienced less shade stress in US as compared with BS treatment. Overall, these results indicate that the association of improved photosynthetic characteristics, sugar and protein accumulation and optimum antioxidative defences could be an effective approach for growing soybean in intercropping environments. Slight shading could be an effective approach for growing soybean in intercropping systems. Soybean responds to slight shade by producing larger leaves to intercept more sunlight. Compared with severe-shading, soybean maintained the optimum chlorophyll contents, high net photosynthetic rate, and improved antioxidant enzyme activities under slight-shading. Through configuring the space deployment in the intercropping system, slight shade could be helpful for optimum growth and yield. Redesigning photosynthesis through slight shade for intercropping systems could meet global food and bioenergy demand. [ABSTRACT FROM AUTHOR]

The cyclic electron flux (CEF) around photosystem I (PSI) was discovered in isolated chloroplasts more than six decades ago, but its quantification has been hampered by the absence of net formation of a product or net consumption of a substrate. We estimated in vivo CEF in leaves as the difference (ΔFlux) between the total electron flux through PSI (ETR1) measured by a near infrared signal, and the linear electron flux through both photosystems by optimised measurement of chlorophyll a fluorescence (LEFfl). Chlorophyll fluorescence was excited by modulated green light from a light-emitting diode at an optimal average irradiance, and the fluorescence was detected at wavelengths >710 nm. In this way, LEFfl matched the gross rate of oxygen evolution multiplied by 4 (LEFO2) in broad-spectrum white actinic irradiance up to half (spinach, poplar and rice) or one third (cotton) of full sunlight irradiance. This technique of estimating CEF can be applied to leaves attached to a plant. Cyclic electron flow around photosystem I (CEF) was discovered in isolated chloroplasts more than 6 decades ago, but its quantification has been elusive. We devised a method capable of estimating CEF in intact leaves attached to a plant. The method involves measurement of (1) the total electron flux through Photosystem I by a near-infrared signal, and (2) the linear electron flux through both photosystems in series by optimising conditions of excitation and detection of chlorophyll fluorescence. [ABSTRACT FROM AUTHOR]

The chlorophyll and carotenoid content, and the spectra of low-temperature fluorescence of the leaves, chloroplasts and isolated pigment–protein complexes in the perennial herbaceous wintergreen plant Ajuga reptans L. (bugle) in different seasons of the year were studied. During winter, these plants downregulate photosynthesis and the PSA is reorganised, including the loss of chlorophyll, possible reductions in the number of functional reaction centres of PSII, and changes in aggregation of the thylakoid protein complexes. We also observed a restructuring of the PSI–PSII megacomplex and the PSII–light-harvesting complex II supercomplex in leaves covered by snow. After snowmelt, the monomeric form of the chl a/b pigment–protein complex associated with PSII (LHCII) and the free pigments were also detected. We expect that snow cover provides favourable conditions for keeping photosynthetic machinery ready for photosynthesis in spring just after snowmelt. During winter, the role of the zeaxanthin-dependent protective mechanism, which is responsible for the dissipation of excess absorbed light energy, is likely to increase. [ABSTRACT FROM AUTHOR]

The barley (Hordeum vulgare L.) chlorina f2 3613 mutant exhibits low photosynthesis and slow growth. This results from downregulation of the levels of photosynthetic antenna proteins caused by the absence of chl b, the major regulator of photosynthetic antennae in land plants. Here, we demonstrate that, when grown in the field in full sunlight, this mutant displays a changed pattern of stomatal responses compared with the parental wild-type cultivar Donaria. However, stomatal regulation of chlorinaf2 3613 plants was restored when plants were placed under a shade cover for several days. The shade cover reduced incident PAR from 2000-2200 mmolm-2 s-1 to 800-880 mmolm-2 s-1 as measured at noon. Contents of ABA, the xanthophyll precursors of ABA biosynthesis and minor antenna proteins, as well as reactive oxygen species levels in stomata and the sensitivity of stomata to exogenously supplied ABA, were determined in leaves of wild-type Donaria and chlorina f2 3613 before and after shading. The results support the view that the restoration of stomatal control in barley chlorina f2 3613 is correlated with an increase in the levels of the minor antenna protein Lhcb6, which has recently been implicated in the enhancement of stomatal sensitivity to ABA in Arabidopsis thaliana (L.) Heynh. [ABSTRACT FROM AUTHOR]

The pea seeds are photosynthetically active until the end of the maturation phase, when the embryonic chlorophylls degrade. However, in some cultivars, the underlying mechanisms are compromised, and the mature seeds preserve green colour. The residual chlorophylls can enhance oxidative degradation of reserve biomolecules, and affect thereby the quality, shelf life and nutritive value of seeds. Despite this, the formation, degradation, and physical properties of the seed chlorophylls are still not completely characterised. So here we address the dynamics of seed photochemical activity in the yellow- and green-seeded pea cultivars by the pulse amplitude modulation (PAM) fluorometric analysis. The experiments revealed the maximal photochemical activity at the early- and mid-cotyledon stages. Thereby, the active centres of PSII were saturated at the light intensity of 15-20 μmol photonsm-2 s-1. Despite of their shielding from the light by the pod wall and seed coat, photochemical reactions can be registered in the seeds with green embryo. Importantly, even at the low light intensities, the photochemical activity in the coats and cotyledons could be detected. The fast transients of the chlorophyll a fluorescence revealed a higher photochemical activity in the coat of yellow-seeded cultivars in comparison to those with the green-seeded ones. However, it declined rapidly in all seeds at the late cotyledon stage, and was accompanied with the decrease of the seed water content. Thus, the termination of photosynthetic activity in seeds is triggered by their dehydration. [ABSTRACT FROM AUTHOR]

Long-distance communications in giant characean internodal cells involve cytoplasmic streaming as an effective means for transportation of regulatory substances. The local illumination of Chara corallina Klein ex C.L. Willdenow internodal cells with an intense 30 s pulse of white light caused a transient increase of modulated chlorophyll fluorescence in cell regions positioned downstream the cytoplasmic flow after a delay whose duration increased with the axial distance from the light source. No changes in fluorescence were observed in cell regions residing upstream of the light spot. The transient increase in actual fluorescence F0 in cell areas exposed to constant dim illumination at large distances from the brightly lit area indicates the transmission of photosynthetically active metabolite between chloroplasts separated by 1–5mm distances. The shapes of fluorescence transients were sensitive to retardation of cytoplasmic streaming by cytochalasin D and to variations in cyclosis velocity during gradual recovery of streaming after an instant arrest of cyclosis by elicitation of the action potential. Furthermore, the analysed fluorescence transients were skewed on the ascending or descending fronts depending on the position of light-modulated cytoplasmic package at the moment of streaming cessation with respect to the point of measurements. The observations are simulated in qualitative terms with a simplified streaming–diffusion model. [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 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]

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]

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]

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]

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]

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]

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]

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]

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]

Stress caused by environmental factors evokes dynamic changes in plant phenotypes. In this study, we deciphered simultaneously the reaction of plant growth and chlorophyll fluorescence related parameters using a novel approach which combines existing imaging technologies (GROWSCREEN FLUORO). Three different abiotic stress situations were investigated demonstrating the benefit of this approach to distinguish between effects related to (1) growth, (2) chlorophyll-fluorescence, or (3) both of these aspects of the phenotype. In a drought stress experiment with more than 500 plants, poly(ADP-ribose) polymerase (PARP) deficient lines of Arabidopsis thaliana(L.) Heynh showed increased relative growth rates (RGR) compared with C24 wild-type plants. In chilling stress, growth of PARP and C24 lines decreased rapidly, followed by a decrease in Fv/Fm. Here, PARP-plants showed a more pronounced decrease of Fv/Fmthan C24, which can be interpreted as a more efficient strategy for survival in mild chilling stress. Finally, the reaction of Nicotiana tabacumL. to altered spectral composition of the intercepted light was monitored as an example of a moderate stress situation that affects chlorophyll-fluorescence related, but not growth-related parameters. The examples investigated in this study show the capacity for improved plant phenotyping based on an automated and simultaneous evaluation of growth and photosynthesis at high throughput. [ABSTRACT FROM AUTHOR]

Leaf reflectance spectral measurements are an emerging non-invasive technique that can be used to derive the photochemical reflectance index (PRI) to assess the physiological state of plants from leaf to ecosystem level. Changes in PRI are associated with changes in the xanthophyll cycle activity and provide an estimate of changes in the effective photochemical quantum efficiency (ΦII) during the growing season. However, we hypothesised that the correlation between PRI and ΦIImight be poor when the xanthophyll cycle is primed for sustained thermal dissipation of the light energy absorbed. To test our hypothesis, we studied the recovery of winter acclimated Jack pine (Pinus banksianaLamb.) seedlings that were exposed to different simulated spring recovery treatments in controlled environments. Different growth temperatures and light intensities were used to dissect the effect of these two factors on chlorophyll fluorescence, pigment composition and leaf reflectance. ΦIIshowed a clear response to temperature whereas PRI was mostly affected by light intensity. In contrast, the de-epoxidation state of the xanthophyll cycle pigments was both temperature and light dependent. Our data suggest that zeaxanthin-independent non-photochemical quenching is employed to various degrees in the different treatments. As a result, within the limits of our experimental setup, PRI could not explain the variation in ΦII. This indicates that an improved understanding of the different energy quenching mechanisms is critical to accurately interpret the PRI signal under environmental conditions where the predominant mode of excess energy dissipation does not involve a dynamic operation of the xanthophyll cycle, but a sustained mechanism of energy dissipation. [ABSTRACT FROM AUTHOR]

The objective of this study was to characterise photosynthesis in terrestrial non-Kranz (NK) C4species, Bienertia sinuspersiciAkhani and Suaeda aralocaspica(Bunge) Freitag & Schütze (formerly Borszczowia aralocaspica), compared with closely related Kranz type C4Suaeda eltonicaIljin and Suaeda taxifoliaStandley, and C3species Suaeda heterophyllaBunge and Suaeda maritimaDumort in subfamily Suaedoideae (Chenopodiaceae). Traditional Kranz type C4photosynthesis has several advantages over C3photosynthesis under certain environmental conditions by suppressing photorespiration. The different photosynthetic types were evaluated under varying levels of CO2and light at 25°C. Both NK and Kranz type species had C4type CO2compensation points (corrected for dark-type respiration) and half maximum saturation of photosynthesis at similar levels of atmospheric CO2(average of 145µbar for the C4species v. 330µbar CO2for C3species) characteristic of C4photosynthesis. CO2saturated rates of photosynthesis per unit chlorophyll was higher in the C3(at ~2.5 current ambient CO2levels) than the C4species, which is likely related to their higher Rubisco content. The amount of Rubisco as a percentage of total protein was similar in NK and Kranz type species (mean 10.2%), but much lower than in the C3species (35%). Light saturated rates of CO2fixation per unit leaf area at 25°C and 340µbar CO2were higher in the Kranz species and the NK C4S. aralocaspicathan in the C3species. In response to light at 340µbar CO2, there was a difference in rates of photosynthesis per unit Rubisco with NK>Kranz>C3species. There were no significant differences between the three photosynthetic types in maximum quantum yields, convexity of light response curves, and light compensation points at 25°C. The water use efficiency (CO2fixed per water transpired) at 340µbar CO2, 25°C and 1000µmolquantam-2s-1was on average 3-fold higher in the C4(NK and Kranz) compared with the C3species. The results show that the NK species have several C4traits like the Kranz type species in subfamily Suaedoideae. [ABSTRACT FROM AUTHOR]

Several mechanisms on acquired heat tolerance and cross adaptation have been proposed; however, relationships to photosynthetic energy partitioning remain unknown. The effects of heat pretreatment on cold and heat tolerance in grapevine leaves of two cultivars (‘Jingxiu', cold sensitive; ‘Beta', cold tolerant) were evident in changes in the antioxidant system, lipid peroxidation, net photosynthesis rate and also in chlorophyll fluorescence according:Y(II)+Y(NPQ)+Y(NO)=1, where Y(II) is the effective PSII quantum yield; Y(NPQ) is regulated energy dissipation as a protective mechanism; and Y(NO) is non-regulated energy dissipation as a damaging mechanism. Heat pretreatment enhanced heat tolerance in the two cultivars, which was associated with less energy partitioned in non-regulated energy dissipation, less lipid peroxidation and higher antioxidant enzyme (catalase, ascorbate peroxidase and guaiacol peroxidase) activities compared with control plants under heat stress. Heat pretreatment also induced cold tolerance in ‘Jingxiu' and ‘Beta' leaves. This cross adaptation seemed to be attributable in part to less non-regulated energy dissipation in pretreated ‘Jingxiu' and ‘Beta' than the controls under cold stress. The evidence that lipid peroxidation was less and antioxidant enzyme activities were higher in pretreated plants under cold stress further corroborated the results from energy partitioning. [ABSTRACT FROM AUTHOR]

Chlorophyll ais the photochemical agent accounting for most oxygenic photosynthesis, that is, over 99.9% of photosynthetic primary activity on Earth. The spectral and energetic properties of chlorophyll acan, at least in part, be rationalised in terms of the solar spectral output and the energetics of oxygen production and carbon dioxide reduction with two photochemical reactions. The long wavelength limit on in vivochlorophyll aabsorption is probably close to the energetic limit: longer wavelengths could not support a high rate and efficiency of oxygenic photosynthesis. Retinal, a β-carotene derivative that is the chromophore of rhodopsin, acts not only as a sensory pigment, but also as an ion-pumping photochemical transducer. Both sensory and energy-transforming rhodopsins occur in oxygenic phototrophs, although the extent of expression and the function of the latter are not well understood. [ABSTRACT FROM AUTHOR]

The receptacle of the sacred lotus is the main source of heat during the thermogenic stage of floral development. Following anthesis, it enlarges, greens and becomes a fully functional photosynthetic organ. We investigated development of photosynthetic traits during this unusual functional transition. There were two distinct phases of pigment accumulation in receptacles. Lutein and photoprotective xanthophyll cycle pigments accumulated first with 64 and 95% of the maximum, respectively, present before anthesis. Lutein epoxide comprised 32% of total carotenoids in yellow receptacles, but declined with development. By contrast, more than 85% of maximum total chlorophyll, β-carotene and Rubisco were produced after anthesis, and were associated with significant increases in maximum electron transport rates (ETR) and photochemical efficiency (Fv/Fm). Leaves and mature receptacles had similar Rubisco content and ETRs (>200μmolm-2s-1), although total chlorophyll and total carotenoid contents of leaves were significantly higher than those of green receptacles. Receptacle δ13C before anthesis was similar to that of leaves; consistent with leaf photosynthesis being the source of C for these tissues. In contrast, mature receptacles had significantly lower δ13C than leaves, suggesting that 14–24% of C in mature receptacles is the result of refixation of respired CO2. [ABSTRACT FROM AUTHOR]

Remotely sensed passive chlorophyll fluorescence emission has a potential to become one of the major global-scale reporter signals on vegetation performance and stress. In contrast to the actively probed parameters such as maximal (FM?) or minimal (F0?) emission, the steady-state chlorophyll fluorescence, Chl-FS, (FM? > Chl-FS > F0?) has not been adequately studied. Using fluorescence imaging of leaves, we explored the modulation of Chl-FS by actinic irradiance and by temperature in laboratory, as well as the changes that occurred in three coniferous and broadleaf plant species grown in field. The experiments revealed that Chl-FS is largely insensitive to the incident irradiance once this is above early morning or late evening levels. The characteristic, pre-noon measured Chl-FS correlated positively with the CO2 assimilation rate when measured in field during the year. It was low and stable in the cold winter months and steeply increased with the spring onset. The high values of the characteristic Chl-FS persisted throughout the vegetation season and rapidly decreased in the fall. The seasonal Chl-FS transitions coincided with the last spring frosts or the first fall frosts that persisted for several consecutive nights. The transitions were marked by an elevated variability of the Chl-FS signal. We propose that the signal variability occurring during the transition periods can be used to detect from satellites the beginning and the end of the photosynthetic activity in evergreen canopies of the temperate zone. [ABSTRACT FROM AUTHOR]

To determine whether the sun-exposed peel of apple fruit has a higher photosynthetic capacity than the shaded peel, fruit peel samples were taken in both early July and early September from the exterior part of the canopy of mature ?Liberty'/M.9 trees for measuring oxygen evolution, key enzymes and metabolites involved in photosynthesis, and chlorophyll fluorescence. Compared with the shaded peel, the sun-exposed peel had higher light-saturated oxygen evolution rate and higher light saturation point, but lower apparent and true quantum yields. The activity of ribulose-1,5-bisphosphate carboxylase/oxygenase, glyceraldehyde-3-phosphate dehydrogenase, phosphoribulokinase, stromal fructose-1,6-bisphosphatase, ADP-glucose pyrophosphorylase and sucrose-phosphate synthase (SPS) were higher in the sun-exposed peel than in the shaded peel on both sampling dates except that no significant difference was found in SPS activity between the two peel types in September. No significant difference was detected in the concentration of key metabolites (G6P, F6P, G1P, and PGA) between the sun-exposed peel and the shaded peel, suggesting that the response of the key enzymes to light exposure is well coordinated. Chlorophyll fluorescence quenching analysis showed that the sun-exposed peel had higher PSII quantum efficiency than the shaded peel at each given PFD, which resulted mainly from the higher photochemical quenching coefficient (qP). The sun-exposed peel had higher thermal dissipation capacity, as indicated by larger NPQ and Fo quenching, than the shaded peel at high PFD. In conclusion, the sun-exposed peel of apple fruit has higher activities of the Calvin cycle enzymes and higher rate of electron transport, leading to higher photosynthetic O2 evolution capacity. It appears that the acclimation of the Calvin cycle activities, thermal dissipation, and electron transport in apple peel are well coordinated in response to light exposure. [ABSTRACT FROM AUTHOR]

Chlorophyll a fluorescence measured in vivo is frequently used to study the role of different processes influencing the distribution of excitation energy in PSII complexes. Such studies are important for understanding the regulation of photosynthetic electron transport. However, at the present time, there is no unified methodology to analyse the energy partitioning in PSII. In this article, we critically assess several approaches recently developed in this area of research and propose new simple equations, which can be used for de-convolution of non-photochemical energy quenching in PSII complexes. [ABSTRACT FROM AUTHOR]

C4 plants are considered to be less sensitive to drought than C3 plants because of their CO2 concentrating mechanism. The C4 grasses, Paspalum dilatatum Poiret (NADP-ME), Cynodon dactylon (L.) Pers (NAD-ME) and Zoysia japonica Steudel (PEPCK) were compared in their response to water deficit imposed by the addition of polyethylene glycol to the nutrient solution in which they were grown. The effects of drought on leaf relative water content (RWC), net photosynthesis, stomatal conductance, carboxylating enzyme activities and chlorophyll a fluorescence were investigated. In C. dactylon the RWC was more sensitive, but the photosynthetic activity was less sensitive, to water deficit than in P. dilatatum and Z. japonica. The decrease of photosynthesis in P. dilatatum under water deficit was not closely related to the activities of the carboxylating enzymes or to chlorophyll a fluorescence. However, decreased activities of ribulose 1,5-bisphosphate carboxylase/oxygenase and phosphoenolpyruvate carboxylase, in addition to decreased stomatal conductance, may have contributed to the decrease of photosynthesis with drought in C. dactylon and Z. japonica. The different responses to water deficit are discussed in relation to the natural habitats of C4 grasses. [ABSTRACT FROM AUTHOR]