Deficiency of phytochrome B alleviates chilling-induced photoinhibition in rice

Food crops of tropical origins, such as rice, are often cultivated in areas with suboptimal temperature regimes. The rice phytochrome B-deficient mutant (phyB) is tolerant of chilling temperatures compared with the wild type (WT) under low irradiance, and unsaturated fatty acids (USFAs) of membrane lipids have been shown to play an important role in chilling resistance. However, the relationship between phytochrome B and membrane lipids has not been empirically investigated. •

We assessed various photosynthesis indexes in phyB and WT rice: chlorophyll content, maximal photochemical efficiency (Fv/Fm) of photosystem II (PSII), the quantum yield of PSII electron transport (ΦPSII), the percentage of oxidizable P700 (P700), nonphotochemical quenching (NPQ), and the de-epoxidized ratio of xanthophyll cycle (A+Z)/(V+A+Z). We also analyzed the ultrastructure and fatty acid desaturases (FADs) and glycerol-3-phosphate acyltransferase (GPAT) genes of the chloroplasts using transmission electron microscopy and real-time PCR. •

After a chilling treatment of 24 h, chloroplast damage and USFA content reduction were more severe in the WT than in the phyB mutant. Genes involved in the synthesis of USFAs in membranes such as FADs and GPAT were more stable in phyB than in WT. Chlorophyll content, Fv/Fm, ΦPSII, and P700 decreased more slowly under chilling stress and recovered more rapidly under optimal conditions in phyB than in WT. The (A+Z)/(V+A+Z) and NPQ increased more rapidly in phyB than in the WT after 24 h of chilling treatment. •

Phytochrome B deficiency in rice with more stabilized chloroplast structure and higher USFA content in membrane lipids could alleviate chilling-induced photoinhibition.