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

Age-dependent changes in the concn (nmol g d. wt^–1) andrelative proportion of polar lipid fatty acids in potato tubertissue were characterized over a 32-month storage period. Astubers advanced in age from 2 to 14 months, a decrease (approximately22%) in concn of both saturated (16:0, 18:0) and unsaturated(18:2, 18:3) fatty acids was evident. This decrease was followedby an exponential increase through 32 months. Electrolyte leakagestudies with excised tissue revealed age-dependent differencesin membrane permeability. The relationship between maximum electrolyteleakage (% total) and tissue age was described by a cubic polynomial.Leakage declined approximately 4% as tissues aged from 2 to7 months; however, from 7 to 24 months, leakage increased 21%.These trends were followed by partial restoration of membranefunction in 24 to 32-month-old tissues, as indicated by attenuatedleakage. Similarly, the trend in double bond index (DBI) withage was defined by a cubic polynomial; however, the minima andmaxima 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 effectof decreasing temperature from 5 to –2 °C on tissuepermeability (after equilibration with the bathing medium) wasalso dependent upon DBI. The higher the DBI, the greater theresistance of the tissue to increased electrolyte leakage inducedby chilling temperatures (r = 0·99, P < 0·05).Although the evidence is largely correlative, it appears thatchanges in the degree of saturation of membrane lipids are relatedto age-dependent fluctuations in membrane integrity and maybe important in dictating chilling sensitivity in potato Potato (Solanum tuberosum L.), tuber age, electrolyte leakage, membrane fatty acids