Stomatal development in barley as a bioassay for cell differentiation: Its use with X-rays and gibberellic acid.

A bioassay for cell differentiation during stomatal development in barley (Hordeum vulgare L.) has been defined. It uses cell kinetics analysis to follow the temporal course of cell divisions in the developmental sequence. The rate of displacement of the divisions along the stomatal rows provides a measure of differentiation. Physical factors affecting differentiation may be tested with intact seedlings. The bioassay showed that X-ray irradiation inhibited the divisions leading to stomatal formation. The inhibition kinetics was similar to the one observed in root meristems. Chemical substances are tested by culturing excised shoots in a synthetic medium. Detached leaves responded to sucrose and light with increasing rates of stomatal divisions. Gibberellic acid (GA3) was assayed for its effects on the growth of the leaf and the differentiation of stomata. GA3 increased the overall length of the leaves without affecting the rates of cell division. The treated cells responded with increased elongation rates and a precocious initiation and completion of cell enlargement. GA3 had no specific effect on stomatal differentiation.