The ‘slender’ mutant of barley (Hordeum vulgare) shows high rates of leaf extension and a reduced temperature threshold for extension growth compared with normal seedlings. The turgor pressure of epidermal and mesophyll cells within the extension zone was unaffected by localized cooling. Measurements of linkage patterns in cell wall carbohydrates isolated from the extension zone showed no variation with genotype or growth temperature, suggesting that the gross chemical architecture of the cell walls was similar.
Differences between genotypes were observed when the rheological properties of extending leaves were measured using an extensiometer. Leaves from mutant seedlings showed greater plastic deformation than those from normal seedlings. These differences were absent in mature leaves or in growing leaves killed in boiling methanol prior to measurement. Differences were observed in the patterns of autolytic release of carbohydrates from cell wall extracts, in the incorporation of radioactivity from 14CO2 into specific components of the extending cell wall and in the amounts of uronic acids released following treatment with pectolytic enzymes. These results are discussed in relation to the hypothesis that the mutation acts by modifying the patterns of turnover of structural components in the extending cell wall, thereby affecting extensibility.