Scanning electron microscopy reveals contrasting effects of liquid nitrogen on seeds of legumes Neonotonia wightii, Phaseolus vulgaris and Tamarindus indica

Cryopreservation remains the technology of choice for the long-term preservation of plant germplasm. The current contribution reports on the response of seeds of N. wightii, P. vulgaris and T. indica to cryopreservation in terms of plantlet survival post cryostorage as well as examination of the external morphology of seed coats using scanning electron microscopy (SEM). Survival was determined in Petri dishes in the laboratory as well as in the soil. The results showed differential responses in seeds of the three tested species. In the case of P. vulgaris, exposure to liquid nitrogen (LN) did not adversely affect seedling emergence or characteristics of the seed coat. For N. wightii and T. indica, cracks in the seed coat that were apparent in control seeds, appeared more frequently following exposure to LN. In the case of the former species, this observation did not yield adverse consequences and seed germination rate did actually increase from 5.8 to 85.9% after LN treatment. However, in the case of T. indica, the initial growth rate of seedlings was delayed relative to the control although the germination rate was improved. It is postulated that seeds of T. indica possibly incurred additional damage to other seed components which might have led to delayed recovery.