The proline-rich proteins (PRPs) form a class of plant cell wall structural proteins. The expression of PRP genes is organ- and tissue-specific and it is induced in response to wounding, infection and other stress conditions, but the role of these proteins in the cell wall during development and stress has not yet been established. Our objective was the characterization of a cDNA clone, termed CanPRP, isolated from a cDNA library of growing epicotyls of Cicer arietinum, and the study of the relationship between its expression and cell wall modifications during growth. CanPRP differential expression was analysed by northern blot through epicotyl growth, under different growth conditions and in different organs of chickpea. CanPRP encodes a putative PRP that contains 15 alternating pentapeptide repeats: Pro-Pro-Val-Tyr-Lys and Pro-Pro-Val-Glu-Lys, typical features of cell wall PRPs. The levels of PRP transcripts are almost undetectable in young epicotyls and increase during epicotyl growth, with the highest levels of expression found once growth begins to cease and the cell wall starts to strengthen. Accordingly, the stem of chickpea displays the highest leve! of expression in the basal internode, with reduced growth, decreasing towards the apex. Expression of the CanPRP clone was induced by osmotic and saline stress which inhibited growth. We conclude that the protein deduced from the CanPRP clone participates in the cell wall-hardening process in either the stress-mediated inhibition of growth or when cell growth ceases as development takes place.
