Effects of the blue light–cryptochrome system on the early process of cold acclimation of Arabidopsis thaliana

Abstract

Although plant cold acclimation (CA) requires low temperature and light to increase the plant’s freezing tolerance, how the light spectra affect the process of CA is not yet fully understood. Here we show that blue light and its photoreceptor, cryptochrome (CRY), regulate signal pathways associated with the early process of CA in Arabidopsis. When cold-acclimated for 1 day under different monochromatic light conditions, the greatest increases in freezing tolerance of wild type plants, evaluated by a photosynthesis quantum efficiency index (Fv/Fm), occurred in plants exposed to blue light and the blue light effect could not be maintained in cry1cry2 mutants. Unexpectedly, freezing tolerance evaluated by a plasma membrane stability parameter (electrolyte leakage, EL) and post-thaw plant growth was higher in cry1cry2 plants than in wild type plants after CA. During CA, blue light irradiation resulted in increases of transcript levels of elongated hypocotyl 5 (HY5) and anthocyanin biosynthesis genes and, in fact, affected anthocyanin contents during the CA process. In contrast, blue light reduced transcript levels of C-repeat binding factor (CBF) and cold regulated (COR) genes. These results collectively suggest that there are multiple CRY-regulated CA pathways and the blue light–CRY system affects CA pathways in complex manners.