|Farrant, J - UNIV-CAPE TOWN-S. AFRICA|
|Pammenter, N - UNI NATAL DURBAN S.AFRICA|
|Berjak, P - UNI NATAL DURBAN S.AFRICA|
Submitted to: Seed Science Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 12, 1997
Publication Date: N/A
Interpretive Summary: Seeds are typically divided into two categories based on their storage physiology. Orthodox seeds survive desiccation and so can be stored using conventional techniques (refrigeration at low humidities). Recalcitrant seeds are sensitive to desiccation so cannot be stored by any established methods. The purpose of this work was to understand processes in maturing recalcitrant seeds so that we may develop methods to store them. The work shows that the category of recalcitrant seeds encompasses numerous species with different developmental patterns. High levels of vacuolation and metabolic activity are associated with extreme recalcitrance while vacuole packing and very low metabolic activity characterize the desiccation tolerant condition.
Technical Abstract: Water contents, desiccation tolerance, respiratory rates and subcellular characteristics of three contrastig seed types were studied during development. Avicennia marina ( a tropical wetland species) and Aesculus hippocastanum (a temperate species) produce recalcitrant seeds and phaseolus vulgaris produces orthox seeds. During development, seeds of A.hippocastanum and P.vulgaris howed a decline in water content and respiration rate with a concomitant increase in desiccation tolerance. These parameters did not change during the development of A.marina seeds once they had become germinable. There was a decrease in the degree of vacuolation and an increase in the deposition of insoluble reserves in seeds of A.hippocastanum and P.vulgaris, while seeds of A.marina remained highly vacuolated and did not accumulated insoluble reserves. Mitochondria and endomembranes showed a regression during the development of seeds of A hippocastanum and P.vulgaris, but remained unchanged in seeds of A.marina. The data are consistent with the hypothesis that extensive vacuolation and high metabolic rates contribute to desiccation sensitivity. However, the development of recalcitrant A.hippocastanum seeds is similar to that of the orthodox P.vulgaris. These data are in accord with the concept of seed recalcitrance being a consequence of truncated development. The results suggest that there may be three categories of seeds: orthodox seeds which develop desiccation tolerance, seeds which show similar development to orthodox seeds but a shed before desiccation tolerance is well developed, and seeds which show no developmental trends giving rise to increased tolerance.