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.