The effects of nitrogen (N) supply restriction on the CO2 assimilation and photosystem 2 (PS2) function of flag leaves were compared between two contrastive Japanese rice cultivars, a low-yield cultivar released one century ago, cv. Shirobeniya (SRB), and a recently improved high-yield cultivar, cv. Akenohoshi (AKN). Both cultivars were solution-cultured at four N supply levels from N4 (control) to N1 (the lowest). With a reduction in N-supply, contents of N (LNC), ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO), and chlorophyll (Chl) in flag leaves decreased in both cultivars. In parallel with this, the net photosynthetic rate (PN), mesophyll conductance (g m), and stomatal conductance (gs) decreased. PN was more dominantly restricted by gm than gs. The values of PN, gm, and RuBPCO content were larger in AKN than SRB at the four N supply levels. The content of Chl greatly decreased with N deficiency, but the reduction in the maximum quantum yield of PS2 was relatively small. Quantum yield of PS2 (ΦPS2) decreased with N deficiency, and its significant cultivar difference was observed between the two cultivars at N1: a high value was found in AKN. The content ratio of Chl/RuBPCO was also significantly low in AKN. The low Chl/RuBPCO is one of the reasons why AKN maintained a comparatively high PN and ΦPS2 at N deficiency. The adequate ratio of N distribution between Chl and RuBPCO is the important prerequisite for the efficient and sustainable photosynthesis in a flag leaf of rice plant under low N-input. and E. Kumagai, T. Araki, F. Kubota.
Abscisic acid (ABA), an important chemical signal from roots, causes physiological changes in leaves, including stomata closure and photoprotection. Furthermore, endogenous ABA concentration in leaves and stomatal behavior vary with the species adapted to different water regimes. In this study, Ficus microcarpa, a hemiepiphyte, Salix warburgii, a hygrophyte, and Acacia confusa, a mesophyte, were used to elucidate the effects of leaf detachment on photosystem II (PSII) efficiency under osmotic- and high-light stresses. Results indicate that, under osmotic- and high-light stresses, PSII efficiency of the detached leaves was lower than that of the attached leaves for all three tree species, when compared at the same levels of stomatal resistance and leaf water potential. Exogenous ABA could mitigate the PSII efficiency decrease of detached F. microcarpa leaves under osmotic- and high-light stresses. Yet, the osmotic stress could raise endogenous ABA concentration in the attached, but not in the detached F. microcarpa leaves. In addition, partial root-zone drying exerted a significant effect on stomatal behavior but not on the water status of F. microcarpa leaves. These observations imply that the stronger ability of PSII in the attached leaves of F. microcarpa under osmoticand high-light stresses was probably due to the protective action of ABA from roots. On the contrary, endogenous ABA level of S. warburgii leaves was very low. In addition, partial root-zone drying produced no significant effect on its stomatal behavior. Therefore, PSII in attached S. warburgii leaves was possibly protected from the damaging effects of excess absorbed energy by signals other than ABA, which were transported from the roots. and J.-H. Weng ... [et al.].
Seedlings of spring barley, meadow fescue, and winter rape were fumigated with 180 μg kg-1 of ozone for 12 d, and effect of O3 on photosynthesis and cell membrane permeability of fumigated plants was determined. Electrolyte leakage and chlorophyll fluorescence were measured after 6, 9, and 12 d of fumigation, while net photosynthetic rate (PN) and stomatal conductance (gs) were measured 9 d after the start of ozone exposure. O3 treatment did not change membrane permeability in fescue and barley leaves, while in rape a significant decrease in ion leakage was noted within the whole experiment. O3 did not change the photochemical efficiency of photosystem 2 (PS2), i.e., Fv/Fm, and the initial fluorescence (F0). The values of half-rise time (t1/2) from F0 to maximal fluorescence (Fm) decreased in fescue and barley after 6 and 9 d of fumigation. PN decreased significantly in ozonated plants, in the three species. The greatest decrease in PN was observed in ozonated barley plants (17 % of the control). The ozone-induced decrease in PN was due to the closure of stomata. Rape was more resistant to ozone than fescue or barley. Apparently, the rape plants show a large adaptation to ozone and prevent loss of membrane integrity leading to ion leakage. and A. Plażek, M. Rapacz. A. Skoczowski.
Photosynthetic responses of potato (Solanum tuberosum L. cv. Chunzao) were examined during potato virus Y (PVYNTN) infection. PVYNTN infection significantly reduced net photosynthetic rate and stomatal conductance, but had little influence on intercellular CO2 concentration. As the disease developed, the maximum carboxylation velocity of ribulose-1,5-bisphosphate carboxylase/oxygenase and the maximum electron transport rate contributing to ribulose-1,5-bisphosphate regeneration gradually decreased, followed by substantial reductions in the relative quantum efficiency of photosystem 2 (PS2) electron transport, the efficiency of excitation energy capture by open PS2 reaction centres, and photochemical quenching, but not in sustained photoinhibition. Thus PVYNTN depressed photosynthesis mainly by interfering with the enzymatic processes in the Calvin cycle which resulted in a down-regulation of electron transport. and Y. H. Zhou ... [et al.].
Secondary soil salinization causes plant stress, which can be relieved by different ratios of red to far-red light (R:FR). Our study aimed to elucidate the role of low R:FR ratios treatments on photosynthesis and growth of tomato seedlings in salinized soils. Tomato seedlings were treated under three R:FR ratios and calcium nitrate was applied simultaneously. The results showed that the treatments under low R:FR ratios stimulated growth parameters of tomato seedlings under calcium nitrate stress, the best impact being achieved at the R:FR ratio of 0.7 in this experiment. Low R:FR ratios treatments increased proline content as well as PSII maximum efficiency, actual electron transport operating efficiency, and photochemical quenching of tomato seedlings under calcium nitrate stress but decreased the value of nonphotochemical quenching. Moreover, low R:FR ratios treatments promoted net photosynthetic rate and increased the expression of a Rubisco gene. In conclusion, low R:FR ratios treatments could improve the salt resistance of greenhouse tomato plants.
Strong inhibition of rates of CO2 assimilation and transpiration, stomatal conductance, and water use efficiency as well as photosystem 2 (PS2) photochemical activity were related to the severity of reddening. The inhibition of photosynthesis in red cotton leaves was due to both decreased photochemical activity and stomatal limitation. Lowered photosynthetic capacity could be one of the main factors of reduced yield in reddening cotton. and V. Velikova ... [et al.].
Plant growth, contents of photosynthetic pigments, photosynthetic gas exchange, and chlorophyll (Chl) fluorescence in soybean [Glycine max (L.) Merr. cv. Heinong37] were investigated after it was inoculated with Sinorhizobium fredii USDA191 or treated with 5 mM (NH4)2SO4 (N5) and 30 mM (NH4)2SO4 (N30), respectively. In the plants following N5 fertilization, not only plant biomass, leaf area, and Chl content, but also net photosynthetic rate (PN), stomatal conductance (gs), carboxylation efficiency (CE), maximum photochemical efficiency (Fv/Fm) of photosystem 2 (PS2), and quantum yield of PS2 (ΦPS2) were markedly improved as compared with the control plants. There were also positive effects on plant growth and plant photosynthesis after rhizobia inoculation, but the effects were much less than those of N5 fertilization. For N30 plants there were no significant positive effects on plant growth and photosynthetic capacity. Plant biomass, PN, and gs were similar to those of N-limited (control) plants. ΦPS2 and photochemical quenching (qP) were obviously declined while content of carotenoids and non-photochemical quenching (qN) were significantly enhanced in N30 treated plants. This indicated that excess N supply may cause some negative effects on soybean plants. and X.-J. Zhou ... [et al.].
In flag leaves of four cultivars of barley (Hordeum vulgare L.) grown in the field under a triple-line-source sprinkler system, that produces a linear soil salinity gradient, a decrease in net carbon dioxide assimilation rate (PN) and stomatal conductance for water vapour (gs) was found. These changes were related to salinity tolerance at moderate salinity. With increasing salinity, PN was saturated at low irradiances and stomatal frequencies increased. A decrease in photosystem 2 (PS2) efficiency was not found in the field after dark adaptation even at high salinity. Salinity induced only small decreases in the actual PS2 efficiency at midday steady-state photosynthesis, indicating that the photosynthetic electron transport was little affected by salinity. Therefore, using PS2 efficiency estimates in attached leaves is probably not a useful tool to screen barley genotypes grown under saline conditions in the field for salinity tolerance. In contrast, excised flag leaves from high salinity plots, once in the laboratory, exhibited a decrease in the variable to maximum chlorophyll fluorescence ratio as compared to excised leaves from control plants. On the other hand, the PN rate might allow for a good discrimination between tolerant and non-tolerant cultivars. and R. Belkhodja ... [et al.].
The effect of four different NaCl concentrations (from 0 to 102 mM NaCl) on seedlings leaves of two corn (Zea mays L.) varieties (Aristo and Arper) was investigated through chlorophyll (Chl) a fluorescence parameters, photosynthesis, stomatal conductance, photosynthetic pigments concentration, tissue hydration and ionic accumulation. Salinity treatments showed a decrease in maximal efficiency of PSII photochemistry (Fv/Fm) in dark-adapted leaves. Moreover, the actual PSII efficiency (ϕPSII), photochemical quenching coefficient (qp), proportion of PSII centers effectively reoxidized, and the fraction of light used in PSII photochemistry (%P) were also dropped with increasing salinity in light-adapted leaves. Reductions in these parameters were greater in Aristo than in Arper. The tissue hydration decreased in salt-treated leaves as did the photosynthesis, stomatal conductance (g s) and photosynthetic pigments concentration essentially at 68 and 102 mM NaCl. In both varieties the reduction of photosynthesis was mainly due to stomatal closure and partially to PSII photoinhibition. The differences between the two varieties indicate that Aristo was more susceptible to salt-stress damage than Arper which revealed a moderate regulation of the leaf ionic accumulation. and H. Hichem, A. El Naceur, D. Mounir.
The effects of simulated acid rain on gas exchange, chlorophyll fluorescence, and anti-oxidative enzyme activity in cucumber seedlings (Cucumis sativus L. cv. Jingchun No. 4) were investigated. Acid rain significantly reduced net photosynthetic rate and mainly non-stomatal factors contributed to the decrease of photosynthesis during the experimental period. The reduced photosynthesis was associated with a decreased maximal photochemical efficiency (Fv/Fm) and the average quantum yield of the photosystem 2 (PS2) reaction centres (ΦPS2). Meanwhile, acid rain significantly increased the activities of guaiacol peroxidase (GPX) and superoxide dismutase (SOD), but decreased the activity of catalase (CAT) together with an increased content of malonyldialdehyde (MDA), Hence the changes in photosynthesis in acid rain treatment might be a secondary effect of acidity damage probably due to lipid peroxidation of lipids and proteins in thylakoid membrane rather than direct effect on PS2 reaction centre. and Jing-Quan Yu, Su-Feng Ye, Li-Feng Huang.