Restricted cell elongation in Arabidopsis hypocotyls is associated with a reduced average pectin esterification level

Background: 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. Results: 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 Arabidopsis hypocotyls. When the average DE% falls below this level, as in two gibberellic acid ( GA) mutants ga1-3 and gai, and plants expressing pectin methyl-esterase ( PME1) from Aspergillus aculeatus, then hypocotyl elongation is reduced. Conclusion: 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.