Freeze-fracture evidence of gel-phase lipid in membranes of senescing cowpea cotyledons

• Published in: Planta Vol. 163; no. 3; pp. 360 - 369
• Main Authors: Platt-Aloia, K.A, Thomson, W.W
• Format: Journal Article
• Language: English
• Published: Germany 01.03.1985
• Subjects: cell membranes; cotyledons; senescence; structure; Vigna unguiculata
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/BF00395144

The structural details of membrane organization in germinating and senescing cotyledons of cowpea (Vigna unguiculata (L.) Walp.) were studied by thin section and freeze-fracture electron microscopy. Germination- and senescence-related changes in the ultrastructure of parenchymal cells of cowpea cotyledons, as detected in thin sections, closely resemble those described for other leguminous seeds. Additionally, electron-dense deposits associated with the membranes, particularly the plasmalemma and endoplasmic reticulum, were seen to increase with advancing senescence. Freeze-fracture electron microscopy demonstrated that the membranes of cotyledons of 2-d-old seedings appear to be normal, with evenly dispersed intramembranous particles. However by 4 d, small areas or domains of the plasmalemma were free of intramembranous particles. These particle-free areas increased in both size and number as senescence progressed. We interpret these particle-free areas to be structural evidence for lateral phase separations of the membrane lipids into microdomains of gel-phase lipid from which intrinsic membrane proteins are excluded. Our results support wide-angle X-ray diffraction studies which have demonstrated the presence of gel-phase lipids in senescing bean cotyledons.