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Histochemical Demonstration of Transitory Esterase Activity in Venturia inaequalis. R. L. Nicholson, Department of Botany and Plant Pathology and Biochemistry, Purdue University, Lafayette, Indiana 47907; J. Kuc(2), and E. B. Williams(3). (2)(3)Departments of Botany and Plant Pathology and Biochemistry, Purdue University, Lafayette, Indiana 47907. Phytopathology 62:1242-1247. Accepted for publication 8 May 1972. DOI: 10.1094/Phyto-62-1242.

Esterase activity was detected histochemically in spores and germlings of Venturia inaequalis during a 12-hr period after inoculation on host and nonhost surfaces. Esterase activity was present at the spore apex prior to germination, disappeared from the elongating germ tube, and reappeared in the appressorium. Morphological development and the pattern of esterase activity were similar for all isolates studied. Activity at the apex of the ungerminated spore was suggested to facilitate germination by a plasticizing or rupturing of the spore wall components. Activity in the appressorium may represent the localization of hydrolytic enzymes necessary for host penetration.