bIII-Gal, a member of the chickpea b-galactosidase family,
is the enzyme responsible for the cell wall autolytic process.
This enzyme, whose activity increases during epicotyl
growth, displays significant hydrolytic activity against cell
wall pectins, and its natural substrate has been determined
as an arabinogalactan from the pectic fraction of the cell wall.
In the present work, the localization of bIII-Gal in different
seedling and plant organs was analyzed by using specific antibIII-
Gal antibodies. Our results revealed that besides its possible
role in cell wall loosening and in early events during
primary xylem and phloem fiber differentiation bIII-Gal
acts on the development of sieve elements. Localization of
the enzyme in this tissue, both in epicotyls and radicles from
seedlings and in the different stem internodes, is consistent
with the reduction in galactan during the maturation of
phloem elements, as can be observed with LM5 antibodies.
Thus, bIII-Gal could act on its natural substrate, the neutral
side chains of rhamnogalacturonan I, contributing to cell wall
reinforcement allowing phloem elements to differentiate,
and conferring the necessary strengthening of the cell wall
to fulfill its function. This work completes the immunolocation
studies of all known chickpea b-galactosidases. Taken
together, our results reflect the broad range of developmental
processes covered by different members of this protein
family, and confirm their crucial role in cell wall remodeling
during tissue differentiation.
