Journal Article

Water relations and leaf expansion: importance of time scale

Rana Munns, John B. Passioura, Jianmin Guo, Ofer Chazen and Grant R. Cramer

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 51, issue 350, pages 1495-1504
Published in print September 2000 | ISSN: 0022-0957
Published online September 2000 | e-ISSN: 1460-2431 | DOI: http://dx.doi.org/10.1093/jexbot/51.350.1495
Water relations and leaf expansion: importance of time scale

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The role of leaf water relations in controlling cell expansion in leaves of water‐stressed maize and barley depends on time scale. Sudden changes in leaf water status, induced by sudden changes in humidity, light and soil salinity, greatly affect leaf elongation rate, but often only transiently. With sufficiently large changes in salinity, leaf elongation rates are persistently reduced. When plants are kept fully turgid throughout such sudden environmental changes, by placing their roots in a pressure chamber and raising the pressure so that the leaf xylem sap is maintained at atmospheric pressure, both the transient and persistent changes in leaf elongation rate disappear. All these responses show that water relations are responsible for the sudden changes in leaf elongation rate resulting from sudden changes in water stress and putative root signals play no part. However, at a time scale of days, pressurization fails to maintain high rates of leaf elongation of plants in either saline or drying soil, indicating that root signals are overriding water relations effects. In both saline and drying soil, pressurization does raise the growth rate during the light period, but a subsequent decrease during the dark results in no net effect on leaf growth over a 24 h period. When transpirational demand is very high, however, growth‐promoting effects of pressurization during the light period outweigh any reductions in the dark, resulting in a net increase in growth of pressurized plants over 24 h. Thus leaf water status can limit leaf expansion rates during periods of high transpiration despite the control exercised by hormonal effects on a 24 h basis.

Keywords: Leaf growth; water stress; salinity.

Journal Article.  7701 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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