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The relationship between photosynthesis, pigment accumulation, and the expression of key light-regulated genes in Solanum lycopersicum hp-1, hp-2 and hp-1.2 photomorphogenetic mutants under conditions of high-intensity light (2000 μm (photons) m−2s−1) was studied. The hp-2 mutant (LA3006) and the hp-1 mutants (LA4012 and LA3538) are deficient in DET1 (De-etiolated 1 and DDB1 (DNA DAMAGE-BINDING PROTEIN 1), respectively, which are components of the CDD complex (COP10, DDB1, DET1). HP mutants are superproducers of various pigments and are sensitive to light. We have shown that HIL (high-intensity light) causes a decrease in PSII activity after 24 and 72 h of irradiation, which was partially restored after 72 h in the WT. The photosynthetic rate noticeably decreased only in LA4012 and LA3538 after 24 h of irradiation. After 72 h, the photosynthetic rate decreased in all mutants, with the exception of hp-1.2 LA0279, but the decrease was most noticeable in LA4012, yet significant changes in the respiration rate were absent. The LA0279 mutant was more capable of accumulating anthocyanin in the cells of the subepidermal parenchyma and chlorenchyma, as well as in the cells at the base of large multicellular glandular trichomes and in the mesophyll. Another important difference was the accumulation of increased amounts of antheraxanthin and phenolic compounds in the leaves of LA0279 after 72 h of HIL irradiation. Unlike LA4012, LA3006, LA0279, and LA3538 sowed a significant increase in the expression levels of CHS, HY5, and FLS genes after 24 h, which may be one of the reasons for the higher adaptive potential of those three mutants. In addition to that in LA3538, strong light-induced stress led to an increased level of flavonol synthase (FLS) expression in the LA3006, LA0279, and LA4012 mutants. We hypothesize that the photosynthetic apparatus (PA) of the LA0279 mutant, which is deficient in the DET1 and DDB1 genes, is most adapted to prolonged HIL. Most likely, the resistance of PA mutants to HIL is due to a variety of factors, which, in addition to the redistribution of carotenoids, may include morphological features associated with the accumulation of anthocyanin in the epidermis, subepidermal layer, mesophyll and trichomes of leaves and with an increase in leaf thickness.

This work focuses on developing light environments for the effective regulation of morphogenesis and ex vitro conditions adaptation in micropropagated raspberry plants on the basis of photomorphogenetic control of physiological processes using light-emitting diodes (LEDs). In experiments with cloned plants growing ex vitro in stressful conditions during acclimation, the effects of optical radiation of various spectral combinations from different photosynthetically active radiation (PAR) spectral regions were studied. The data on the plant development and state of the photosynthetic apparatus, features of photosynthetic gas exchange and transpiration, accumulation of photosynthetic pigments, light curves of photosynthesis, and data on growth processes in light modes using combined quasimonochromatic radiation (either mixture of red, green, and blue light or red, far-red, and blue light) with various ratio of the distinct spectral regions were obtained. Photosynthetic apparatus functional activity under different light conditions was studied with chlorophyll fluorescence determination, and plant stress responses to growing under artificial spectral light conditions were characterized. The experiments were accompanied by detailed plant phenotyping at the structural and functional levels. Plant acclimation and photosynthetic improvements in response to added far-red and green light wavelengths to the main red-blue spectrum have been elucidated.

Dynamics of the photosynthetic apparatus' (PA) structural and functional parameters during the day was investigated in euhalophyte Salicorniaperennans Willd., crynohalophyte Limoniumgmelinii (Willd.) O. Kuntze, and glycohalophyte Artemisiasantonica L. The greatest PA activity judging from the rate of СО2 consumption/release by the leaves was observed in the morning. In salt-accumulating (S. perennans) and salt-eliminating (A. santonica) species, the rate of photosynthesis was greater than in L. gmelinii plants possessing the systems of salt excretion. In A. santonica and S. perennans, the content of green pigments decreased during the day, while it remained permanent in L. gmelinii. During the day, the ratio between plastid lipids and pigments increased in A. santonica and S. perennans. In chloroplast lipids from S. perennans, a decrease in the relative content of monogalactosyldiacylglycerol (MGDG) was compensated for by a rise in relative content of digalactosyldiacylglycerol (DGDG), with the contribution of sulfoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG) remaining the same. In the chloroplasts from L. gmelinii, the proportion of neutral lipids MGDG and DGDG did not change in contrast to the level of anionic lipids SQDG and PG. In A. santonica, we detected changes in both neutral and anionic lipids. A high proportion of unsaturated FA (UFA) (over 70%) in the total pool of FA was mainly accounted for by α-linolenic acid. It was found that the proportion of saturated FA tended to increase in the evening. All the revealed structural and functional reorganizations of PA associated with fluctuation of pigment-lipid resources of thylakoid membranes were adaptive and aimed at optimization of photosynthesis under specific environmental conditions.

The impacts of high-intensity light (HIL) (4 h) and UV-B radiation (1 h) on the photosynthetic activity, content of photosynthetic and UV-absorbing pigments (UAPs), activity of antioxidant enzymes (ascorbate peroxidase (APX) and guaiacol-dependent peroxidase (GPX)), content of thiobarbituric acid reactive substances (TBARs), expression of some light-regulated genes in 25-day-old wild type (WT) and the cryptochrome 1 (Cry1) hy4 mutant of A. thaliana Col-0 plants grown under blue light (BL) were studied. HIL and UV-B treatments led to decreases in the photosynthetic rate (Pn), photochemical activity of PSII (FV/FM) and PSII performance index (PIABS) of WT and mutant plants grown under high-intensity BL (HBL) and moderate intensity BL (MBL). However, in HBL plants, the decrease in the photosynthetic activity in hy4 plants was significantly greater than that in WT plants. In addition, hy4 HBL plants demonstrated lowered UAP and carotenoid contents as well as lower activity of APX and GPX enzymes. The difference in the decline in the photosynthetic activity of WT and hy4 plants grown at MBL in response to HIL was nonsignificant, while that in response to UV-B was small. We assume that the deficiency in cryptochrome 1 under HIL irradiation disrupts the interaction between HY5 and HFR1 transcription factors and photoreceptors, which affects the transcription of light-induced genes, such as CAB1, PSY and PAL1 linked to carotenoid and flavonoid biosynthesis. It was concluded that PA stress resistance in WT and hy4 plants depends on the light intensity and reduced stress resistance of hy4 at HBL, is likely linked to low UAP and carotenoid contents as well as lowered APX and GPX enzyme activities in hy4 mutants.

The photosynthetic acclimation of extremophile Eutrema salsugineum plants to red light (RL) (14 days, 150 μmol photons m−2 s-1, 660 nm) and the expression of the key photoreceptor apoprotein genes, transcription factors (TFs) and associated with phytochrome system MIR (microRNA) genes were studied. RL exposure induced an increase in the content of anthocyanin and total phenolic compounds and the level of Chls was decreased. The photosystem 2 electron transport rate and the number of open reaction centres (qL) were not changed in RL plants, however, the levels of non-photochemical quenching (NPQ) and the regulated quantum yield of non-photochemical quenching Y(NPQ) were significantly higher in the RL plants. The rate of CO2 uptake was decreased by almost 1.4-fold but the respiration and transpiration rates, as well as the stomatal conductance were not changed in the RL plants. An increase in the expression of the photoreceptor apoprotein genes PHYA, PHYB and PHYC, the TF genes PIF4, PIF5 and miR395, miR408, miR165 and decreases in the levels of the transcripts of the TF gene HY5 and miR171, miR157, and miR827 were detected. The acclimation effect of photosynthetic apparatus to RL was accompanied by an increase of pigment content such as total phenolic compounds and carotenoids and it is due to the changes in the expression of the apoprotein phytochrome genes PHYA, PHYB, PHYC and phytochrome signalling TFs (PIF4, PIF5 and HY5) as well as MIR genes associated with phytochrome system.

Thickness reduction of stratospheric ozone layer is one of the environmental threats that leads to shared increase of UV-B radiation reaching the Earth’s surface. Mechanisms of adaptation and damage of the photosynthetic apparatus (PA) in higher plants are considered in this review. Mn-containing water-oxidizing complex, D1 and D2 proteins, quinone molecules, disruption of thylakoid membrane integrity, and a number of Calvin cycle enzymes, first of all Rubisco, are the first targets of UV radiation. This review examines various mechanisms that can protect the PA against UV radiation. A shift of pro-/antioxidant balance towards antioxidants, synthesis of UV-absorbing pigments, and a number of other mechanisms are considered in this review. Reactive oxygen species, UVR8 protein, and photoreceptors such as phytochrome and cryptochrome are included in the UV-transduction chain. UV-induced inhibition of photosynthesis and growth processes together with the positive effects of UV manifesting in an enhancement of the biosynthesis of different pigments such as flavonoids and carotenoids and increasing stress resistance of the PA are also discussed.

Cadmium (Cd) is among the elements that exhibit a pronounced toxic effect on a variety of physiological and metabolic processes. Photosynthesis is one of the main processes of autotrophic organisms. The negative effect of cadmium on the photosynthetic apparatus leads to inhibition of many metabolic pathways that ensure the vital activity of plants. Cadmium can have a direct effect on photosystem II, decreasing the electron transfer rate and inhibiting the oxygen-generating complex. Besides that, under the cadmium influence, there is a violation of the structure and synthesis of pigments, a quantity reduction in open reaction center (RC), as well as inhibition of enzymes in the dark phase of photosynthesis. In addition, Cd can indirectly affect photosynthesis as a result of changes in plant water metabolism, stomata closure, and reduction in CO2 availability for assimilation centers. Under oxidative stress caused by cadmium, the integrity of thylakoid membranes is impaired, as well as the rate of photosynthesis decreases as a result of inhibition of the activity of CO2 fixation enzymes. At the level of the whole plant, disruption of the photosynthesis process is accompanied by a decrease in the growth rate and productivity of plants. The review discusses the toxic effects of cadmium both directly on photosynthesis and on other processes associated with it.

Structural and molecular parameters of photosynthetic apparatus in plants with different strategies for the accumulation of salts were investigated. CO2 gas exchange rate, content of pigments, mesostructure, chloroplast ultrastructure and the biochemical composition of the membrane structural components in leaves were measured. The objects of the study were euhalophytes (Salicornia perennans, Suaeda salsa, Halocnemum strobilaceum), crynohalophyte (Limonium gmelinii), glycohalophyte (Artemisia santonica). Euhalophytes S. perennans and S. salsa belong to the plants of the halosucculent type, three other species represent the xerophilic type. The highest photosynthetic activity estimated by the average parameters of CO2 gas exchange rate in the leaves was observed in S. perennans plants. Plants of the xerophyte type including both H. strobilaceum euhalophyte and cryno- and glycohalophytes are described by lower values of these characteristics. Larger cells with a great number of chloroplasts and a high content of membrane glycerolipids and unsaturated C18:3 fatty acid, but with smaller pigment and light-harvesting complexes size characterise the features of euhalophytes with a succulent leaf type. Thus, features of the mesostructure, ultrastructure, and supramolecular interactions of the halophyte PA were closely related to the functional parameters of gas exchange, and were characterised by the strategy of species in relation to the accumulation of salts, the life form of plants, and the attitude to the method of water regulation.

The effects of high-intensity light (HIL, 4 and 24 h) and UV-B (1 h) on the net photosynthesis rate, activity of photosystem II (PSII), content of photosynthetic pigments, anthocyanin and UV-absorbing pigments as well as the expression of certain light-responsive genes (HY5,CAB1) chalcone synthase (CHS) and main antioxidants enzyme genes (APX1, GPX and GR) in the leaves of phyB and phyA mutant A. thaliana plants were studied. Both UV-B and 4 and 24 h HIL decreased the PSII maximum quantum yield (Fv/Fm), PSII performance index (PIABS), photosynthesis and respiration rates in plants. Moreover, all stress treatments increased the dissipation of the absorbed energy (DI0/RC) as well as the flux of absorbed energy per RC (ABS/RC). The maximal changes in photosynthesis and chlorophyll fluorescence parameters were observed in the phyB mutant. The WT and the phyA mutant showed similar responses. In addition, the phyB mutant exhibited decreases in the expression of genes encoding enzyme CHS, the transcription factor HY5 and the antioxidant enzymes APX1 and GPX. One of the possible mechanisms protecting the photosynthetic apparatus from light excess or UV radiation is the elevated content of various pigments that can act as antioxidants or optical filters. We assume that the greater decrease in photosynthetic activity in the phyB mutant under HIL and UV-B conditions was due to the decreased content of carotenoids and UV-absorbing pigments in this mutant.

Light-converting polypropylene spunbond was first used in the study of the key physiological parameters of plants. A comparative study of the functioning of the photosynthetic apparatus and the dynamics of growth in late cabbage plants (Olga variety) and leaf lettuce (Emerald variety) was conducted using the ordinary nonwoven polypropylene fabric (spunbond) (density 30 g·m-2) and the spunbond containing a photoluminophore (PL) (1.6% yttrium oxysulfide doped with europium). The plants were grown in a glass greenhouse without spunbond and under the spunbond containing and not containing the PL that transforms a part of UV-radiation into red light radiation. The use of the spunbond led to a decrease in the rate of photosynthesis, activity of the photosystem 2, and the accumulation of plant biomass and to an increase in the stomatal conductance. By contrast to unmodified spunbond, the application of the spunbond containing the PL led to an increase in the rate of photosynthesis, the water-use efficiency (WUE), and the accumulation of the total biomass of plants by 30-50% but to a decrease in the transpiration rate and the stomatal conductance. It is assumed that the positive effect of the PL is associated with an increase in the fraction of fluorescent red light, which enhances photosynthetic activity and accelerates plant growth.

The effect of UV-A radiation (365 nm) and the protective effect of preillumination with red light (RL, 664 nm, 10 min) or with a combination of red and far-red light (FRL, 727 nm, 10 min) on the activity of the PSII as well as the expression levels of selected genes, especially those encoding chloroplast proteins (sAPX, tAPX, CAB1, and D1), were studied in leaves of the 26-d-old hy3 mutant of Arabidopsis thaliana, which is deficient in the phytochrome B apoprotein. The effects were compared with corresponding effects observed in the hy2 mutant of A. thaliana, which is deficient in the phytochrome chromophore. Illumination with UV-A decreased the photosynthetic pigment content, the maximum photochemical quantum yield of PSII (Fv/Fm), and the effective quantum yield of PSII (ΦPSII). The reduction of the Fv/Fm ratio and ΦPSII was more pronounced in the mutants as compared to wild-type plants (WT). The preillumination of the leaves with RL caused a significant reduction in the inhibitory effect of UV-radiation on the PSII activity in the WT plants, but it caused only a small decrease in the hy3 mutant. The preillumination of leaves with RL and FRL combination compensated the protective effect of RL on the UV-induced decrease of the fluorescence parameters in the WT. Such reversibility is typical for involvement of red/far-red reversible phytochromes at low intensity light. The results suggest an important role of red/far-red reversible phytochromes (phytochrome B) in the resistance of PSII to UV-A radiation caused by changes in contents of either carotenoids or other UV-absorbing pigments probably through biosynthesis of these pigments. The data also demonstrated that phytochrome B and other phytochromes can affect the PSII stress resistance by the fast regulation of the expression of genes encoding antioxidant enzymes and transcription factors at the step of gene transcription.

The effects of high-intensity light (HIL) on the activity of photosystem II (PSII) and photosynthesis in wild-type (WT) and single (phyB2, phyB1, phyA and cry1), double (phyB1B2, phyAB2 and phyAB1) and triple (phyAB1B2 and cry1phyAB1) mutants of Solanum lycopersicum were studied. In addition, changes in the activity of the antioxidant enzymes ascorbate peroxidase, glutathione reductase and guaiacol peroxidase as well as the photosynthetic pigment and anthocyanin contents in the leaves of phyB2 and cry1phAB1 mutants under HIL were examined. When plants were irradiated with HIL (2 h), the PSII resistance of the cry1phyAB1 mutant was the lowest, while the resistance of WT and single mutants excluding cry1 was the highest. The effect of HIL on PSII activity in all double mutants and the phyAB1B2 mutant was intermediate between the effects on the WT and the cry1phyAB1 mutant. The intensity of oxidative processes in the cry1phyAB1 mutant was higher than that in WT and phyB2, but in cry1phyAB1, the activity of antioxidant enzymes and the anthocyanin content were lower. The low resistance of the cry1phyAB1 mutant to HIL may be due to the low antioxidant activity of key enzymes and the reduced pigment content, which are consistent with the reduced expression of CHS and sAPX genes in the cry1phyAB1 mutant.

Study of the functional state of the photosynthetic apparatus in winter triticale under conditions of salinity (120 mM NaCl) has been carried out. It is shown that the initial stress response (up to 24–48 hours) is characterized by a 35% reduction in stomatal conductance, an increase in the RuBisCo activity (up to 37 μmol NADH/min g), and a high rate of electron transport (up to 502 μmol DCPIP/mg Chl h). The response of plants after 48 hours of salinity is associated with a significant increase in stomatal conductance (up to 68.3 nmol/m2 s), as well as the decline in rate of electron transport (up to 222 μmol DCPIP/mg Chl h), the RuBisCo activity (up to 22 μmol NADH/min g), and the rate of photosynthesis (up to 10.96 μmol CO2/m2 s). In addition, plants preserve their functional photosynthetic apparatus under conditions of continuous salinity (lasting for more than 48 h) reducing the efficiency of photosynthesis.

The influence of phytochrome B overproduction in 50- to 60-day-old transgenic potato plants (Solanum tuberosum L., lines Dara 5 and Dara 12 with moderate and intense expression of PHYB, respectively) on the resistance of photosynthetic apparatus to UV-B irradiation was investigated. In plants unexposed to UV-B, there was no significant difference in photosynthetic rates (P n) and fluorescence parameters (F v/F m, qN, qP) between the nontransformed (NT) line and Dara-5 and Dara-12 lines, whereas the content of photosynthetic pigments per 1 cm2 leaf area was higher in the transgenic plants. Irradiation with UV-B resulted in the decrease in photosynthetic rate in NT plants by 35–45%, whereas in Dara-12 line this rate was lowered by only 20–25%. Exposure to UV-B reduced the amplitudes of both fast and slow components of delayed fluorescence (DF), which indicated the diminished efficiency of photosystem II (PSII). The decrease in the maximum amplitude of the slow DF component was markedly lower in Dara-12 (19%) than in NT line (33%). The maximal photochemical quantum yield of PSII (F v/F m ratio) in plants exposed to UV-B was also suppressed stronger in NT line than in Dara-12. The line Dara-5 had intermediate position among other lines in terms of UV-B resistance of photosynthesis and PSII activity, but it was closer to NT than to Dara-12. Thus, the potato plants actively expressing the gene of Arabidopsis phytochrome B apoprotein (PHYB) demonstrated a higher resistance of photosynthetic apparatus to UV-B radiation compared to nontransformed plants. The elevated UV-B tolerance is most likely related to the increased leaf content of chlorophyll, carotenoids, and flavonoids.

Improving the efficiency of growing plants in phytotrons is largely linked to the introduction of advanced technologies, providing the optimization of the light conditions. The use of modern light sources such as light emitting diodes (LEDs) or induction lamps can reduce the energy consumption for growing plants due to the high light output, long work and control of the spectrum of irradiation. Comparative studies of growth processes and activity of the photosynthetic apparatus of plants of Basil (Ocimum basilicum L.) variety Ararat, when using LEDs and induction lamps with an energy capacity of 64 and 150 W, respectively were done. The light intensity was 80-85 μmol photons• m-2•s-1 under LEDs white light and 240-260 μmol photons•m-2•s-1 under induction lamps. CO2 gas exchange, the content of pigments and growth processes in plants grown in hydroponic conditions were estimated. The rate of photosynthesis under induction lamp was more than 2 times higher than under LEDs (2.6±0.4 and 1.2±0.3 μmol CO2•m-2•s-1, respectively), although there was a slight decrease in the content of the chlorophylls (a + b) to 0.71±0.01 mg/g dry weigh compared to 0.83±0.03 for LEDs. More than twofold increase in the rate of photosynthesis did not result in the same increase in the accumulation of plant biomass that may be connected with different light saturation of growth processes and photosynthesis. The efficiency of biomass accumulation per 1 W of energy power for a period of 40 days under LEDs was 1.7 times higher than under the irradiation of induction lamp. Significant difference in photosynthetic efficiency was not detected. At elevated concentrations of CO2 the rates of photosynthesis were comparable as a result of higher values of the quantum yield of photosynthesis, activity ribulose-1,5-bisphosphate carboxylase/oxygenase (RUBISCO) and the efficiency of carboxylation in LEDs plants. The investigation of structural and functional parameters of the photosynthetic apparatus and growth processes under the action of different light intensity showed the complex nature of the changes of some processes during long-term exposure to light of different intensity and spectral composition.

Structural and functional parameters and redox homeostasis in leaves of Artemisia santonica L. under environment conditions of Elton lake (the southeast region of the European part of Russia) were measured. The highest photosynthetic apparatus (PA) activity in A. santonica leaves on CO2 gas exchange as well as the highest content of green pigments was observed in the morning. Maximum share of violaxanthin cycle key pigments – zeaxanthin (Zx) and antheraxanthin (Ax) was observed in the afternoon and decreased in the evening. Lipids/chlorophyll (Chl) ratio increased in the evening due to the decrease in Chl concentration, and content of linolenic acid (С18:3n3) was decreased in the middle of the day. The content of TBA-reacting products increased 1.4-fold in the middle of the day, and decreased approximately 2-fold in the evening. The decrease of the activity was observed in diurnal dynamics of superoxide dismutase (SOD) and polyphenol oxidase (PPO). Increased accumulation of phenols and flavonoids, as well as free amino acids (FAA) in A. santonica leaves was observed in the middle of the day. Thus, the ability of A. santonica plants to resist the soil salinization, high levels of solar illumination and temperature consists of a number of protectively-adaptive reactions of metabolic and photosynthetic control.

The photosynthetic responses of 25-day-old Arabidopsis phyA phyB double mutant (DM) compared with the wild type (WT) to UV-B radiation (1Wm-2, 30min) were investigated. UV-B irradiation led to reduction of photosystem 2 (PS-2) activity and the photosynthetic rate. In plants grown under both white and red light (λm - 660nm) the reduction was greater in DM plants compared to the WT. Without UV-B irradiation a decrease in PS-2 activity was observed in DM grown under RL only. It is assumed that the lower content of UV-absorbing pigments and carotenoids observed in DM may be one of the reasons of reduced PS-2 resistance to UV-B. Higher decrease in activities under UV in DM plants grown under RL compared to DM plants grown under white light is likely due to the lack of activity of cryptochromes in plants grown under red light. Rates of post-stress recovery of photosynthetic activity of DM compared with WT plants under white and red light of low intensity were studied. Almost complete recovery of the activity was found which was not observed under dark conditions and in the presence of a protein synthesis inhibitor, chloramphenicol. It is assumed that phytochrome system participates in stress-protective mechanisms of the photosynthetic apparatus to UV-radiation.

Hordeum vulgare L. cv. Bartom seedlings grown on a substrate without or with zeolite were exposed to 450 and 1,000 µmol of Cd(NO3)2. Adding the zeolite to a substrate (+Si) resulted in the accumulation of mono- and polysilicic acids in the leaves, an increase in the growth of seedlings and biomass production, a decrease of the contents of thiobarbituric acid reactive substances (TBARs), and an increase in the activities of the antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX) and guaiacol peroxidase (GPX). The negative effects of Cd2+, which were reflected in loss of chlorophyll contents and a decrease of the photosynthesis rate, as well as an increase of TBARs contents were observed in the (−Si)-plants to a greater extent than in the (+Si)-plants. The activities of SOD, APX and GPX increased in the barley leaves of (−Si)- and (+Si)-seedlings with an increase of Cd2+ concentration in the acting solution. At the same time the values of the ratios between TBARs concentrations and the activities of SOD, APX and GPX in (−Si)-plants were higher than that in (+Si)-plants both under optimal conditions and with Cd stress. This suggests that the use of Si-rich mineral zeolite for growing barley stimulates metabolism and increases the resistance of plants to cadmium stress through a shift in the dynamic equilibrium between the rate of oxidative destruction and the activity of antioxidant systems in favor of the latter.

The structural-functional characteristics of the cells of wild type CC-124 and Brc-1 mutant of the unicellular green algae Chlamydomonas reinhardtii while growing in the dark and light were studied. It has been shown that the cells of the wild type in heterotrophic and mixotrophic growth conditions had a well developed structure and high functional activity due to the ability of the cells to synthesize chlorophyll both in the light and in the dark. The cells of Brc-1 mutant lost their ability to synthesize chlorophyll in the dark and the cells' color was orange due to brc-1 mutation in the nuclear gene LTS3 that regulated the activity of Mg-chelatase enzyme. In the dark the mutant cells accumulated protoporphyrin IX and had a weakly developed structure with low functional activity. It has been ascertained that due to high content of protoporphyrin IX even a short-term exposure of the cells of Brc-1 mutant to the light was accompanied by very strong destructive changes in all the membranes in a cell: plasmalemma, chloroplast, mitochondrion, shells of the nucleus and vacuoles. The reasons of these significant damages of the membrane components and O2-gas exchange in the cells of Brc-1 mutant are discussed.

The effect of preillumination with low intensity (10μmol quanta m(-2)s(-1), 10min) light of different wavelengths in the spectral range of 550-730nm on photosynthesis and activity of PSII, the content of photosynthetic pigments and H2O2, as well as the peroxidase activity in the leaves of 26-d-old Arabidopsis thaliana wild-type (WT) plants in response to UV-A radiation was studied. UV-A decreased the activity of the PSII, the content of Chl a, Chl b and carotenoids, as well as increased the peroxidase activity and H2O2 level in the WT leaves. Preillumination of the leaves with red light (RL, λmax=664nm) reduced the inhibitory effect of UV radiation on photosynthesis and activity of the PSII, indicated by delayed light emission as well as the H2O2 level, but increased the peroxidase activity in the leaves compared to illumination by UV radiation only. Illumination with RL alone and the subsequent exposure of plants to darkness increased the peroxidase activity and the transcription activity of genes of the transcription factors APX1 and HYH. Preillumination of leaves with RL, then far red light (FRL, λmax=727nm) partially compensated the effect of the RL for all studied parameters, suggesting that the active form of phytochrome (PFR) is involved in these processes. Preillumination with the wavelengths of 550, 594 and 727nm only did not have a marked effect on photosynthesis. The hy2 mutant of Arabidopsis with reduced synthesis of the phytochrome B chromophore showed decreased resistance of PSII to UV-A compared with the WT of Arabidopsis. UV radiation reduced Chl a fluorescence much faster in the hy2 mutant compared to the WT. Preillumination of the hy2 mutant with RL did not affect the PSII activity and H2O2 level in UV-irradiated leaves. It is assumed that the formation of the increased resistance of the photosynthetic apparatus of Arabidopsis to UV-A radiation involves PFR and the antioxidant system of plants, partly by inducing transcriptional activity of some antioxidant and transcription factors genes.

We studied the influence of prolonged (a few weeks) and short-term (a few hours) periodical elevation of the ambient CO2 concentration ([Ca]) on the photosynthetic apparatus and carbohydrate content in the third leaf of three-week-old cucumber (Cucumis sativus L.) plants. On the basis of experimental data and subsequent modeling, we revealed the limiting processes in the photosynthetic apparatus functioning: Rubisco activity, the rate of ribulose bisphosphate (CO2 acceptor) regeneration, the rate of triose phosphate utilization in the Calvin cycle, and the influence of stomata on the photosynthesis rate. An increase in soluble carbohydrate content and a decrease in starch accumulation at a short-term [Ca] elevation indicate an important role of carbohydrate accumulation and their partition between organs in the regulation of the photosynthesis. We concluded that periodic [Ca] elevation can be used to improve plant productivity.

The 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.

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.

CO2 exchange, variable chlorophyll fluorescence, the intensity of lipid peroxidation (POL), and the activity of antioxidant enzymes in leaves of two-week-old pea seedlings (Pisum sativum L.) exposed to 0.01, 0.1, and 1 mM aqueous solutions of Cd(NO3)2 for 2 h were studied. Incubation with Cd2+ ions resulted in a reduction of the maximum quantum efficiency of photosynthesis, CO2 uptake rate, and photosystem II (PSII) activity, as assessed by F v/F 0 ratio. The intensity of POL in leaves of all treated seedlings was below or close to the control level. The activity of superoxide dismutase (SOD) and glutathione reductase (GR) increased in all treatments; the activity of ascorbate peroxidase (AP) exceeded the control level only in seedlings exposed to the high Cd2+ concentration (1 mM), and the activity of peroxidase increased at the low concentration (0.01 mM). We found that the reduction in the activity of the photosynthetic apparatus under conditions of 2-h-long Cd2+-induced stress was not related to an intensification of POL processes. It was concluded that stimulation of the activity of antioxidant enzymes—SOD, GR, AP, and peroxidase—is a pathway for pea plant adaptation to toxic effect of cadmium.

Quantitative and qualitative characteristics of pigment composition and gas exchange were studied in chlorophyll mutants of pea, Pisum sativum L.: chlorotica 2004 and 2014. The mutant 2004 had light-green color, whereas the mutant 2014 has yellow-green leaves and stems; they contained about 80 and 50% of chlorophyll, respectively, compared to the initial line. cv. Torsdag. Leaves of the mutant 2004 had significantly lower carotene content and accumulated more lutein and violaxanthin. In the mutant 2014, the contents of chlorophyll and all carotenoids were reduced almost proportionally. The quantum efficiency of photosynthesis was by 29–30% lower in the mutants, and it was 1.5–2 times higher in F1 hybrids, as compared to control plants. Our data allow us to conclude that the impairment of photosynthesis in the mutant 2014 is caused by the changed mesostructure of leaves, whereas in the mutant 2004, it may be caused by an impairment of photosystem reaction centers.

Seedlings of 10-day-old lettuce ( Lactuca sativa L., cultivar Berlin) were preilluminated by low intensity red light ( λ max = 660 nm, 10 min, 5 μmol quanta m −2 s −1 ) and far-red light ( λ max = 730 nm, 10 min, 5 μmol quanta m −2 s −1 ) to study the effect of pre-treatment on photosynthesis, photochemical activity of photosystem II (PSII), the contents of photosynthetic and UV-A-absorbing pigments (UAPs) and H 2 O 2 , as well as total and ascorbate peroxidase activities in cotyledonary leaves of seedlings exposed to UV-A. UV radiation reduced the photosynthetic rate ( P n ), the activity of PSII, and the contents of Chl a and b , carotenoids and UAPs in the leaves, but increased the content of H 2 O 2 and the total peroxidase activity. Preillumination with red light removed these effects of UV. In turn, the illumination with red light, then far-red light removed the effect of the red light. Illumination with red light alone increased the content of UAPs, as well as peroxidase activity. It is suggested that higher resistance of the lettuce photosynthetic apparatus to UV-A radiation is associated with involvement of the active form of phytochrome B, thereby increasing peroxidase activities as well as UAPs and saving preservation of photosynthetic pigment contents due to pre-illumination with red light.

The extent of damage caused to the photosynthetic machinery of 10-d-old wheat seedlings by short-term exposure to mild heat, their capacity to recover from it and the possible roles of H2O2, SOD, catalase and ascorbate peroxidase on the recovery process were investigated. Seedlings were subjected to heat treatments at 40/42/44 °C for 20 min in the dark and allowed to grow for 72 h in light of different irradiances (40-800 μE m(-2) s(-1)) at 20 °C for recovery from heat induced damage. Complete or partial recovery of photosynthetic activities was observed in the seedlings treated at 40 °C and 42 °C, but not at 44 °C. Our data suggest that the balance between (pro)oxidant and antioxidant levels poised by heat stress subsequent light is the crucial factor for the extent of recovery from heat induced damage.

The nature of photosynthetic recovery was investigated in 10-d-old wheat (Triticum aestivum L., cv. Moskovskaya-35) seedlings exposed to temperatures of 40 and 42 degrees C for 20 min and to temperature 42 degrees C for 40 min in the dark. The aftereffect of heat treatment was monitored by growing the heat-treated plants in low/moderate/high light at 20 degrees C for 72h. The net photosynthetic rates (P(N)) and the fluorescence ratios F(v)/F(m) were evaluated in intact primary leaves and the rates of cyclic and non-cyclic photophosphorylation were measured in the isolated thylakoids. At least two temporally separated steps were identified in the path of recovery from heat stress at 40 and 42 degrees C in the plants growing in high and moderate/high light, respectively. Both photochemical activity of the photosystem II (PSII) and the activity of CO(2) assimilation system were lowered during the first step in comparison with the corresponding activities immediately after heat treatment. During the second step, the photosynthetic activities completely or partly recovered. Recovery from heat stress at 40 degrees C was accompanied by an appreciably higher rate of cyclic photophosphorylation in comparison with control non-heated seedlings. In pre-heated seedlings, the tolerance of the PSII to photoinhibition was higher than in non-treated ones. The mode of acclimation to different light intensities after heat exposures is analyzed.