Effects of Gibberellic Acid and Gold Light on Germination, Enzyme Activities, and Amino Acid Pool Size in a Dwarf Strain of Watermelon

Gibberellic acid (GA(3)) promotes and continuous gold light inhibits germination of seeds of a dwarf strain (WB-2) of watermelon [Citrullus lanatus (Thunb.) Matsu. and Nakai]. Osmotic inhibition of germination with mannitol in light-grown seeds of WB-2 was only slightly reversed by GA(3) at the concentrations used, whereas, GA(3) substantially relieved osmotic inhibition in dark-grown seeds.The effects of GA(3) and gold light on development of catalase and invertase activities and on levels of free amino acids in germinating seeds of WB-2 were examined. Light depressed development of catalase and invertase activity. Levels of free amino acids increased more slowly in embryonic axes of light- than dark-incubated seeds, but in cotyledons higher levels of amino acids were maintained in light-grown seeds. GA(3) accelerated the development of catalase activity in whole embryos and invertase activity in embryonic axes, but did not significantly affect invertase activity in cotyledons during germination. GA(3) had little effect on amino acid pools in cotyledons and embryonic axes.