Sucrose metabolism at three leaf development stages in bean plants

Sucrose metabolism was studied at three leaf development stages in two Phas eolus vulgaris L. cultivars, Tacarigua and Montalban. The changes of enzyme activities involved in sucrose metabolism at the leaf development stages w ere: (1) Sink (9-11 % full leaf expansion, FLE): low total sucrose phosphat e synthase (SPS) activity, and higher acid invertase (AI) activity accompan ied by low sucrose synthase (SuSy) synthetic and sucrolytic activities. (2) Sink to source transition (40-47 % FLE): increase in total SPS and SuSy ac tivities, decrease in AI activity. (3) Source (96-97 % FLE): high total SPS activity, increased SuSy activities, decreased AI activity. The hexose/suc rose ratio decreased from sink to source leaves in both bean cultivars, The neutral invertase activity was lower than that of AI; it showed an insigni ficant decrease during the sink-source transition.