Powstawanie wolnych rodników w rozwoju szarej pleśni na liściach poinsecji [The generation of free radicals in the development of grey mould on poinsettia leaves]

Abstract

Participation of superoxide anion and hydroxyl radical as well as lipoxygenase (LOX) activity and chemiluminescence in the development of grey mould on poinsettia leaves of the cvs.: Coco White – moderately resistant and Malibu Red - susceptible to Botryotinia fuckeliana (B. cinerea) were investigated. In both poinsettia cultivars, the level of superoxide anion radical increased with the disease development. On later dates following inoculation, the content of O₂^·– in the diseased leaf areas of the susceptible cultivar was 2-fold larger than in grey mould symptom areas of the moderately resistant cultivar. The postinfection generation of a strongly reactive hydroxyl radical was found in the cultivar susceptible to the pathogen. The level of ^·–OH in the last hours afier inoculation was 10 fold higher in grey mould spots than in healthy senescing leaves of that cultivar. Tlie activity of LOX exhibited opposite tendencies of changes in the both genotypes examined after the infection. In the first hours after inoculation, the enzyme activity was Low, whereas after 3^rd day it significantly increased in diseased leaf areas and in their surroundings. However, in the moderately resistant cultivar the activity of lipoxygenase thoughout the first 3 days of the disease activity was relatively high and then decreased. Poinsettia leaves infected with B. cinerea emitted chemiluminescence. Kinetics and the intensity of ultraweak chemiluminescence depended on the cultivars of poinsettia and on the degree of the disease development. The postinfection increase of chemiluminescence was particularly visible in the zone surrounding diseased areas in the susceptible cultivar.