Impact of High Irradiance and Light Quality on Physiological Parameters in A. thaliana hy4 Mutants.

The effects of high irradiance on PSII activity, pigment content and gene expression in Arabidopsis thaliana (L.) Heynh. hy4 mutant with cryptochrome 1 deficiency and wild type grown in light of different spectral composition (LDSC) were studied. A. thaliana wild type (WT) and hy4 mutant plants were grown for 20 days in white light (100 μmol photon/m2 s), then, the plants were grown for 3 days under red (RL), blue (BL) and green (GL) light at a ratio of RL : BL : GL = 4 : 1 : 0; 4 : 1 : 0.3 or only on BL, after which they were irradiated with HIL (4 h, 1000 μmol photon/m2 s). In all variants, HIL irradiation caused a decrease in PSII activity, which was most significant in the BL treatment in hy4. The most significant decreases in the contents of photosynthetic pigments, UV-absorbing pigments and anthocyanins under LDSC were observed only on BL in the mutant. Additionally, in all the variants, the transcript levels of genes encoding key antioxidant and involved in carotenoid and anthocyanin biosynthesis enzymes were lower in hy4 than in the WT. Moreover, in all the treatment group HIL induced the accumulation of zeaxanthin and a decrease in the violaxanthin. It is assumed that the mechanisms used to counteract oxidative stress induced by HIL include the accumulation of pigments such as carotenoids and anthocyanins, as well as the mechanisms of zeaxanthin-related nonphotochemical quenching and the quenching through the accumulation of β-carotene. However, the contents of the pigments appear to play decisive roles in protecting the Arabidopsis photosynthetic apparatus from HIL. [ABSTRACT FROM AUTHOR]