We conducted an experiment to assess the predictive capability of a leaf optical meter for determining leaf pigment status of Acer mono Maxim., A. ginnala Maxim., Quercus mongolica Fisch., and Cornus alba displaying a range of visually different leaf colors during senescence. Concentrations of chlorophyll (Chl) a, Chl b, and total Chl [i.e., Chl (a+b)] decreased while the concentration of carotenoids (Car) remained relatively static for all species as leaf development continued from maturity to senescence. C. alba exhibited the lowest average concentration of Chl (a+b), Chl a, and Car, but the highest relative anthocyanin concentration, while Q. mongolica exhibited the highest Chl (a+b), Chl b, and the lowest relative anthocyanin concentration. A. mono exhibited the highest Chl a and Car concentrations. The relationships between leaf pigments and the values measured by the optical meter generally followed an exponential function. The strongest relationships between leaf pigments and optical measurements were for A. mono, A. ginnala, and Q. mongolica (R2 ranged from 0.64 to 0.95), and the weakest relationships were for C. alba (R2 ranged from 0.13 to 0.67). Moreover, optical measurements were more strongly related to Chl a than to Chl b or Chl (a+b). Optical measurements were not related to Car or relative anthocyanin concentrations. We predicted that weak relationships between leaf pigments and optical measurements would occur under very low Chl concentrations or under very high anthocyanin concentrations; however, these factors could not explain the weak relationship between Chl and optical measurements observed in C. alba. Overall, our results indicated that an optical meter can accurately estimate leaf pigment concentrations during leaf senescence - a time when pigment concentrations are dynamically changing - but that the accuracy of the estimate varies across species., Future research should investigate how species-specific leaf traits may influence the accuracy of pigment estimates derived from optical meters., G. Y. Li, D. P. Aubrey, H. Z. Sun., and Obsahuje bibliografii
Fluorescence microscopy and physiological examination revealed the presence of an inner cylinder of active photosynthetic cells located below the endodermis-like layer in stems of four of the six taxa of the tribe Salicornieae (Chenopodiaceae). and S. Redondo-Gómez ... [et al.].
Electrochromic changes of the Qy absorption bands of chromophores (dimeric and monomeric bacteriochlorophylls and bacteriopheophytins) were measured in reaction centres from purple photosynthetic bacteria Rhodobacter sphaeroides. The observed electrochromic effects could be decomposed to changes dne to negative charge on the acceptor quinone complex and positive charge on the dimer. The coiďumed additivity (superposition) of the electrochromic effects indicated that the chromophores had fixed geometry in redox transitions. The Qy absorption band of the bacteriopheophytin proved to be a very sensitive indicator of the relaxational processes of electric charges (protons and/or cations) in the vicinity of the quinones: (7) the bandwidth was affected by pH around 10 which was close to the pK of protonation of the reduced primary quinone, (2) absorption changes at 748 nm were observed after flash excitation with time constant characteristic to that of light- induced proton binding in reaction centres.
Experiments were conducted to investigate the effects of exogenous progesterone on photochemical efficiency of PSII and turnover of D1 protein under heat stress during the grain-filling stage. Heat stress resulted in increases of hydrogen peroxide production, malondialdehyde content, and relative electrolytic leakage in wheat leaves, but these responses were alleviated by foliar application of progesterone. Meanwhile, activities of superoxide dismutase, catalase, and peroxidase were significantly improved in progesterone-pretreated leaves. Along with the alleviation of oxidative stress, higher abundances of STN8 and phosphorylated D1 protein and lower total D1 protein content in the PSII reactive center were observed in progesterone-pretreated leaves relative to controls. Consequently, progesterone raised the potential photochemical efficiency, actual photochemical efficiency, and electron transfer rate. These results indicate that foliar application of progesterone can effectively alleviate heat-induced PSII damage by enhancing antioxidant capability and regulating phosphorylation of D1 protein in wheat leaves., R. L. Xue, S. Q. Wang, H. L. Xu, P. J. Zhang, H. Li, H. J. Zhao., and Obsahuje seznam literatury
Air-grown tobacco (Nicotiana tabacum L.) plants were transferred for one week into a low oxygen atmosphere (2 kPa O2, LO) to study both immediate and long-term effects of the suppression of photorespiration on net photosynthetic rate (PN), plant morphology, and chloroplast ultrastructure. The PN and the leaf conductance for CO2 increased upon exposure of attached tobacco leaves to LO. These results may suggest that under LO, external CO2 is used to consume the radiant energy normally utilized in photorespiration by net CO2 assimilation at the expense of an increased rate of transpiration. The increase in the coefficient of nonphotochemical fluorescence quenching indicates that under LO, (surplus) radiant energy is also dissipated as heat. Prolonged LO-treatment of tobacco resulted in a decrease in the PN (measured in air) and in a reduction in the number of starch grains in the chloroplasts. Concomitantly, large lipid globuli appeared in the chloroplasts and the distance between the thylakoids forming the grana decreased. These changes in the ultrastructure of chloroplasts may have contributed to the decline in the PN. The LO-treated plants were considerably smaller than the control plants maintained in air. This appears to have resulted from a reduction in the rate of leaf area expansion at the expense of an increase in the specific mass of the leaves. This long-term response to LO-treatment may allow the plants to conserve water. and A. Migge ... [et al.].
Watermelon [Citrullus lanatus (Thunb.) Mansfeld] is a photophilic plant, whose net photosynthetic rate was significantly decreased when seedlings were grown under low light condition. However, treatment with 100 mg kg-1 5-aminolevulinic acid (ALA) could significantly restore the photosynthetic ability under the environmental stress. The parameters of leaf gas exchange, chlorophyll modulated fluorescence and fast induction fluorescence of the ALA-treated plants were higher than that of the control. Additionally, ALA treatment increased the activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX). Nevertheless, the treatment of diethyldithiocarbamate (DDC), an inhibitor of SOD activity, dramatically depressed photosynthesis of watermelon leaves, while ALA could reverse the inhibition of DDC. Therefore, it can be deduced that ALA promotion on photosynthesis of watermelon leaves under low light stress is attributed to its promotion on antioxidant enzyme activities, and the increased activities of the enzymes, which are mainly located near the reaction centers of PSI, can scavenge superoxide anions, leading to an increase of apparent electron transport rate and an alleviation of photosynthetic photoinhibition under the stressed environment. and Y.-P. Sun, Z.-P. Zhang, L.-J. Wang.