Reproductive morphogenesis in kiwifruit in relation to polyamines

Polyamines act as plant growth substances and have been implicated in floral morphogenesis. Ovary development in kiwifruit varies according to flower sexuality. The objective of the present study was to examine the relationship between polyamines and the reproductive development in both female and male flowers of Actinidia deliciosa. The endogenous level of free and conjugated polyamines was characterized during flower morphogenesis, from shortly after bud burst until full bloom. Ovaries were also inoculated in vitro (20 days after bud burst) and grown on media both with and without hormones (indole-acetic acid and gibberellic acid), in both the presence and the absence of polyamines (putrescine, spermidine and spermine). Putrescine and spermidine were detected in the reproductive structures of both male and female flowers, while spermine was detectable only in traces. The concentration of free polyamines was generally higher in the female than in the male genotype. The Pu/Sd -ratio consistently decreased in the conjugated fraction. The main effect of polyamines on ovary growth in vitro was a reduction in necrosis, which was mainly due to spermidine and spermine. The endogenous level of free and conjugated polyamines in the flower buds and the growth capabilities of the ovaries in vitro, suggest that these compounds play a role in reproductive morphogenesis of kiwifruit.