Abiotic stresses induce phosphoenolpyruvate carboxylase (PEPC) expression in C3 plants which suggests PEPC function in plant adaptation to stresses. Here, we studied the response of photosynthesis to short-term drought stress in rice seedlings overexpressing C4 PEPC from maize and millet. The transgenic lines exhibited 1.2-5.5 fold of PEPC activities than the wild type before the treatment, while 1.5-8.5 fold after five or ten days of water deficit. Net photosynthetic rate (P N) declined less during the water stress and recovered more after rewatering in the transgenic lines. These changes were accompanied with changes in the stomatal conductance (g s). The lower decrease in P N and g s resulted in significantly higher intrinsic water use efficiency in the transgenic rice lines after ten days of water withdrawal. There were no significant differences between the wild type and transgenic lines in maximum photochemical efficiency of PSII and photochemical quenching. The nonphotochemical quenching and the quantum efficiency of PSII maintained both higher in transgenic lines than those in the wild type during drought stress. This indicated that the transgenic lines could dissipate more excess energy to heat to protect PSII. Our result suggested that the increased PEPC activities in rice could alleviate the decrease of photosynthesis during short-term drought stress., Z. S. Ding, X. F. Sun, S. H. Huang, B. Y. Zhou, M. Zhao., and Obsahuje seznam literatury
Heat stress has become more common in recent years, limiting wheat production in Huang-Huai-Hai plain in China. To identify the effect of long-term heat stress on wheat production, two heat-resistant (JM44, JM23) and two heat-sensitive (XM26, GC8901) wheat varieties were sown in heat tents and normal conditions, and heat stress (9 to 12℃ higher than control) was imposed for seven days at post-anthesis. All varieties under heat stress exhibited early senescence and reduced grain-filling rate, while the grain-filling period of heat-tolerant varieties was longer than that of the heat-sensitive. Furthermore, long-term heat stress significantly reduced kernel mass, grain number, harvest index, chlorophyll content, maximum quantum yield of PSⅡ photochemistry, effective quantum yield of PSⅡ photochemistry, photosynthetic rate, and transpiration efficiency. In addition, the distribution of dry matter to vegetative organs, catalase activity, and malondialdehyde content increased. These results indicated that the lesser yield reduction of heat-resistant varieties (11-26%) than that of heat-sensitive (16-37%) is due to relatively higher antioxidative and photosynthetic performance and higher assimilation in the grain from vegetative organs.
The response of tomato (Solanum lycopersicum L.) to abiotic stress has been widely investigated. Recent physiological studies focus on the use of osmoprotectants to ameliorate stress damage, but experiments at a field level are scarce. Two tomato cultivars were used for an experiment with saline water (6.57 dS m-1) and subsurface drip irrigation (SDI) in a silty clay soil. Rio Grande is a salinity-tolerant cultivar, while Heinz-2274 is the salt-sensitive cultivar. Exogenous application of proline was done by foliar spray at two concentrations (10 and 20 mg L-1) during the flowering stage. Control plants were treated with saline water without proline. Proline at the lower concentration (10 mg L-1) increased dry mass of different plant organs (leaves, stems, and roots) and it improved various chlorophyll a fluorescence parameters compared with controls. Regarding mineral nutrition, K+ and P were higher in different organs, while low accumulation of Na+ occurred. However, Mg2+ was very high in all tissues of Rio Grande at the higher concentration of proline applied. Thus, the foliar spray of proline at 10 mg L-1 increased the tolerance of both cultivars. The growth of aboveground biomass of Heinz-2274 was enhanced by 63.5%, while Rio Grande improved only by 38.9%., B. Kahlaoui, M. Hachicha, S. Rejeb, M. N. Rejeb, B. Hanchi, E. Misle., and Obsahuje bibliografii
The effects of elevated growth temperature (ambient + 3.5°C) and CO2 (700 μmol mol-1) on leaf photosynthesis, pigments and chlorophyll fluorescence of a boreal perennial grass (Phalaris arundinacea L.) under different water regimes (well watered to water shortage) were investigated. Layer-specific measurements were conducted on the top (younger leaf) and low (older leaf) canopy positions of the plants after anthesis. During the early development stages, elevated temperature enhanced the maximum rate of photosynthesis (Pmax) of the top layer leaves and the aboveground biomass, which resulted in earlier senescence and lower photosynthesis and biomass at the later periods. At the stage of plant maturity, the content of chlorophyll (Chl), leaf nitrogen (NL), and light response of effective photochemical efficiency (ΦPSII) and electron transport rate (ETR) was significantly lower under elevated temperature than ambient temperature in leaves at both layers. CO2 enrichment enhanced the photosynthesis but led to a decline of NL and Chl content, as well as lower fluorescence parameters of ΦPSII and ETR in leaves at both layers. In addition, the down-regulation by CO2 elevation was significant at the low canopy position. Regardless of climate treatment, the water shortage had a strongly negative effect on the photosynthesis, biomass growth, and fluorescence parameters, particularly in the leaves from the low canopy position. Elevated temperature exacerbated the impact of water shortage, while CO2 enrichment slightly alleviated the drought-induced adverse effects on P max. We suggest that the light response of ΦPSII and ETR, being more sensitive to leaf-age classes, reflect the photosynthetic responses to climatic treatments and drought stress better than the fluorescence parameters under dark adaptation. and Z.-M. Ge ... [et al.].
The gas exchange, parameters of chlorophyll fluorescence, contents of pigments, and activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), as well as lipid peroxidation were investigated in two field-grown coffee species, Coffea arabica and C. liberica, exposed to drought and re-hydration. Drought caused a more pronounced inhibition of net photosynthetic rate in C. liberica compared to C. arabica. The de-epoxidation of xanthophyll cycle pigments at midday estimated by leaf reflectance was much higher in C. arabica than in C. liberica, but no significant change was found in response to drought. Under moderate drought, the activities of SOD and APX increased significantly only in C. arabica. The maximum photochemical efficiency of photosystem 2, PS2 (Fv/Fm) at predawn did not change and there was no lipid peroxidation during this time. Under severe drought Fv/Fm decreased and initial fluorescence (F0) increased for both species, and SOD activity increased, APX activity remained relatively high, and malondialdehyde (MDA) accumulated in C. arabica, while APX decreased in C. liberica. The photosynthetic apparatus of C. arabica was completely recovered after 5 d of re-irrigation as indicated by the restoration of Fv/Fm to the control values. A lack of recovery upon rewatering of C. liberica indicated irreversible damage to PS2. Hence compared to C. liberica, C. arabica possesses a higher desiccation-induced antioxidative protection and higher portion of the total pigment pool used in photoprotection, which might aid alleviating photoinhibitory damage during desiccation and photosynthesis recovery when favourable conditions are restored. and Z.-Q. Cai ... [et al.].
The aim of this study was to assess the impact of the mitochondrial alternative oxidase (AOX) pathway on energy metabolism in chloroplasts, and evaluate the importance of the AOX in alleviating drought-induced photoinhibition in pepper (Capsicum annuum L.). Inhibition of AOX pathway decreased photosynthesis and increased thermal energy dissipation in plants under normal conditions. It indicated that AOX pathway could influence chloroplast energy metabolism. Drought reduced carbon assimilation. Photoinhibition was caused by excess of absorbed light energy in spite of the increase of thermal energy dissipation and cyclic electron flow around PSI (CEF-PSI). Upregulation of AOX pathway in leaves experiencing drought would play a critical role in protection against photoinhibition by optimization of carbon assimilation and PSII function, which would avoid over-reduction of photosynthetic electron transport chain. However, inhibition of AOX pathway could be compensated by increasing the thermal energy dissipation and CEF-PSI under drought stress, and the compensation of CEF-PSI was especially significant., W. H. Hu, X. H. Yan, Y. He, X. L. Ye., and Obsahuje bibliografii
Two lichen species collected in maritime Antarctica (King George Island) were exposed under laboratory conditions to excess irradiance to evaluate the response of photosystem 2 (PS2). The response was measured on fully hydrated lichen thalli at 5 °C by means of a modulated fluorometer using chlorophyll (Chl) fluorescence induction curve supplemented with analysis of quenching mechanisms. Chl fluorescence parameters [i.e. ratio of variable to maximum Chl fluorescence (FV/FM), quantum yield of PS2 photochemical reactions (Φ2), quenching coefficients] were evaluated before and several times after exposition to high irradiance in order to characterise the extent of photoinhibition, fast and slow phase of recovery. Strong irradiance (2 000 μmol m-2 s-1) caused high degree of photoinhibition, particularly higher in fruticose (Usnea antarctica) than in foliose (Umbilicaria decussata) lichen species. Fast phase of recovery from photoinhibition, corresponding to regulatory mechanisms of PS2, was more apparent in U. decussata and Φ2 than in U. antarctica and FV/FM and Φ2 within 40 min after photoinhibitory treatment. It was followed by a slow phase lasting several hours, corresponding to repair and re-synthesis processes. After photoinhibitory treatment, recovery of non-photochemical quenching (NPQ) was faster and more pronounced in U. decussata than in U. antarctica. Significant differences were found between the two species in the rate of recovery in fast-(qE) and slow-recovering (qT+I) component of NPQ. and M. Barták, H. Vráblíková, J. Hájek.
Wheat (Triticum aestivum L.) cv. Jimai22 was used to evaluate the effect of ethylene evolution rate (EER) and 1-aminocyclopropane-1-carboxylic acid (ACC) and their relations with photosynthesis and photochemical efficiency in plants well-watered (WW) and under a severe water deficit (SWD). SWD caused a noticeable reduction in the grain mass. The marked increases in both EER and the ACC concentration were observed under SWD; it was reversed effectively by exogenous spermidine (Spd) or amino-ethoxyvinylglycine (AVG). Thermal images indicated that SWD increased obviously the temperature of flag leaves, mainly due to the decrease in transpiration rate under SWD. Exogenous Spd or AVG decreased to some extent the temperature of the flag leaves. The strong decline in photosynthetic rate (PN) and stomatal conductance as well as the photodamage of PSII were also observed under SWD after 14 and 21 days after anthesis (DAA). Intercellular CO2 concentration was reduced at 7 DAA, but slightly increased at 14 and 21 DAA under SWD, indicating that the decreased PN at 7 DAA might result from stomatal limitations, while the decline after 14 and 21 DAA might be attributed to nonstomatal limitations. Correlation analysis suggested that EER and ACC showed negative relations to photosynthesis and photochemical efficiency. Data obtained suggested that the effects of SWD were mediated predominantly by the increase in EER and ACC concentration, which greatly decreased the leaf photosynthesis and photochemical efficiency, and, therefore, reduced the grain mass. Application of Spd or AVG reduced the EER and ACC, and thus positively influenced photosynthesis and photochemical efficiency under SWD., W. Yang, Y. Yin, W. Jiang, D. Peng, D. Yang, Y. Cui, Z. Wang., and Obsahuje bibliografii
The specific features of the structural and functional organisation of the photosynthetic apparatus (PSA) were studied in wild halophytes representing three strategies of salt tolerance: euhalophyte Salicornia perennans, crynohalophyte Limonium gmelinii, and glycohalophyte Artemisia santonica. The sodium content in aboveground parts of the plants corresponded to the strategy of salt tolerance. The photosynthetic cells of the euhalophyte were large and contained a higher number of chloroplasts than those in other species. In contrast, the number of cells per a leaf area unit was lower in S. perennans as compared to cryno- and glycohalophytes. Thereupon, the cell and chloroplast surface area per leaf area unit declined in the following sequence: A. santonica > L. gmelinii > S. perennans. However, the large cells of euhalophyte contained chloroplasts of larger sizes with 4- to 5-fold higher chlorophyll (Chl) content per chloroplast and Chl concentration in chloroplast volume unit. Also, chloroplasts of S. perennans were characterised by the higher content of glyco- and phospholipids. Qualitative composition of fatty acids (FA) in lipids isolated from the chloroplast-enriched fraction was similar in all three species; however, the index of unsaturation of FA was higher in glycohalophyte A. santonica than those in two other species. Under natural condition, PSA of all three halophytes showed high resistance to soil salinity. The results indicated tolerance of PSII to the photodamage in halophytes. The high rate of electron transport through PSII can be important to prevent oxidative damage of PSA in halophytes under strong light and hight temperature in vivo. Thus, the strategy of salt tolerance is provided by both the leaf anatomical structure and the ultrastructure of photosynthetic membranes, which is determined in particular by the specific composition of lipids., O. A. Rozentsvet, E. S. Bogdanova, L. A. Ivanova, L. A. Ivanov, G. N. Tabalenkova, I. G. Zakhozhiy, V. N. Nesterov., and Seznam literatury
The altitudinal effects on photosynthesis were measured on progenies of three populations of Rosa platyacantha Schrenk from altitudes of 1,170 (L); 1,580 (M); and 1,920 (H) m a. s. l. During the day, net photosynthetic rate (PN) decreased in all populations due to the high air temperature in the summer. The H population showed a significantly lower PN at noon compared to other populations. The midday depression of PN occurred in L and M populations due to stomatal limitations, while PN inhibition was associated with PSII activity decline in the H population. In order to avoid photodamage, the plants of H population triggered active antioxidant defenses with a higher enzyme activity and redox ratio of ascorbate at midday compared to the L and M populations. However, more oxidative injury still occurred in the H plants at noon due to higher lipid peroxidation. Our results indicated that the provenance significantly affected photosynthesis in R. platyacantha from northwestern China., S. H. Yang, J. J. Wei, H. Ge., and Obsahuje bibliografii