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Articles

Translucent Tissue Defects in Solanum tuberosum L. ¹

II. Alterations in Lipolytic Acyl Hydrolase, Lipoxygenase, and Morphology of Mitochondria and Amyloplasts

United States Department of Agriculture, Agricultural Research Service, Red River Valley Potato Research Laboratory ^,4, 311 5th Avenue, NE, East Grand Forks, Minnesota 56721, Department of Horticulture and Landscape Architecture, University of Minnesota, St. Paul, Minnesota 55108, United States Department of Agriculture, Agricultural Research Service, Metabolism and Radiation Research Laboratory, Fargo, North Dakota 58105

We analyzed a physiological defect that involved translucent-like tissue which occurred randomly in potato tubers (Solanum tuberosum L., cv Kennebec) after 8 months of storage. The translucent areas had reduced lipoxygenase (0.73-fold) and lipolytic acyl hydrolase (0.27-fold) activities. The effect(s) of these reduced enzyme activities in vivo is uncertain, but they may have influenced composition, turnover and permeability of membranes because potato lipid is primarily membranous in nature. Electron micrographs of the translucent tissue revealed a discernible decrease in the number of starch granules compared to normal/healthy tissue. A few remaining amyloplasts, which still contained starch granules, possessed large electrondense areas (stroma) within the organelle. Mitochondria in translucent tissue appeared to be present in increased numbers, were aggregated, had fewer but swollen cristae, and, morphologically, were of irregular size and shape suggestive of division. The result of this tuber defect appeared, in part, to be an exaggerated or accelerated form of senescence.

³ Present address: 376 Washington Avenue #1, Sunnyvale, CA 94086.

¹ Agricultural Experiment Station, University of Minnesota Scientific Journal Series No. 14274.

⁴ A laboratory cooperatively operated by the Northern States Area, Agricultural Research Service, United States Department of Agriculture, the Minnesota Agricultural Experiment Station, the North Dakota Agricultural Experiment Station, and the Red River Valley Potato Grower's Association.