EFFECTS OF LIGHT AND TEMPERATURE ON SEED DORMANCY AND GIBBERELLIN-STIMULATED GERMINATION IN ARABIDOPSIS-THALIANA - STUDIES WITH GIBBERELLIN-DEFICIENT AND GIBBERELLIN-INSENSITIVE MUTANTS

Effects of light and temperature on gibberellin (GA(-induced seed germ ination were studied in Arabidopsis thaliana (L.) Heynh. with the use of GA-deficient (gal) mutants, mutants with a strongly reduced sensiti vity to GA (gai) and with the recombinant gai/gal. Seeds of the gal mu tant did not germinate in the absence of exogenous GAs, neither in dar kness, nor in light, indicating that GAs are absolutely required for g ermination of this species. Wild-type and gai seeds did not always req uire applied GAs in light. The conclusion that light stimulates GA bio synthesis was strengthened by the antagonistic action of tetcyclacis, an inhibitor of GA biosynthesis. In wild-type, gal and gai/gal seeds l ight lowered the GA requirement, which can be interpreted as an increa se in sensitivity to GAs. In gai and gai/gal seeds light became effect ive only after dormancy was broken by either a chilling treatment of o ne week or a dry after-ripening period at 2-degrees-C during some mont hs. The present genetic and physiological evidence strongly suggests t hat temperature regulates the responsiveness to light in A. thaliana s eeds. The responsiveness increases during dormancy breaking, whereas t he opposite occurs during induction of dormancy (8 days at 15-degrees- C pre-incubation). Since light stimulates the synthesis of GAs as well as the responsiveness to GAs, temperature-induced changes in dormancy may indirectly change the capacities to synthesize GAs and to respond to GAs. GA sensitivity is also directly controlled by temperature. It is concluded that both GA biosynthesis and sensitivity to GAs are not the primary controlling factors in dormancy, but are essential for ge rmination.