Osmotic stress and abscisic acid induce expression of the wheat Em genes

The early-methionine-labelled (Em) polypeptide is the single most abundant cytosolic protein of dry wheat embryos. It is encoded by messenger RNA which accumulates during the later (maturation) stages of embryogenesis. The accumulation of Em mRNA can be induced in isolated developing embryos, in culture, by the application of the plant growth regulator, abscisic acid, which prevents precocious germination. Precocious germination is also inhibited by the culture of embryos under conditions of osmotic stress when accumulation of Em mRNA is induced. This induction occurs in the absence of any significant increase in the endogenous levels of embryonic abscisic acid although there is a requirement for the continued presence of the growth regulator. Additionally, expression of Em genes can be repeated during early germination, if imbibing embryos are subjected to osmotic stress. Induction of Em-gene expression by osmotic stress is consistent with the proposed role of the Em polypeptide in mediating the remarkable tolerance of cereal embryos to the programmed desiccation undergone during their maturation.