Enhancement of apical hook curvature caused by phytochrome action in tomato seedlings.

Abstract

Light signals initiate hook opening and cotyledon unfolding in dicotyledonous seedlings. Surprisingly, we have found that light enhances apical hook closing (curvature) rather than opening in the early stage of tomato seedlings. Our results: 1) Red light (R) or far-red light (FR) enhances hook curvature. 2) phyA mediates the FR action. 3) The FR-absorbing form of phytochrome (Pfr) causes hook curvature in the presence of IAA. 4) Pfr reduced the ethylene production in the hook portion. 5) Ethylene or gibberellin causes hook opening. Additionally, we recently found that the angle of hook curvature greatly increased under continuous irradiation of R or FR when cotyledons were tightly covered by seed coats. Here, we also report the influence of cotyledons and seed coats on phytochrome-mediated apical hook curvature.