EFFECTS OF LIGHT ON THE ACCUMULATION OF ABSCISIC-ACID AND EXPRESSION OF AN EARLY CYSTEINE-LABELED METALLOTHIONEIN GENE IN MICROSPORES OF TRITICUM-AESTIVUM DURING INDUCED EMBRYOGENIC DEVELOPMENT

A cloned cDNA to the wheat (Triticum aestivum) early cysteine-labeled metallothionein has many characteristics of a molecular marker for pol len embryogenesis in this plant. This transcript was not detected in u ninucleate microspores at the time of culture or in pollen at any stag e during normal ontogeny; its mRNA did begin to increase in embryogeni c microspores within 6 h of culture, peaked at around 24 h, declined, then leveled off through the 21-day-old embryoid stage. Additionally, the accumulation of the embryoid-abundant EcMt gene transcript showed a direct and positive correlation with an increase of ABA in embryogen ic microspores and developing pollen embryoids. Irradiating cultures w ith high intensity white light or with far-red, or blue light, suppres sed EcMt transcript accumulation and the ability of microspores to for m embryoids; however, light did not affect ABA concentrations during t he early stages of culture. These results suggest that although a prom oter of pollen embryogenesis in bread wheat, ABA alone cannot maintain the sporophytic differentiation of microspores subjected to inhibitor y regimes of light in vitro. Whether or not light acts directly or ind irectly in suppressing EcMt gene expression and pollen embryogenesis r emains unknown.