Editorial: Molecular basis of the response of photosynthetic apparatus to light and temperature stress

2 Pags. This article was submitted to Plant Cell Biology, a section of the journal Frontiers in Plant Science.- © 2017 Picorel, Alfonso and Velitchkova. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY).Work in the laboratory of RP and MA was supported by Grant AGL2014-55300-R from Ministry of Economy and Competitiveness (MINECO) of Spain. Work in MV laboratory was supported by Swiss National Science Foundation under BSRP (IZEBZO-143169/1).Peer reviewe

Antioxidative Defense, Suppressed Nitric Oxide Accumulation, and Synthesis of Protective Proteins in Roots and Leaves Contribute to the Desiccation Tolerance of the Resurrection Plant Haberlea rhodopensis

The desiccation tolerance of plants relies on defense mechanisms that enable the protection of macromolecules, biological structures, and metabolism. Although the defense of leaf tissues exposed to solar irradiation is challenging, mechanisms that protect the viability of the roots, yet largely unexplored, are equally important for survival. Although the photosynthetic apparatus in leaves contributes to the generation of oxidative stress under drought stress, we hypothesized that oxidative stress and thus antioxidative defense is also predominant in the roots. Thus, we aimed for a comparative analysis of the protective mechanisms in leaves and roots during the desiccation of Haberlea rhodopensis. Consequently, a high content of non-enzymatic antioxidants and high activity of antioxidant enzymes together with the activation of specific isoenzymes were found in both leaves and roots during the final stages of desiccation of H. rhodopensis. Among others, catalase and glutathione reductase activity showed a similar tendency of changes in roots and leaves, whereas, unlike that in the leaves, superoxide dismutase activity was enhanced under severe but not under medium desiccation in roots. Nitric oxide accumulation in the root tips was found to be sensitive to water restriction but suppressed under severe desiccation. In addition to the antioxidative defense, desiccation induced an enhanced abundance of dehydrins, ELIPs, and sHSP 17.7 in leaves, but this was significantly better in roots. In contrast to leaf cells, starch remained in the cells of the central cylinder of desiccated roots. Taken together, protective compounds and antioxidative defense mechanisms are equally important in protecting the roots to survive desiccation. Since drought-induced damage to the root system fundamentally affects the survival of plants, a better understanding of root desiccation tolerance mechanisms is essential to compensate for the challenges of prolonged dry periods

Photobleaching of photosynthetic pigments in spinach thylakoid membranes. Effect of temperature, oxygen and DCMU

The time dependence of photobleaching of photosynthetic pigments under high light illumination of isolated spinach thylakoid membranes at 22 and 4°C was investigated. At 22°C, the bleaching at 678, 472 and 436 nm was prominent but lowering the temperature up to 4°C during illumination prevented the pigments from bleaching almost completely. The accelerating effect on pigment photobleaching by the presence of 3-(3,4 dichlorophenyl)-1,1- dimethyl-urea) - (DCMU), a well-known inhibitor of the electron transport and known to prevent photosystem I (PSI) and photosystem II (PSII) against photoinhibitory damage, was also suppressed at low temperature. At 22°C in the presence and absence of DCMU, the decrease of the absorption at 678 and 472 nm was accompanied by a shift to the shorter wavelengths. To check the involvement of reactive oxygen species in the process, pigment photobleaching was followed in anaerobiosis. The effects of the three different environmental factors - light, temperature and DCMU - on the dynamics of photobleaching are discussed in terms of different susceptibility of the main pigment-protein complexes to photoinhibition. © 2003 Elsevier B.V. All rights reserved.M.V. gratefully acknowledges a fellowship from the Ministry of Education and Culture of Spain. This work was supported by Ministry of Science and Technology of Spain (Grant BMC2002-00031).Peer Reviewe

Effect of Low Light on Photosynthetic Performance of Tomato Plants—Ailsa Craig and Carotenoid Mutant <i>Tangerine</i>

The effects of a five-day treatment with low light intensity on tomato plants—Ailsa Craig and tangerine mutant—at normal and low temperatures and after recovery for three days under control conditions were investigated. The tangerine tomato, which has orange fruits, yellowish young leaves, and pale blossoms, accumulates prolycopene rather than all-trans lycopene. We investigated the impact of low light at normal and low temperatures on the functioning and effectiveness of photosynthetic apparatuses of both plants. The photochemical activities of Photosystem I (PSI) and Photosystem II (PSII) were assessed, and the alterations in PSII antenna size were characterized by evaluating the abundance of PSII-associated proteins Lhcb1, Lhcb2, CP43, and CP47. Alterations in energy distribution and interaction of both photosystems were analyzed using 77K fluorescence. In Aisla Craig plants, an increase in thylakoid membrane fluidity was detected during treatment with low light at a low temperature, while for the tangerine mutant, no significant change was observed. The PSII activity of thylakoids from mutant tangerine was more strongly inhibited by treatment with low light at a low temperature while low light barely affected PSII in Aisla Craig. The obtained data indicated that the observed differences in the responses of photosynthetic apparatuses of Ailsa Craig and tangerine when exposed to low light intensity and suboptimal temperature were mainly related to the differences in sensitivity and antenna complexes of PSII

The Role of Alternative Electron Pathways for Effectiveness of Photosynthetic Performance of <i>Arabidopsis thaliana</i>, Wt and <i>Lut2</i>, under Low Temperature and High Light Intensity

A recent investigation has suggested that the enhanced capacity for PSI-dependent cyclic electron flow (CEF) and PSI-dependent energy quenching that is related to chloroplast structural changes may explain the lower susceptibility of lut2 to combined stresses—a low temperature and a high light intensity. The possible involvement of alternative electron transport pathways, proton gradient regulator 5 (PGR5)-dependent CEF and plastid terminal oxidase (PTOX)-mediated electron transfer to oxygen in the response of Arabidopsis plants—wild type (wt) and lut2—to treatment with these two stressors was assessed by using specific electron transport inhibitors. Re-reduction kinetics of P700+ indicated that the capacity for CEF was higher in lut2 when this was compared to wt. Exposure of wt plants to the stress conditions caused increased CEF and was accompanied by a substantial raise in PGR5 and PTOX quantities. In contrast, both PGR5 and PTOX levels decreased under the same stress conditions in lut2, and inhibiting PGR5-dependent pathway by AntA did not exhibit any significant effects on CEF during the stress treatment and recovery period. Electron microscopy observations demonstrated that under control conditions the degree of grana stacking was much lower in lut2, and it almost disappeared under the combined stresses, compared to wt. The role of differential responses of alternative electron transport pathways in the acclimation to the stress conditions that are studied is discussed

UV-B response of greening barley seedlings

The relationship between the greening stage of barley seedlings and their response to UV-B irradiation was studied. Etiolated barley seedlings (Hordeum vulgare L., cv. Alfa) greened 12, 24 and 48 h were exposed to UV-B irradiation (312 nm) for 5 h. As a result of UV-B treatment the rate of CO2 fixation and chlorophyll contents decreased but flavonoids, UV-B-induced compounds and carotenoids increased. The inhibition of photosynthesis in green plants was lower in comparison to greening ones. The 12 h greening plants were more sensitive to UV-B treatment than the plants greening 24 h and particularly 48 h, estimated by the quantum efficiency of PSII photochemistry and the oxygen production rate. The levels of flavonoids and UV-B induced compounds enhanced with increasing the greening time. Activity of antioxidant enzymes catalase, peroxidase and superoxide dismutase increased during the seedlings greening and as a result of UV-B irradiation, but the pattern of isoforms remained similar to those found in the controls. UV-B preferentially induced Cu,Zn-superoxide dismutase. Increase of UVB induced synthesis of antioxidant enzymes is in line with their important role in the plant response to UV-B stress. Data presented show that the response of barley seedlings to UV-B irradiation is related to the development stage of photosynthetic apparatus

Different kinetics of photoinactivation of photosystem I-mediated electron transport and P700 in isolated thylakoid membranes

Photoinactivation kinetics of photosystem I (PSI)-mediated electron transport rate was compared to that of P700 content at room (22 °C) and low (4 °C) temperatures in isolated spinach thylakoid membranes. The high light treatment was carried out under aerobic and anaerobic conditions. At 22 °C the decrease of electron transport rate showed first order exponential kinetics. The amount of P700 decreased linearly, being less affected in the first hours of illumination. During photoinhibition at 4 °C in the presence of oxygen, the kinetics of inactivation of PSI photochemical activity and the content of P700 were different. It was found that 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) had different protective effect on the electron transport rate and on P700 content at both temperatures. Treatment with high light intensity under N2 atmosphere had no effect on the electron transport rate or P700 content. The possible degradation of PSI reaction centre proteins was determined using immunoblot methods. In the presence of linear electron transport at 22 °C correlation between formation of toxic hydroxyl radicals and inhibition of oxygen uptake was observed.M.V. gratefully acknowledges a Postdoctoral Fellowship from the Ministry of Education and Culture of Spain. This work was supported by DGICYT grant PB98-1632.Peer Reviewe

Valorization of a plant β-amylase: Immobilization and dataset on the kinetic process

The data presented in this article are related to the research article titled “Immobilization nd topochemical mechanism of a new β-amylase extracted from Pergularia tomentosa” (Lahmar et al., 2017) [1]. This article documented information on the determination of the molecular weight of the β-amylase, the method of its immobilization and a comparison of the kinetic mechanism between the free and the immobilized forms by a mathematical method. Fresh Pergularia tomentosa was collected from Tunisia and a special method for β-amylase extraction was followed (Yotova et al., 2000) [2]. Public dissemination of this dataset will allow further analyses of the data