Calcium in Potato Tuber Cell Walls in Relation to Tissue Maceration byErwinia carotovorapv.atroseptica

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Abstract
Increases in the concentration of calcium in nutrient solutions supplied to potato plants of the cultivars Superior and Russet Burbank resulted in tubers with increased concentrations of calcium. High-calcium tubers, when injected with either cell suspensions or pectolytic enzyme preparations from Erwinia carotovora pv. atroseptica and incubated under anaerobic conditions, were more resistant to tissue maceration than low-calcium tubers. Electrolyte leakage from sections of high-calcium tubers also was lower than that from sections of low-calcium tubers when immersed in pectolytic enzyme preparations. As the calcium content of cell walls in the medulla and peel of Superior tubers increased from 0.012 to 0.058% and from 0.073 to 0.445%, respectively, the amount of galacturonic acid recovered increased from 19.6 to 27.4% and from 13.9 to 21.3%, respectively. Cell wall preparations from Russet Burbank tubers had consistently higher amounts of calcium than those from Superior tubers: 0.167-0.314% in the medulla and 0.120-0.610% in the peel. The amount of galacturonate recovered from these cell walls was similarly greater: 25.9-30.0% in the medulla and 20.9-24.2% in the peel. The percentage of wall protein did not vary, however. The reduction of Erwinia soft rot in high-calcium tubers can be attributed in part to the decrease in maceration by pectolytic enzymes that is related to the enhancement of structural integrity of cell walls and membranes by increasing calcium levels. Growth and spread of the pathogen through the tuber tissues are decreased as a result of this effect on tissue maceration.