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Expansins are now generally accepted to be the key regulators of wall extension during plant growth. The aim of this study was to characterize expansins in wheat coleoptiles and determine their roles in regulating cell growth. Endogenous and reconstituted wall extension activities of wheat coleoptiles were measured. The identification of beta-expansins was confirmed on the basis of expansin activity, immunoblot analysis, and beta-expansin inhibition. Expansin activities of wheat coleoptiles were shown to be sensitive to pH and a number of exogenously applied factors, and their optimum pH range was found to be 4.0 to 4.5, close to that of alpha-expansins. They were induced by dithiothreitol, K(+), and Mg(2+), but inhibited by Zn(2+), Cu(2+), Al(3+), and Ca(2+), similar to those found in cucumber hypocotyls. An expansin antibody raised against TaEXPB23, a vegetative expansin of the beta-expansin family, greatly inhibited acid-induced extension of native wheat coleoptiles and only one protein band was recognized in Western blot experiments, suggesting that beta-expansins are the main members affecting cell wall extension of wheat coleoptiles. The growth of wheat coleoptiles was closely related to the activity and expression of expansins. In conclusion, our results suggest the presence of expansins in wheat coleoptiles, and it is possible that most of them are members of the beta-expansin family, but are not group 1 grass pollen allergens. The growth of wheat coleoptiles is intimately correlated with expansin expression, in particularly that of beta-expansins.

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AbstractsExpansins, found in the cell wall, have the unique ability to induce immediate cell wall extension. In this study, a β-expansin gene (TaEXPB23) isolated from wheat (Triticum aestivum L.) coleoptiles was transformed to tobacco (Nicotiana tabacum) to investigate its role in plant growth and development. TaEXPB23 was preferentially expressed in wheat coleoptile and a close correlation between TaEXPB23 expression and coleoptile growth was observed. The over-expression of TaEXPB23 in tobacco also resulted in accelerating growth of leaves and internodes at earlier developmental stages, and it was involved in regulating plant development.