Elicitation of cotton isoperoxidases by Aspergillus flavus and other fungi pathogenic to cotton

The distribution of peroxidase(s) in non-inoculated cotton bolls and flowers was qualitatively determined. The soluble and bound forms of cotton peroxidase(s) were investigated for changes elicited by fungal infection. Inoculation of cotton bolls, 30 days post anthesis, with Aspergillus flavus, Fusarium equiseti, Fusarium moniliforme, Fusarium semitectum or Rhizoctonia solani followed by a 6-day incubation period stimulated soluble peroxidase activity by 2- to 6-fold. In addition, fungal stress elicited two to five distinct soluble peroxidase isozymes not observed or at very low levels in non-inoculated controls. The pl values by isoelectric focusing for these isoperoxidases were 4·25, 4·35, 4·50, 4·65, 4·75 and 4·83. The pI 4·50 form was produced in controls and was also the major isozyme in the stress profiles. Each cotton-pathogen combination produced a unique peroxidase profile. No differences between control and fungal-stressed bolls were observed with either the specific activity or the peroxidase profile in the case of ionically-bound or covalently-bound classes of the enzyme.