Changes in lipid molecular species and sterols of microsomal membranes during aging of potato (Solanum tuberosum L.) seed-tubers.
Changes in sterols and the molecular species composition of polar lipids from microsomal membranes were characterized as a prerequisite to determining how lipid chemistry affects membrane susceptibility to peroxidation during aging of potato tubers. Polar lipid content of the microsomal fraction fell 17% (protein basis) as tubers aged from 22 to 38 mon at 4 degrees C. In younger seed-tubers, PC concentration (protein basis) was the highest, followed by digalactosyldiacylglycerol (DGDG), PE, monogalactosyldiacylglycerol (MGDG), and PI. PC and PE increased 14 and 27%, respectively, whereas glycolipids fell 64 and PI 43% with advancing age. These changes resulted in PC and PE dominating the microsomal membrane lipids of 38-mon-old tubers. Nonpositional analysis of lipid molecular species across lipid pools showed an increase in 16:0/18:3, 18:3/18:3, and 18:2/18:3 (PC and PE only), and a decline in 18:2/18:2 and 16:0/18:2 (except for MGDG) with advancing tuber age. The increase in 18:3-bearing species effected a linear increase in double-bond index (DBI) of PC and PE during aging. The DBI of DGDG did not change with age; however, it fell 65% for MGDG, resulting in an overall decrease in average microsomal DBI. In addition, A5-avenasterol and stigmasterol concentrations increased 1.6- and 3.3-fold, respectively, effecting a significant increase in the sterol/phospholipid ratio with advancing tuber age. The increase in sterol/phospholipid ratio and the possibility that the increased unsaturation of microsomal membranes reflects a compensatory response to maintain optimal membrane function in light of the age-induced loss of galactolipid and PI are discussed.
Zabrouskov
Vladimir
V
Department of Horticulture and Landscape Architecture, Washington State University, Pullman 99164-6414, USA.
Knowles
N Richard
NR
D007425:Intracellular Membranes / Q000378:metabolism*; D050356:Lipid Metabolism; D008861:Microsomes / Q000378:metabolism*; D012639:Seeds / Q000254:growth & development* / Q000378:metabolism; D011198:Solanum tuberosum / Q000196:embryology / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013261:Sterols / Q000378:metabolism*
D013261:Sterols