The control of apical bud growth and senescence by auxin and gibberellin in genetic lines of peas

Pea (Pisum sativum L.) lines G2 (dwarf) and NGB1769 (tall) (Sn Hr) produce flowers and fruit under long (LD) or short (SD) days, but senesce only under LD. Endogenous gibberellin (CA) levels were inversely correlated with photoperiod (over 9-18 h) and senescence: GA(20) was 3-fold and GA(1) was 10- to 11-fold higher in flowering SD G2 shoots, and the vegetative tissues within the SD apical bud contained 4-fold higher levels of GA(20), as compared with the LD tissues. Prefloral G2 plants under both photoperiods had GA(1) and GA(20) levels similar to the flowering plants under LD. Levels of indole-3-acetic acid (IAA) were similar in G2 shoots in LD or SD; SD apical bud vegetative tissues had a slightly higher IAA content. Young floral buds from LD plants had twice as much IAA as under SD. In NGB1769 shoots GA(1) decreased after flower initiation only under LD, which correlated with the decreased growth potential. We suggest that the higher GA(1) content of G2 and NGB1769 plants under SD conditions is responsible for the extended vegetative growth and continued meristematic activity in the shoot apex. This and the increased IAA level of LD floral buds may play a role in the regulation of nutrient partitioning, since more photosynthate partitions to reproductive tissue under LD conditions, and the rate of reproductive development in LD peas is faster than under SD.