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Inhibition of Penicillium expansum Polygalacturonase Activity by Increased Apple Cell Wall Calcium. William S. Conway, Research plant pathologist, USDA, ARS, Horticultural Crops Quality Laboratory, BARC-West, Beltsville, MD 20705; Kenneth C. Gross(2), Charles D. Boyer(3), and Carl E. Sams(4). (2)Plant physiologist, USDA, ARS, Horticultural Crops Quality Laboratory, BARC-West, Beltsville, MD 20705; (3)Professor, Department of Horticulture, The Pennsylvania State University, University Park 16802; (4)Associate professor, Department of Plant and Soil Science, University of Tennessee, Knoxville 37996. Phytopathology 78:1052-1055. Accepted for publication 29 February 1988. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1988. DOI: 10.1094/Phyto-78-1052.

Apples were pressure infiltrated at harvest with solutions of CaCl2 and stored at 0 C. After 6 mo, fruit were removed from storage and cell walls were extracted and analyzed for Ca content. Polygalacturonase was purified from the decayed area of nontreated apples that had been inoculated with Penicillium expansum. Cell wall Ca content was positively correlated with the percent Ca used in the infiltration solutions. Extracted walls with varying Ca content were then used as substrate for P. expansum polygalacturonase to test the effect of wall Ca on in vitro enzyme activity. Approximately 60% less product was formed when high Ca cell walls were used as substrate compared with low Ca cell walls. Since Ca is known to stabilize the cell wall, decay in apples with high levels of Ca may be decreased because maceration by polygalacturonase is reduced.