Predicting the effects of increased ultraviolet-B (UV-B) radiation due to stratospheric ozone depletion on temperate desert ecosystems requires better knowledge of the ecophysiological response of common moss species. The aim of the current work was to determine whether elevated UV-B radiation affected photosynthetic performance and chloroplast ultrastructure of two moss crusts and whether response differences were observed between the crusts. In laboratory experiments, Bryum argenteum and Didymodon vinealis, which show microdistributions and are dominant in soil crusts at the Tengger Desert, Northern China, were subjected to four levels of UV-B radiation of 2.75 (control), 3.08, 3.25, and 3.41 W m-2 for 10 days, simulating 0, 6, 9, and 12% of stratospheric ozone at the latitude of Shapotou, respectively. The results showed that chlorophyll a fluorescence parameters (i.e., the maximal quantum yield of PSII photochemistry, the effective quantum yield of PSII photochemistry, and photochemical quenching coefficient), pigment contents, soluble protein contents, and the ultrastructure were negatively influenced by elevated UV-B radiation and the degree of detrimental effects significantly increased with the intensity of UV-B radiation. Moreover, results indicated that B. argenteum was probably more sensitive to supplementary UV-B radiation than D. vinealis. Therefore, we propose the use of B. argenteum crusts as a bioindicator of responses to elevated UV-B radiation., R. Hui, X. R. Li, R. L. Jia, L. C. Liu, R. M. Zhao, X. Zhao, Y. P. Wei., and Obsahuje bibliografii
Monitoring some parameters would help to overcome the difficulties that can affect in vitro-grown plants during the crucial step of their acclimatization. Thus, after the determination of net photosynthesis and other parameters during acclimatization of in vitro-grown olive plantlets, we concluded that three months after the transfer to ex vitro, the in vitro-grown olive plants become well acclimated. In fact, even though the net photosynthesis, relatively high in vitro, recorded low values after 15 d from the transfer, it reverted back to its standard rates after 180 d of acclimatization. Transpiration and stomatal conductance first increased significantly with a maximum of 6.22 mmol(H2O) m-2 s-1 and 1.8 mmol(H2O) m-2 s-1, respectively, but they regressed to very low values after 180 d of acclimatization. Some changes in the leaf anatomy were also observed; the reduction of stomata density and inversely, the increase of trichome density, especially on the abaxial side of the leaves, were observed., A. Chaari-Rkhis, M. Maalej, A. Chelli-Chaabouni, L. Fki, N. Drira., and Obsahuje seznam literatury
Glyphosate herbicide caused oxidative stress and exhibited negative effects on photosynthesis and gas exchange of peanut [Arachis hypogaea L. cv. Giza (G) 5 and 6] leaves. We demonstrated that glyphosate caused various morphological symptoms, such as chlorosis, yellowing, and appearance of curly edges in leaves treated with high doses of herbicide in both cultivars; however, the G5 cultivar was more sensitive and showed severer symptoms. Glyphosate lowered photosynthesis and reduced contents of pigments and proteins as well as free amino acids in both cultivars. The gas-exchange parameters, such as photosynthetic (P N) and transpiration rate (E), were highly altered by the glyphosate application. For example, P N and E were reduced by 65 and 61%, respectively, in G5 treated with high dose of glyphosate compared with control. Antioxidant enzymes, such as peroxidase, catalase, ascorbate peroxidase, and superoxide dismutase were induced by both low and high concentrations in the glyphosate-treated leaves. Moreover, the level of lipid peroxidation, indicated by a malondialdehyde content, as well as the hydrogen peroxide content increased in the glyphosate-treated leaves. However, an increase in total antioxidant activity was detected in leaves and this reflected changes in the antioxidant status and accumulation of antioxidants as a defense mechanism against glyphosate toxicity in peanut., D. E. M. Radwan , K. A. Fayez., and Obsahuje seznam literatury
Alkalies are important agricultural contaminants complexly affecting plant metabolism. In this study, rice seedlings were subjected to alkaline stress (NaHCO3:Na2CO3 = 9:1; pH 8.9) for 30 days. The results showed that stress mightily reduced net photosynthetic rate (PN), but slightly decreased transpiration rate and stomatal conductance. This indicated that decline of PN might be a result of nonstomatal factors. Alkaline stress caused a large accumulation of Na+ in leaves up to toxic concentration, which possibly affected chloroplast ultrastructure and photosynthesis. We found that alkaline stress reduced chlorophyll fluorescence parameters, such as ratios of Fv′/Fm′, Fv/Fm, photosystem (PS) II efficiency, and electron transport rates in rice plants, i.e. it influenced the efficiencies of photon capture and electron transport by PSII. This might be a main reason for the decrease of PN under such conditions. Deficiency of minerals could be another reason for the decline of PN. Alkaline stress lowered contents of N, K, Cu, Zn, P, and Fe in rice plants. In addition, the stress strongly affected metabolism of amino acids. This might be caused by imbalance in carbon metabolism as a result of photosynthesis reduction., Z.-H. Wu, C.-W. Yang, M.-Y. Yang., and Obsahuje bibliografii
Although plant performance under elevated CO2 (EC) and drought has been extensively studied, little is known about the leaf traits and photosynthetic performance of Stipa bungeana under EC and a water deficiency gradient. In order to investigate the effects of EC, watering, and their combination, S. bungeana seedlings were exposed to two CO2 regimes (ambient, CA: 390 ppm; elevated, EC: 550 ppm) and five levels of watering (-30%, -15%, control, +15%, +30%) from 1 June to 31 August in 2011, where the control water level was 240 mm. Gas exchange and leaf traits were measured after 90-d treatments. Gas-exchange characteristics, measured at the growth CA, indicated that EC significantly decreased the net photosynthetic rate (PN), water-use efficiency, nitrogen concentration based on mass, chlorophyll and malondialdehyde (MDA) content, while increased stomatal conductance (gs), intercellular CO2 concentration (Ci), dark respiration, photorespiration, carbon concentration based on mass, C/N ratio, and leaf water potential. Compared to the effect of EC, watering showed an opposite trend only in case of PN. The combination of both factors showed little influence on these physiological indicators, except for gs, Ci, and MDA content. Photosynthetic acclimation to EC was attributed to the N limitation, C sink/source imbalance, and the decline of photosynthetic activity. The watering regulated photosynthesis through both stomatal and nonstomatal mechanisms. Our study also revealed that the effects of EC on photosynthesis were larger than those on respiration and did not compensate for the adverse effects of drought, suggesting that a future warm and dry climate might be unfavorable to S. bungeana. However, the depression of the growth of S. bungeana caused by EC was time-dependent at a smaller temporal scale., H. Wang, G. S. Zhou, Y. L. Jiang, Y. H. Shi, Z. Z. Xu., and Obsahuje bibliografii
To analyze acclimation of Euterpe edulis seedlings to changes in light availability, we transferred three-year-old seedlings cultivated for six months under natural shade understory [= 1.3 mol(photon) m-2 d-1] to a forest gap [= 25.0 mol(photon) m-2 d-1]. After the transfer, changes in chlorophyll fluorescence and leaf gas-exchange parameters, as well as in the light-response curves of photosynthesis and photosynthetic induction parameters, were analyzed during the following 110 days. Simultaneously measured photosynthetic characteristics in the shaded seedlings grown in understory served as the control. Despite the fact that the understory seedlings were under suboptimal conditions to achieve their light-saturated net photosynthetic rate (PNmax), light-response curves and photosynthetic induction parameters indicated that the species had the low respiration rate and a fast opening of stomata in response to the intermittent occurrence of sunflecks, which exerted a feed-forward stimulation on PNmax. Sudden exposure to high light induced photoinhibition during the first week after the transfer of seedlings to gap, as it was shown by the abrupt decline of the maximal quantum yield of PSII photochemistry (Fv/Fm). The photoinhibition showed the time-dependent dynamics, as the Fv/Fm of the seedlings transferred to the forest gap recovered completely after 110 days. Furthermore, the net photosynthetic rate increased 3.5-fold in relation to priorexposure values. In summary, these data indicated that more than 21 days was required for the shade-acclimated seedlings to recover from photoinhibition and to relax induction photosynthetic limitations following the sudden exposure to high light. Moreover, the species responded very quickly to light availability; it highlights the importance of sunflecks to understory seedlings., A. O. Lavinsky, F. P. Gomes, M. S. Mielke, S. França., and Obsahuje bibliografii
Our study examined the relationship between photosynthetic performance and activities of key photosynthetic enzymes to understand the photosynthetic variation and reasons for the variation during dormancy induction under different photoperiods in peach (Prunus persica L. cv. Chunjie). Furthermore, the study explained the changes in the key enzymes from the viewpoint of differential proteomics. The results showed that the leaf net photosynthetic rate (PN) and stomatal conductance tended to decrease, while the intercellular CO2 concentration rose, which indicated that the reduced PN resulted from nonstomatal limitation. During the dormancy induction period, the activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC) declined, which was the main reason for the reduced PN. Two-dimensional electrophoresis maps and differential protein identification demonstrated that the decrease in activity of the photosynthetic enzymes was mainly due to enzymatic degradation. The enzyme degradation by a long-day treatment occurred later and to a lesser degree than that of the short-day treatment. In the long-day treatment, the carboxylation activity of Rubisco was higher than that of the control treatment, and the PEPC activity and the ratio of the PEPC/Rubisco activity were lower than the corresponding activities during the control treatment. These differences under long-day conditions were significant but did not occur in the short-day treatment, suggesting that the C4 pathway might be more active under short-day conditions., H.-S. Zhang, D.-M. Li, Q.-P. Tan, H.-Y. Gao, D.-S. Gao., and Obsahuje bibliografii
Different pigments often occur together and affect photosynthetic characteristics of the respective leaf portions. In this study, photosynthetic activity in variegated leaves of five cultivars of the ornamental and medicinal plant, Coleus × hybridus hort., was estimated by image analysis and point data measurements of major chlorophyll (Chl) fluorescence parameters and related to the amount of photosynthetic pigments measured with a Chl meter or spectrophotometrically in leaf extracts. Significant differences in Chl and carotenoid (Car) contents were noticed among differentially pigmented sectors of a leaf and among the cultivars. Although the higher Chl concentration was noticed in purple parts compared to green parts of the leaves, the values of minimal and maximal fluorescence yield at the dark- and light-adapted state (F0, Fm, F0', Fm', respectively) were a little lower than those in the green sectors, indicating photoprotective effects provided by anthocyanins and Car, more abundant in the red parts. The lowest Chl and Car content was detected in creamy-yellow and pink sectors and this contributed to low F0, Fm, and Fm', maximal quantum yield of PSII photochemistry, and nonphotochemical and photochemical quenching but high PSII maximum efficiency and effective quantum yield of PSII photochemistry. Both methods of Chl fluorescence analysis revealed heterogeneity in capture, transfer, and dissipation of excitation energy but Chl fluorescence imaging was more suitable in examining very narrow pigmented leaf areas., M. Borek, R. Bączek-Kwinta, M. Rapacz., and Seznam literatury
Leafless Duvalia velutina Lavranos (Apocynaceae) is an
arido-active stem succulent common in the arid region southwest of the Arabian Peninsula. This region is characterized by a short wet season with erratic rainfall and a long dry season with high temperature and high irradiance. We investigated the survival strategy of D. velutina by studying nurse association, gas exchange, and chlorophyll fluorescence. Results showed that D. velutina exhibited the strict nurse association with shade for protection against heat and high irradiance. Results also showed that D. velutina is an obligate CAM plant with ample physiotypic plasticity involving a shift to CAM-idling under prolonged drought. Chlorophyll fluorescence measurements revealed water stress-induced reduction of PSII activity occurring in concomitance with a marked rise of nonphotochemical quenching and chlorenchyma anthocyanin content. These results reflected photoprotective capacity involving nonradiative excess energy dissipation and antioxidative attributes. We concluded that the complex survival strategy of D. velutina in its natural arid habitat includes a multifaceted interplay of nurse association, physiotypic plasticity, and photoprotective mechanisms., Y. S. Masrahi, T. A. Al-Turki, O. H. Sayed., and Obsahuje seznam literatury
Water deficit is an important exogenous factor that enhances the influx of sucrose into sugarcane (Saccharum spp.) stem internodes during ripening, when photosynthetic ability in supplying sinks is essential. The aim of this study was to test the hypothesis that drought tolerance in sugarcane is associated with an effective antioxidant protection during the ripening phase that might maintain a favorable redox balance in chloroplasts and protect photosynthesis under drought conditions. Two commercial sugarcane varieties, IACSP94-2094 (tolerant) and IACSP96-2042 (sensitive), with contrasting behavior under water deficit, were subjected to water withholding during the ripening stage. Our results revealed that the tolerant variety was less affected by water deficit, maintaining photosynthesis for a longer period and showing a faster recovery after rehydration as compared to the sensitive one. As consequence, the tolerant variety faced lesser excess of light energy at PSII. The maintenance of photosynthesis under water deficit and its fast recovery after rehydration resulted in the lower leaf H2O2 concentration and favorable redox status in the drought-tolerant genotype, which was associated with stimulation of superoxide dismutase during ripening. Our results also revealed that ferric superoxide dismutase isoforms were strongly enhanced under drought conditions, playing an important role in chloroplast redox homeostasis., C. R. G. Sales, P. E. R. Marchiori, R. S. Machado, A. V. Fontenele, E. C. Machado, J. A. G. Silveira, R. V. Ribeiro., and Obsahuje seznam literatury