Oxygen Status of Potato Tuber Tissue in Relation to Maceration by Pectic Enzymes ofErwinia carotovora

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Abstract
Tissue maceration in tubers injected with filter-sterilized culture filtrate containing pectolytic enzymes from E. carotovora (Ec) was compared to that produced by injections of viable suspensions of Ec at low and ambient O2 levels. Both types of injection resulted in rapid decay of tuber tissue under low O conditions; in contrast, no decay occurred in tissue incubated in air. Lesions formed in enzyme-injected anaerobic tubers were similar to those induced by inoculation with cells of Ec. Absence of maceration in air was not attributable to loss of enzyme activity at the injection site. Pectate lyase (PL) activity declined almost 5-fold when culture filtrates were stored aerobically for 96 h; however, macerating activity was still present. Furthermore, cultures of Ec grew more rapidly and reached higher population levels when cultured aerobically in vitro than under anaerobic conditions. Under aerobic conditions a host-mediated response affecting pectic enzyme substrates and/or activity may contribute to the initial resistance of potato tubers to bacterial soft rot infection before direct inhibition of bacterial growth occurs.

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