Leaf extension in the slender barley mutant: delineation of the zone of cell expansion and changes in translatable mRNA during leaf development

The slender mutant of barley (Hordeum vulgare L.) results from an alteration to a single nuclear gene. Plants homozygous for the mutant allele have long, attenuated leaves as a result of a greatly increased extension rate. Although the growth rate at any one position in the extension zone appears not to differ between slender and normal (wild-type) barley, in slender the length of the zone over which cells extend is approximately 50% greater than that in normal barley. Epidermal cells are both longer and narrower in slender, so the whole-plant phenotype is mirrored at the cell level. Translation in vitro of RNA extracted from successive sections of the young primary leaf, followed by one-dimensional SDS-PAGE separation, facilitated the alignment of equivalent developmental stages in the two genotypes, but failed to demonstrate major differences between the two genotypes. Two-dimensional separation of translation products from total leaf tissue revealed a few small differences between normal and slender. Growth of plants at 8°C compared with 20°C caused changes in some translation products, with one (unknown) product decreasing in abundance in cold-treated normal tissue but not in slender tissue.