Extension growth in a barley mutant with reduced sensitivity to low temperature

Abstract

SUMMARYThe ' 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 ^*CO2 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.

Why do leaves and leaf cells of N-limited barley elongate at reduced rates?

“…Similarly, in the one study where cell turgor was measured directly within the growing zone of cereal leaves, a¯at turgor pro®le was found, indicating that developmental changes in elongation rates were brought about by accompanying changes in wall properties (Thomas 1990). A similar conclusion was reached for temperature-dependent changes in cell elongation rates (Thomas et al 1989;Pollock et al 1990). Unfortunately, these studies did not include a detailed analysis of kinematic growth parameters nor was cell osmotic pressure (OP) determined.…”

Biophysical limitation of leaf cell elongation in source-reduced barley

“…The studies involved five different grasses, included a wide range of treatments, investigated leaf 1, 3 or 4, displayed large variation in absolute leaf elongation velocity and showed large differences in residual elongation velocity following plant preparation for turgor analyses. Yet, on average, turgor deviated little (0.53±0.05 MPa; n=11 values; Thiel et al 1988;Thomas et al 1989;Pollock et al 1990;Arif and Tomos 1993;Fricke et al 1997;Thompson et al 1997;Martre et al 1999;present study).…”

“…Averaged over all experiments, residual elongation velocity was 46% and 42% in control and source-reduced plants, respectively. The window-cut approach has been used previously and percent residual elongation velocities were either similar (Fricke et al 1997) or higher (Thomas et al 1989;Pollock et al 1990;Martre et al 1999). Most likely, the latter studies reduced leaf elongation velocity less because leaf 1 was investigated, inflicting only damage to the coleoptile, or plants were incubated overnight following cutting of the window.…”

Apoplast Acidification in Growing Barley (Hordeum vulgare L.) Leaves

“…The similarity in results for expression, protein level and activity may be a coincidence, but more likely reflects a true difference between growing and nongrowing barley leaf tissues. (Claussen et al, 1997;Tode & Lüthen, 2001), temperature (Stoddart & Lloyd, 1986;Pollock et al, 1990) hormones (especially auxin, e.g. : Rayle & Cleland, 1970;Hager et al, 1971;Rayle & Cleland, 1992;Claussen et al, 1997;Tode & Lüthen, 2001;Hager, 2003;Grebe, 2005;Kutschera, 2006) and light (Van Volkenburgh & Cleland, 1980;Stahlberg & Van Volkenburgh, 1999).…”