Influence of Additional White, Red and Far-Red Light on Growth, Secondary Metabolites and Expression of Hormone Signaling Genes in Scots Pine under Sunlight.

The influence of short-term additional white (WL), red (RL) and far-red (FRL) light and combined RL+FRL on the physiological morphological and molecular characteristics of two-year-old Scots pine plants grown in a greenhouse under sunlight was studied. Additional RL and RL+FRL increased the number of xylem cells, transpiration and the expression of a group of genes responsible for the biosynthesis and signaling of auxins (AUX/IAA, ARF3/4, and ARF16) and brassinosteroids (BR-α-RED and BRZ2), while the expression of genes related to the signaling pathway related to jasmonic acid was reduced. Additionally, WL, RL and RL+FRL increased the content of proanthocyanidins and catechins in young needles; however, an increase in the expression of the chalcone synthase gene (CHS) was found under RL, especially under RL+FRL, which possibly indicates a greater influence of light intensity than observed in the spectrum. Additional WL increased photosynthetic activity, presumably by increasing the proportion and intensity of blue light; at the same time, the highest transpiration index was found under RL. The results obtained indicate that the combined effect of additional RL+FRL can accelerate the development of pine plants by increasing the number of xylem cells and increasing the number of aboveground parts but not the photosynthetic activity or the accumulation of secondary metabolites.

Potential Role of Phytochromes A and B and Cryptochrome 1 in the Adaptation of Solanum lycopersicum to UV-B Radiation.

UV-B causes both damage to the photosynthetic apparatus (PA) and the activation of specific mechanisms that protect the PA from excess energy and trigger a cascade of regulatory interactions with different photoreceptors, including phytochromes (PHYs) and cryptochromes (CRYs). However, the role of photoreceptors in plants' responses to UV-B radiation remains undiscovered. This study explores some of these responses using tomato photoreceptor mutants (phya, phyb1, phyab2, cry1). The effects of UV-B exposure (12.3 µmol (photons) m-2 s-1) on photosynthetic rates and PSII photochemical activity, the contents of photosynthetic and UV-absorbing pigments and anthocyanins, and the nonenzymatic antioxidant capacity (TEAC) were studied. The expression of key light-signaling genes, including UV-B signaling and genes associated with the biosynthesis of chlorophylls, carotenoids, anthocyanins, and flavonoids, was also determined. Under UV-B, phyab2 and cry1 mutants demonstrated a reduction in the PSII effective quantum yield and photosynthetic rate, as well as a reduced value of TEAC. At the same time, UV-B irradiation led to a noticeable decrease in the expression of the ultraviolet-B receptor (UVR8), repressor of UV-B photomorphogenesis 2 (RUP2), cullin 4 (CUL4), anthocyanidin synthase (ANT), phenylalanine ammonia-lease (PAL), and phytochrome B2 (PHYB2) genes in phyab2 and RUP2, CUL4, ANT, PAL, and elongated hypocotyl 5 (HY5) genes in the cry1 mutant. The results indicate the mutual regulation of UVR8, PHYB2, and CRY1 photoreceptors, but not PHYB1 and PHYA, in the process of forming a response to UV-B irradiation in tomato.

Impact of varying light spectral compositions on photosynthesis, morphology, chloroplast ultrastructure, and expression of light-responsive genes in Marchantia polymorpha.

Marchantia polymorpha is a convenient model for studying light of different spectral compositions on various physiological and biochemical processes because its photoreceptor system is vastly simplified. The influence of red light (RL, 660 nm), far-red light (FRL, 730 nm), blue light (BL, 450 nm), and green light (GL, 525 nm) compared to white light (high-pressure sodium light (HPSL), white LEDs (WL 450 + 580 nm) and white fluorescent light (WFL) on photosynthetic and transpiration rates, photosystem II (PSII) activity, photomorphogenesis, and the expression of light and hormonal signaling genes was studied. The ultrastructure of the chloroplasts in different tissues of the gametophyte M. polymorpha was examined. FRL led to the formation of agranal chloroplasts (in the epidermis and the chlorenchyma) with a high starch content (in the parenchyma), which led to a reduced intensity of photosynthesis. BL increased the transcription of genes for the biosynthesis of secondary metabolites - chalcone synthase (CHS), cellulose synthase (CELL), and L-ascorbate peroxidase (APOX3), which is consistent with the increased activity of low-molecular weight antioxidants. FRL increased the expression of phytochrome apoprotein (PHY) and cytokinin oxidase (CYTox) genes, but the expression of the phytochrome interacting factor (PIF) gene decreased, which was accompanied by a significant change in gametophyte morphology. Analysis of crosstalk gene expression, and changes in morphology and photosynthetic activity was carried out.

Effects of iron oxide nanoparticles (Fe3O4) and salinity on growth, photosynthesis, antioxidant activity and distribution of mineral elements in wheat (Triticum aestivum).

Soil salinisation is one of the main abiotic stresses decreasing crop productivity. Here, we show that the plant treatment with iron oxide (Fe3 O4 ) nanoparticles (NPs) may be a promising solution for reducing the negative impact of soil salinity on plant performance. For this purpose, effects of the NPs on growth, photosynthesis, pro-/antioxidant, redox balance and the content of mineral elements in 19-day-old wheat (Triticum aestivum ) plants under soil salinity were studied. Seed treatment with NPs (200 and 500mg L-1 ) enhanced growth and photosynthetic rate in leaves. Moderate salinity stress (150mMNaCl) led to a decrease in plant biomass as well as the rate of photosynthesis and PSII activity; leaf photosynthetic characteristics were also suppressed by lower (75mMNaCl) salinity treatment. However, seed pre-treatment with the NPs partially eliminated the negative effect of the salt on growth, PSII activity and photosynthesis. Also, we observed a decrease in the content of malondialdehyde (MDA) and an increase in ascorbate and total peroxidase activity in the plant leaves upon combined treatment with NaCl and the NPs compared with treatment with NaCl alone. The combined treatment with the NPs and salinity also led to a noticeable increase in the content of Fe and Mn in the shoot. It was concluded that Fe3 O4 NPs can enhance plant growth by improving photosynthetic characteristics, antioxidant balance and the availability of iron and manganese ions, under conditions of soil salinisation.

Probing the Influence of Novel Organometallic Copper(II) Complexes on Spinach PSII Photochemistry Using OJIP Fluorescence Transient Measurements.

Modern agricultural cultivation relies heavily on genetically modified plants that survive after exposure to herbicides that kill weeds. Despite this biotechnology, there is a growing need for new sustainable, environmentally friendly, and biodegradable herbicides. We developed a novel [CuL2]Br2 complex (L = bis{4H-1,3,5-triazino[2,1-b]benzothiazole-2-amine,4-(2-imidazole) that is active on PSII by inhibiting photosynthetic oxygen evolution on the micromolar level. [CuL2]Br2 reduces the FV of PSII fluorescence. Artificial electron donors do not rescind the effect of [CuL2]Br2. The inhibitory mechanism of [CuL2]Br2 remains unclear. To explore this mechanism, we investigated the effect of [CuL2]Br2 in the presence/absence of the well-studied inhibitor DCMU on PSII-containing membranes by OJIP Chl fluorescence transient measurements. [CuL2]Br2 has two effects on Chl fluorescence transients: (1) a substantial decrease of the Chl fluorescence intensity throughout the entire kinetics, and (2) an auxiliary "diuron-like" effect. The initial decrease dominates and is observed both with and without DCMU. In contrast, the "diuron-like" effect is small and is observed only without DCMU. We propose that [CuL2]Br2 has two binding sites for PSII with different affinities. At the high-affinity site, [CuL2]Br2 produces effects similar to PSII reaction center inhibition, while at the low-affinity site, [CuL2]Br2 produces effects identical to those of DCMU. These results are compared with other PSII-specific classes of herbicides.

The biomineralization of silica induced stress tolerance in plants: a case study for aluminum toxicity.

Biomineralization in plant roots refers to the process of cell-induced self-assembly to form nanostructures on the root surface. Silicon (Si) is the second most abundant element in soils, and beneficial to plant growth. Meanwhile, silicon is shown to participate in the process of biomineralization, which is useful for improving mechanical strength and alleviating biotic and abiotic stress, for example silicic acid polymerizes to form amorphous silica (SiO2-nH2O) in the process of growing to resist fungi and environmental stress. This process alters physical and chemical properties of cell wall. However, the mechanistic basis of this process remains unclear. Aluminum toxicity is a major constraint affecting plant performance in acid soil. This paper summarizes recent research advances in the field of plant biomineralization and describes the effects of silicon biomineralization on plant aluminum tolerance and its adaptive significance, using aluminum toxicity as a case study.

The Effect of Short-Term Heating on Photosynthetic Activity, Pigment Content, and Pro-/Antioxidant Balance of A. thaliana Phytochrome Mutants.

The effects of heating (40 °C, 1 and 2 h) in dark and light conditions on the photosynthetic activity (photosynthesis rate and photosystem II activity), content of photosynthetic pigments, activity of antioxidant enzymes, content of thiobarbituric acid reactive substances (TBARs), and expression of a number of key genes of antioxidant enzymes and photosynthetic proteins were studied. It was shown that, in darkness, heating reduced CO2 gas exchange, photosystem II activity, and the content of photosynthetic pigments to a greater extent in the phyB mutant than in the wild type (WT). The content of TBARs increased only in the phyB mutant, which is apparently associated with a sharp increase in the total peroxidase activity in WT and its decrease in the phyB mutant, which is consistent with a noticeable decrease in photosynthetic activity and the content of photosynthetic pigments in the mutant. No differences were indicated in all heated samples under light. It is assumed that the resistance of the photosynthetic apparatus to a short-term elevated temperature depends on the content of PHYB active form and is probably determined by the effect of phytochrome on the content of low-molecular weight antioxidants and the activity of antioxidant enzymes.

Influence of Light of Different Spectral Compositions on Growth Parameters, Photosynthetic Pigment Contents and Gene Expression in Scots Pine Plantlets.

The photoreceptors of red light (phytochromes) and blue light (cryptochromes) impact plant growth and metabolism. However, their action has been barely studied, especially in coniferous plants. Therefore, the influence of blue (maximum 450 nm), red (maximum 660 nm), white light (maxima 450 nm + 575 nm), far-red light (maximum 730 nm), white fluorescent light and dark on seed germination, growth, chlorophyll and carotenoid contents, as well as the transcript levels of genes involved in reception, photosynthesis, light and hormonal signaling of Scots pine plantlets, was investigated. The highest values of dry weight, root length and photosynthetic pigment contents were characteristic of 9-day-old plantlets grown under red light, whereas in the dark plantlet length, seed vigor, seed germination, dry weight and pigment contents were decreased. Under blue and white lights, the main studied morphological parameters were decreased or close to red light. The cotyledons were undeveloped under dark conditions, likely due to the reduced content of photosynthetic pigments, which agrees with the low transcript levels of genes encoding protochlorophyllide oxidoreductase (PORA) and phytoene synthase (PSY). The transcript levels of a number of genes involved in phytohormone biosynthesis and signaling, such as GA3ox, RRa, KAO and JazA, were enhanced under red light, unlike under dark conditions. We suggest that the observed phenomena of red light are the most important for the germination of the plantlets and may be based on earlier and enhanced expression of auxin, cytokinin, gibberellin and jasmonate signaling genes activated by corresponding photoreceptors. The obtained results may help to improve reforestation technology; however, this problem needs further study.

Effects of Novel Photosynthetic Inhibitor [CuL2]Br2 Complex on Photosystem II Activity in Spinach.

The effects of the novel [CuL2]Br2 complex (L = bis{4H-1,3,5-triazino [2,1-b]benzothiazole-2-amine,4-(2-imidazole)}copper(II) bromide complex) on the photosystem II (PSII) activity of PSII membranes isolated from spinach were studied. The absence of photosynthetic oxygen evolution by PSII membranes without artificial electron acceptors, but in the presence of [CuL2]Br2, has shown that it is not able to act as a PSII electron acceptor. In the presence of artificial electron acceptors, [CuL2]Br2 inhibits photosynthetic oxygen evolution. [CuL2]Br2 also suppresses the photoinduced changes of the PSII chlorophyll fluorescence yield (FV) related to the photoreduction of the primary quinone electron acceptor, QA. The inhibition of both characteristic PSII reactions depends on [CuL2]Br2 concentration. At all studied concentrations of [CuL2]Br2, the decrease in the FM level occurs exclusively due to a decrease in Fv. [CuL2]Br2 causes neither changes in the F0 level nor the retardation of the photoinduced rise in FM, which characterizes the efficiency of the electron supply from the donor-side components to QA through the PSII reaction center (RC). Artificial electron donors (sodium ascorbate, DPC, Mn2+) do not cancel the inhibitory effect of [CuL2]Br2. The dependences of the inhibitory efficiency of the studied reactions of PSII on [CuL2]Br2 complex concentration practically coincide. The inhibition constant Ki is about 16 µM, and logKi is 4.8. As [CuL2]Br2 does not change the aromatic amino acids' intrinsic fluorescence of the PSII protein components, it can be proposed that [CuL2]Br2 has no significant effect on the native state of PSII proteins. The results obtained in the present study are compared to the literature data concerning the inhibitory effects of PSII Cu(II) aqua ions and Cu(II)-organic complexes.

Effects of Iron Oxide Nanoparticles (Fe3O4) on Growth, Photosynthesis, Antioxidant Activity and Distribution of Mineral Elements in Wheat (Triticum aestivum) Plants.

Engineered nanoparticles (NPs) are considered potential agents for agriculture as fertilizers and growth enhancers. However, their action spectrum differs strongly, depending on the type of NP, its concentrations, and plant species per se, ranging from growth stimulation to toxicity. This work aimed to investigate effects of iron oxide (Fe3O4) NPs on growth, photosynthesis, respiration, antioxidant activity, and leaf mineral content of wheat plants. Wheat seeds were treated with NP for 3 h and plants were grown in the soil at two light intensities, 120 and 300 µmol (photons) m-2·s-1, followed by physiological assessment at several time points. High NP treatment (200 and 500 mg·L-1) enhanced plant growth, photosynthesis and respiration, as well as increasing the content of photosynthetic pigments in leaves. This effect depended on both the light intensity during plant growth and the age of the plants. Regardless of concentration and light intensity, an effect of NPs on the primary photochemical processes was not observed. Seed treatment with NP also led to increased activity of ascorbate peroxidase and reduced malondialdehyde (MDA) content in roots and leaves. Treatment with Fe3O4 also led to noticeable increases in the leaf Fe, P, and K content. It is concluded that iron oxide (Fe3O4)-based NP could enhance plant growth by improving photosynthetic performance and the availability of Fe and P.

Influence of Light of Different Spectral Compositions on the Growth, Photosynthesis, and Expression of Light-Dependent Genes of Scots Pine Seedlings.

Varying the spectral composition of light is one of the ways to accelerate the growth of conifers under artificial conditions for the development of technologies and to obtain sustainable seedlings required to preserve the existing areas of forests. We studied the influence of light of different quality on the growth, gas exchange, fluorescence indices of Chl a, and expression of key light-dependent genes of Pinus sylvestris L. seedlings. It was shown that in plants growing under red light (RL), the biomass of needles and root system increased by more than two and three times, respectively, compared with those of the white fluorescent light (WFL) control. At the same time, the rates of photosynthesis and respiration in RL and blue light (BL) plants were lower than those of blue red light (BRL) plants, and the difference between the rates of photosynthesis and respiration, which characterizes the carbon balance, was maximum under RL. RL influenced the number of xylem cells, activated the expression of genes involved in the transduction of cytokinin (Histidine-containing phosphotransfer 1, HPT1, Type-A Response Regulators, RR-A) and auxin (Auxin-induced protein 1, Aux/IAA) signals, and reduced the expression of the gene encoding the transcription factor phytochrome-interacting factor 3 (PIF3). It was suggested that RL-induced activation of key genes of cytokinin and auxin signaling might indicate a phytochrome-dependent change in cytokinins and auxins activity.

Impact of high irradiance and UV-B on the photosynthetic activity, pro-/antioxidant balance and expression of light-activated genes in Arabidopsis thaliana hy4 mutants grown under blue light.

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.

Effect of high-intensity light and UV-B on photosynthetic activity and the expression of certain light-responsive genes in A. thaliana phyA and phyB mutants.

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.

Deficiencies in phytochromes A and B and cryptochrome 1 affect the resistance of the photosynthetic apparatus to high-intensity light in Solanum lycopersicum.

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.

24-Epibrassinolide alleviates the toxic effects of NaCl on photosynthetic processes in potato plants.

Brassinosteroids are promising agents for alleviating the negative effects of salinity on plants, but the mechanism of their protective action is far from being understood. We investigated the effect of pretreatment with 24-epibrassinolide (24-EBL) on the photosynthetic and physiological parameters of potato plants under progressive salinity stress caused by root application of 100 mM NaCl. Salinity clearly inhibited primary photosynthetic processes in potato plants by reducing the contents of photosynthetic pigments, photosynthetic electron transport and photosystem II (PSII) maximal and effective quantum yields. These negative effects of salinity on primary photosynthetic processes were mainly due to toxic ionic effects on the plant's ability to oxidize the plastoquinone pool. Pretreatment with 24-EBL alleviated this stress effect and allowed the maintenance of plastoquinone pool oxidation and the efficiency of photosystem II photochemistry to be at the same levels as those in unstressed plants; however, the pretreatment did not affect the photosynthetic pigment content. 24-EBL pretreatment clearly alleviated the decrease in leaf osmotic potential under salinity stress. The stress-induced increases in lipid peroxidation and proline contents were not changed under brassinosteroid pretreatment. However, 24-EBL pretreatment increased the peroxidase activity and improved the K+/Na+ ratio in potato leaves, which were likely responsible for the protective 24-EBL action under salt stress.

Influence of photoluminophore-modified agro textile spunbond on growth and photosynthesis of cabbage and lettuce plants.

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.

Comparative photosynthetic responses of Norway spruce and Scots pine seedlings to prolonged water deficiency.

Stressors of different natures, including drought stress, substantially compromise the ability of plants to effectively and safely utilize light energy. We investigated the influence of water stress on the photosynthetic processes in Picea abies and Pinus sylvestris, two species with contrasting drought sensitivities. Spruce and pine seedlings were exposed to polyethylene glycol 6000-induced water deficits of different intensities and durations. The maintenance of photosystem I (PSI) oxidation in spruce required increased photosynthetic control and led to the increased reduction of the plastoquinone pool, which was not the case in pine seedlings. As a result of increased excitation pressure, photosystem II (PSII) inactivation was observed in spruce plants, whereas in pine, the decreased PSII photochemistry was likely due to sustained non-photochemical quenching. Downregulation of PSII photochemistry and maintenance of PSI in an oxidized state were linked with the prevention of oxidative stress, even under severe water deficit. The decreased photosynthetic pigment content and photosynthetic gene expression suggested the coordinated downregulation of photosynthetic apparatus components under water stress to reduce light energy absorption. In summary, the observed adaptative mechanisms of pine and spruce to water stress may be similar to the well-studied adaptative mechanisms to winter stress, which may indicate the universality of protective mechanisms under various stresses in conifers.

Impact of UV-B radiation on the photosystem II activity, pro-/antioxidant balance and expression of light-activated genes in Arabidopsis thaliana hy4 mutants grown under light of different spectral composition.

The effect of UV-B irradiation on the photosystem II (PSII) activity, the content of photosynthetic and UV-absorbing pigments (UAPs), activity of antioxidant enzymes such as catalase (CAT) and peroxidase (POD), as well as H2O2 content in 25-day-old wild type (WT) and the cryptochrome 1 (Cry1) mutant hy4 of Arabidopsis thaliana Col-0 plants was studied. In addition, expression of photoreceptor genes Cry1, Cry2 and UVR8, photomorphogenetic gene COP1 and transcription factors genes HY5, HYH, the gene of chlorophyll-binding protein of the PSII CAB1 as well as the flavonoid biosynthesis genes CHS, PAL and thylakoid ascorbate peroxidase gene tAPX was examined. It has been shown that UV-B leads to a decrease in the photochemical activity of PSII (FV/FM) and the PSII performance index (PIABS) of WT plants grown on white (WL) and red (RL) light and also hy4 mutants grown on WL, RL and blue light (BL). In plants grown on BL and WL, the decrease in the PSII photochemical activity was significantly greater in hy4 compared to WT. The PSII of WT plants grown in BL was resistant to UV-B. The UAPs content of hy4 grown on BL and WL was lower than that in WT. The POD and CAT activities of WT grown in BL were significantly higher than in the mutant. In WT and hy4 plants grown in RL, a noticeable difference in these enzymes activity was not found. In both types of plants grown in BL and RL, the expression of photomorphogenetic genes HYH, HY5 markedly increased after UV-B treatment but the expression of the UV-B photoreceptor gene UVR8 was reduced in hy4 grown in BL and RL. It is assumed that reduced resistance of PSII in hy4 plants grown in BL and WL can be associated with low UAPs content as well as lowered POD and CAT activities. In addition, we suggest the lowered expression of UVR8 and COP1 genes caused by Cry1 deficiency leads to a shift of balance of oxidants and antioxidants towards oxidants.

Impact of weak water deficit on growth, photosynthetic primary processes and storage processes in pine and spruce seedlings.

We investigated the influence of 40 days of drought on growth, storage processes and primary photosynthetic processes in 3-month-old Scots pine and Norway spruce seedlings growing in perlite culture. Water stress significantly affected seedling water status, whereas absolute dry biomass growth was not substantially influenced. Water stress induced an increase in non-structural carbohydrate content (sugars, sugar alcohols, starch) in the aboveground part of pine seedlings in contrast to spruce seedlings. Due to the relatively low content of sugars and sugar alcohols in seedling organs, their expected contribution to osmotic potential changes was quite low. In contrast to biomass accumulation and storage, photosynthetic primary processes were substantially influenced by water shortage. In spruce seedlings, PSII was more sensitive to water stress than PSI. In particular, electron transport in PSI was stable under water stress despite the substantial decrease of electron transport in PSII. The increase in thermal energy dissipation due to enhancement of non-photochemical quenching (NPQ) was evident in both species under water stress. Simultaneously, the yields of non-regulated energy dissipation in PSII were decreased in pine seedlings under drought. A relationship between growth, photosynthetic activities and storage processes is analysed under weak water deficit.

The impact of the phytochromes on photosynthetic processes.

This review describes the phytochrome system in higher plants and cyanobacteria and its role in regulation of photosynthetic processes and stress protection of the photosynthetic apparatus. A relationship between the content of the different phytochromes, the changes in the ratios of the physiologically active forms of phytochromes to their total pool and the resulting influence on photosynthetic processes is reviewed. The role of the phytochromes in the regulation of the expression of genes encoding key photosynthetic proteins, antioxidant enzymes and other components involved in stress signaling is elucidated.