phot1 and phot2 Mediate Blue Light-Induced Transient Increase in Cytosolic Ca²⁺ in Arabidopsis leaves

Abstract

phot1 and phot2 are blue-light (BL) receptors that mediate phototropism, chloroplast movements, and stomatal opening in Arabidopsis thaliana. Physiological studies have suggested that cytosolic Ca²⁺ plays a pivotal role in these BL-induced responses. We examined a BL-induced increase in cytosolic Ca²⁺ in leaves of transgenic A. thaliana of wild types, phot1 and phot2 mutants, and phot1 phot2 double mutants expressing the Ca²⁺-sensitive luminescent protein aequorin. The results indicate that phot1 increased the cytosolic Ca²⁺ at lower fluence rates and phot2 at higher fluence rates. The contribution of phot1 in the absence of phot2, calculated from the percent differences in the elevation of cytosolic Ca²⁺ between the phot2 mutant and phot1 phot2 double mutant, is similar to its contribution in the presence of phot2, the percent differences between wild type and phot1 mutant, suggesting that phot1 and phot2 act independently in mediating the BL-induced increase in cytosolic Ca²⁺.