The effects of UV-B radiation (1 W m-2, 1 and 2 h) on PSII activity, chloroplast structure, and H2O2 contents in leaves of 26-d-old Arabidopsis thaliana phyA phyB double mutant (DMut) compared with the wild type (WT) were investigated. UV-B decreased PSII activity and affected the H2O2 content in WT and DMut plants grown under white light (WL). The chloroplast structure changes in DMut plants exposed to UV were more significant than that in WT. Reductions in maximal and real quantum photochemical yields and increase in the value of thermal dissipation of absorbed light energy per PSII RC and the amount of QB-nonreducing centers of PSII were bigger in mutant compared to WT plants grown both under WL and red light. Such difference in action of UV-B on WT and DMut can be explained by higher content of UV-absorbing pigments and carotenoids in WT leaves compared with DMut., V. D. Kreslavski, A. N. Shmarev, V. Yu. Lyubimov, G. A. Semenova, S. K. Zharmukhamedov, G. N. Shirshikova, A. Yu. Khudyakova, S. I. Allakhverdiev., and Obsahuje bibliografické odkazy
The response of barley (Hordeum vulgare L. cv. Akcent) to various photosynthetic photon flux densities (PPFDs) and elevated [CO2] [700 μmol (CO2) mol-1; EC] was studied by gas exchange, chlorophyll (Chl) a fluorescence, and pigment analysis. In comparison with barley grown under ambient [CO2] [350 μmol (CO2) mol-1; AC] the EC acclimation resulted in a decrease in photosynthetic capacity, reduced stomatal conductance, and decreased total Chl content. The extent of acclimation depression of photosynthesis, the most pronounced for the plants grown at 730 μmol m-2 s-1 (PPFD730), may be related to the degree of sink-limitation. The increased non-radiative dissipation of absorbed photon energy for all EC plants corresponded to the higher de-epoxidation state of xanthophylls only for PPFD730 barley. Further, a pronounced decrease in photosystem 2 (PS2) photochemical efficiency (given as FV/FM) for EC plants grown at 730 and 1 200 μmol m-2 s-1 in comparison with AC barley was related to the reduced epoxidation of antheraxanthin and zeaxanthin back to violaxanthin in darkness. Thus the EC conditions sensitise the photosynthetic apparatus of high-irradiance acclimated barley plants (particularly PPFD730) to the photoinactivation of PS2. and I. Kurasová ... [et al.].
Young (12 years old) Norway spruce {Picea abies [L.] Karst.) trees were exposed to ambient CO2 or ambient + 350 |niiol(C02) moL' continuously over 2 growing seasons in open-top chambers, under field conditions of a mountain stand. Comprehesive analysis of CO2 assimílation was performed after 4 and 22 weeks of the second growing season to evaluate the influence of elevated atmospheric CO2. A combination of gas exchange and a mathematical model of ribulose-l,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity was ušed. After 4 weeks of exposure no statistically significant stimulation of the radiant energy and CO2 saturated rate of CO2 uptake (ENsat) by the elevated CO2 concentration was found. Yet after 24 weeks a statistically significant depression of Ejvjsa, (38 %) and carboxylation efficiency (32 %) was observed. Depression of photosynthetic activity by elevated CO2 resulted from a decrease in the RuBPCO carboxylation rate. The electron transport rate was also modified similarly to the rate of RuBP formation. An accompanying decrease in nitrogen content of the needles (by 12 %) together with an increase in total saccharides (by 34 %) was observed after 24 weeks of exposure to enhanced CO2.
Groups of Actinidia deliciosa A. Chev. C.F. Liang et A.R. Ferguson var. deliciosa kiwifruit plants were subjected to soil water shortage (D), while other groups were well irrigated (I). Variations in chlorophyll (Chl) a fluorescence indices and leaf gas exchange were determined once plants were severely stressed (25 d after the beginning of the D-cycle). Daily maximum values of photosynthetic photon flux density (PPFD) were ca. 1 650 µmol(photon) m-2 s-1, while air temperatures peaked at 34.6 °C. High irradiance per se did not greatly affect the efficiency of photosystem (PS) 2, but predisposed its synergistic reduction by D co-occurrence. Fluorescence showed transient photodamage of PS2 with a complete recovery in the afternoon in both D and I plants. Upon re-watering the efficiency of PS2 was suboptimal (95 %) at day 2 after irrigation was reinitiated. At early morning of the day 5 of re-watering, photosynthesis and stomatal conductance recovered at about 95 and 80 % of I vines, respectively, indicating some after-stress effect on stomatal aperture. Once excessive photons reached PS2, the thermal dissipation of surplus excitation energy was the main strategy to save the photosynthetic apparatus and to optimize carbon fixation. The rather prompt recovery of both Chl a fluorescence indices and net photosynthetic rate during re-watering indicated that kiwifruit photosynthetic apparatus is prepared to cope with temporary water shortage under Mediterranean-type-climates. and G. Montanaro, B. Dichio, C. Xiloyannis.
WN6 (a stay-green wheat cultivar) and JM20 (control) were used to evaluate the effects of exogenous cytokinin on photosynthetic capacity and antioxidant enzymes activities in flag leaves. Results showed that WN6 reached the higher grain mass, which was mainly due to the higher photosynthetic rate resulting from the higher maximal quantum yield of PSII photochemistry (ΦPSII) and probability that a trapped exaction transfers an electron into the electron transport chain beyond QA (Ψo), and lower relative variable fluorescence intensity at the J-step (Vj). Exogenous 6-benzylaminopurine (6-BA) enhanced antioxidant enzymes activities and decreased malondialdehyde (MDA) content. Enhanced Ψo and electron transport rate (ETR), and decreased Vj contributed to improved photosynthetic rate in the 6-BA treatment. In addition, exogenous 6-BA significantly increased endogenous zeatin (Zt) content, which was significantly and positively correlated with the antioxidant enzyme activity and ΦPSII, implying that higher Zt content was responsible for the improved antioxidant status and photosynthetic performance., D. Q. Yang, Y. L. Luo, W. H. Dong, Y. P. Yin, Y. Li, Z. L. Wang., and Obsahuje bibliografii
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.
Flooding stress (FS) induced changes in pigment and protein contents and in photochemical efficiency of thylakoid membranes of chloroplasts were investigated during senescence of primary leaves of rice seedlings. Leaf senescence was accompanied by loss in 2,6-dichlorophenolindophenol (DCPIP) photoreduction, rate of oxygen evolution, quantum yield of photosystem 2 with an increase in MDA accumulation, and non-photochemical quenching (NPQ) of chlorophyll fluorescence. These changes were further aggravated when the leaves during this period experienced FS. The increase in NPQ value under stress may indicate photosynthetic adaptation to FS. and S. K. Mishra ... [et al.].
A greenhouse study was performed in order to investigate the effects of three arbuscular mycorrhizal fungi (AMF) species on vegetative growth, water relations, and mineral composition parameters of snapdragon (Antirrhinum majus cv. Bells white) under irrigation from different water sources. Five irrigation treatments included using purely desalinized (fresh) water (DW), as a control, three different blends of DW with saline ground water from a well with increasing salinity, and one with 100% of saline well water. Inoculation with AMF enhanced growth rates and a relative water content of snapdragon plants grown under well-water irrigation. AMF also improved the leaf water potential and increased water-use efficiency of the plants. Shoot and root dry masses were higher in the AMF-treated plants than those in AMF-free plants. In both shoots and roots, concentrations of total P, Ca2+, N, Mg2+, and K+ were higher in the AMF-treated plants compared with AMF-free plants under salt-stress conditions. Shoot Cl- and Na+ concentrations were lower in the AMF-treated plants than those in the AMF-free plants grown under well-water irrigation. Snapdragon plants exhibited a high degree of dependency on AMF; it improved plant growth rates and leaf water relations, particularly, with increasing salinity of irrigation water., Y. I. El-Nashar., and Obsahuje bibliografii
Spinach (Spinacia oleracea L. cv. Clermont) leaves grown in open-top chambers and exposed to three different concentrations of ozone were measured for gas exchange, chlorophyll a fluorescence, antioxidant systems, and lipid peroxidation at the end of growing season. High O3 concentration reduced Fv/Fm, indicating that the efficiency in the energy conversion of photosystem 2 (PS2) was altered. The rate of non-cyclic electron transport rate and the capacity to reduce the quinone pool were also affected. The development of non-photochemical quenching was not high enough to decrease the photon excess in the PS2. The limitation of photosynthetic activity was probably correlated with stomata closure and with an increase in intercellular CO2 concentration. Under oxidative stress, superoxide dismutase (SOD) activity was stimulated in parallel with lipid peroxidation. We did not find any differences in the ascorbate (AsA) pool and ascorbate peroxidase (APX) or glutathione reductase (GR) activities between air qualities. Small, but similar responses were observed in spinach leaves exposed to ambient ozone concentration. and A. Calatayud ...[et al.].
Soil moisture is the main limiting factor for vegetation growth at shell ridges in the Yellow River Delta of China. The objective of this study was to explore the soil moisture response of photosynthetic parameters and transpiration in Tamarix chinensis Lour., a dominant species of shell ridges. Leaf photosynthetic
light-response parameters and sap flow were measured across a gradient of relative soil water content (RWC), from drought (23%) to waterlogging (92%) conditions. Leaf photosynthetic efficiency and stem sap flow of T. chinensis showed a clear threshold response to soil moisture changes. Leaf net photosynthetic rate, water-use efficiency (WUE), light-saturation point, apparent quantum yield, maximum net photosynthetic rate, and dark respiration rate peaked at moderately high RWC, decreasing towards high and low values of RWC. However, peak or bottom RWC values substantially differed for various parameters. Excessively high or low RWC caused a significant reduction in the leaf photosynthetic capacity and WUE, while the high photosynthetic capacity and high WUE was obtained at RWC of 73%. With increasing waterlogging or drought stress, T. chinensis delayed the starting time for stem sap flow in the early morning and ended sap flow activity earlier during the day time in order to shorten a daily transpiration period and reduce the daily water consumption. The leaf photosynthetic capacity and WUE of T. chinensis were higher under drought stress than under waterlogging stress. Nevertheless, drought stress caused a larger reduction of daily water consumption compared to waterlogging, which was consistent with a higher drought tolerance and a poor tolerance to waterlogging in this species. This species was characterized by the low photosynthetic capacity and low WUE in the range of RWC between 44 and 92%. The RWC of 49-63% was the appropriate range of soil moisture for plant growth and efficient physiological water use of T. chinensis seedlings., J. B. Xia, Z. G. Zhao, J. K. Sun, J. T. Liu, Y. Y. Zhao., and Obsahuje bibliografii