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The role of cryptochrome 1 in photosynthetic processes and pro-/antioxidant balance in the Arabidopsis thaliana plants was studied. Wild type (WT) and hy4 mutant deficient in cryptochrome 1 grown for 20 d under red (RL, 660 nm) and blue (BL, 460 nm) light at an RL:BL = 4:1 ratio were kept for 3 d in different lights: RL:BL = 4:1, RL:BL:GL = 4:1:0.3 (GL - green light, 550 nm), and BL, then were exposed to high irradiance (4 h). Activity of PSII and the rate of photosynthesis in WT and hy4 decreased under the high irradiance in all spectral variants but under BL stronger decrease in the activity was found in the hy4 mutant than in WT. We assumed that lowered resistance of photosynthetic apparatus in the hy4 mutant may be associated with the low activity of the main antioxidant enzymes and reduced content of low-molecular-mass antioxidants in the mutant compared to the WT.

The role of cryptochrome 1 in photosynthetic processes and pro-/antioxidant balance in the Arabidopsis thaliana plants was studied. Wild type (WT) and hy4 mutant deficient in cryptochrome 1 grown for 20 d under red (RL, 660 nm) and blue (BL, 460 nm) light at an RL:BL = 4:1 ratio were kept for 3 d in different lights: RL:BL = 4:1, RL:BL:GL = 4:1:0.3 (GL - green light, 550 nm), and BL, then were exposed to high irradiance (4 h). Activity of PSII and the rate of photosynthesis in WT and hy4 decreased under the high irradiance in all spectral variants but under BL stronger decrease in the activity was found in the hy4 mutant than in WT. We assumed that lowered resistance of photosynthetic apparatus in the hy4 mutant may be associated with the low activity of the main antioxidant enzymes and reduced content of low-molecular-mass antioxidants in the mutant compared to the WT. [ABSTRACT FROM AUTHOR]

The light spectral composition acting through a set of photoreceptors, such as cryptochromes and phytochromes, plays an important role in maintaining sustainable photosynthesis. An impact of cryptochrome 1 deficiency and additions of green light (GL) against the background of red (RL) and blue (BL) (different ratios of RL:BL:GL) on the activity of the photosynthetic apparatus, the content of photosynthetic pigments, pro-/antioxidant balance, and expression of some genes in the leaves of 23-d-old Arabidopsis thaliana hy4 mutant plants was studied. The deficiency of cryptochrome 1 at RL/BL ratio of 4:1 led to a decrease in the rate of photosynthesis, photosystem II activity, and activity of ascorbate peroxidase and total peroxidase but to an increase in the content of products reacting with thiobarbituric acid. However, in the presence of additional GL, this difference for photosynthetic parameters either decreased or was absent, likely due to a GL-induced decrease in the content of active cryptochrome. [ABSTRACT FROM AUTHOR]

The effects of the quality of light on the content of phytochrome interacting factors (PIFs) such as PIF3, PIF4 and PIF5, as well as the expression of various light-dependent microRNAs, in adult Arabidopsis thaliana pif mutant plants (pif4, pif5, pif3pif5, pif4pif5, pif3pif4pif5) were studied. We demonstrate that under blue light, the pif4 mutant had maximal expression of most of the studied microRNAs (miR163, miR319, miR398, miR408, miR833) when the PIF4 protein in plants was reduced. This finding indicates that the PIF4 protein is involved in the downregulation of this group of microRNAs. This assumption is additionally confirmed by the fact that under the RL spectrum in pif5 mutants, practically the same miRNAs decrease expression against the background of an increase in the amount of PIF4 protein. Unlike the WT and other mutants, the pif4 mutant responded to the BL spectrum not only by activating the expression of light-dependent miRNAs, but also by a significant increase in the expression of transcription factors and key light signalling genes. These molecular reactions do not affect the activity of photosynthesis but may be involved in the formation of a light quality-dependent phenotype. [ABSTRACT FROM AUTHOR]

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 s) and low (40 μmol quanta m s) 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-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. [ABSTRACT FROM AUTHOR]

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 (P n), photochemical activity of PSII (F V /F M) and PSII performance index (PI ABS) 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. [Display omitted] • The stress resistance of the photosynthetic apparatus in wild-type Arabidopsis was higher than that in the hy4 mutant. • The contents of leaf pigments and antioxidant enzyme activities were higher in the wild type than in the mutant. • Damage to the photosynthetic apparatus depended on the blue light intensity and cryptochrome 1 content. [ABSTRACT FROM AUTHOR]

The photosynthetic responses of 25-day-old Arabidopsis phyA phyB double mutant (DM) compared with the wild type (WT) to UV-B radiation (1 W m − 2 , 30 min) 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 (λ m - 660 nm) 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. [ABSTRACT FROM AUTHOR]

Highlights: [•] We studied the effect of preillumination with red light on photosynthetic parameters. [•] Oxidant-/antioxidant balance in Arabidopsis thaliana. [•] Response to UV-A. [Copyright &y& Elsevier]