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Cell Isoperoxidases in Sweet Potato Plants in Relation to Mechanical Injury and Ethylene

Paul Urban^b

^a Department of Biological Sciences, Union College, Schenectady, New York 12308, ^b Electron Microscopy Laboratory, Veterans Administrations Hospital, Albany, New York 12208

Leaves and storage roots of sweet potato plants (Ipomea batatas) showed the same qualitative isoperoxidase patterns and a similar distribution of distinctive isoperoxidases between the cell protoplast and cell wall free, ionically bound, and covalently bound fractions. No changes in the qualitative isoenzyme spectrum were found in relation to age, mechanical injury, or ethylene action. Thus, as in tobacco plants, the cell isoperoxidases in sweet potato did not reflect the possible differential mRNA synthesis in relation to organ, age, or injury. Transcription does not seem to be a limiting factor in injury- and ethylene-dependent peroxidase enhancement during the first 24 hr.

The contribution of the wall ionically bound and protoplast fractions was highest in young and old leaves, respectively. In the protoplast and wall ionically and covalently bound fractions, 14, 6, and 5 isoenzyme bands were found; in addition, 4 bands, not detected in the protoplast, were also revealed in the covalently bound fraction. The distinctive "juvenile" and, developing with age, "mature" isoforms were mainly found in the ionically bound and protoplast fractions, respectively.

The injury-enhanced and/or ethylene-enhanced peroxidase development was most pronounced in young leaves. Ethylene suppressed some injury-enhanced, had no effect on some other injury-enhanced, and greatly promoted some of the injury-unaffected or enhanced isoperoxidases. After ethylene removal, an increase in the "mature" isoforms was found in the protoplast of intact leaves.

Electron microscopy of leaves revealed peroxidase in membrane-bound vesicles located mainly in the vacuole; a thin layer of reaction products was also found on the wall's outer surface. No Golgi apparatus were seen in the cells of control or ethylene-treated intact leaves. In ethylene-treated intact or injured leaves accumulations of reaction products between the plasmalemma and wall were also found. Numerous Golgi apparatus with dark stained vesicles were seen in injured, and especially in injured and ethylene-treated leaves; the vacuolar bodies seemed to occur in very great number.