Studies on bulb formation and dormancy in bulbous plants by molecular biological approach

Molecular biological studies were used to investigate the hypothesis that the induction of bulb formation and the induction of bulb dormancy are the same phenomenon. Shoot explants were taken from in vitro immature leaves of hyacinth (Hyacinthus orientalis L. cv. Delft Blue) and cultured at 25℃ on MS medium containing NAA and BA. The explants formed bulbs four after the cold treatment at 5℃, whereas bulb formation was supressed without cold treatment. ABA promoted bulb formation without cold treatment. By flundone, bulb formation of the cold treated explants was inhibited. Under bulb-forming conditions, endogenous ABA content increased. These results suggest that bulb formation is induced by low temperature and regulated by ABA. Thus, the controlling methods are bulb forming conditions are obtainable by cold treatment or BAB without cold treatment and non-bulb forming conditions are by non-cold treatment or fluridone with cold treatment. Differential display analysis of genes induced by low temperature and ABA in bulb formation of hyacinth was conducted. Differential PCR amplified fragments between cold-treated and non-cold-treated shoot samples were observed. Six differential PCR amplified fragments were commonly expressed both in the cold and ABA treatments, and two were suppressed in both treatments. The cDNA amplified fragments observed in both treatments might be related to bulb formation in hyacinth. The partial sequences of the cDNA clones obtained from 18 specific gene fragments by low temperature (designated as HL clones) were carried out. Eight HL clones had over 80% identity with identified sequences with FASTA program. The HL clones of cDNA induced by low temperature and ABA were homologous to genome DNA of A. thaliana or O. sativa. Three HL clones showed partial identity with starch phosphorylase gene of I. batatas. Some HL clones were homologous to genes or mRNAs of which the function had been suggested. It is possible that HL clones of which the functions were not clarified are novel genes related to bulb formation.