Peroxidase activity and isozyme analysis of pearl millet seedlings and their implications in downy mildew disease resistance

Abstract

Investigation has been carried out on differential expression of peroxidase isozymes in pearl millet seedlings inoculated with downy mildew disease-causing pathogen Sclerospora graminicola. Two-day-old seedlings of eight different pearl millet cultivars were assessed for downy mildew disease reaction under greenhouse conditions. Based on the results, pearl millet cultivars, IP 18292 and IP 18294, were categorized as highly resistant, P 310-17 and MBH 110 as resistant, 5141 B and 81 B as susceptible and 23 B and HB 3 as highly susceptible. Time-course study of peroxidase analysed spectrophotometrically showed increased activity at 8 and 16 h after inoculation in highly resistant cultivar (IP 18292) and highly susceptible cultivar (HB 3), respectively. Time-dependent expression as analysed by isoelectric focusing (IEF) recorded 22 isozymes with pI ranging from 3.6 to 9.8 in highly resistant and induced-resistant seedlings, whereas highly susceptible seedlings showed only 12 isozymes. Cultivar-specific studies showed 55.2 and 54.9, 40.9 and 44.8, 40.8 and 41.9, and 33.6 and 32.9 units of peroxidase activity in highly resistant, resistant, susceptible and highly susceptible seedlings at constitutive level, respectively, and there was a clear-cut difference between them. On inoculation highly resistant, resistant and induced-resistant seedlings recorded increase in enzyme activity, whereas susceptible and highly susceptible seedlings recorded decrease in enzyme activity. The same observation was also recorded in native-PAGE analysis.