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The effects of additional far-red light (FRL) on the photosynthetic and growth parameters of Lactuca sativa plants grown for 30 d and on the photosynthetic activity of the plants under high irradiance [4 h; 1,500 μmol(photon) m-2 s-1] were studied. The plants were grown under coloured light-emitting diodes at a ratio of red light (RL): blue light (BL): green light (GL): far-red light (FRL) = 0.7:1:0.3:0.4 or RL:BL:GL:FRL = 0.7:1:0.3:0.8 (test, T). Additional FRL led to an increase in plant biomass, height, and leaf area but to a decrease in photosynthesis and respiration rates. However, PSII activity was greater in plants with additional FRL. It is suggested that the increase in biomass occurred mainly due to an increase in leaf area but not in photosynthesis. In addition, PSII in the experiment was less resistant to high irradiance. The possible direct and indirect influences of the FRL on growth and photosynthesis were considered.

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.