INDUCTION OF ENT-KAURENE BIOSYNTHESIS BY LOW-TEMPERATURE IN DWARF PEAS

Germinating pea (Pisum sativum L.) seeds of two dwarf cultivars, "Progress No. 9" and "Green Arrow," and two tall cultivars, "Alaska" and "Alderman," were treated with low temperature (3-5-degrees-C) for 14 days and then transferred to normal growing conditions (19-21-degrees-C for 16 h/14.5-16.5-degrees-C for 8 h) for an additional 10 days. Biosynthesis of [C-14]ent-kaurene from [C-14]2-mevalonic acid (2-MVA) was assayed in cell-free enzyme extracts prepared from shoot tips 10 days after cold treatment and was compared with activity in enzyme extracts prepared from noncold-treated, 10-day-old control plants. Shoot lengths of cold-treated plants were measured throughout a 35-day period and compared with shoot lengths of plants grown without cold treatment for 25-35 days. Low temperature induced a five- to 10-fold enhancement of ent-kaurene, hence potentially gibberellin (GA), biosynthesis in seedlings of the two dwarf cultivars but not in the tall cultivars. However, the lack of an increase in growth rate in the cold-treated dwarfs indicated that endogenous GA biosynthesis remained blocked at some point beyond ent-kaurene in the biosynthetic pathway. Since the late-flowering "Alderman" cultivar did not exhibit enhanced biosynthesis of ent-kaurene, it appears that if vernalization in late-flowering cultivars of peas is correlated with enhanced GA biosynthesis, it is not the early part of the biosynthetic pathway which is affected.