STARCH BREAKDOWN DURING BANANA RIPENING - SUCROSE SYNTHASE AND SUCROSE-PHOSPHATE SYNTHASE

Starch contents, respiration rates, sucrose synthase (SS) activity, and sucrose phosphate synthase (SPS) activity in crude extract or in partially purified preparations were comparatively studied during fruit development and ripening in either attached or detached bananas. Data showed that while SS activity is almost abolished during ripening, SPS activity increased concomitantly to starch disappearance and sugar accumulation, confirming that it may be the enzyme involved in the process. The process is slower for attached fruits [final sucrose content 6%, SS activity 5 units (U), and SPS activity 33 U] when compared to the detached fruits (final sucrose content 12%, no SS activity, and SPS activity 50 U). During development of the fruit SPS was present but showed a very low activity, while SS activity was high and was kept constant during all of the starch synthesis phase falling during starch breakdown (climacteric) to a lower level (30 U) and then disappearing (postclimacteric).