ARE SEASONAL DORMANCY PATTERNS IN ARABIDOPSIS-THALIANA REGULATED BY CHANGES IN SEED SENSITIVITY TO LIGHT, NITRATE AND GIBBERELLIN

Imbibed seeds of Arabidopsis thaliana (L.) Heynh., passed annually through a pattern of changes in dormancy. Dormancy was broken in summer and re-induced in autumn-winter. A second small germination flush occurred in early spring. The role of sensitivity to light, nitrate and gibberellins (GAs) in regulating annual dormancy patterns and germination was studied with the use of GA-deficient (gal-2) and wild-type seeds. Dark-incubated seeds were exposed to a natural temperature regime for periods up to 18 months and at regular intervals germination capacity of portions of seeds was tested at laboratory conditions. Germination data fitted as logistic dose response curves showed that sensitivity to light varied with the seasons in both genotypes. From interpretation of curve parameters, it is proposed that the observed sensitivity changes involve alterations in the number of receptors, in the binding characteristics of the receptors and/or in the response chain initiated by ligand-receptor interaction. In this response chain GA biosynthesis is stimulated (wild type) and sensitivity to GAs is enhanced (wild type, gal-2). GA sensitivity is also directly influenced by temperature, thus without the interference of light. However, the significance of direct regulation of GA requirement seemed to diminish with prolonged incubation outdoors, whereas reversible changes in light sensitivity remained clear. Therefore, we propose that seasonal dormancy patterns are mainly regulated by changes in sensitivity to light. GA sensitivity contributes to this pattern but is not primarily controlling dormancy. The GA requirement for germination is obvious as gal-2 seeds did not germinate at any time of the year when deprived of applied GAs. However, GA biosynthesis is not required for dormancy control, as a dormancy pattern was also observed in the absence of the capacity to synthesize GAs. Nitrate or sensitivity to nitrate did not contribute to the regulation of dormancy and germination of this species. © 1994 Annals of Botany Company.