Expansins and coleoptile elongation in wheat

Summary.

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 β-expansins was confirmed on the basis of expansin activity, immunoblot analysis, and β-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 α-expansins. They were induced by dithiothreitol, K⁺, and Mg²⁺, but inhibited by Zn²⁺, Cu²⁺, Al³⁺, and Ca²⁺, similar to those found in cucumber hypocotyls. An expansin antibody raised against TaEXPB23, a vegetative expansin of the β-expansin family, greatly inhibited acid-induced extension of native wheat coleoptiles and only one protein band was recognized in Western blot experiments, suggesting that β-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 β-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 β-expansins.