Antimicrobial proteins from cowpea root exudates:: inhibitory activity against Fusarium oxysporum and purification of a chitinase-like protein

Plants exude a variety of substances through their external surfaces and from germinating seeds, some of which have an inhibitory action against plant pathogens. The aim of this study was the investigation and characterization of defense proteins present in exudates from roots of cowpea seedlings (Vigna un-guiculata (L.) Walp.). Root exudates were collected from seedlings that were grown hydroponically in three different media, including, 100 mM sodium acetate buffer pH 4.5, water pH 6.0 and 100 mM sodium phosphate buffer pH 7.5. The proteins from these exudates were analyzed by SDS-PAGE and SDS-Tricine-PAGE and the presence of antimicrobial proteins in the exudates was investigated by immunological and enzymatic assays. Results showed that roots from cowpea seedlings contained beta-1,3-Glucanases, chitinases and lipid transfer proteins (LTPs), all of which may potentially function as plant defense proteins. Immunolocalization of one of these proteins, chitinase, revealed its presence in the xylem cell wall vessel elements. These exudates also demonstrated an inhibitory effect on the growth of the fungus, Fusariuin oxysporum, in vitro. The results suggest that plant roots may exude a variety of proteins that may function to repress the growth of root pathogenic fungi.