The effect of UV-A radiation (365 nm) and the protective effect of preillumination with red light (RL, 664 nm, 10 min) or with a combination of red and far-red light (FRL, 727 nm, 10 min) on the activity of the PSII as well as the expression levels of selected genes, especially those encoding chloroplast proteins (sAPX, tAPX, CAB1, and D1), were studied in leaves of the 26-d-old hy3 mutant of Arabidopsis thaliana, which is deficient in the phytochrome B apoprotein. The effects were compared with corresponding effects observed in the hy2 mutant of A. thaliana, which is deficient in the phytochrome chromophore. Illumination with UV-A decreased the photosynthetic pigment content, the maximum photochemical quantum yield of PSII (Fv/Fm), and the effective quantum yield of PSII (ΦPSII). The reduction of the Fv/Fm ratio and ΦPSII was more pronounced in the mutants as compared to wild-type plants (WT). The preillumination of the leaves with RL caused a significant reduction in the inhibitory effect of UV-radiation on the PSII activity in the WT plants, but it caused only a small decrease in the hy3 mutant. The preillumination of leaves with RL and FRL combination compensated the protective effect of RL on the UV-induced decrease of the fluorescence parameters in the WT. Such reversibility is typical for involvement of red/far-red reversible phytochromes at low intensity light. The results suggest an important role of red/far-red reversible phytochromes (phytochrome B) in the resistance of PSII to UV-A radiation caused by changes in contents of either carotenoids or other UV-absorbing pigments probably through biosynthesis of these pigments. The data also demonstrated that phytochrome B and other phytochromes can affect the PSII stress resistance by the fast regulation of the expression of genes encoding antioxidant enzymes and transcription factors at the step of gene transcription., V. D. Kreslavski, F.-J. Schmitt, C. Keuer, T. Friedrich, G. N. Shirshikova, S. K. Zharmukhamedov, A. A. Kosobryukhov, S. I. Allakhverdiev., and Seznam literatury
In a chlorophyll(Chl)-deficient ch5 mutant of Arabidopsis thaliana the thylakoid membrane of which is more loosely arranged than that of the wild type we characterized the xanthophyll cycle (VAZ cycle) components (violaxanthin - V, antheraxanthin - A and zeaxanthin - Z) in comparison with the wild type grown under three low irradiances. As the irradiance increased from 30 to 250 pmol m'^ s'i, the total amount of components of the VAZ cycle decreased in both biotypes, but those of the ch5 mutant decreased more slowly than did those of the wild type. In both biotypes, the relative amoímts of V and A decreased as the irradiance increased, and that of Z increased, but the increase and decrease in the ch5 mutant was slower than in the wild type. The epoxidation index showed that the VAZ cycle operated at a similar efficiency in both biotypes (between 30 and 250 pmol m‘2 s'*), but that the ch5 mutant worked at a capacity 3.5-13.5 % lower than did the wild type, depending on the irradiance. Thus in Chl-deficient mutants, the VAZ cycle operates at a lower capacity than in the wild type, and the mutants are more sensitive to the changes in irradiance.
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 sustainable production of upland cotton, an economically important fiber crop, is threatened by changing environmental factors including high temperatures and low-soil water content. Both high heat and low-soil water can reduce net photosynthesis resulting in low fiber yields or poor fiber quality. Leaf chlorophyll content has a direct relationship with photosynthetic rate. Understanding how high heat and low-soil water affect chlorophyll content can identify opportunities for breeding improvement that will lead to sustainable fiber yields. A two-year field trial located in Maricopa Arizona measured leaf chlorophyll content, available soil water, ambient air temperatures, and cotton growth measurements collected by a high-clearance tractor equipped with proximal sensors. The results showed that low-soil water significantly increased leaf chlorophyll content, while high temperatures significantly reduced content. Structured equation modeling revealed that cotton may divert available resources to leaf area and chlorophyll content for the production of photosynthates during periods of high temperatures.
Understanding distribution and transport of carbon assimilates and photosynthesis contribution to grain yield in wheat spike is important in assessing the photosynthetic process under stress conditions. In this study, photosynthetic characteristics were evaluated in a pot experiment. Transport of spike photosynthates to grain was demonstrated using 14C isotope tracer technique. Yield and key enzyme activities of C3 and C4 pathways were examined after anthesis in wheat cultivars of different drought resistance. The ear net photosynthetic rate, chlorophyll content of the spike bracts (glume, lemma, and palea), and relative water content slightly decreased under water deficit in drought resistant variety Pubing 143 (Pub) during the grain filling stage, whereas all parameters decreased significantly in drought sensitive variety Zhengyin 1 (Zhe). Grain 14C-photosynthate distribution rate fell by 3.8% in Pub and increased by 3.9% in Zhe. After harvest, the water-use efficiency of Zhe dropped by 18.7% under water deficit. Rubisco activity in ear organs declined significantly under water deficit, whereas activity of C4 pathway enzymes was significantly enhanced, especially that of phosphoenolpyruvate carboxylase and NADP-malate dehydrogenase. Water deficit exerted lesser influence on spike photosynthesis in Pub. Ear organs exhibited delayed senescence. Accumulation of photosynthetic carbon assimilates in ear bracts occurred mainly during the early grain filling and photosynthates were transported in the middle of grain filling. C4 pathway enzymes seem to play an important function in ear photosynthesis. We speculate that the high enzyme activity of the C4 pathway and the increased capacity of photosynthetic carbon assimilate transport were the reasons for the drought tolerance characteristics of ears., S. Jia, J. Lv, S. Jiang, T. Liang, C. Liu, Z. Jing., and Obsahuje bibliografii
Over-expression of chloroplastic glycerol-3-phosphate acyltransferase gene (LeGPAT) increased unsaturated fatty acid contents in phosphatidylglycerol (PG) of thylakoid membrane in tomato. The effect of this increase on the xanthophyll cycle and chloroplast antioxidant enzymes was examined by comparing wild type (WT) tomato with the transgenic (TG) lines at chilling temperature (4 °C) under low irradiance (100 µmol m-2 s-1). Net photosynthetic rate and the maximal photochemical efficiency of photosystem (PS) 2 (Fv/Fm) in TG plants decreased more slowly during chilling stress and Fv/Fm recovered faster than that in WT plants under optimal conditions. The oxidizable P700 in both WT and TG plants decreased during chilling stress under low irradiance, but recovered faster in TG plants than in the WT ones. During chilling stress, non-photochemical quenching (NPQ) and the de-epoxidized ratio of xanthophyll cycle in WT plants were lower than those of TG tomatoes. The higher activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) in TG plants resulted in the reduction of O2-. and H2O2 contents during chilling stress. Hence the increase in content of unsaturated fatty acids in PG by the over-expression of LeGPAT could alleviate photoinhibition of PS2 and PS1 by improving the de-epoxidized ratio of xanthophyll cycle and activities of SOD and APX in chloroplast. and N. Sui ... [et al.].
Leaf adaptatíons of Quercus ilex L., Phillyrea latifolia L. and Pistacia lentiscus L. to various environmental conditions námely from the viewpoint of the differences of leaf area, dry mass, chlorophyll (Chl) content, sclerophylly index, succulence index and net photosynthetic rate are shown. Irradiance was the most important factor to miluence leaf temperature, stomatal conductance (g^) and transpiration rate (E). Under canopy layer low red-far red ratio reduced Pn- Shade leaves were enriched by Chl b. Chl content and sclerophylly index were good leaf characteristics to express adaptability of plants to microclimate.
The effect of supplementary UV-B radiation on Korean pine (Pinus koraiensis Sieb. et Zucc) was investigated. Compared with the control, the T1, T2, and T3 UV-B treatments increased by 1.40, 2.81, and 4.22 kJ m-2 d-1, respectively. Gas-exchange parameters, photosynthetic pigment concentrations, contents of secondary metabolites, epicuticular wax, free radical, malondialdehyde (MDA), and the activities of antioxidant enzymes were determined after 40 d of exposure. The concentrations of chlorophyll (Chl) a, Chl b, total Chl, carotenoid (Car), and the ratio Chl a/b in the pine needles were in the following order: T1 > T2 > T3. Compared with the control, the contents of flavonoids and epicuticular wax significantly decreased in all levels of supplementary UV-B radiations (p<0.05). Moreover, the contents of hydrogen peroxide (H2O2) and MDA significantly increased with the enhanced UV-B radiations (p<0.05). Korean pine can increase the catalase, ascorbate peroxidase, and superoxide dismutase activities to prevent oxidative stress by supplementary UV-B radiation. However, its defence mechanism is not efficient enough to prevent UV-B-induced damage. and Y. G. Zu ... [et al.].
The photosynthetic and growth responses of A. mangium to different photosynthetic photon flux density (PPFD) during early seedling establishment (36 d after sowing) were investigated. Shade-grown A. mangium seedlings exhibited lower chlorophyll (Chl) a/b ratio, higher Chl and carotenoid (Car) contents, and higher total Chl/Car ratio than sun-grown seedlings. Sun-grown seedlings showed significantly higher photosynthetic capacity and total plant dry mass. High PPFD was crucial for the successful early establishment and robust growth of A. mangium seedlings. and Hua Yu, Bee-Lian Ong.
Leaf conductance (g), net photosynthetic carbon fixation rate (Pyi), leaf protein concentration and ribulose-l,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity were examined in baldcypress {Taxodium distichum L.) seedlings subjected to rhizosphere hypoxia. Seedlings grown in nutrient solution were treated with either air or N2. Changes in g. Pyj, leaf protein concentrations and RuBPCO activity in response to the treatments were measured at 12, 24, and 48 h. In a second experiment, similar measurements were conducted on plants grown in soil medium under either flooded or drained conditions over a period of 28 d. Under rhizosphere hypoxia, both g and Pyj were reduced significantly at 24 and 48 h as compared to control plants while there were no significant differences in leaf protein concentrations between treatments. RuBPCO activity, however, was reduced significantly (27 % reduction) at 48 h. In flooding experiment, g and decreased on days 3, 5, and 10 significantly. RuBPCO activity was significantly lower in flooded plants as compared to control (aerated) plants on day 3 and 5 following initiation of flooding. bi this experiment, g and began to improve after day 10, to as much as 97 and 87 % of control by day 28, respectively. RuBPCO activity which had decreased significantly by day 3, remained significantly lower on day 5 and slightly (but not significantly) lower than in control plants during the remainder of the experiment. Present data support the hypothesis that in baldcypress seedlings, reduced RuBPCO activity is among the early signals of flood-stress contributing to the loss of leaf Pyj. In addition, plant acclimated to the stress conditions during the long-term experiment indicating that some flood-tolerant tree species such as baldcypress may occupy wet sites due to such capabilities.