Peroxidase and chitinase isoenzyme activities during root infection of Chinese cabbage with Plasmodiophora brassicae

Abstract

Roots of two Chinese cabbage (Brassica campestris L. ssp. pekinensis) varieties, one tolerant and one susceptible, were inoculated with Plasmodiophora brassicae in liquid medium and in soil. Chitinase and peroxidase activities were determined in roots and shoots 1–21 days after inoculation with resting spores of Plasmodiophora and the enzyme activities compared with healthy tissue of the same age. In infected roots of the susceptible variety ‘Granat’ chitinase activity was higher than in the control 10 days after inoculation with spores. In the tolerant variety ‘Parkin’ we detected an increase in chitinase activity at the same time, which was about twice that of ‘Granat’. Chitinase activity in ‘Granat’ was also enhanced on day 13, 14 and 17 after inoculation, whereas chitinase activity in ‘Parkin’ was lower in the infected roots than in the controls during that period. In the shoots no correlation between chitinase activity and infection in the two varieties was observed. Chitinase from Chinese cabbage was further characterized and showed a pH optimum at pH 4.5–5.5 and a temperature optimum at 35–45°C. After isoelectric focusing 7 isoenzymes were discovered, but there were almost no differences between infected and healthy root extracts. Two isoenzymes with pI 8.7 and 8.8 showed cross‐reactivity with an antiserum against bean chitinases. The molecular mass of these isoenzymes was determined as 33 kDa. Total peroxidase activity was generally higher in root tissue of both varieties than in the shoots. Peroxidase activity was increased most prominently in infected ‘Granat’ roots on day 13 after inoculation and of both varieties on day 17 compared to the controls. In clubbed tissue of ‘Granat’ a specific peroxidase isoenzyme appeared the first time 21 days after inoculation and was most prominent 28–30 days after inoculation. This isoenzyme had a molecular mass of ca 24 kDa and a pI of ca 8.8. With respect to our results the strategy of the Plasmodiophorales for plant attack is discussed.