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.