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The response of plasma membrane lipid composition in callus of the halophyte Spartina patens (Poaceae) to salinity stress¹

²DuPont Bio-Based Materials, Chestnut Run Plaza 728/1411, P.O. Box 80728, Wilmington, Delaware 19880-0728 USA; ³Halophyte Biotechnology Center, Graduate College of Marine Studies, University of Delaware, 700 Pilottown Road, Lewes, Delaware 19958 USA

ABSTRACT

Callus cultures of the salt marsh grass Spartina patens were examined to determine changes and consistencies in membrane lipid composition in response to salt. Major membrane lipid classes remained stable at all salinity levels (0, 170, 340 mmol/L). However, the membrane protein to lipid ratio decreased significantly in response to elevated NaCl. Callus plasma membrane (PM) consisted predominantly of sterols, about 60% (mol%) of the total lipids. Glycolipid was the second largest lipid class, making up about 20% (mol%) of the total. With increasing salinity, the relative percentage of sitosterol decreased, while that of campesterol increased. The phospholipid species detected were phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylserine (PS), and phosphatidylinositol (PI). When callus was grown at 340 mmol/L NaCl, PC increased significantly. PI and PS were also significantly elevated in salinity treatments. Only 24–32% of the PM fatty acids were common plant membrane fatty acids, C16, C18, C20, and C22, while over 60% were the less common fatty acids, C11 and C14. Membrane fluidity remained stable in response to growth medium salinity. The findings on membrane responses to salinity will facilitate a better understanding of this halophyte's tactics for salt tolerance.

Key Words: halophyte • lipid • membrane composition • plasma membrane • Poaceae • salinity • salt tolerance • Spartina patens