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
Sunflowers were treated with mixing proportions of NaCl, Na2SO4, NaHCO3, and Na2CO3. Effects of salt and saltalkaline mixed stress on growth, photosynthesis, chlorophyll fluorescence, and contents of inorganic ions and organic acids of sunflower were compared. The growth of sunflower decreased with increasing salinity. The contents of photosynthetic pigments did not decrease under salt stress, but their contents decreased sharply under
salt-alkaline mixed stress. Net photosynthetic rates, stomatal conductance and intercellular CO2 concentration decreased obviously, with greater reductions under salt-alkaline mixed stress than under salt one. Fluorescence parameters showed no significant differences under salt stress. However, maximal efficiency of PSII photochemistry, photochemical quenching coefficient, electron transport rate, and actual PSII efficiency significantly decreased but non-photochemical quenching increased substantially under salt-alkaline mixed stress. Under salt-alkaline mixed stress, sunflower leaves maintained a low Na+- and high K+ status; this may be an important feature of sunflower tolerance to salinity. Analysis of the mechanism of ion balance showed that K+ but not Na+ was the main inorganic cation in sunflower leaves. Our results indicated that the change in organic acid content was opposite to the change of Cl-, and the contribution of organic acid to total charge in sunflower leaves under both stresses decreased with increasing salinity. This may be a special adaptive response to stresses for sunflower. Sunflower under stress conditions mainly accumulated inorganic ions instead of synthesizing organic compounds to decrease cell water potential in order to save energy consumption. and J. Liu, D.-C. Shi.
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
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
Plant traits of Malcolmia littorea growing at the Botanic Garden of Rome and transplanted from the wild population developing along the Latium coast (Italy) were analyzed. The highest photosynthetic rates [PN, 22.5 ± 0.5 μmol(CO2) m-2 s-1], associated to the highest chlorophyll content (Chl, 60 ± 5 SPAD units), and respiration rates [R, 11.1 ± 0.2 μmol(CO2) m-2 s-1] were reached in spring, when mean air temperature (Tm) was in the range 17°C to 23°C. PN, Chl, and R decreased by 86, 38, and 59% in summer when mean maximum air temperature (Tmax) was 30.3 ± 2.6°C. Leaf water potential decreased by 34% in summer compared to the spring value, and it was associated to a relative water content (RWC) of 74 ± 4%, and to a water-use efficiency (WUE) of 2.15 ± 0.81 μmol(CO2) mmol-1(H2O). Moreover, also low air temperatures determined a significant PN and R decreases (by 52 and 40% compared to the maximum, respectively). Responsiveness of gross photosynthetic rate (Pg) to R was higher than that to PN as underlined by the slope of the regression line between the two variables. The results underlined a low tolerance to both high- and low air temperatures of M. littorea. The selected key traits (R, WUE, Chl) by the discriminant analysis might be used to monitor the M. littorea wild population in the long time. The ex situ cultivated plants could be propagated and used to increase the individuals number of the wild population. and L. Gratani ... [et al.].
An experiment was performed to study gas exchange and chlorophyll fluorescence responses of rice (Oryza sativa L.) to various regimes, such as flooding-midseason drying-flooding (FDF), flooding-midseason drying-saturation (FDS), and flooding-rain-fed (FR) regimes. Compared to FDF, FR resulted in an obvious decrease in net photosynthetic rate (PN), due to the decrease in stomatal conductance and the increase in stomatal limitation. In contrast, FDS plants did not suffer stomatal limitation and had comparable PN with FDF plants. For diurnal light-saturated electron transport rate and saturation irradiance, FDF performed the best, which was followed by FDS and FR successively. FR and FDS plants tended to suffer from midday depression. FDS reduced irrigated water by 17.2% compared to FDF for comparable yields. The results suggested that FDS can be an effective irrigation regime to save water., X. H. Wu, W. Wang, X. L. Xie, C. M. Yin, K. J. Xie., and Obsahuje bibliografii