Slender barley, an extension growth mutant

Abstract

Abstract Slender barley arises from a mutation in a single nuclear-gene and has pleiotropic effects on growth and development. Plants homozygous for the mutant allele have a greatly increased leaf extension rate, resulting in long and attenuated leaves. The difference in growth rate is accentuated at low temperature. Individual epidermal cells are both longer and narrower in slender, so the whole-plant phenotype is mirrored at the cell level. Whilst the slender phenotype can be mimicked in normal plants by the application of gibberellin, endogenous levels are low. In addition, unlike the normal plants, embryo-less half-seeds of slender show GA-independent secretion of α-amylase. Unlike mature leaf tissue of normal and slender plants which have similar cell wall rheology, young slender leaves are much more plastic than the corresponding normal. Differential screening of cDNA libraries has led to the identification of at least five genes with altered patterns of expression in slender. Described in detail are expression patterns for two of these; pcD1311 encoding a shoot peroxidase, and WPRP1 encoding a prolinerich protein thought to have a structural role in the cell wall. Gene expression at low temperatures suggests that slender is abnormally insensitive to temperature reduction at the molecular level. This is consistent with leaf extension continuing at lower than normal temperatures in slender compared with normal.