| Summary: | <p>Abstract</p> <p>Background</p> <p>Cell elongation is mainly limited by the extensibility of the cell wall. Dicotyledonous primary (growing) cell walls contain cellulose, xyloglucan, pectin and proteins, but little is known about how each polymer class contributes to the cell wall mechanical properties that control extensibility.</p> <p>Results</p> <p>We present evidence that the degree of pectin methyl-esterification (DE%) limits cell growth, and that a minimum level of about 60% DE is required for normal cell elongation in <it>Arabidopsis </it>hypocotyls. When the average DE% falls below this level, as in two gibberellic acid (GA) mutants <it>ga1-3 </it>and <it>gai</it>, and plants expressing pectin methyl-esterase (<it>PME1</it>) from <it>Aspergillus aculeatus</it>, then hypocotyl elongation is reduced.</p> <p>Conclusion</p> <p>Low average levels of pectin DE% are associated with reduced cell elongation, implicating PMEs, the enzymes that regulate DE%, in the cell elongation process and in responses to GA. At high average DE% other components of the cell wall limit GA-induced growth.</p>
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