| Abstract
| - The potential role of xyloglucan endotransglycosylase (XET) in GA-stimulated cell elongation was investigated during leaf expansion in barley (Hordeum vulgare L.). XET activity in aqueous extracts of leaves was detected in all segments along the elongating blade of leaf 1 of seedlings, but was at highest levels in basal segments. Leaf 1 elongation rates of gibberellin (GA)-responsive dwarf mutants were lower than the wild type, and accompanied by reduced levels of XET activity. Leaf elongation rates of the dwarfs increased following treatment with gibberellic acid (GA3) associated with higher levels of XET activity. The slender mutant, crossed into a dwarfing background, exhibited high rates of leaf 1 elongation and high levels of XET activity without added GA3. The elongation of leaf 3 in a GA-responsive dwarf mutant was also studied. Treatment with GA3 resulted in blade and sheath lengths being 5-fold and 7-fold (respectively) the lengths of controls, and again there were increases in blade and sheath XET activities. To investigate the basis for changes in XET activity levels two XET-related cDNA clones were isolated. RNAs detected by the two clones occurred at the highest levels in basal segments of rapidly elongating leaves, but they had different distribution patterns along the leaf. Overall, the data indicate that an XET-like activity is detectable in barley leaves, that the activity level and related.
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