Lipid composition and molecular organization in plasma membrane-enriched fractions from senescing cotyledons [phase behaviour, senescence, Phaseolus vulgaris]
1980
Lees, G.L. | Thompson, J.E. (Waterloo Univ., Ontario (Canada). Dept. of Biology)
Plasma membrane fractions isolated from cotyledons of Phaseolus vulgaris L. cv. Kinghorn at various stages of senescence showed no significant change in fatty acid saturation with advancing senescence. However, the sterol: phospholipid ratio increased by about 400% as senescence intensified. The lipid phase transition temperature of the membranes, which was measured by wide-angle x-ray diffraction, also rose from a point well below the growing temperature for young tissue to about 50 deg C for membrane from extensively senescent 9-day-old tissue. This means that by day 4 of germination there was a mixture of liquid-crystalline and gel phase phospholipid in the membrane matrices. Crystallinity attributable to sterol-sterol interaction was also apparent in the diffraction patterns, for senescent membranes. The co-existence of gel and liquid-crystalline phase phospholipid in the aging membranes as well as the crystalline sterol aggregates presumably render the storage cells of cotyledons leaky and may thus facilitate the translocation of hydrolyzed food reserves into the vascular network
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