Differential expression of two barley XET-related genes during coleoptile growth

Plant cell elongation depends on the physical properties of the primary cel l wall. Because xyloglucan endotransglycosylases (XETs) are enzymes that me diate cleavage and rejoining of the beta(1-4)-XG backbone of primary cell w all, they are potentially involved in cell elongation. In this paper, the g rowth of the barley coleoptile was related to the expression patterns of tw o genes from this family (hvEXT, hvXEB) in experiments where coleoptile elo ngation Varied according to light/dark treatments in order to assess the po tential role of these genes in cell elongation. In dark-grown and light-gro wn coleoptiles, growth rate variations were associated with altered levels of expression of hvEXT and hvXEB: they were higher in dark-grown than in li ght-grown seedlings, and decreased after 5 d in darkness, and after 4 d in continuous light. In 4-d-old seedlings, coleoptile elongation decreased sig nificantly 4 h after the onset of a continuous white-light irradiation, and hvXEB and hvEXT mRNA levels decreased, respectively, 2 h and 4 h after the onset of white-light irradiation. Moreover, the distribution of hvXEB and hvEXT along the coleoptiles of 4-d-old dark-grown seedlings were different. Altogether, these results suggest a complex pattern of temporal and positi onal expression for the different genes of the XET-related family.