Role of Endogenous Gibberellins in Cold-Induced Stem Elongation and Flowering of Japanese Radish (Raphanus sativus L.).

Abstract

Eighteen endogenous gibberellins (GAs) which belong to the early 13-hydroxylation pathway and the early non-hydroxylation pathway of GA-biosynthesis were identified by combined gas chromatography/mass spectrometry (GC/MS) in shoots of a cold-requiring plant, Raphanus sativus L. Contents of GA1 and GA4, the probable endogenous biologically-active GAs, increased in the stem during a long-day condition (LD) both with or without a prior cold treatment (CT); however, the increase was greater with CT than without it. In contrast to the contents of 3β-hydroxylated GAs (i.e. GA1 and GA4), that of GA34, a 2β-hydroxylated GA, was decreased significantly by CT and LD, indicating that CT and LD activated the 3β-hydroxylation and inactivated the 2β-hydroxylation during the course of GA-biosynthesis. GA1 and GA4 contents in the leaf decreased during LD subsequent to CT, whereas they increased with LD alone. The increase in GA1 and GA4 contents in the stem probably promoted the cold-induced stem elongation and flowering of R. sativus.