Effects of low growth temperature on metabolism of polar glycerolipids in Brassica napus leaves.

摘要

Brassica napus (var. Tower) leaves grown at low temperatures (5 or 10;Molecular species analyses showed that levels of 16:3/18:3 MGDG increase with growth at low temperatures. Labelling in MGDG molecular species revealed that leaves grown at low temperatures have a greater capacity to synthesize 16:3/18:3. This occurs by a series of five in situ desaturation reactions, from palmitic/oleic acid (16:0/18:1) to palmitic/linoleic acid (16:0/18:2), palmitoleic/linoleic acid (16:1/18:2), hexadecadienic/linolenic acid (16:2/18:2), hexadecadienoic/linolenic acid (16:2/18:3) and finally to 16:3/18:3. Retention of radiodioactivity in 16:0/18:2 MGDG, defined a pool more slowly desaturated, presumably used for DGDG synthesis. A model was proposed for synthesis of chloroplastic MGDG and DGDG molecular species.;Levels of 18:3/18:3 cytosolic molecular species increased in DGDG and decreased in MGDG, as growth temperatures were reduced. This suggested stimulated galactosylation of the MGDG species. Analysis of MGDG galactose and glycerol moieties indicated that both had similar labelling kinetics. The rapid labelling of glycerol implicated a direct source of glycerol-3-phosphate for chloroplastic MGDG synthesis.;Preliminary experiments suggested desaturation of 16 carbon and 18 carbon fatty acids could be observed in cell free homogenates and in isolated chloroplasts.