RESPONSE OF THE RECALCITRANT SEEDS OF AVICENNIA-MARINA TO HYDRATED STORAGE - EVENTS OCCURRING AT THE ROOT PRIMORDIA

This study was undertaken to test the hypotheses that germinative meta bolism of recalcitrant seeds in storage induces a requirement for addi tional water, which may result in the development of mild water stress , and that a reduction of the rate of this germinative metabolism will increase the storage lifespan of recalcitrant seeds. Studies were und ertaken on seeds of Avicennia marina (Forssk.) Vierh. and concentrated on root primordia as these constitute the tissue that undergoes most change during storage. Encapsulating seeds from which the pericarp had been removed (naked seeds) in an alginate gel increased storage lifes pan fourfold compared with naked seeds. Measures of metabolic rate suc h as time to first germination in storage and rate of protein synthesi s did not indicate differences between alginate-coated and naked seeds , although ultrastructural observations indicated that both germinativ e and deteriorative processes were occurring more slowly in the algina te-coated seeds. Measures of water content and water and turgor potent ials did not reveal signs of a mild water stress in either treatment. However, the number of seeds visibly contaminated with fungi and the r apidity with which this contamination became apparent were much reduce d in alginate-coated seeds. It is suggested that fungal contamination constitutes a major cause of deterioration in stored, hydrated seeds o f A. marina (and possibly other recalcitrant seed species) and the mai n effect of the alginate coating was to reduce the incidence of fungal contamination.