Effect of preillumination with red light on photosynthetic parameters and oxidant-/antioxidant balance in Arabidopsis thaliana in response to UV-A

Adaptation processes in Halomicronema hongdechloris, an example of the light-induced optimization of the photosynthetic apparatus on hierarchical time scales

Oxygenic photosynthesis in Halomicronema hongdechloris, one of a series of cyanobacteria producing red-shifted Chl f, is adapted to varying light conditions by a range of diverse processes acting over largely different time scales. Acclimation to far-red light (FRL) above 700 nm over several days is mirrored by reversible changes in the Chl f content. In several cyanobacteria that undergo FRL photoacclimation, Chl d and Chl f are directly involved in excitation energy transfer in the antenna system, form the primary donor in photosystem I (PSI), and are also involved in electron transfer within photosystem II (PSII), most probably at the ChlD1 position, with efficient charge transfer happening with comparable kinetics to reaction centers containing Chl a. In H. hongdechloris, the formation of Chl f under FRL comes along with slow adaptive proteomic shifts like the rebuilding of the D1 complex on the time scale of days. On shorter time scales, much faster adaptation mechanisms exist involving the phycobilisomes (PBSs), which mainly contain allophycocyanin upon adaptation to FRL. Short illumination with white, blue, or red light leads to reactive oxygen species-driven mobilization of the PBSs on the time scale of seconds, in effect recoupling the PBSs with Chl f-containing PSII to re-establish efficient excitation energy transfer within minutes. In summary, H. hongdechloris reorganizes PSII to act as a molecular heat pump lifting excited states from Chl f to Chl a on the picosecond time scale in combination with a light-driven PBS reorganization acting on the time scale of seconds to minutes depending on the actual light conditions. Thus, structure-function relationships in photosynthetic energy and electron transport in H. hongdechloris including long-term adaptation processes cover 10-12 to 106 seconds, i.e., 18 orders of magnitude in time.

Interplay among photoreceptors determines the strategy of coping with excess light in tomato

This study investigates photoreceptor's role in the adaption of photosynthetic apparatus to high light (HL) intensity by examining the response of tomato wild type (WT) (Solanum lycopersicum L. cv. Moneymaker) and tomato mutants (phyA, phyB1, phyB2, cry1) plants to HL. Our results showed a photoreceptor-dependent effect of HL on the maximum quantum yield of photosystem II (Fv/Fm) with phyB1 exhibiting a decrease, while phyB2 exhibiting an increase in Fv/Fm. HL resulted in an increase in the efficient quantum yield of photosystem II (ΦPSII) and a decrease in the non-photochemical quantum yields (ΦNPQ and ΦN0) solely in phyA. Under HL, phyA showed a significant decrease in the energy-dependent quenching component of NPQ (qE), while phyB2 mutants showed an increase in the state transition (qT) component. Furthermore, ΔΔFv/Fm revealed that PHYB1 compensates for the deficit of PHYA in phyA mutants. PHYA signaling likely emerges as the dominant effector of PHYB1 and PHYB2 signaling within the HL-induced signaling network. In addition, PHYB1 compensates for the role of CRY1 in regulating Fv/Fm in cry1 mutants. Overall, the results of this research provide valuable insights into the unique role of each photoreceptor and their interplay in balancing photon energy and photoprotection under HL condition.

The crosstalk of far-red energy and signaling defines the regulation of photosynthesis, growth, and flowering in tomatoes

This study investigated the effect of light intensity and signaling on the regulation of far-red (FR)-induced alteration in photosynthesis. The low (LL: 440 μmol m-2 s-1) and high (HL: 1135 μmol m-2 s-1) intensity of white light with or without FR (LLFR: 545 μmol m-2 s-1 including 115 μmol m-2 s-1; HLFR: 1254 μmol m-2 s-1 + 140 μmol m-2 s-1) was applied on the tomato cultivar (Solanum Lycopersicon cv. Moneymaker) and mutants of phytochrome A (phyA) and phytochrome B (phyB1, and phyB2). Both light intensity and FR affected plant morphological traits, leaf biomass, and flowering time. Irrespective of genotype, flowering was delayed by LLFR and accelerated by HLFR compared to the corresponding light intensity without FR. In LLFR, a reduced energy flux through the electron transfer chain along with a reduced energy dissipation per reaction center improved the maximum quantum yield of PSII, irrespective of genotype. HLFR increased net photosynthesis and gas exchange properties in a genotype-dependent manner. FR-dependent regulation of hormones was affected by light signaling. It appeared that PHYB affected the levels of abscisic acid and salicylic acid while PHYA took part in the regulation of CK in FR-exposed plants. Overall, light intensity and signaling of FR influenced plants' photosynthesis and growth by altering electron transport, gas exchange, and changes in the level of endogenous hormones.

Ultraviolet-B radiation in relation to agriculture in the context of climate change: a review

Over the past few decades, the amount of ultraviolet-B radiation (UV-B) reaching the earth's surface has been altered due to climate change and stratospheric ozone dynamics. This narrow but highly biologically active spectrum of light (280-320 nm) can affect plant growth and development. Depletion of ozone and climate change are interlinked in a very complicated manner, i.e., significantly contributing to each other. The interaction of climate change, ozone depletion, and changes in UV-B radiation negatively affects the growth, development, and yield of plants. Furthermore, this interaction will become more complex in the coming years. The ozone layer reduction is paving a path for UV-B radiation to impact the surface of the earth and interfere with the plant's normal life by negatively affecting the plant's morphology and physiology. The nature and degree of the future response of the agricultural ecosystem to the decreasing or increasing UV-B radiation in the background of climate change and ozone dynamics are still unclear. In this regard, this review aims to elucidate the effects of enhanced UV-B radiation reaching the earth's surface due to the depletion of the ozone layer on plants' physiology and the performance of major cereals.

Chromatin Remodeling Complex SWR1 Regulates Root Development by Affecting the Accumulation of Reactive Oxygen Species (ROS)

Reactive oxygen species (ROS), a type of oxygen monoelectronic reduction product, play integral roles in root growth and development. The epigenetic mechanism plays a critical role in gene transcription and expression; however, its regulation of ROS metabolism in root development is still limited. We found that the chromatin remodeling complex SWR1 regulates root length and lateral root formation in Arabidopsis. Our transcriptome results and gene ontology (GO) enrichment analysis showed that the oxidoreductase activity-related genes significantly changed in mutants for the Arabidopsis SWR1 complex components, such as arp6 and pie1, and histone variant H2A.Z triple mutant hta8 hta9 hta11. The three encoding genes in Arabidopsis are the three H2A.Z variants hta8, hta9, and hta11. Histochemical assays revealed that the SWR1 complex affects ROS accumulation in roots. Furthermore, chromatin immunoprecipitation quantitative real-time PCR (ChIP-qPCR) analysis showed that the reduced H2A.Z deposition in oxidoreductase activity-related genes caused ROS to accumulate in arp6, pie1, and hta8 hta9 hta11. H2A.Z deposition-deficient mutants decreased after the trimethylation of lysine 4 on histone H3 (H3K4me3) modifications and RNA polymerase II (Pol II) enrichment, and increased after the trimethylation of lysine 27 on histone H3 (H3K27me3) modifications, which may account for the expression change in oxidoreductase activity-related genes. In summary, our results revealed that the chromatin complex SWR1 regulates ROS accumulation in root development, highlighting the critical role of epigenetic mechanisms.

Nano-priming as emerging seed priming technology for sustainable agriculture-recent developments and future perspectives

Nano-priming is an innovative seed priming technology that helps to improve seed germination, seed growth, and yield by providing resistance to various stresses in plants. Nano-priming is a considerably more effective method compared to all other seed priming methods. The salient features of nanoparticles (NPs) in seed priming are to develop electron exchange and enhanced surface reaction capabilities associated with various components of plant cells and tissues. Nano-priming induces the formation of nanopores in shoot and helps in the uptake of water absorption, activates reactive oxygen species (ROS)/antioxidant mechanisms in seeds, and forms hydroxyl radicals to loosen the walls of the cells and acts as an inducer for rapid hydrolysis of starch. It also induces the expression of aquaporin genes that are involved in the intake of water and also mediates H2O2, or ROS, dispersed over biological membranes. Nano-priming induces starch degradation via the stimulation of amylase, which results in the stimulation of seed germination. Nano-priming induces a mild ROS that acts as a primary signaling cue for various signaling cascade events that participate in secondary metabolite production and stress tolerance. This review provides details on the possible mechanisms by which nano-priming induces breaking seed dormancy, promotion of seed germination, and their impact on primary and secondary metabolite production. In addition, the use of nano-based fertilizer and pesticides as effective materials in nano-priming and plant growth development were also discussed, considering their recent status and future perspectives.

Effect of Photoconversion Coatings for Greenhouses on Electrical Signal-Induced Resistance to Heat Stress of Tomato Plants

The use of photoconversion coatings is a promising approach to improving the quality of light when growing plants in greenhouses in low light conditions. In this work, we studied the effect of fluoropolymer coatings, which produce photoconversion of UV-A radiation and violet light into blue and red light, on the growth and resistance to heat stress of tomato plants (Solanum lycopersicum L.). The stimulating effect of the spectrum obtained as a result of photoconversion on plant growth and the activity of the photosynthesis process are shown. At the same time, the ability to withstand heat stress is reduced in plants grown under a photoconversion coating. Stress electrical signals, which normally increase resistance, in such plants have a much weaker protective effect on the photosynthetic apparatus. The observed effects are apparently explained by a decrease in the concentration of H₂O₂ in plants grown using photoconversion technologies, which leads to a shift in the development program towards increased productivity to the detriment of the protective function. Thus, when using photoconversion technologies in agricultural practice, it is necessary to pay increased attention to maintaining stable conditions during plant cultivation.

Effect of Long-Term of He-Ne Laser Light Irradiation on Selected Physiological Processes of Triticale

In agriculture, the bio-stimulating properties of laser light increase the yielding capacity of crop species. The experiment aimed to determine the pre-sowing effect of irradiation time with laser He-Ne red light of triticale grains (×Triticosecale Wittm. ex A.Camus) on germination and selected morphological and physiological parameters of seedlings and plants grown from them. The highest values of germination indexes were found for grains irradiated with laser for 3 h. In relation to the control, the elongation growth of seedlings was stimulated in grains irradiated with light for 3 h and inhibited for 24 h. The values of the fresh and dry mass of seedlings changed depending on the exposure time. He-Ne light did not significantly affect the degree of destabilization of seedling cell membranes. Biometric analysis of plants grown from irradiated grains showed different reactions of triticale organs to the irradiation time. Red light clearly stimulated the increase in the value of organ mass. Chlorophyll content in leaves was higher in plants grown from grains irradiated for 3 h. Photosynthetic activity did not change significantly relative to the control. The fluorescence emission indexes were mostly lower than in the control, which indicated a positive effect of the laser. In general, the red light of the laser stimulated the morphology and physiology of seedlings and plants, although, for some features, long exposure to red light caused a slight reduction effect.

Effects of red and blue light on leaf anatomy, CO2 assimilation and the photosynthetic electron transport capacity of sweet pepper (Capsicum annuum L.) seedlings

BACKGROUND

The red (R) and blue (B) light wavelengths are known to influence many plant physiological processes during growth and development, particularly photosynthesis. To understand how R and B light influences plant photomorphogenesis and photosynthesis, we investigated changes in leaf anatomy, chlorophyll fluorescence and photosynthetic parameters, and ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) and Calvin cycle-related enzymes expression and their activities in sweet pepper (Capsicum annuum L.) seedlings exposed to four light qualities: monochromatic white (W, control), R, B and mixed R and B (RB) light with the same photosynthetic photon flux density (PPFD) of 300 μmol/m2·s.

RESULTS

The results revealed that seedlings grown under R light had lower biomass accumulation, CO2 assimilation and photosystem II (PSII) electron transportation compared to plants grown under other treatments. These changes are probably due to inactivation of the photosystem (PS). Biomass accumulation and CO2 assimilation were significantly enriched in B- and RB-grown plants, especially the latter treatment. Their leaves were also thicker, and photosynthetic electron transport capacity, as well as the photosynthetic rate were enhanced. The up-regulation of the expression and activities of Rubisco, fructose-1, 6-bisphosphatase (FBPase) and glyceraldehyde-phosphate dehydrogenase (GAPDH), which involved in the Calvin cycle and are probably the main enzymatic factors contributing to RuBP (ribulose-1, 5-bisphosphate) synthesis, were also increased.

CONCLUSIONS

Mixed R and B light altered plant photomorphogenesis and photosynthesis, mainly through its effects on leaf anatomy, photosynthetic electron transportation and the expression and activities of key Calvin cycle enzymes.

Responses of He-Ne laser on agronomic traits and the crosstalk between UVR8 signaling and phytochrome B signaling pathway in Arabidopsis thaliana subjected to supplementary ultraviolet-B (UV-B) stress

UV-B acclimation effects and UV-B damage repair induced by a 632.8-nm He-Ne laser were investigated in Arabidopsis thaliana plants in response to supplementary UV-B stress. There was an increasing trend in growth parameters in the combination-treated plants with He-Ne laser and UV-B light compared to those stressed with enhanced UV-B light alone during different developmental stages of plants. The photosynthetic efficiency (Pn) and survival rates of seedlings were significantly higher in the combination treatments than UV-B stress alone. The expression of UVR8, phytochrome B (PhyB), and their mediated signal responsive genes such as COP1, HY5, and CHS were also significantly upregulated in plants with the laser irradiation compared with other groups without the laser. Levels of flavonol accumulation in leaves and capsule yield of He-Ne laser-treated plants were increased. The phyB-9 mutants were more sensitive to enhanced UV-B stress and had no obvious improvements in plant phenotypic development and physiological damage caused by enhanced UV-B stress after He-Ne laser irradiation. Our results suggested that UVR8 and its mediated signaling pathway via interaction with COP1 can be induced by He-Ne laser, and these processes were dependent on cytoplasmic PhyB levels in plant cells, which might be one of the most important mechanisms of He-Ne laser on UV-B protection and UV-B damage repair. These current data have also elucidated that the biostimulatory effects of He-Ne laser on Arabidopsis thaliana plants would happen not only during the early growth stage but also during the entire late developmental stage.

The effect of light quality on the pro-/antioxidant balance, activity of photosystem II, and expression of light-dependent genes in Eutrema salsugineum callus cells

The antioxidant balance, photochemical activity of photosystem II (PSII), and photosynthetic pigment content, as well as the expression of genes involved in the light signalling of callus lines of Eutrema salsugineum plants (earlier Thellungiella salsuginea) under different spectral light compositions were studied. Growth of callus in red light (RL, maximum 660 nm), in contrast to blue light (BL, maximum 450 nm), resulted in a lower H₂O₂ content and thiobarbituric acid reactive substances (TBARS). The BL increased the activities of key antioxidant enzymes in comparison with the white light (WL) and RL and demonstrated the minimum level of PSII photochemical activity. The activities of catalase (CAT) and peroxidase (POD) had the highest values in BL, which, along with the increased H₂O₂ and TBARS content, indicate a higher level of oxidative stress in the cells. The expression levels of the main chloroplast protein genes of PSII (PSBA and PSBD), the NADPH-dependent oxidase gene of the plasma membrane (RbohD), the protochlorophyllide oxidoreductase genes (POR B, C) involved in the biosynthesis of chlorophyll, and the key photoreceptor signalling genes (CIB1, CRY2, PhyB, PhyA, and PIF3) were determined. Possible mechanisms of light quality effects on the physiological parameters of callus cells are discussed.

Photochemical activity and the structure of chloroplasts in Arabidopsis thaliana L. mutants deficient in phytochrome A and B

The reduced content of photoreceptors, such as phytochromes, can decrease the efficiency of photosynthesis and activity of the photosystem II (PSII). For the confirmation of this hypothesis, the effect of deficiency in both phytochromes (Phy) A and B (double mutant, DM) in 7-27-day-old Arabidopsis thaliana plants on the photosynthetic activity was studied in absence and presence of UV-A radiation as a stress factor. The DM with reduced content of apoproteins of PhyA and PhyB and wild type (WT) plants with were grown in white and red light (WL and RL, respectively) of high (130 μmol quanta m^-2 s^-1) and low (40 μmol quanta m^-2 s^-1) intensity. For DM and WT grown in WL, no notable difference in the photochemical activity of PSII was observed. However, the resistance of the photosynthetic apparatus (PA) to UV-A and the rate of photosynthesis under light saturation were lower in the DM compared to those in the WT. Growth in RL, when the photoreceptors of blue light-cryptochromes-are inactive, resulted in the significant decrease of the photochemical activity of PSII in DM compared to that in WT including amounts of Q_B-non-reducing complexes of PSII and noticeable enhancement of thermal dissipation of absorbed light energy. In addition, marked distortion of the thylakoid membrane structure was observed for DM grown in RL. It is suggested that not only PhyA and PhyB but also cryptochromes are necessary for normal functioning of the PA and formation of the mechanisms of its resistance to UV-radiation.

Role of phytochromes A and B in the regulation of cell death and acclimatory responses to UV stress in Arabidopsis thaliana

Plants coordinate their responses to various biotic and abiotic stresses in order to optimize their developmental and acclimatory programmes. The ultimate response to an excessive amount of stress is local induction of cell death mechanisms. The death of certain cells can help to maintain tissue homeostasis and enable nutrient remobilization, thus increasing the survival chances of the whole organism in unfavourable environmental conditions. UV radiation is one of the environmental factors that negatively affects the photosynthetic process and triggers cell death. The aim of this work was to evaluate a possible role of the red/far-red light photoreceptors phytochrome A (phyA) and phytochrome B (phyB) and their interrelations during acclimatory responses to UV stress. We showed that UV-C treatment caused a disturbance in photosystem II and a deregulation of photosynthetic pigment content and antioxidant enzymes activities, followed by increased cell mortality rate in phyB and phyAB null mutants. We also propose a regulatory role of phyA and phyB in CO2 assimilation, non-photochemical quenching, reactive oxygen species accumulation and salicylic acid content. Taken together, our results suggest a novel role of phytochromes as putative regulators of cell death and acclimatory responses to UV.

Alternation of light/dark period priming enhances clomazone tolerance by increasing the levels of ascorbate and phenolic compounds and ROS detoxification in tobacco (Nicotiana tabacum L.) plantlets

The effect of the alternation of light/dark periods (AL) (16/8 min light/dark cycles and a photosynthetic photon flux density (PPFD) of 50 μmol photons m(-2) s(-1) for three days) to clarify the mechanisms involved in the clomazone tolerance of tobacco plantlets primed with AL was studied. Clomazone decreased PSII activity, the net photosynthetic rate (Pn), and the ascorbate and total polyphenol contents and increased H2O2 and starch grain accumulation and the number of the cells that underwent programmed cell death (PCD). The pretreatment with AL reduced the inhibitory effect of clomazone on the PSII activity and photosynthesis, as indicated by the decreases in the H2O2 and starch grain accumulation and the PCD levels, and increased the content of ascorbate and certain phenolic compounds, such as chlorogenic acid, neochlorogenic acid and rutin. The AL treatment could promote photorespiration via post-illumination burst (PIB) effects. This alternative photorespiratory electron pathway may reduce H2O2 generation via the consumption of photochemical energy, such as NADH+H(+). At 10 days (D10) of AL treatment, this process induced moderate stress which stimulates H2O2 detoxification systems by increasing the activity of antioxidant enzymes and the biosynthesis of antioxidant components. Therefore, the PCD levels provoked by clomazone were noticeably decreased.

He-Ne laser preillumination improves the resistance of tall fescue (Festuca arundinacea Schreb.) seedlings to high saline conditions

In this paper, we explored the protective effect and physiochemical mechanism of He-Ne laser preillumination in enhancement of tall fescue seedlings tolerance to high salt stress. The results showed that salt stress greatly reduced plant growth, plant height, biomass, leaf development, ascorbate acid (AsA) and glutathione (GSH) concentration, the enzymatic activities, and gene expression levels of antioxidant enzymes such as catalase (CAT) and glutathione reductase (GR) and enhanced hydrogen peroxide (H2O2) content, superoxide radical (O2 (·-)) generation rates, membrane lipid peroxidation, relative electrolyte leakage, the enzymatic activities, and gene expression levels of superoxide dismutase (SOD), ascorbate peroxidase (APX), and peroxidase (POD), compared with controls. However, He-Ne laser preillumination significantly reversed plant growth retardation, biomass loss, and leaves development decay induced by salt stress. And the values of the physiochemical parameters observed in salt-stressed plants were partially reverted or further increased by He-Ne laser. Salt stress had no obvious effect on the transcriptional activity of phytochromeB, whereas He-Ne laser markedly enhanced its transcriptional level. Preillumination with white fluorescent lamps (W), red light (RL) of the same wavelength, or RL, then far-red light (FRL) had not alleviated the inhibitory effect of salt stress on plant growth and antioxidant enzymes activities, suggesting that the effect of He-Ne laser on improved salt tolerance was most likely attributed to the induction of phytochromeB transcription activities by the laser preillumination, but not RL, FRL or other light sources. In addition, we also utilized sodium nitroprusside (SNP) as NO donor to pre-treat tall fescue seedlings at the same conditions, and further evaluated the differences of physiological effects between He-Ne laser and NO in increasing salt resistance of tall fescue. Taken together, our data illustrated that He-Ne laser preillumination contributed to conferring an increased tolerance to salt stress in tall fescue seedlings due to alleviating oxidative damage through scavenging free radicals and inducing transcriptional activities of some genes involved in plant antioxidant system, and the induction of phytochromeB transcriptional level by He-Ne laser was probably correlated with these processes. Moreover, this positive physiochemical effect seemed more effective with He-Ne laser than NO molecule.

Effects of polyaromatic hydrocarbons on photosystem II activity in pea leaves

The acute effects of three typical polyaromatic hydrocarbons (PAHs): naphthalene (Naph), phenanthrene (Phen) and fluoranthene (Flu) on photochemical activity of photosystem II (PSII) in detached leaves of 3-week-old pea plants were studied. The leaves were exposed in water with PAHs under white light for 0.5-72 h. The activity of PSII was examined by prompt and delayed chlorophyll a (Chl a) fluorescence. The effects of PAHs depended on their concentration and exposure time. This dependency was more significant in the presence of chemical stressors (Triton X-100 or acetone) or under high intensity irradiance. Increased content of PAHs and long-term exposure (24-72 h) led to significant reduction of the maximum photochemical quantum efficiency (Fv/Fm) of PS II, changes in the polyphasic fluorescence induction (OJIP), and to decreasing amplitudes of fast and slow components of delayed Chl a fluorescence. The damage of PSII depended on water solubility of a given type of PAHs, their concentration and exposure time. During short-time exposure the compound with highest water-solubility - naphthalene - revealed the strongest effect. During long-time exposure the compounds with low water-solubility -Phen, Flu-revealed the strongest effect as the corresponding PAH accumulates in the thylakoids especially when the solution is oversaturated containing a solid phase. The reduction of PSII activity at the presence of naphthalene (30 mg L(-1)) was accompanied by transient generation of H2O2 as well as swelling of thylakoids and distortion of cell plasma membranes, which was indicated by electron microscopy images. Distortion of thylakoid membranes due to accumulation of PAHs as well as the development of oxidative stress seems to be the main pathways of PAHs influencing the photochemical activity of PS II.

Pretreatment with alternation of light/dark periods improves the tolerance of tobacco (Nicotiana tabacum) to clomazone herbicide

This work analyses the effects of alternation of light/dark periods pretreatment (AL) in tobacco plantlets (Nicotiana tabacum L. cv.Virginie vk51) growing in solution with low concentration of the clomazone herbicide. The experimentation has been carried out by exposing the plantlets to successive and regulated periods of light (16min light/8min dark cycles, PAR 50μmolm(-2)s(-1)) for three days. The photosynthesis efficiency was determined by mean of the chlorophyll fluorescence and JIP-test. The AL pretreatment improved the clomazone tolerance; this has been observed by the increase in the leaf area of the plant, the maximal photochemical quantum efficiency of PSII (Fv/Fm), the actual PSII efficiency (ФPSII), the performance index (PIabs), the electron flux beyond Quinone A (1-VJ), and also by the diminution of the energy dissipating into heat (DI0/RC). Furthermore, AL pretreatment led to low accumulation of hydrogen peroxide (H2O2) which proves that the scavenging enzymatic system have been activated before clomazone treatment. In the plantlets pretreated with AL, with regard to the ascorbate content, some of antioxidant enzyme whose function is associated with it have continued to scavenge reactive oxygen species (ROS) induced by clomazone, such as ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR). So, the observed photooxidative damages induced by clomazone herbicide were noticeably reduced.