SLENDER BARLEY, AN EXTENSION GROWTH MUTANT

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, result ing in long and attenuated leaves. The difference in growth rate is ac centuated at low temperature. Individual epidermal cells are both long er and narrower in slender, so the whole-plant phenotype is mirrored a t the cell level. Whilst the slender phenotype can be mimicked in norm al plants by the application of gibberellin, endogenous levels are low . In addition, unlike the normal plants, embryo-less half-seeds of sle nder show GA-independent secretion of a-amylase. Unlike mature leaf ti ssue of normal and slender plants which have similar cell wall theolog y, young slender leaves are much more plastic than the corresponding n ormal. Differential screening of cDNA libraries has led to the identif ication 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 proline-ric h protein thought to have a structural role in the cell wall. Gene exp ression at low temperatures suggests that slender is abnormally insens itive to temperature reduction at the molecular level. This is consist ent with leaf extension continuing at lower than normal temperatures i n slender compared with normal.