Superinduction of the Em gene in rice suspension cells in the presence of ABA and cycloheximide

The Em gene in rice (Oryzae sativa L.) cell suspensions is strongly induced in the presence of abscisic acid (ABA) or in the presence of an osmoticum such as NaCl. Experiments were conducted to determine the impact of protein synthesis inhibitors on Em mRNA accumulation as part of a study to further characterize regulation of this gene in rice. When rice cell suspensions w ere incubated in the presence of ABA or NaCl and either 10 mu M cycloheximi de (resulting in a 42% inhibition of net protein synthesis) or 100 CIM cycl oheximide plus 10 mu M chloramphenicol (93% inhibition of net protein synth esis), Em mRNA accumulated to a level more than twofold greater than in cel l suspensions treated with either ABA or NaCl alone. Neither cycloheximide nor chloramphenicol alone or in combination induced Em gene expression. Whe n rice cells were exposed to 50 mu M ABA for 1 h and then transferred to me dium without ABA, Em transcript abundance increased until 24 h and then dec lined. The rate of this decline was slower in the presence of the protein s ynthesis inhibitors. The results indicate that de novo protein synthesis is not required for ABA or NaCl induction of Em gene expression in rice suspe nsion cells and that superinduction can occur when protein synthesis is onl y partially blocked in the cell population.