The relationship and properties of pectic glycosidases produced by host and pathogen during anthracnose disease of avocado

Polygalacturonase activity was substantially induced in avocado fruit after infection with Colletotrichum gloeosporioides. The enzyme was extracted from healthy and infected tissues of inoculated fruits and purified about 13-fold by DEAE-cellulose column. Both enzyme preparations gave a single fraction after elution from the column, though thermal inactivation and disc electrophoretic studies indicated two components in the enzyme fraction of the infected tissue as compared to a single component in the fraction of the healthy one. The two components were quantitatively separated by CM-cellulose chromatography and characterized as fungal and avocado polygalacturonases, respectively. The fungal polygalacturonase constitutes approximately 16 per cent of the total activity in the infected tissue and was not detected in the healthy mesocarp. The fungal enzyme attacked pectic acid by random mechanism of hydrolysis and showed higher activity with non-methylated pectic substrates. Digalacturonic acid was not attacked by the fungal polygalacturonase. The pH optima of the last enzyme was 5·5 and 4·5 for pectic and trigalacturonic acids, respectively. The avocado polygalacturonase showed lower stability to temperature inactivation and higher K_m value as compared to the fungal enzyme. The results demonstrated that softening of the mesocarp during anthracnose development is primarily due to induction of the avocado polygalacturonase.