BASIC CHITINASES ARE CORRELATED WITH THE MORPHOGENIC RESPONSE OF FLAXCELLS

Flax (Linum usitatissimum) hypocotyl protoplasts immobilized in a calc ium-alginate matrix give rise to embryo-like structures. A direct corr elation was established between the presence of a set of ionically-bou nd cell wall proteins, which includes the basic polypeptides P184 and P183 with an apparent molecular mass of 25 kDa, and this morphogenic r esponse. Microsequencing of tryptic fragments from P184 and P183 indic ated homologies with the chitinase family. These homologies were confi rmed by demonstrating that, after renaturation, such proteins express a potential chitinase activity in SDS-PAGE gel containing glycol chiti n as synthetic substrate. Using degenerate primers from P184 internal sequences, we isolated one partial genomic sequence of a chitinase of 626 bp from which a putative 74-amino acid sequence, disrupted by one intron, was deduced. High degrees of homology with several plant chiti nases, including those expressed during somatic embryogenesis or in se eds, were observed. P184 microsequences match the corresponding sequen ce deduced from the chitinase PCR-fragment perfectly.