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The photosynthetic characteristics of Haberlea rhodopensis plants from two habitats in Western Rhodope Mountain (in the regions of Trigrad and Wonderful bridges) were studied. Although the plants from both habitats were exposed to sun during part of the day, their leaves were morphologically similar to those of shade plants. The desiccation-induced damages on membrane integrity were characterized by electrolyte leakage and lipid peroxidation. Photochemical activity, energy distribution between the two photosystems and physicochemical properties of thylakoid membranes were estimated by means of chlorophyll fluorescence, 77K fluorescence and particle microelectrophoresis measurements. The mutual organization of PSI-LHCI and PSII-LHCII complexes and spillover between them were similar in thylakoids isolated from well-hydrated plants from Trigrad and Wonderful bridges. Under desiccation up to 8% RWC the F735/F685 ratio at excitation with 472 nm (chl b) remained almost unchanged in thylakoid membranes from Wonderful bridges while it decreased considerably in thylakoid membranes from Trigrad. The thylakoid membranes from Wonderful bridges showed a less alteration in energy distribution between both photosystems in response to dehydration. Dehydration induced stronger modifications in thylakoid membranes of plants from Trigrad, expressed by higher [ABSTRACT FROM AUTHOR]

The effect of high temperature (HT) and dehydration on the activity of photosynthetic apparatus and its ability to restore membrane properties, oxygen evolution, and energy distribution upon rehydration were investigated in a resurrection plant, Haberlea rhodopensis. Plants growing under low irradiance in their natural habitat were desiccated to air-dry state at a similar light intensity [about 30 μol(photon) m −2 s −1] under optimal day/night (23/20°C) or high (38/30°C) temperature. Our results showed that HT alone reduced the photosynthetic activity and desiccation of plants at 38°C and it had more detrimental effect compared with desiccation at 23°C. The study on isolated thylakoids demonstrated increased distribution of excitation energy to PSI as a result of the HT treatment, which was enhanced upon the desiccation. It could be related to partial destacking of thylakoid membranes, which was confirmed by electron microscopy data. In addition, the surface charge density of thylakoid membranes isolated from plants desiccated at 38°C was higher in comparison with those at 23°C, which was in agreement with the decreased membrane stacking. Dehydration led to a decrease of amplitudes of oxygen yields and to a loss of the oscillation pattern. Following rehydration, the recovery of CO 2 assimilation and fluorescence properties were better when desiccation was performed at optimal temperature compared to high temperature. Rehydration resulted in partial recovery of the amplitudes of flash oxygen yields as well as of population of S 0 state in plants desiccated at 23°C. However, it was not observed in plants dehydrated at 38°C. [ABSTRACT FROM AUTHOR]

The recovery of photosynthetic activity during rehydration of Haberlea rhodopensis from drought- and freezing-induced desiccation were investigated. The water uptake during the initial 15 h was slow thus preventing cellular damages. The results showed faster recovery of quantum efficiency of PSII in plants rehydrated after freezing stress (RAF) compared to plants rehydrated after drought stress (RAD) and the most significant differences between them were evident after 9-15 h of rehydration. Following rehydration, PSI activity recovered faster compared to PSII and in contrast to PSII, its activity was higher in RAD compared to RAF plants. During the first hours of rehydration, prominent alterations in energy transfer between photosynthetic complexes occurred as revealed by 77 K fluorescence of isolated thylakoids. High proportion of thermal energy dissipation in dry plants and during the first hours of rehydration protects them from photooxidation; the role of PSII reaction center quenching during the recovery was suggested. [ABSTRACT FROM AUTHOR]

The acclimation to high light, elevated temperature, and combination of both factors was evaluated in tomato ( Solanum lycopersicum cv. M82) by determination of photochemical activities of PSI and PSII and by analyzing 77 K fluorescence of isolated thylakoid membranes. Developed plants were exposed for six days to different combinations of temperature and light intensity followed by five days of a recovery period. Photochemical activities of both photosystems showed different sensitivity towards the heat treatment in dependence on light intensity. Elevated temperature exhibited more negative impact on PSII activity, while PSI was slightly stimulated. Analysis of 77 K fluorescence emission and excitation spectra showed alterations in the energy distribution between both photosystems indicating alterations in light-harvesting complexes. Light intensity affected the antenna complexes of both photosystems stronger than temperature. Our results demonstrated that simultaneous action of high-light intensity and high temperature promoted the acclimation of tomato plants regarding the activity of both photosystems in thylakoid membranes. [ABSTRACT FROM AUTHOR]

Abstract: To understand the mechanism of the photoprotective and antioxidative functions of carotenoids, it is essential to have a profound knowledge of their excited electronic and vibronic states. In the present study we investigate the most powerful antioxidants: β-carotene and lutein by means of resonance Raman spectroscopy. The aim was to study in detail their Raman spectra in solution at room temperature and their changes as a function of temperature. To measure the spectra in their natural environment pyridine has been used as a solvent. It has been chosen because of its polarizability (n =1.5092) which is close to that of membrane lipids and proteins. The temperature dependence of the most intensive ν 1 band in the range from 77K to 295K at 514.5nm excitation has been obtained. It was found that in pyridine the Cing frequency, its intensity, line shape, and line width are very sensitive to the temperature (the sensitivity being different for the two studied carotenoids). The observed linear temperature dependence of the Cing frequency is explained by a mechanism involving changes of the vibronic coupling and the extent of π-electron delocalization. The different behavior of the temperature-induced broadening of the ν 1 band and its intensity for the two studied carotenoids can be associated with the different nature of their solid matrices: glassy for β-carotene and crystalline-like for lutein, owing to their different chemical structures. [Copyright &y& Elsevier]

UV-B responses of three rice ( Oryza sativa L.) cultivars (Sasanishiki, Norin 1 and Surjamkhi) with different photolyase activity were investigated. Carbon dioxide assimilation data support that Sasanishiki was less sensitive to UV-B than Norin 1 and Surjamkhi. UV-B radiation sharply decreased the content of Rubisco protein in Surjamkhi and has no effect in Sasanishiki. The photochemical activities of photosystem (PS) 1 and PS 2 was slightly affected by UV-B treatment. The content of H2O2 and the activities of antioxidant enzymes, catalase (CAT), peroxides (POX) and superoxide dismutase (SOD) were enhanced after UV-B treatment. The activities of CAT and POX isoenzymes in Sasanishiki were more enhanced by UV-B radiation than those in Norin 1 and Surjamkhi. [ABSTRACT FROM AUTHOR]

Haberlea rhodopensis Friv. is unique with its ability to survive desiccation to an air-dry state during periods of extreme drought and freezing temperatures. To understand its survival strategies, it is important to examine the protective mechanisms not only during desiccation but also during rehydration. We investigated the involvement of alternative cyclic electron pathways during the recovery of photosynthetic functions after freezing-induced desiccation. Using electron transport inhibitors, the role of PGR5-dependent and NDH-dependent PSI-cyclic electron flows and plastid terminal oxidase were assessed during rehydration of desiccated leaves. Recovery of PSII and PSI, the capacity of PSI-driven cyclic electron flow, the redox state of plastoquinone pool, and the intersystem electron pool were analyzed. Data showed that the effect of alternative flows is more pronounced in the first hours of rehydration. In addition, the NDH-dependent cyclic pathway played a more determining role in the recovery of PSI than in the recovery of PSII. [ABSTRACT FROM AUTHOR]

The effect of UV-B irradiation at temperatures of 22 and 4 °C on flash induced oxygen yields, photochemical activity, and energy transfer in pea thylakoid membranes in the absence and presence of scavengers of reactive oxygen species (ROS) was studied. Three different scavengers were used: dimethyl sulfoxide (DMSO), histidine (His), and n-propyl gallate (nPG). As result of the UV-B treatment of isolated membranes, the flash oxygen yields were considerably affected - the amplitudes decreased and the oscillation pattern was lost. The analysis of the flash oxygen yields and initial oxygen burst showed alterations of a number of oxygen evolving centers in the S0 state as well as changes of decay kinetics of the oxygen burst under continuous irradiation. ROS scavengers exhibited more or less expressed protective effects, nPG being the most effective against UV-B induced damages of the flash oxygen yields. At both the temperatures, photosystem II (PS II) mediated electron transport was more sensitive to the UV-B treatment in comparison with photosystem I (PS I). The analysis of 77 K fluorescence spectra showed that the fluorescence ratio F735/F685 increased by the UV-B treatment probably due to a redistribution of excitation energy between both photosystems most likely caused by partial unstacking and due to a decrease of PS II fluorescence resulting from reaction center-type quenching. The nPG was the most powerful scavenger which protected the oxygen evolution capacity of PS II in the absence and presence of an exogenous electron acceptor to the highest extent. [ABSTRACT FROM AUTHOR]

The role of exogenously applied phytohormone methyl jasmonate (MeJA) in counteracting the ultraviolet B (UV-B) stress in barley seedlings was investigated. Barley seedlings ( Hordeum vulgare L., cv. Alfa) 4 days old were supplied with 5 × 10−5 m MeJA through the roots for 3 days and then exposed for 2 days for 5 h per day to UV-B (312 nm, biological effectiveness of UV-B radiation 28.8 kJ m−2day−1). The rate of 14CO2 fixation, PSI and PSII activities and chlorophyll content decreased, but flavonoids, H2O2, malondialdehyde, proline and UV-B induced compounds increased after UV-B treatment. The rate of photosynthetic oxygen evolution was more strongly inhibited by UV-B-irradiation than PSI and PSII efficiency. MeJA itself increased the content of free proline, which acts as a stress protector due to its radical scavenging ability. Increased superoxide dismutase, catalase and peroxidase (POX) activities in the leaves and in the roots and the POX isoforms induction revealed the MeJA involvement in plant tolerance to oxidative stress caused by UV-B irradiation. It was shown that pre-treatment with MeJA counteracted UV-B stress. Therefore, it was suggested that MeJA could acts as a mediator in plant defense responses to UV-B irradiation by enhancing the activity of antioxidant system and free radical scavenging capability of plant cells. [ABSTRACT FROM AUTHOR]