phot1 and phot2 mediate blue light-induced transient increases in cytosolic Ca 2+ differently in Arabidopsis leaves

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 100; no. 14; pp. 8583 - 8588
• Main Authors: Harada, Akiko, Sakai, Tatsuya, Okada, Kiyotaka
• Format: Journal Article
• Language: English
• Published: 08.07.2003
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1336802100

Phototropins (phot1 and phot2) are blue light (BL) receptors that mediate phototropism, chloroplast movements, and stomatal opening in Arabidopsis thaliana . Physiological studies have suggested that Ca 2+ in the cytoplasm plays a pivotal role in these BL-induced responses. A phot1-mediated increase in cytosolic Ca 2+ was reported in deetiolated seedlings of A. thaliana ; however, the contribution of phot2 remains unknown. We examined a BL-induced transient increase in cytosolic free Ca 2+ in leaves of transgenic A. thaliana of WT plants, phot1 and phot2 mutants, and phot1 phot2 double mutants expressing the Ca 2+ -sensitive luminescent protein aequorin. phot1 and phot2 had different photosensitivities: phot1 increased cytosolic Ca 2+ at lower fluence rates (0.1–50 μmol·m -2 ·s -1 ) and phot2 increased it at higher fluence rates (1–250 μmol·m -2 ·s -1 ). By using Ca 2+ channel blockers, Ca 2+ chelating agents, and inhibitors of phospholipase C, we further demonstrated that both phot1 and phot2 could induce Ca 2+ influx from the apoplast through the Ca 2+ channel in the plasma membrane, whereas phot2 alone induced phospholipase C-mediated phosphoinositide signaling, which might result in Ca 2+ release from internal Ca 2+ stores. These results suggest that phot1 and phot2 mediate the BL-induced increase in cytosolic free Ca 2+ differently.