Studies on the Relationship between Gibberellin Metabolism and Daylength in Normal and Non-flowering Red Clover (Trifolium pratenseL.)

Feeding experiments on tillers of a non-flowering red cloversegregate indicated that the promotive effect of gibberellinupon stem extension and flowering occured only under inductivelong days (LD). Furthermore, floral initiation took place inLD only when free gibberellin exceeded an unspecified criticallevel. Various intermediates in fungal gibberellin synthesis were fedin a similar fashion but none exerted any effect upon reproductivegrowth. Studies using ³H-gibberellin A₃ (GA₃) showed that innormal (flowering) material GA₃ was more rapidly metabolizedin short days than in long days. Qualitative differences ingibberellin metabolism between normal and non-flowering genotypeswere revealed by radio-isotope studies. Non-flowering materialrapidly degraded GA₃ under LD conditions to a biologically inactivecompound chromatographically indentical with allo-gibberic acid,whereas normal plants metabolized GA₃ more slowly producinga compund similar to gibberellenic acid. The implications ofthese results are discussed in terms of the mechanism of stemelongation and floral initiation.