title: Phot1 and phot2 mediate blue light-induced transient increases in cytosolic Ca2+ differently in Arabidopsis leaves.
abstract: 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 Ca2+ in the cytoplasm plays a pivotal role in these BL-induced responses. A phot1-mediated increase in cytosolic Ca2+ 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 Ca2+ in leaves of transgenic A. thaliana of WT plants, phot1 and phot2 mutants, and phot1 phot2 double mutants expressing the Ca2+-sensitive luminescent protein aequorin. phot1 and phot2 had different photosensitivities: phot1 increased cytosolic Ca2+ at lower fluence rates (0.1-50 micromol x m-2 x s-1) and phot2 increased it at higher fluence rates (1-250 micromol x m-2 x s-1). By using Ca2+ channel blockers, Ca2+ chelating agents, and inhibitors of phospholipase C, we further demonstrated that both phot1 and phot2 could induce Ca2+ influx from the apoplast through the Ca2+ channel in the plasma membrane, whereas phot2 alone induced phospholipase C-mediated phosphoinositide signaling, which might result in Ca2+ release from internal Ca2+ stores. These results suggest that phot1 and phot2 mediate the BL-induced increase in cytosolic free Ca2+ differently.
authors.affiliation: RIKEN Plant Science Center, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Harada
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Sakai
authors.forename: Kiyotaka
authors.initials: K
authors.lastname: Okada
mesh_terms: D000331:Aequorin / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics / Q000502:physiology / Q000528:radiation effects*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000502:physiology / Q000528:radiation effects*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000528:radiation effects*; D002614:Chelating Agents / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008027:Light; D008163:Luminescent Measurements; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D008954:Models, Biological; D010750:Phosphoproteins / Q000235:genetics / Q000502:physiology / Q000528:radiation effects*; D018524:Phototropism / Q000502:physiology*; D018515:Plant Leaves / Q000378:metabolism / Q000528:radiation effects*; D017346:Protein Serine-Threonine Kinases; D011994:Recombinant Proteins / Q000096:biosynthesis; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
chemical_list: D029681:Arabidopsis Proteins; D002121:Calcium Channel Blockers; D002614:Chelating Agents; D004791:Enzyme Inhibitors; D008565:Membrane Proteins; C423903:PHOT2 protein, Arabidopsis; D010750:Phosphoproteins; D011994:Recombinant Proteins; D000331:Aequorin; C103646:NPH1 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases; D010738:Type C Phospholipases