IDENTIFICATION OF STABLE-PLANT CYSTATIN NEMATODE PROTEINASE COMPLEXESUSING MILDLY DENATURING GELATIN/POLYACRYLAMIDE GEL-ELECTROPHORESIS/

The biochemical interactions between two cystatins from rice seeds, or yzacystatin I (OCI) and oryzacystatin II (OCII), and the cysteine prot einases from three plant parasitic nematodes, Meloidogyne hapla. M. in cognita and M. javanica, were assessed using standard protease assays and mildly denaturing gelatin/polyacrylamide gel electrophoresis (gela tin/PAGE). Activity detected in extracts of preparasitic second-stage larvae (J2) from M. hapla was optimal at pH 5.5 and was inhibited in v itro by the cysteine proteinase inhibitors trans epoxysuccinyl-L-leucy lamido-(4-guanidino) butane, hen egg cystatin, OCI, and OCII. As demon strated by class-specific activity staining, all the activity measured between pH 3.5 and pH 7.5 was accounted for by a major proteinase for m, Mhp1, and two minor forms, Mhp2 and Mhp3. Mhps were also detected i n extracts and excretions of parasitic J2 and adult females, indicatin g their continuous expression throughout development of M. hapla, and their possible involvement in the extracellular degradation of protein s. Interestingly, the two plant cysteine proteinase inhibitors OCI and OCII showed different degrees of affinity for the major proteinase fo rm, Mhp1. Both inhibitors almost completely inactivated this proteinas e in native conditions but, unlike OCII, OCI conserved a high affinity for Mhp1 during mildly denaturing gelatin/PAGE, showing the different ial stabilities of the OCI/Mhp1 and OCII/Mhp1 complexes. In contrast t o Mhp1, the major cysteine proteinases detected in the two closely rel ated species M. incognita and M. javanica were strongly inhibited by O CII, while the inhibition by OCI was partly prevented during electroph oresis. This species-related efficiency of plant cystatins against nem atode cysteine proteinases could have practical implications when plan ning their use to control nematodes of the genus Meloidogyne.