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Articles

Pectin Esterase in Relation to Leaf Abscission in Coleus and Phaseolus¹

Department of Botany and Plant Pathology, Iowa State University, Ames, Iowa 50010, Department of Biology, Boston University, Boston, Massachusetts 02215

Pectin esterase (PE) activities in abscission zones, other portions of leaves, and adjacent stem tissues were compared in attached leaves and abscissing petioles (previously debladed) of Coleus blumei Benth. and Phaseolus vulgaris L., cv. Canadian Wonder. Earlier findings of Osborne in bean were confirmed and changes in PE activity in coleus were shown to resemble those in bean in some respects. In both plants PE was lower in the distal portion of abscission zones of abscissing petioles than in that portion of attached leaves but this difference was not as large or as consistently clear-cut in coleus as in bean. The general level of PE activity was an order of magnitude lower and changes associated with abscission were smaller in coleus than in bean. Auxin treatment of debladed petioles of coleus prevented abscission and resulted in small increases in PE activity in abscission zones and most of the other regions sampled. The largest increase was observed in the stem tissue adjacent to the attached leaf opposite the debladed, auxin treated one.

The activity of coleus PE was highest in the pH range from 7.3 to 7.6. The pH of distal tissue from abscission zones of abscissing petioles was 5.8. This was 0.7 pH units lower than that of proximal tissue from the same zones.

PE from both coleus and bean appears to be denatured by freezing and/or thawing.

³ Present address: Institute of Statistics, Texas A&M University. College Station, Texas 77840.

⁴ Present address: University of Udaipur, Jodhpur, Rajasthan, India.

¹ This work was supported in part by research grants (GB1916 and GB5333) from the National Science Foundation. One of the authors (L.L.R.D.) was supported by funds provided to Boston University by the federal College Work-Study Program of the Office of Education, Department of Health, Education, and Welfare.