Cell wall hydrolases have been assumed to be involved in the regulation of seed germination, mostly through their contribution to the cell
wall disassembly associated with endosperm cap weakening. In Cicer arietinum (a non-endospermic leguminosae seed), we have focused our
research directly on the elongation process of the embryonic axes themselves during germination. The genes encoding cell wall proteins, previously
implicated in the elongation of chickpea epicotyls, might also be involved in the expansion of embryonic axis cells, and the modulation
of their expression could be part of the control of the germinative process. Thus, chickpea α-expansins and xyloglucan endotransglycosylase/
hydrolase (XTH) acting on the cellulose/xyloglucan network seem to be involved in the elongation of both chickpea epicotyls and embryonic
axes, although the products of different genes perform their actions on each organ. Among the four known cDNAs encoding chickpea α-
expansins, Ca-EXPA1 was the only isoform highly expressed in embryonic axes during germination. In contrast to epicotyl elongation, the
genes encoding cell wall β-galactosidases, involved in pectin degradation, were not expressed during germination, suggesting no role in embryonic
axis elongation, mainly due to the different metabolism of pectins during cell wall loosening in embryonic axis or epicotyl cells. The results
concerning CanST-1 and -2, encoding two growth-related cell wall proteins, suggested that these genes were not involved in elongation of
embryonic axes during germination. The transcription pattern of Cap28, which encodes a glutamic acid rich cell wall protein of unknown function,
indicated a role in the development of the embryonic axes during germination.
