Partitioning of [14C]sucrose and Acid Invertase Activity in Reproductive Organs of Pepper Plants in Relation to Their Abscission Under Heat Stress

The effect of heat stress on processes related to carbohydratepartitioning was investigated in young bell pepper (Capsicumannum L. cv. Maor) plants in relation to abscission of theirreproductive organs at different stages of development. None of the reproductive organs abscised after 5 d in a normalday/night temperature regime (25/18 °C). With a temperatureregime of 35 °C day, 25 °C night, abscission occurredin only a small portion of the flower buds and none of the flowersand fruitlets. However, when temperatures in the day and nightwere reversed (25/35 °C, day/night) all the buds and someof the flowers abscised during that time period. The young fruitat the first node did not abscise under any temperature regime.The abscission rate of the flower buds was reduced under heatstress if the developing fruit at the first node had been removed. High temperature during either the light or dark periods reducedthe export of ¹⁴C]sucrose from the source leaf (fed for 48h with ¹⁴C]sucrose). Both heat stress and fruit presence reduced the relative amountof ¹⁴C]sucrose which was exported to the flower buds, flowersand roots. Likewise, these treatments reduced the concentrationof reducing sugars in the reproductive organs. Concomitantly,the heat stress and fruit presence on the first node reducedthe activity of soluble acid invertase in the flower buds andthe roots, but not in young leaves. Overall, the results show that heat stress causes alternationin sucrose distribution in the plant, but may also have specificeffects on metabolic activities related to sucrose import andutilization in flower buds and flowers which in turn may enhancetheir abscission. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acid invertase, heat stress, reproductive organs, sink leaves