THE ROLE OF ABA AND GA IN BARLEY-GRAIN DORMANCY - A COMPARATIVE-STUDYBETWEEN EMBRYO AND ALEURONE DORMANCY

In this paper we give an overview of data obtained in an investigation of the response to abscisic acid (ABA) and gibberellic acid (GA(3)) o f isolated barley embryos and aleurone layers, in relation to dormancy and germination of kernels. Analysis of inhibition of germination and induction of Rab mRNA expression demonstrated that embryos dissected from dormant kernels of Hordeum distichum L., cv. Triumph, were more r esponsive to ABA than those of non-dormant kernels of the same variety . Embryos of the rapidly germinating Hordeum vulgare L., cv. Himalaya, showed the lowest response to this phytohormone. GA(3) could only enh ance the germination of the dormant Triumph kernels. Isolated aleurone layers showed the same differences in responsiveness to ABA as the em bryos, with aleurones of dormant Triumph being most responsive. A reve rsed relationship was obtained for the responsiveness of the aleurone layers to GA(3), which, based on a-amylase secretion, proved to be the highest for Himalaya and the lowest for dormant Triumph. Moreover, el ectron microscopy revealed that already prior to aleurone isolation fr om de-embryonated kernels, a substantial portion of the aleurone cells of cv. Himalaya underwent ultrastructural changes related to hydrolas e synthesis, secretion, and release. Thus, the aleurone of these fast- germinating kernels showed some autonomy in reserve mobilization. Our data acknowledges the fact that apart from embryo germination, the ale urone function is also impaired in dormant barley kernels. Although we do not exclude the possible role of endogenous hormone levels, the im paired function of both embryo and aleurone is reflected in their horm one responsiveness.