THE MYROSINASE-BINDING PROTEIN FROM BRASSICA-NAPUS SEEDS POSSESSES LECTIN ACTIVITY AND HAS A HIGHLY SIMILAR VEGETATIVELY EXPRESSED WOUND-INDUCIBLE COUNTERPART

This communication demonstrates that proteins in the family of myrosin ase-binding proteins (MBP) present in seeds of Brassica napus possess lectin activity, binding most efficiently to p-aminophenyl alpha-D-man nopyranoside-agarose, and to some extent to N-acetylglucosamine -agaro se, A cDNA encoding a vegetatively expressed, wound-inducible counterp art to these seed MBP was isolated and characterised. Upon wounding, t his MBP transcript accumulated in old and young leaves, and was system ically expressed in the young plant. Additionally, the wound-induced M BP transcript increased in abundance after treating the young plants w ith methyl jasmonate (MeJA), jasmonic acid (JA) or abscisic acid (ABA) , and to some extent in response to the ethylene precursor 1-aminocycl opropane-1-carboxylic acid. Expression induced by wounding, ABA or JA was antagonised by simultaneous feeding of the plants with salicylic a cid. MBP polypeptides accumulated in MeJA-treated plants. The myrosina ses redistributed from the soluble fraction into the insoluble fractio n of a tissue extract after induction. The most abundant MBP (94 kDa) partitioned in the insoluble fraction, while two larger MBP (103 kDa a nd 108 kDa) were present only in the soluble fraction of extracts obta ined fi om the control or MeJA-treated plant tissues.