Composition of Stigmatic Exudate, Nectar and Pistil of Watermelon, Citrullus lanatus (Thunb.) Matsum. & Nakai, Before and After Pollination

Abstract

The composition of stigmatic exudate, nectar, stigma tissue and style tissue was studied in watermelon flowers at 25/20°C (day/night) as the flowers aged after opening, and in unpollinated and pollinated flowers at 30/25°C. The stigmatic exudate contained fructose, glucose, sucrose, and polysaccharide which increased during ageing. Pollination also resulted in an increase in the secretion of these compounds by the stigma. Killed ethanol-extracted pollen was not as effective as live pollen, as less sugar and no polysaccharide was secreted. The fatty acid composition of stigma lipids did not change as a response to pollination. Linolenic acid was the major fatty acid in the lipids of stigmas, ovaries and pollen; high levels of lipids were present in pollen. The current results provide the quantitative composition of the stigmatic exudate which has been shown previously by microscopy to increase within minutes of pollination of watermelon flowers.