Changes of carbohydrates in pepper (Capsicum annuum L) flowers in relation to their abscission under different shading regimes

Abscission of pepper flowers is enhanced under conditions of low light and high temperature. Our study shows that pepper flowers accumulate assimilates, particularly in the ovary, during the day time, and accumulate starch, which is then metabolized in the subsequent dark period. With the exception of the petals, the ovary contains the highest total amounts of sugars and starch, compared with other flower parts and contains the highest total activity, as well as activity calculated on fresh mass basis, of sucrose synthase, in accordance with the role of this enzyme in starch biosynthesis. Low light intensity or leaf removal decreased sugar accumulation in the flower and subsequently caused flower abscission. The threshold of light intensity for daily sugar accumulation in the sink leaves was much lower than in flowers, resulting in higher daytime accumulation of sugars in the sink leaves than in the adjacent flower buds under any light intensity, suggesting a competition for assimilates between these organs. Flowers of bell pepper cv. 'Maor' and `899' (sensitive to abscission) accumulated less soluble sugars and starch under shade than the flowers of bell pepper cv. 'Mazurka' and of paprika cv. 'Lehava' (less sensitive). The results suggest that the flower capacity to accumulate sugars and starch during the day is an important factor in determining flower retention and fruit set. (C) 1996 Annals of Botany Company