INVOLVEMENT OF CA2-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID-STIMULATED POLLEN GERMINATION( IN 1)

The role of 1-aminocyclopropane-1-carboxylic acid (ACC) in pollen germ ination was investigated in several plant species. It was found that A CC stimulated in vitro pollen germination in all five species of plant s tested. EGTA and phenothiazine inhibited the increase in the germina tion rate induced by ACC. Free Ca2+ levels in the cytosol ([Ca2+](cyt) ) in ungerminated and germinated pollen were 136 and 287 nM, respectiv ely. Adding 0.25 mM ACC to the germination medium increased the [Ca2+] (cyt) in germinated pollen up to 450 nM. When pollen was treated with both 0.25 mM ACC and 3.6 mu M inositol 1,4,5-trisphosphate, the [Ca2+] (cyt) increased to 850 nM, and pollen germination was also stimulated. In the presence of Li+, an inhibitor of inositol monophosphatase, the [Ca2+](cyt) was reduced to 155 nM, and the ACC-stimulated pollen germ ination was inhibited. The data provided evidence for the involvement of Ca2+ as a messenger in the stimulative effect of ACC on pollen germ ination.