Summary. Expansins are now generally accepted to be the key regula- tors 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 ac- tivities of wheat coleoptiles were measured. The identification of -ex- pansins was confirmed on the basis of expansin activity, immunoblot analysis, and -expansin inhibition. Expansin activities of wheat coleop- tiles were shown to be sensitive to pH and a number of exogenously ap- plied factors, and their optimum pH range was found to be 4.0 to 4.5, close to that of -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 -expansin family, greatly in- hibited acid-induced extension of native wheat coleoptiles and only one protein band was recognized in Western blot experiments, suggesting that -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 sug- gest the presence of expansins in wheat coleoptiles, and it is possible that most of them are members of the -expansin family, but are not group 1 grass pollen allergens. The growth of wheat coleoptiles is inti- mately correlated with expansin expression, in particularly that of -ex- pansins. Keywords: Cell extension; Cell elongation growth; Cell wall; Ex- pansin; Wheat coleoptile. Abbreviations: DTT dithiothreitol; EDTA disodium ethylenediaminete- traacetate; PVDF polyvinylidene fluoride membrane. Introduction Expansins are cell wall proteins that induce cell wall ex- tension in vitro and cell expansion in vivo by disrupting hydrogen bonds between cellulose microfibrils and matrix polymers (McQueen-Mason and Cosgrove 1994, Cos- grove 1999). Since they were first isolated from cucumber hypocotyls (McQueen-Mason et al. 1992), expansins have been identified in many plant species and organs (Cos- grove 1997, 2000; Cho and Cosgrove 2002; Li et al. 2003; Kwasniewski and Szarejko 2006). Previous research has shown that expansins participate in the process of plant growth. For example, Huang et al. (2000) reported a close relationship between the expression of expansin genes and rice coleoptile elongation in response to different oxygen concentrations. In another study, maize roots in low water potentials were able to continue growing by increasing the extensibility of the cell walls and this was correlated with an increase in expansin activity and transcript accumula- tion (Wu et al. 2001). The expansin superfamily of plant proteins is made up of four families, designated -expansin (EXPA), -ex- pansin (EXPB), expansin-like A (EXLA), and expansin- like B (EXLB) (Sampedro and Cosgrove 2005). -Expansin and -expansin proteins are known to have cell wall-loosening activity and to be involved in cell ex- pansion and other developmental events during which cell wall modification occurs. -Expansin proteins and some, but not all, -expansin proteins are implicated as catalysts of “acid growth’’. While a role of -expansins in cell ex- tension has been reported for many plants (McQueen-Ma- son and Rochange 1999, Cosgrove 2000), -expansins were originally represented by group 1 allergens of grass pollen (Cosgrove et al. 1997), which constitute a divergent group of -expansin family expressed at high levels in the pollen of grasses but not of other plant groups, with addi- tional research suggesting -expansins are more abundant Expansins and coleoptile elongation in wheat Qiang Gao 1,2 , Meirong Zhao 1 , Feng Li 1 , Qifang Guo 1 , Shichao Xing 1 , Wei Wang 1 1 State Key Laboratory of Crop Biology, College of Life Science, Shandong Agricultural University,Tai’an, Shandong 2 Chemical Engineering Department, XuZhou College of Industrial Technology, Xuzhou, Jiangsu Received 18 October 2007; Accepted 14 January 2008; Published online 26 August 2008 © Springer-Verlag 2008 Protoplasma (2008) DOI 10.1007/s00709-008-0303-1 PROTOPLASMA Printed in Austria Correspondence: Wei Wang, State Key Laboratory of Crop Biology, College of Life Science, Shandong Agricultural University, Tai’an, Shan- dong, 271018, People’s Republic of China. E-mail: wangw@sdau.edu.cn