Freezing Tolerance Acquisition during Seed Development of Pisum Sativum L.1

Acquisition of freezing tolerance during the seed development of Pisum sativum L. cv. Akabana was studied in relation to changes in growth, dry matter accumulation, and water content. Seeds were cooled down rapidly by direct plunging into liquid nitrogen, so that below a determined water content, tissues could vitrify with the consequent survival of seeds. The proportion of seeds that were able to germinate after immersion in liquid nitrogen increased from nearly 0% at about 35 days after flowering to more than 90% at 50 days after flowering. The time at which freezing tolerance was acquired coincided with the time at which seeds rapidly decreased their fresh matter. The reduction in fresh matter was due to a loss of water (water content between 40 and 25%) but not of dry matter, which continued increasing for some time. These results suggest that the water content is a critical factor in the development of freezing tolerance in seeds. However, other factors (like the solutes which accumulate later) may also contribute to vitrification and, therefore, to the survival of seeds to liquid nitrogen exposure. Additional