Chemical compositions and physical states of chloroplast lipids related to atrazine resistance in Conyza canadensis L.

Abstract

A comparison of the chemical composition and physical states of chloroplast lipids, of atrazine-resistant (R) and sensitive (S) biotypes of Conyza canadensis L. (horseweed), in the rosetta stage showed: (1) the R biotype contains lower amounts of polar lipids in its thylakoids, as expressed on a chlorophyll basis, than the S biotype. (2) The chloroplasts of the R biotype have higher contents of monogalactosyl diacylglycerol (MGDG) and lower contents of digalactosyl diacylglycerol (DGDG) and phosphatidylglycerol (PG), than those of the S biotype. (3) The chloroplast total lipids exhibit a higher degree of unsaturation in the R biotype. This is due to a higher level of linolenic acid, and a lower level of palmitic acid in the glycolipids. The fatty acid compositions of the phospholipids, except that of PG, do not differ significantly. (4) The lipid matrix of the thylakoid membranes of the R biotype is more fluid than that of the S biotype, as measured by the fluorescence polarization technique. The results are discussed in terms of whether these differences are responsible for the herbicide resistance.