Biochemical and ultrastructural features related to male sterility in the dioecious species Actinidia deliciosa

Kiwifruit (Actinidia deliciosa var. deliciosa) is a dioecious plant whose flowers are morphologically hermaphrodite yet functionally unisexual. The objective of this study was to investigate the male sterility of female flowers in kiwifruit through an integrated biochemical and cytohistological approach. High levels of free and trichloroacetic acid (TCA)-insoluble conjugated polyamines (PAs) were found to be associated with pollen degeneration. Carbohydrate levels greatly differed when comparing mature to degenerated pollen from the anthers of male-fertile and male-sterile flowers, respectively. In the cytoplasm, carbohydrates strongly decreased in the degenerated pollen, whereas in the cell wall, their levels remained consistent. The degenerated pollen showed a poorly sculptured sexine, an anomalous nexine, and an intine consisting of a single stratum only. Through in vitro culture of anthers from male-sterile plant, the pollen occasionally reached the binucleate stage. The structural anomalies in the pollen of the male-sterile plant and the alterations in PA and carbohydrate contents, together with the results of the in vitro anther culture, suggest that the male sterility in this species could be under both sporophytic and gametophytic control.