Correlations Between Electrolyte Leakage and Degree of Saturation of Polar Lipids from Aged Potato (Solanum tuberosum L) Tuber Tissue

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Abstract
Age-dependent changes in the concn (nmol g d. wt−1) and relative proportion of polar lipid fatty acids in potato tuber tissue were characterized over a 32-month storage period. As tubers advanced in age from 2 to 14 months, a decrease (approximately 22%) in concn of both saturated (16:0, 18:0) and unsaturated (18:2, 18:3) fatty acids was evident. This decrease was followed by an exponential increase through 32 months. Electrolyte leakage studies with excised tissue revealed age-dependent differences in membrane permeability. The relationship between maximum electrolyte leakage (% total) and tissue age was described by a cubic polynomial. Leakage declined approximately 4% as tissues aged from 2 to 7 months; however, from 7 to 24 months, leakage increased 21%. These trends were followed by partial restoration of membrane function in 24 to 32-month-old tissues, as indicated by attenuated leakage. Similarly, the trend in double bond index (DBI) with age was defined by a cubic polynomial; however, the minima and maxima were the opposite of those for electrolyte leakage vs. age. The regression of DBI upon leakage was inverse and linear (r = −0·97, P < 0.01). Furthermore, the effect of decreasing temperature from 5 to −2 °C on tissue permeability (after equilibration with the bathing medium) was also dependent upon DBI. The higher the DBI, the greater the resistance of the tissue to increased electrolyte leakage induced by chilling temperatures (r = 0·99, P < 0·05). Although the evidence is largely correlative, it appears that changes in the degree of saturation of membrane lipids are related to age-dependent fluctuations in membrane integrity and may be important in dictating chilling sensitivity in potato