VARIABILITY IN LIGHT GIBBERELLIN AND NITRATE REQUIREMENT OF ARABIDOPSIS-THALIANA SEEDS DUE TO HARVEST TIME AND CONDITIONS OF DRY STORAGE

Freshly harvested seeds of Arabidopsis thaliana harvested in different seasons showed considerable variability in requirement for light (wil d type), gibberellins (GAs)(wild type, GA deficient, gal-2 mutant) and nitrate. Generally, sensitivity to light was high in seed lots harves ted between September and March and significantly lower in those harve sted between April and June. Sensitivity to GAs varied in a nearly par allel way. These differences in sensitivity can be attributed to condi tions during seed development, like temperature and nitrate availabili ty. Endogenous nitrate levels varied enormously amongst seed lots (abo ut a factor 600) and were weakly correlated to the germination capacit y at 10-degrees-C after 15 min of red light irradiation. In addition, differences in sensitivity to nitrate may be responsible for the enorm ous differences in light requirement between seed lots. Other unknown factors may contribute as well. At a germination temperature of 10-deg rees-C seeds were much more sensitive to GAs and light than at 24-degr ees-C. The degree of dormancy rapidly declined upon dry storage of the seeds. Loss of dormancy was accelerated with increasing storage tempe rature; the requirements for light and GAs became less strict. Sensiti vity to GAs increased and seeds that initially only responded to conti nuous irradiation with white fluorescent light, responded to a single red light pulse after 15 months of dry storage at 2-degrees-C. It is d emonstrated that studies on germination and dormancy of A. thaliana ar e hampered by the large variability of seed material and the relativel y high rate of after-ripening.