Abstract
Generally, the bolting (stem elongation from rosette plants) of winter annuals is believed to be induced by an increase in the level of GA that occurs after a certain period of chilling (vernalization), and deficiency of GA make the plant keep rosette style. Lack of the direct evidence proving the above assumption in radish plants urged us to assume the presence of an anti-bolting compound; it actively keeping rosette habit through inhibition of growth of internode (bolting). Anti-bolting activity was detected in an extract of rosette shoot of radish plants by an assay using seedlings cultured in vitro. The causal compound that strongly inhibited bolting was isolated and identified as hexadecatrienoic acid monoglyceride. This compound did not inhibit leaf production at the apical meristem indicating that it merely inhibits the growth of internode. The compound disappeared completely after the vernalization and the bolting commenced thereafter. The results suggest that the release from the inhibition by the anti-bolting compound can trigger initiation of bolting.
