Analysis of chitinase isoenzymes in sorghum seedlings inoculated with 'Fusarium thapsinum' or 'F. proliferatum'

Abstract

An investigation was conducted on the chitinase isoenzymes in various tissues of 1-week-old sorghum seedlings that had been inoculated with the fungal pathogens Fusarium thapsinum and Fusarium proliferatum. Electrophoresis of non-denatured extracts on SDS-PAGE gels revealed at least 11 bands of activity. Using native PAGE gels, seven acidic isoenzymes and four basic isoenzymes were identified. Two acidic chitinases were expressed constitutively and their activity did not differ between control and inoculated seedlings. The activity of the other acidic isoenzymes increased in all tissues following inoculation. The activities of both inducible and constitutive acidic chitinase isoenzymes were higher in the scutellum than in other tissues. Inducible basic chitinases increased only in the roots and shoots after infection, while the activity of basic chitinases decreased in the seed and scutellum. The pattern of chitinase isoenzymes from dormant caryopses was different from that in seed-derived tissues in the seedling. Generally, seedling tissues infected with Fusarium fungi had higher levels of acidic isoenzymes and lower levels of basic isoenzymes than dormant caryopses. The findings were consistent with hypotheses that acidic chitinases are primarily involved in active defence responses, while basic chitinases are part of pre-formed defence mechanisms.