Bimodal patterns of floral gene expression over the two seasons that kiwifruit flowers develop

Polymerase chain reaction fragments with homology to the Arabidopsis floral meristem identity genes LEAFY and APETALA1 have been isolated from kiwifru it (Actinidia deliciosa [A. Chev.] C. F. Liang and A. R. Ferguson) and have been named ALF and AAP1, respectively. Northern hybridisation analyses hav e shown that ALF and AAP1 have bimodal patterns of annual expression in dev eloping first-order axillary buds and their subsequent shoots. This pattern of expression is consistent with the 2-year cycle of axillary bud, flower and fruit development observed in kiwifruit, The first period of expression was early in first-order bud development (late spring of the first growing season), when second-order meristems are initiated, and the second, approx imately 10 months later, when those meristems differentiate flowers (late s pring of the second growing season), In situ hybridisation analyses on axil lary buds collected during late spring of the first growing season have sho wn ALF expression throughout the developing first-order buds and AAP1 expre ssion was localised in developing second-order axillary meristems, During t he spring of the second growing season, transcript accumulation for both AL F and AAP1 is localised in differentiating flowers, Our results show that i mportant developmental events are occurring very early in kiwifruit first-o rder axillary bud development (spring of the first growing season) and it i s likely that this includes floral commitment (evocation).