V. Yu. Lyubimov

Preillumination of excised spinach leaves with red light increases resistance of photosynthetic apparatus to UV radiation

Leaves of spinach (Spinacia oleracea, cv. Ispolinskii) were preilluminated by low-intensity light (1.0 and 1.5 W/m2, 0.5–3.0 h) with wavelengths ranging from 530 to 730 nm to study the effect of this pretreatment on the activity of photosystem II (PS II), content of photosynthetic pigments, and peroxidase activity in excised leaves exposed to UV-A irradiation. Irradiation of leaves with UV-A suppressed the activity of PS II, reduced the content of chlorophylls (a + b) and carotenoids, and increased the peroxidase activity. Preillumination of leaves with red light (RL, 620–660 nm) alleviated the inhibitory action of UV-A on PS II activity and reduced the pigment losses but increased the peroxidase activity in leaves and thylakoid membrane preparations, as compared to the respective effects of UV-A light applied without preillumination. The preexposure of leaves to red light alternating with far-red light (FR, 730 nm) removed partly the influence of RL on the parameters under study, which indicates the involvement of phytochrome active form, PFR into stress-induced defense responses in leaves. It is supposed that elevated resistance of photosynthetic apparatus to UV-A radiation was formed with the involvement of PFR and the antioxidant system induced by oxidative stress after preillumination of leaves with red light

Growth, photosynthesis, and metabolism of sugar beet at an early stage of exposure to elevated CO2

The effects of CO2 concentration (Ca) on growth, photosynthesis, and the activity of enzymes associated with the translocation and assimilation of CO2 were studied in sugar beet (Beta vulgaris L. subsp. saccharifera, cv. Ramonskaya) plants. The plants were grown in controlled-climate chamber to the stage of 3–4 leaves and then used in experiments. Experimental plants were exposed in boxes to doubled Ca (700 µl/l, 2C plants), whereas control plants were kept in a chamber with ambient atmosphere (350 µl/l, 1C plants). As compared with 1C plants, in 3 and 8 days, the leaf area of 2C plants increased by 14 and 26%, respectively. The rate of their photosynthesis (Pn) measured in 3, 6, and 8 days increased by 85, 47, and 52%, respectively, whereas in normal air, the values of Pn in 2C plants were by 12, 19, and 15% lower than in 1C plants. After 8-day growth, the content of soluble carbohydrates in the leaves of 2C plants attained 7.2%, being by 80% greater than in 1C plants; the content of starch did not exceed 3%. The total content of chlorophylls a and b in the leaves of 2C plants was by 14% greater than in 1C plants, but their ratio was essentially the same. The level of protein in 2C plants was by 13.4% lower than in 1C plants. The activity and content of Rubisco in 1C and 2C plants were similar. As compared with 1C plants, in 2C plants the activity of soluble carbonic anhydrase (sCA) was lower by 34% in 3 days and by 18% in 8 days; the activity of carbonic anhydrase of membrane preparations (mCA), was lower by 24 and 77%, respectively. Catalase activity in 2C plants became by 8% lower than in 1C plants only after 8 days. A reduction in the photosynthetic ability of 2C plants in ambient atmosphere, a decrease in activity of sCA and, especially, of mCA observed together with invariable activity and content of Rubisco in the leaf extracts are interpreted as early symptoms of acclimation of young plants of sugar beet to elevated CO2.

Adaptive Mechanisms of Photosynthetic Apparatus to UV Radiation

Adaptive mechanisms of higher plant photosynthetic apparatus to UV radiation are discussed in the review. Particular attention is paid to the various mechanisms that protect photosynthetic machinery from damage injury and the role of reactive oxygen species, phenolic compounds, and phytochrome system. The effects of the increased content of active form of phytochrome B and its content on photosynthetic activity and adaptation to stress are examined. A relation between the action of UV radiation on photosynthetic activity and the state of phytochromes and pro-/antioxidant balance is considered.

Morphological features of vanadium dioxide microcrystals grown from the gas phase

A gas-phase synthesis of vanadium dioxide (VO2) is presented and morphological features of the crystals grown by this method are described. Using the proposed method, VO2 microcrystals having the shapes of continuous rods and plates, as well as rods with a longitudinal rectangular cavity, can be obtained. The possible mechanisms of growth are considered with allowance for the different crystal shapes and features of the synthesis.

Phytochrome B-dependent regulation of reductive phase of photosynthetic carbon assimilation

The experiments were conducted with 10-day-old seedlings of wheat (Triticum aestivum L). Phytochrome B was activated using an array of light diodes emitting light in the red spectral region (RL) and inactivated by an array of light diodes emitting far-red light (FRL). At the end of the night dark period (8 h), activity of the chloroplastic GAP-dehydrogenase complex (the sequence of reactions: 3-PGA → 1,3-PGA → 3-GAP) was 1.0−1.2 μmol of oxidized NADPH/(min g fr wt of the leaf). When the leaves of intact plants were exposed to a maximal dose of RL (20 min at 17.5 kJ/m2), enzyme activity rose by 100–120%. Longer exposure to RL (30 and 40 min) did not cause further activation. Successive exposure to RL and FRL (20 min at 3.0 kJ/m2) completely negated a stimulatory effect of RL. It was shown that as little as 5-min-long exposure to RL increased the rate of 3-GAP formation by 20–25%, and enzyme activity rose linearly when radiation dose was elevated. Determination of the lifetime of RL-activated state by its decrease in plants placed in darkness showed that decay occurred with τ1/2 of 50−60 min when RL was switched off. Thus, a phytochrome B-induced regulation of reducing enzyme complex governing the reductive pentose phosphate cycle was discovered. Judging from the kinetics of attenuation of the activated state, phytochrome B apparently does not affect de novo synthesis of the enzyme. Since the investigated metabolic process consists of two coupled reactions controlled by kinase and dehydrogenase, the place and mechanism of action of the phytochrome system remain unknown.

Growth in the UV-A irradiation resistance of the photosynthetic apparatus of lettuce seedlings as a result of activation of phytochrome B

This paper studies how UV-A irradiation and preirradiation of 10-day lettuce seedlings (Lactuca sativa L.) with red light (λmax = 664 nm, 10 min, 1 W m−2) affect the activity of the photosynthetic apparatus, content of chlorophylls a and b, and H2O2 in leaves, as well as peroxidase activity. Growth in the UV-A resistance of the photosynthetic apparatus was discovered, and the role of the antioxidant system and phytochrome B in the mechanisms of how the high UV-A resistance of the photosynthetic apparatus is formed was considered.

Mechanism of enhancing photosystem 2 thermoresistance in wheat plants by chlorocholine chloride.

It is shown that pretreatment of wheat seeds with chlorocholine chloride reduces inhibition of photosystem 2 activity in the first leaves of 10-day-old wheat variety Moskovskaya 35 seedlings caused by heating at 39–41°C for 5–20 min and improves its poststress recovery, probably due to activation of antioxidant enzymes and increase in the level of low molecular weight antioxidants.

Response of photosynthetic apparatus in Arabidopsis thaliana L. mutant deficient in phytochrome A and B to UV-B

The effects of UV-B radiation (1 W m–2, 1 and 2 h) on PSII activity, chloroplast structure, and H2O2 contents in leaves of 26-d-old Arabidopsis thaliana phyA phyB double mutant (DMut) compared with the wild type (WT) were investigated. UV-B decreased PSII activity and affected the H2O2 content in WT and DMut plants grown under white light (WL). The chloroplast structure changes in DMut plants exposed to UV were more significant than that in WT. Reductions in maximal and real quantum photochemical yields and increase in the value of thermal dissipation of absorbed light energy per PSII RC and the amount of QB-nonreducing centers of PSII were bigger in mutant compared to WT plants grown both under WL and red light. Such difference in action of UV-B on WT and DMut can be explained by higher content of UV-absorbing pigments and carotenoids in WT leaves compared with DMut.

Synthesis and modification of micro-and nanorods of vanadium oxides

A method for the gas-phase synthesis of single-crystalline micro-and nanorods of vanadium pentoxide (V2O5) has been developed based on the thermal decomposition of vanadium chloride vapor. Using this technique, it is possible to obtain separate micro-and nanorods (with thicknesses ranging from 50 nm to 5 μm and a length of up to 7 mm), planar arrays, and three-dimensional structures. The temperature dependence of the resistance of individual microrods of vanadium oxides in various degrees of oxidation has been measured.

Aftereffect of heat shock on activity of the photosynthetic apparatus and lipid peroxidation in wheat leaves

AbstractsThe dynamics of development of oxidative stress and poststress recovery of the photosynthetic apparatus in leaves of 10-day-old wheat seedlings subjected to heat shock (40, 42, and 44°C) for 20 min and exposed to light for 72 h are studied. The effect of pretreatment temperature and light intensity on recovery of the photosynthetic apparatus and its resistance to photostress and repeated heat shock is examined.