Floralabscission in capsicum under high temperature: Role of endogenous hormones and polyamines

High temperature during reproductive stage limits the productivity in capsicum by inducing abscission of floral buds and flowers. In order to understand the mechanism of high temperature induced floral abscission, investigations were carried out on ethylene biosynthesis, indole acetic acid (IAA), abscisic acid (ABA), cytokinins and polyamines in two capsicum cvs, Arka Mohini (susceptible) and Arka Gaurav (relatively tolerant) subjected to temperatures, 35/25°C and 25/20°C (day/night) during reproductive stage. Under high temperature, susceptible cv. Arka Mohini showed 72.4 and 52.4% abscission in floral buds and flowers in contrast to tolerant cv. Arka Gaurav, which recorded 41.1 and 25.1% abscission, respectively. At 35/25°C, ethylene production, ACC (1-aminocyclopropane carboxylic acid)-oxidase activity, and ACC and ABA contents increased, and auxins (IAA) and cytokinins [zeatin riboside (ZR) and dihydrozeatin riboside (DHZR)] contents declined in the floral buds and flowers; the effect was pronounced in the susceptible cultivar Arka Mohini. Free polyamines, putrescine, spermidine and spermine contents under high temperature increased significantly in the reproductive parts, with pattern of polyamine changes being differential in the cultivars. While putrescine increase was greater under high temperature in both the floral organs of the susceptible cv. Arka Mohini, the increase in spermidine and spermine was dominant in the tolerant cv. Arka Gaurav. These results implicated that the floral abscission in capsicum under high temperature is associated with increased biosynthesis of ethylene, and ABA and putrescine accumulation concomitant with decline in IAA and cytokinins.