Qualitative and Quantitative Analysis of Endogenous Gibberellins in Raphanus sativus L. during Cold Treatment and the Subsequent Growth

Abstract

Effects of cold treatment and day length on endogenous gibberellins (GAs) in the stems and leaves of Japanese radish (Raphanus sativus L. cv. Taibyo-sobutori) were investigated. The concentrations of putative active GAs (GA₁ and GA₄) and their precursors (GA₉ and GA₂₀) in both stems and leaves of R. sativus grown without cold treatment were higher in the long-day condition than the short-day condition. The concentrations of the above four GAs in the stems and leaves generally tended to decrease during the cold treatment, although GA₁ in the stems was at almost the same level before and after the cold treatment. These results suggest that the GA biosynthesis is promoted by the long-day condition rather than cold treatment. Considering that application of GAs after the cold treatment as well as cultivation in the long-day condition after cold treatment induces the bolting of R. sativus, both the cold treatment and activation of GA biosynthesis by cultivation in the long-day condition seem to be essential to the bolting, although it remains to be seen whether the cold treatment affects sensitivity or responsiveness of the stems to GAs. It was also shown that the endogenous levels of GAs in the upper part of the bolting stem were one or two orders of magnitude higher than those in the stem in the rosette plant.