Quantitative and qualitative changes in cell wall polysaccharides in relation to growth and cell wall loosening in Lactuca sativa hypocotyls

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Abstract
The correlation between hypocotyl elongation, cell wall loosening and changes in cell wall polysaccharides was studied using intact lettuce seedlings grown in the dark or in light together with gibberellic acid (GA) and/or 5‐fluorodeoxyuridine (FUDR). The following results were obtained:1) The production of pectic, hemicellulosic and cellulosic polysaccharides look place in parallel with hypocotyl elongation, which was substantially affected by different growth conditions.2) The mole percentage sugar composition of pectic and hemicellulosic polysaccharides changed in response to dark, light, GA, or FUDR treatments.3) The amounts of xylose and glucose in hemicellulosic polysaccharides and those of galactosc, rhumnose and uronic acid in pectic polysaccharides increased in parallel with hypocotyl elongation.4) Statistical analysis of the quantitative relationship between sugars composing polysaccharides revealed that the uronic acid content changed in parallel with those of rhamnose and galactose in pectic polysaccharides, and the content of xylose varied in parallel with those of fucose and glucose.5) The content of hemicellulosic polysaccharides was correlated with cell wall loosening represented by a decrease in the minimum stress‐relaxation time. Changes in the stress‐relaxation time value were correlated with those in the content of araltinose and galactose in hemicellulosic polysaccharides.Based on these results, the relationship between hypocotyl elongation, changes in cell wall polysaccharides, and cell wall loosening is discussed with respect to the effect of GA and FUDR on hypocotyl elongation.