CHITINASE ISOENZYMES IN NEAR-ISOGENIC WHEAT LINES CHALLENGED WITH RUSSIAN WHEAT APHID, EXOGENOUS ETHYLENE, AND MECHANICAL WOUNDING

Russian wheat aphid (RWA) infestation, ethylene exposure, and mechanic al wounding resulted in differential expression of chitinase (EC 3.2.1 .14) isoenzymes in near-isogenic wheat lines susceptible and resistant to the RWA. Isoelectric focusing (IEF) and non-denaturing IEF gels re vealed the existence of multiple isoenzymes of chitinase with a wide r ange of isoelectric points, ranging from 9.7 (basic) to 3.4 (acidic). Seven bands were observed in the resistant and susceptible untreated p lants (pI values of approximately 9.5, 9.2, 8.8, 8.5, 8.4, 7.8 and 5.0 ) on IEF gels. RWA infestation resulted in the expression of an additi onal band (approximately pI 5.5) whereas ethylene exposure resulted in the induction of two additional isoenzymes (approximately pI 4.1 and 6.8). Mechanical wounding also induced the isoenzyme with pI of 4.1. I soelectrical focusing (IEF) in liquid medium confirmed the multiple is oenzymes obtained with IEF gels. Five different peaks with chitinase a ctivity were detected in control plants (pI values of 9.2, 7.8, 5.0, 4 .1, and 3.6) after IEF. RWA infestation, ethylene and mechanical wound ing caused the induction of additional isoenzyme peaks. Differential e xpression of chitinolytic activity was also observed between the near- isogenic wheat lines.