Calcium requirement for ethylene‐dependent responses involving 1‐aminocyclopropane‐1‐carboxylic acid oxidase in radicle tissues of germinated pea seeds*

Abstract

ABSTRACTThe Ca2+ requirements of ethylene‐dependent responses were investigated in germinating seeds of Pisum sativum L. using 1‐aminocyclopropane‐1‐carboxylic acid (ACC) oxidase (Ps‐ACO1), ACC synthase (Ps‐ACS2) and class I β‐1,3‐glucanase as molecular markers. Ethylene biosynthesis and responsiveness are localized to the elongation and differentiation zones of the pea radicle. Ethylene treatment induced ectopic root hair formation in the cell elongation zone and promoted root hair elongation growth in the radicles of germinated seeds. Characterized Ca2+ antagonists, including EGTA, lanthanum, verapamil, ruthenium red, W‐7, lithium and neomycin, were used to test for the involvement of the apoplastic and the intracellular Ca2+‐pool, the Ca2+/calmodulin complex and the phoshoinositide (PI) cycle in the ethylene responses. Ca2+ release from internal pools, but no appreciabe apoplastic Ca2+, is involved in the transcriptional induction by ethylene of Ps‐ACO1 and in ectopic root hair formation in the radicle elongation zone of germinated pea seeds. Furthermore, the Ca2+/calmodulin complex and the PI cycle seem to be involved in these ethylene responses. In contrast, both the intracellular and the apoplastic Ca2+‐pools are required for the negative and positive ethylene responses to the gene expression of PS‐ACS2 and class I β‐1,3‐glucanase, respectively; and, apoplastic Ca2+ also promotes root hair elongation growth. Tissues from adult plants and germinating seeds exhibit temporal and spatial differences in the signal/response coupling by Ca2+ of ethylene‐regulated processes.