Photorespiration and photoprotection of grapevine (<Emphasis Type="Italic">Vitis vinifera</Emphasis> L. cv. Cabernet Sauvignon) under water stress

In order to investigate the photoprotective function of photorespiration in grapevine under water stress, potted grapevines (Vitis vinifera L. cv. Cabernet Sauvignon) were randomly divided into three uniform groups for well-watered [watered every morning to keep the relative water content (RWC) of soil over 70 %], water-stress adapted (drought-adapted at 30 % relative soil water content for 30 days), and water stress without adaptation treatment (water-stressed to 30 % relative soil water content for 3 days). Net assimilation rate (A _N), stomatal conductance (g _s), substomatal CO₂ concentration (C _i), transpiration rate (E), actual photochemical efficiency of PSII (Φ_PSII), and maximum photochemical efficiency of PSII (F_v/F_m) were recorded by combining measurements of gas exchange and chlorophyll fluorescence. Gross photorespiration (P_r), photosynthetic electron partitioning (J_C/J_T), photochemical quenching coefficient (qP), and non-photochemical quenching (NPQ) were also calculated. The ratio of net assimilation rate to transpiration rate (A _N/E) was used as an indicator of water use efficiency (WUE). A _N, apparent P_r, Φ_PSII, F_v/F_m, qp, and g _s decreased, NPQ increased, and gross P_r sustained at a high level under water stress. This suggests that both photorespiration and energy dissipation play important roles in protecting photosynthetic apparatus against photoinhibition. C _i in water-stressed plants without adaptation treatment increased, which indicates the leaves suffered a non-stomatal limitation, while the water-stress adaped plants only suffered a stomatal limitation indicated by low C _i.     

Rehydration of Sugar Beet Plants after Water Stress: Effect of Cytokinins

The possibility to improve the recovery of sugar beet plants after water stress by application of synthetic cytokinins N⁶-benzyladenine (BA) or N⁶-(m-hydroxybenzyl)adenosine (HBA) was tested. Relative water content (RWC), net photosynthetic rate (P_N), transpiration rate (E), stomatal conductance (g_s), chlorophyll (Chl) a and Chl b contents, and photosystem 2 efficiency characterized by variable to maximal fluorescence ratio (F_v/F_m) were measured in control plants, in water-stressed plants, and after rehydration (4, 8, 24, and 48 h). Water stress markedly decreased parameters of gas exchange, but they started to recover soon after irrigation. Application of BA or HBA to the substrate or sprayed on leaves only slightly stimulated recovery of P_N, E, and g_s in rehydrated plants, especially during the first phases of recovery. Chl contents decreased only under severe water stress and F_v/F_m ratio was not significantly affected by water stress applied. Positive effects of BA or HBA application on Chl content and F_v/F_m ratio were mostly not observed.     

Interactions of Elevated CO2 Concentration and Drought Stress on Photosynthesis in Eucalyptus Cladocalyx F. Muell

Response of net photosynthetic rate (P _N), stomatal conductance (g _s), intercellular CO₂ concentration (c _i), and photosynthetic efficiency (F_v/F_m) of photosystem 2 (PS2) was assessed in Eucalyptus cladocalyx grown for long duration at 800 (C₈₀₀) or 380 (C₃₈₀) μmol mol^-1 CO₂ concentration under sufficient water supply or under water stress. The well-watered plants at C₈₀₀ showed a 2.2 fold enhancement of P _N without any change in g _s. Under both C₈₀₀ and C₃₈₀, water stress decreased P _N and g _s significantly without any substantial reduction of c _i, suggesting that both stomatal and non-stomatal factors regulated P _N. However, the photosynthetic efficiency of PS2 was not altered. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of water stress and high temperature on gas exchange and chlorophyll fluorescence in Triticum aestivum L.

Wheat plants grown in controlled growth chambers were exposed to drought stress (DS) and high temperature (HT) singly and in combination (DS+HT). The effects of these two stresses on net photosynthetic rate (P _N), stomatal conductance (g _s), intercellular CO₂ concentration (C _i), quantum efficiency of photosystem 2 (Φ_PS2), variable to maximum chlorophyll (Chl) fluorescence (F_v/F_m), photochemical (q_p) and non-photochemical (NPQ) Chl fluorescence, and yield were investigated. Grain yield was decreased by 21 % due to DS, while it was increased by 26 % due to HT. P _N, g _s, C _i, and Chl fluorescence were dramatically reduced to DS, HT, and their interaction, except NPQ which showed an increase due to HT.     

Interactions of Elevated CO2 Concentration and Drought Stress on Photosynthesis in Eucalyptus Cladocalyx F. Muell

Response of net photosynthetic rate (P _N), stomatal conductance (g _s), intercellular CO₂ concentration (c _i), and photosynthetic efficiency (F_v/F_m) of photosystem 2 (PS2) was assessed in Eucalyptus cladocalyx grown for long duration at 800 (C₈₀₀) or 380 (C₃₈₀) µmol mol^-1 CO₂ concentration under sufficient water supply or under water stress. The well-watered plants at C₈₀₀ showed a 2.2 fold enhancement of P _N without any change in g _s. Under both C₈₀₀ and C₃₈₀, water stress decreased P _N and g _s significantly without any substantial reduction of c _i, suggesting that both stomatal and non-stomatal factors regulated P _N. However, the photosynthetic efficiency of PS2 was not altered.     

Genotypic differences in the responses of gas exchange,chlorophyll fluorescence,and antioxidant enzymes to aluminum stress in <Emphasis Type="Italic">Festuca arundinacea</Emphasis>

In this study, the gas exchange, chlorophyll fluorescence, and antioxidant activity in eight tall fescue cultivars were investigated under aluminum stress. The results showed that the net photosynthetic rate (P _N) and stomatal conductance (g _s) were decreased, while the intercellular CO₂ concentration (C_i) was stable or increased under Al stress conditions. The efficiency of excitation capture by open PSII reaction centers (F′_v/F′_m), the maximum quantum yield of PSII photochemistry (F _v/F _m), the quantum yield of PSII electron transport (Φ_PSII), and the photochemical quenching (qP) were also decreased after Al stress, while the non-photochemical quenching (NPQ) was increased. Moreover, Al stress increased the antioxidant activities and MDA contents in each tall fescue cultivars. However, there was a lot genotype differences between the Al-tolerant and Al-sensitive cultivars. Cv. Barrington was the most sensitive cultivar and cv. Crossfire 2 was the most tolerant cultivar. The excessive excitation energy could not be dissipated efficiently by antenna pigments, and reactive oxygen species could not be scavenged efficiently, thereby resulting in membrane lipid peroxidation in cv. Barrington under Al stress conditions.     

Photosynthetic responses of radish (<Emphasis Type="Italic">Raphanus sativus</Emphasis> var. <Emphasis Type="Italic">longipinnatus</Emphasis>) plants to infection by turnip mosaic virus

Plant growth, chlorophyll (Chl) content, photosynthetic gas exchange, ribulose-1,5-bisphosphate carboxylase (RuBPCO) enzyme activity, and Chl fluorescence in radish (Raphanus sativus var. longipinnatus) plants were examined after turnip mosaic virus (TuMV) infection. Plant fresh mass, dry mass, Chl content, net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), and RuBPCO activity were significantly lower in infected plants after 5 weeks of virus infection as compared to healthy plants. The 5-week virus infection did not induce significant differences in intercellular CO₂ concentration (C _i, photochemical efficiency of photosystem 2, PS2 (F_v/F_m), excitation capture efficiency of open PS2 reaction centres (F_v'/F_m'), effective quantum efficiency of photosystem 2 (ΔF/F_m'), and photochemical quenching (q_P), but non-photochemical quenching (q_N) and alternative electron sink (AES) were significantly enhanced. Thus the decreased plant biomass of TuMV-infected plants might be associated with the decreased photosynthetic activity mainly due to reduced RuBPCO activity.     

Effects of cadmium and salicylic acid on growth, spectral reflectance and photosynthesis of castor bean seedlings

Salicylic acid (SA) is a potent signaling molecule in plants and is involved in eliciting specific responses to biotic and abiotic stresses. The aim of this study is to investigate whether the exogenous application of SA can improve cadmium (Cd) induced inhibition of photosynthesis in castor bean (Ricinus communis L.) plants. The effects of SA and Cd on plant growth, spectral reflectance, pigment contents, chlorophyll fluorescence and gas exchange were examined in a hydroponic cultivation system. Results indicate that Cd exposure significantly decreased the dry biomass, photosynthetic rate (P_n), stomatal conductance (G_s), intercellular CO₂ concentration (C_i), pigment contents, quantum yield of PS II photochemistry (F_v/F_m), and effective quantum yield of PS II (??PS II) in the plants. Pretreatment with SA alone reduced the biomass and P_n in castor bean plants, whereas pigment contents, F_v/F_m and ??PS II remained unaffected. Reduced G_s, C_i and E, as well as increased stomatal limitation (L_s) and water use efficiency (WUE), were observed in plants pretreated with 500???M SA alone, whereas plants treated with 250???M SA were unaffected. Under Cd stress, SA pretreatment led to a significant decrease in P_n, G_s, E, C_i, and chlorophyll contents (Chl a, Chl b, Chl a+b, Car, Chl a/b), and an increase in L_s and WUE. Cd exposure enhanced spectral reflectance in the range 550?C680?nm and 750?C1,050?nm. It also decreased the normalized difference vegetation index (_chlNDI), the modified red edge simple ratio index (mSR₇₀₅), the red edge position (REP), water band index, and red/green ratio, whereas the structure independent pigment index (SIPI) was increased. Significant correlations (P?<?0.01) between spectral indices (mSR₇₀₅, _chlNDI, REP, red/green ratio) and pigment contents. SA significantly worsened plant growth and photosynthesis in Cd-stressed castor bean plants, in which a stomatal limitation was involved. The leaf spectral reflectance is a sensitive indicator in determining Cd toxicity in plants.     

Wheat cultivars selected for high Fv/Fm under heat stress maintain high photosynthesis,total chlorophyll,stomatal conductance,transpiration and dry matter

The chlorophyll fluorescence parameter F_v/F_m reflects the maximum quantum efficiency of photosystem II (PSII) photochemistry and has been widely used for early stress detection in plants. Previously, we have used a three‐tiered approach of phenotyping by F_v/F_m to identify naturally existing genetic variation for tolerance to severe heat stress (3 days at 40°C in controlled conditions) in wheat (Triticum aestivum L.). Here we investigated the performance of the previously selected cultivars (high and low group based on F_v/F_m value) in terms of growth and photosynthetic traits under moderate heat stress (1 week at 36/30°C day/night temperature in greenhouse) closer to natural heat waves in North‐Western Europe. Dry matter accumulation after 7 days of heat stress was positively correlated to F_v/F_m. The high F_v/F_m group maintained significantly higher total chlorophyll and net photosynthetic rate (P_N) than the low group, accompanied by higher stomatal conductance (g_s), transpiration rate (E) and evaporative cooling of the leaf (ΔT). The difference in P_N between the groups was not caused by differences in PSII capacity or g_s as the variation in F_v/F_m and intracellular CO₂ (C_i) was non‐significant under the given heat stress. This study validated that our three‐tiered approach of phenotyping by F_v/F_m performed under increasing severity of heat was successful in identifying wheat cultivars differing in photosynthesis under moderate and agronomically more relevant heat stress. The identified cultivars may serve as a valuable resource for further studies to understand the physiological mechanisms underlying the genetic variability in heat sensitivity of photosynthesis.     

Drought effect on photosynthetic activity,osmolyte accumulation and membrane integrity of two <Emphasis Type="Italic">Cicer arietinum</Emphasis> genotypes

Drought was induced in chickpea (Cicer arietinum L.) genotypes (ChK 3226 and ILC 3279) differing in yield capacity. Water stress (S1, RWC around 55–50%; S2, RWC ≤ 40%) drastically reduced stomatal conductance (g _s) and net photosynthetic rate (P _N) in both genotypes. ILC 3279 showed greater photosynthetic capacity (A _max) decreases. Maximum PSII photochemical efficiency (F_v/F_m), photochemical quenching (q_P), total chlorophylls (Chls) and carotenoids (Cars) content showed stability in both genotypes under stress, but in S2 ILC 3279 presented an increase in basal fluorescence (F₀) and a greater reduction in estimation of quantum yield of linear electron transport (Φ_e) than ChK 3226. Membrane damage evaluated by electrolyte leakage occurred earlier and was greater in ILC 3279. It also presented a decrease of total fatty acids (TFA) along drought, while in ChK 3226 greater amounts of TFA were observed in S1. In rehydration, P _N of S1 plants completely recovered (ILC 3279) or remained slightly below control (ChK 3226). As regards S2 plants, ILC 3279 showed stronger P _N and g _s reductions than ChK 3226, despite both genotypes totally recovered A _max and chlorophyll (Chl) a fluorescence. ChK 3226 recovered more efficiently from membrane damage. Under control conditions, greater amounts of most of the studied soluble metabolites occurred in ChK 3226 plants. Malate and citrate decreased with water stress (S2) in both genotypes. Sucrose and pinitol (that had a higher concentration than sucrose in both genotypes) increased in ILC 3279 (S1 and S2), and decreased in ChK 3226 (S2). In ILC 3279 proline and asparagine followed similar patterns. Genotypes showed a similar shoot dry mass (DM) in control plants, but root DM was higher in ChK 3226. Drought reduced root and shoot DM in ChK 3226 already under S1, while in ILC 3279 root DM was unaffected by drought and shoot biomass decreased only in S2. Root/shoot ratio was always higher in ChK 3226 but tended to decrease under stress, while the opposite was observed in ILC 3279. No pods were obtained from control plants of both genotypes, or droughted ILC 3279 plants. ChK 3226 produced pods under S1 (higher yield) and S2. Under stress conditions, ChK 3226 was less affected in photosynthetic activity and membrane integrity, showing a better tolerance to drought. This agrees with the better yield of this genotype under water stress. Distinct strategies seem to underlie the different physiological responses of the two genotypes to water deficit. In spite of its significant solutes accumulation, ILC 3279 was more affected in photosynthetic activity and membrane integrity during water stress than ChK 3226, which showed better yield under drought. A relation could not be established between solutes accumulation of ILC 3279 and yield.     

Effects of ambient O<Subscript>3</Subscript> on wheat during reproductive development: Gas exchange,photosynthetic pigments,chlorophyll fluorescence,and carbohydrates

The current concentrations of O₃ have been shown to cause significant negative effects on crop yield. The present levels of ozone may not induce visible symptoms in most of plants, but can result in substantial losses in reproductive output. This paper considers the impact of ambient O₃ on gas exchange, photosynthetic pigments, chlorophyll (Chl) fluorescence and carbohydrate levels in the flag leaf of wheat plants during various stages of reproductive development using open-top chambers. Mean O₃ concentration was 45.7 ppb during wheat growth and 50.2 ppb after flag leaf development. Reproductive stage showed higher exceedence of O₃ above 40 ppb compared to the vegetative stage. Diurnal variations in net photosynthetic rate (P _N) and stomatal conductance (g _s), intercellular CO₂ concentration (C _i), Fv/Fm ratio, photosynthetic pigments, soluble sugars, and starch were measured at 10, 30, and 50 days after flag leaf expansion (DAFE). The results showed reductions in P _N, g _s, F_v/F_m ratio, photosynthetic pigments and starch, and increases in C _i, F₀, and soluble sugars in nonfiltered chambers (NFCs) compared to filtered chambers (FCs). Maximum changes in measured parameters were observed at 50 DAFE (i.e. grain filling and setting phase). Diurnal variation in P _N showed double peaked curve in both FCs and NFCs, but delayed peak and early depression in NFCs. Stomatal conductance was significantly lower in NFCs. The study suggests that higher prevalence of ambient O₃ during reproductive development led to significant alteration in physiological vitality of wheat having potential negative influence on yield.     

Effect of Cd on growth, photosynthetic gas exchange, and chlorophyll fluorescence of wild and Cd-sensitive mutant rice

Growth, photosynthetic gas exchange, and chlorophyll fluorescence characteristics were investigated in wild type (WT) and Cd-sensitive mutant rice (Oryza sativa L.) plants using 50 μM Cd treatment for 12 d followed by a 3-d recovery. Under Cd stress, net dry mass and pigment contents were significantly lower in the mutant plants than in the WT. The mutant had lower net photosynthetic rate (P _N), transpiration rate (E), and stomatal conductance (g _s) than WT rice, however, it had higher intercellular CO₂ concentration (C _i), indicating that non-stomatal factors accounted for the inhibition of P _N. Maximal photochemical efficiency of photosystem 2 (F_v/F_m), effective quantum yield of PS2 (Φ_PS2), and photochemical quenching (q_P) decreased much in the mutant under Cd stress. Cd content in roots and leaves of the mutant was significantly higher than those in the WT. Hence Cd toxicity was associated with the marked increases in Cd contents of plant tissue. After the recovery for 3 d, the WT rice had higher capacity to recover from Cd injury than the mutant.     

Gibberellic acid affects growth and flowering of Philodendron‘Black Cardinal’

Changes in net photosynthetic rate (P_N), stomatal conductance (g_s), intercellular CO₂ concentrations (C_i), transpiration rate (E) and water use efficiency (WUE) were measured in Plantago major L. plants grown under sufficient soil water supply or under soil water stress conditions. The plants had high P_N in a wide range of soil water potential and temperature regimes. Soil water had little effect on P_N under ambient CO₂ concentrations, which was explained by a high carboxylation rate, but increased the dark respiration rate. Carboxylation activity at low C_i depended on RuBP regeneration, whereas at high C_i it depended on the phosphate regeneration rate. The g_s and E values were low in plants under stress as compared to the controls that resulted in an increase of WUE. The results obtained show that Plantago major plants have different ways of adaptation to soil water deficit conditions.     

Photosynthesis and PSII functionality of drought-resistant and drought-sensitive weeping lovegrass plants

World areas subject to drought are expected to increase under conditions of climate change. The purpose of this study is to clarify the response of grass species that can grow and produce under water stress. Therefore leaf photosynthesis, chlorophyll fluorescence and pigment content response to water stress were studied in two varieties of the C₄ grass Eragrostis curvula. Two-year-old plants of cv Ermelo and Consol were grown in plastic pots. Drought stress was imposed by withholding irrigation for 15 days and then rewatering for 5 days. During drought relative water content (RWC) decreased 65% in cv Ermelo, while lower reductions of RWC were observed in cv Consol. During the experiment in cv Ermelo increasing drought stress severity caused large decreases in photosynthetic rates, maximal PSII photochemical efficiency (F_V/F_M) and leaf pigment content. Cv Consol showed small variations in these parameters. Compared to cv Consol, after 15 days of drought, effective PSII quantum yield (Φ_II) was significantly lower in cv Ermelo. Reductions of Φ_II were related to significant reductions of open PSII energy capture efficiency (F′_V/F′_M). Photosynthetic response to increasing PPFD levels and to internal CO₂ concentration (C_i) were reduced by drought in cv Ermelo. Compared to well-watered control plants and to cv Consol, drought stressed plants of cv Ermelo showed also reductions of the initial slope of photosynthetic response to C_i and in the photosynthetic rate measured at saturating C_i. Moreover stomatal conductance (g) of both cvs decreased during drought. However, g was lower in drought stressed plants of cv Consol than in cv Ermelo. Water stress caused large reductions in leaf chlorophyll and carotenoid content in cv Ermelo, and small reductions in cv Consol. In drought-sensitive cv Ermelo water stress reduced the capabilities to down regulate PSII functionality through thermal energy dissipation. Results suggest that drought resistance of cv Consol, can be attributed to a higher water use efficiency.     

Leaf gas exchange and chlorophyll a fluorescence in soybean leaves infected by Phakopsora pachyrhizi

Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, is one of the most important foliar diseases affecting soybean production worldwide. This study aimed to investigate the photosynthetic performance (leaf gas exchange, chlorophyll (Chl) a fluorescence images and photosynthetic pigment pools) of soybean plants sprayed with Acibenzolar‐S‐Methyl (ASM) and the fungicide epoxiconazole + pyraclostrobin (Epo+Pyr) and further inoculated with P. pachyrhizi. The ASR symptoms progressed much faster on the leaves of plants from the control treatment (water spray) in comparison with the ASM and Epo+Pyr treatments. In general, the values for the leaf gas exchange parameters net carbon assimilation rate (A), stomatal conductance to water vapour (g_s), internal CO₂ concentration (C_i) and transpiration rate (E) increased for the infected plants sprayed with ASM or Epo+Pyr in comparison with plants from the control treatment. The values for the initial fluorescence (F_o), maximal fluorescence (F_m), maximal photosystem II quantum efficiency (F_v/F_m), effective photosystem II quantum yield (Y(II)) and quantum yield of regulated energy dissipation (Y(NPQ)) were consistently higher for the ASM and Epo+Pyr treatments in comparison with the control treatment at advanced stages of fungal infection. By contrast, the values for quantum yield of non‐regulated energy dissipation (Y(NO) were significantly lower for the ASM and Epo+Pyr treatments. The concentrations of total Chl a+b and carotenoids significantly increased for infected plants sprayed with ASM and Epo+Pyr in comparison with plants from the control treatment. The results of this study demonstrated that the spray of soybean plants with either ASM or Epo+Pyr contributed to reduce the negative effect of ASR on the photosynthesis of soybean plants.     

Silicon partially preserves the photosynthetic performance of rice plants infected by Monographella albescens

Leaf scald, caused by Monographella albescens, is one of the major diseases in rice worldwide. This study investigated the effect of silicon (Si) on the photosynthetic gas exchange parameters [net CO₂ assimilation rate (A), stomatal conductance to water vapour (g_s), transpiration rate (E)] and internal CO₂ concentration (C_i), chlorophyll (Chl) fluorescence a parameters [minimal fluorescence (F₀), maximum fluorescence (F_m), maximum quantum yield of photosystem II (F_v/F_m)], photochemical quenching coefficient (q_p), effective quantum yield of PSII [Y(II)], quantum yield of regulated energy dissipation [Y(NPQ)] and quantum yield dissipation non‐regulated [Y(NO)] and the concentrations of pigments in rice plants grown in nutrient solutions containing either 0 (?Si) or 2 mM Si (+Si) and non‐inoculated or inoculated with M. albescens. Leaf scald severity decreased with higher foliar Si concentration. For the inoculated +Si plants, A, g_s and E were significantly higher in comparison with the inoculated ?Si plants, in which C_i was significantly increased. Similarly, the concentrations of Chl_a, Chl_b, total Chl_a+b and carotenoids were higher for the +Si plants in comparison with the ?Si plants. Changes in the images of Chl a fluorescence were first observed precisely on the ?Si plants leaves in comparison with the +Si plants. A decrease of q_P and Y(II) in inoculated ?Si plants, in comparison with the inoculated +Si plants, was accompanied by an increase in Y(NPQ) and Y(NO). Notably, the extent of the leaf areas was much more evident for Y(II) and q_P in comparison with F₀, F_m and F_v/F_m, suggesting that Y(II) and q_P were good predictors in detecting the early effects of leaf scald on the leaf photosynthesis. For the +Si non‐inoculated plants, changes in Y(II) were associated with alterations in both Y(NPQ) and Y(NO) compared with non‐inoculated ?Si plants. In conclusion, the photosynthetic performance (as demonstrated by the gas exchange and Chl a fluorescence parameters) and the pigment pools of rice plants infected with M. albescens were preserved by Si supply and, therefore, provided an increase in rice resistance against leaf scald.     

Bioregulators protected photosynthetic machinery by inducing expression of photorespiratory genes under water stress in chickpea

Globally, water deficit is one of the major constraints in chickpea (Cicer arietinum L.) production due to substantial reduction in photosynthesis. Photorespiration often enhances under stress thereby protecting the photosynthetic apparatus from photoinhibition. Application of bioregulators is an alternative to counter adverse effects of water stress. Thus, in order to analyze the role of bioregulators in protecting the photosynthetic machinery under water stress, we performed an experiment with two contrasting chickpea varieties, i.e., Pusa 362 (Desi type) and Pusa 1108 (Kabuli type). Water deficit stress was imposed at the vegetative stage by withholding water. Just prior to exposure to water stress, plants were pretreated with thiourea (1,000 mg L^?1), benzyladenine (40 mg L^?1), and thidiazuron (10 mg L^?1). Imposed water deficit decreased relative water content (RWC), photosynthetic rate (P_N), quantum efficiency of PSII (F_v/F_m), and enhanced lipid peroxidation (LPO). However, bioregulator application maintained higher RWC, P_N, F_v/F_m, and lowered LPO under water stress. Expression of Rubisco large subunit gene (RbcL) was low under water stress both in the Kabuli and Desi type. However, bioregulators strongly induced its expression. Although poor expression of two important photorespiratory genes, i.e., glycolate oxidase and glycine decarboxylase H subunit, was observed in Desi chickpea under imposed stress, bioregulators in general and cytokinins in particular strongly induced their expression. This depicts that the application of bioregulators protected the photosynthetic machinery by inducing the expression of RbcL and photorespiratory genes during water deficit stress.     

Effects of exogenous putrescine on gas-exchange characteristics and chlorophyll fluorescence of NaCl-stressed cucumber seedlings

The effects of 10 mM putrescine (Put) treated by spraying on leaves on growth, chlorophyll content, photosynthetic gas-exchange characteristics, and chlorophyll fluorescence were investigated by growing cucumber plants (Cucumis sativus L. cv. ChangChun mici) using hydroponics with or without 65 mM NaCl as a salt stress. Salt stress caused the reduction of growth such as leaf area, root volume, plant height, and fresh and dry weights. Furthermore, net photosynthesis rate (P _n), stomatal conductance (g _s), intercellular CO₂ concentration (C _i), and transpiration rate (T _r) were also reduced by NaCl, but water use efficiency (WUE; P _n/T _r) showed a tendency to be enhanced rather than reduced by NaCl. However, Put alleviated the reduction of P _n by NaCl, and showed a further reduction of C _i by NaCl. The reduction of g _s and T _r by NaCl was not alleviated at all. The enhancement of WUE by NaCl was shown to have no alleviation at day 1 after starting the treatment, but after that, the enhancement was gradually reduced till the control level. Maximum quantum efficiency of PSII (F _v/F _m) showed no effects by any conditions based on the combination of NaCl and Put, and in addition, kept constant values in plants grown in each nutrient solution during this experimental period. The efficiency of excitation energy capture by open photosystem II (PSII) (F _v′/F _m′), actual efficiency of PSII (Φ_PSII), and the coefficient on photochemical quenching (qP) of plants with NaCl were reduced with time, and the reduction was alleviated till the control level by treatment with Put. The F _v′/F _m′, Φ_PSII, and qP of plants without NaCl and/or with Put showed no variation during the experiment. Non-photochemical quenching of the singlet excited state of chlorophyll a (NPQ) showed quite different manner from the others as mentioned above, namely, continued to enhance during the experiment.     

The effect of chromium and aluminum on growth,root morphology,photosynthetic parameters and transpiration of the two barley cultivars

The effect of aluminum and chromium on two barley genotypes differing in Al tolerance was studied in a hydroponic experiment. Al stress decreased plant growth, biomass production, chlorophyll content and photosynthetic efficiency determined as variable to maximum chlorophyll fluorescence ratio (F_v/F_m), net photosynthetic rate (P_N), intercellular CO₂ concentration (c_i), stomatal conductance (g_s) and transpiration rate (E) less in an Al-tolerant genotype Gebeina than in an Al-sensitive genotype Shang 70–119. Cr stress also caused marked reduction in growth and photosynthetic traits in barley plants. Higher reduction was observed at pH 4.0 as compared to pH 6.5. Combined stress of Cr and Al, caused further reduction in growth and photosynthetic parameters.     

Photosystem II energy use,non-photochemical quenching and the xanthophyll cycle in Sorghumbicolor grown under drought and free-air CO2 enrichment(FACE) conditions

The present study was carried out to test the hypothesis thatelevated atmospheric CO₂ (Ca) will alleviate over‐excitationof the C₄ photosynthetic apparatus and decrease non‐photochemicalquenching (NPQ) during periods of limited water availability. Chlorophyll a fluorescencewas monitored in Sorghum bicolor plants grown under a free‐aircarbon‐dioxide enrichment (FACE) by water‐stress (Dry) experiment.Under Dry conditions elevated Ca increased the quantum yield ofphotosystem II (φPSII) throughout the day throughincreases in both photochemical quenching coefficient (q_p)and the efficiency with which absorbed quanta are transferred toopen PSII reaction centres (F_v′/F_m′).However, in the well‐watered plants (Wets) FACE enhanced φPSIIonly at midday and was entirely attributed to changes in F_v′/F_m′_. Underfield conditions, decreases in φPSII under Dry treatmentsand ambient Ca corresponded to increases in NPQ but the de‐epoxidation stateof the xanthophyll pool (DPS) showed no effects. Water‐stress didnot lead to long‐term damage to the photosynthetic apparatus asindicated by φPSII and carbon assimilation measuredafter removal of stress conditions. We conclude that elevated Caenhances photochemical light energy usage in C₄ photosynthesisduring drought and/or midday conditions. Additionally,NPQ protects against photo‐inhibition and photodamage. However,NPQ and the xanthophyll cycle were affected differently by elevatedCa and water‐stress.