Coordinated action of β-galactosidases in the cell wall of embryonic axes during chickpea germination and seedling growth

The plant cell wall is a dynamic structure whose constant modification is necessary for plant cells to grow and divide. In the cell walls of chickpea (Cicer arietinum) there are at least four β-galactosidases, whose presence and location in embryonic axes during the first 48 h of seed imbibition are discussed in this paper. We examined their roles as cell wall-modifying enzymes in germinative and/or post-germinative events. At the start of germination, only βV-Gal, and to a lesser extent βIV-Gal, appear in the axes before rupture of the testa, suggesting they are related to germination sensu stricto. Once the testa has broken, the four β-galactosidases are involved in growth and differentiation of the axes. Immunolocation of the different proteins in axes, which in part confirms previous results in seedlings and plants, allows assignment of post-germinative roles to βI-Gal and βIII-Gal as cell wall modifiers in vascular tissue elements. βIV-Gal and βV-Gal participate in the initial events of germination in which cell walls are involved: βV-Gal in cell proliferation, detachment of root cap cells and initial vascular tissue differentiation; both of them in xylem maturation; and βIV-Gal in thickening of the primary cell wall. Together with other cell wall-modifying enzymes, such as expansins and XTH, chickpea galactosidases might function in a sequential order in turnover of the primary cell wall, allowing the elongation of embryonic axes during seed germination.