Differential accumulation of β-1,3-glucanase and chitinase isoforms in pepper stems infected by compatible and incompatible isolates of Phytophthora capsici

Abstract

Phytophthora capsici infection induced the synthesis and accumulation of β-1,3-glucanases and chitinases in the stem tissues of pepper plants. The hydrolase increase started soon after inoculation with P. capsici . After the appearance of symptoms on the pepper stems, the accumulation of β-1,3-glucanases became much pronounced in the incompatible interaction. However, induction of chitinases by P. capsici infection was very similar in both compatible and incompatible interactions, except that the enzyme activity was somewhat higher in the incompatible interaction at 4 days after inoculation. The use of polyacrylamide gel electrophoresis (PAGE) and isoelectric focusing gels could detect and quantitate the isoforms of the two hydrolases in pepper plants. The direct detection of β-1,3-glucanases on PAGE gels revealed two acidic isoforms Ga 1 and Ga 2. The pI 4·8 isoform Ga 2 may be associated with the expression of resistance to P. capsici , because its high activity per unit protein amount was detected only in the incompatible interaction 3–4 days after inoculation. Most basic isoforms of β-1,3-glucanases were induced and accumulated in both the compatible and incompatible interactions, suggesting a possible involvement of the hydrolases in the infection process rather than in the resistance expression. The pI 8·8 isoform of β-1,3-glucanase was constitutively expressed in pepper stems, irrespective of P. capsici infection or mercuric chloride-treatment. No significant differences in electrophoretic patterns of chitinase isoforms were found between the compatible and incompatible interactions. A 32 kDa chitinase was identified on SDS-PAGE gels after its renaturation by treatment with deionized Triton X-100.