Journal Article

Cell wall water content has a direct effect on extensibility in growing hypocotyls of sunflower (<i>Helianthus annuus</i> L.)

Carol Evered, Bhavita Majevadia and David Stuart Thompson

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 58, issue 12, pages 3361-3371
Published in print September 2007 | ISSN: 0022-0957
Published online September 2007 | e-ISSN: 1460-2431 | DOI: https://dx.doi.org/10.1093/jxb/erm183

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It has been proposed that spacing between cellulose microfibrils within plant cell walls may be an important determinant of their mechanical properties. A consequence of this hypothesis is that the water content of cell walls may alter their extensibility and that low water potentials may directly reduce growth rates by reducing cell wall spacing. This paper describes a number of experiments in which the water potential of frozen and thawed growing hypocotyls of sunflower (Helianthus annuus L.) were altered using solutions of high molecular weight polyethylene glycol (PEG) or Dextran while their extension under constant stress was monitored using a creep extensiometer (frozen and thawed tissue was used to avoid confounding effects of turgor or active responses to the treatments). Clear reductions in extensibility were observed using both PEG and Dextran, with effects observed in hypocotyl segments treated with PEG 35 000 solutions with osmotic pressures of ≥0.21 MPa suggesting that the relatively mild stresses required to reduce water potentials of plants in vivo by 0.21 MPa may be sufficient to reduce growth rates via a direct effect on wall extensibility. It is noted, therefore, that the water binding capacity of plant cell walls may be of ecophysiological importance. Measurements of cell walls of sunflower hypocotyls using scanning electron microscopy confirmed that treatment of hypocotyls with PEG solutions reduced wall thickness, supporting the hypothesis that the spatial constraint of movement of cellulose microfibrils affects the mechanical properties of the cell wall.

Keywords: Cell wall extensibility; extensiometry; PEG; plant growth; sunflower; water relations

Journal Article.  6469 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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