Acyl lipids in Arabidopsis and all other plants have a myriad of diverse functions. These include providing the core diffusion barrier of the membranes that separates cells and subcellular organelles. This function alone involves more than 10 membrane lipid classes, including the phospholipids, galactolipids, and sphingolipids, and within each class the variations in acyl chain composition expand the number of structures to several hundred possible molecular species. Acyl lipids in the form of triacylglycerol account for 35% of the weight of Arabidopsis seeds and represent their major form of carbon and energy storage. A layer of cutin and cuticular waxes that restricts the loss of water and provides protection from invasions by pathogens and other stresses covers the entire aerial surface of Arabidopsis. Similar functions are provided by suberin and its associated waxes that are localized in roots, seed coats, and abscission zones and are produced in response to wounding. This chapter focuses on the metabolic pathways that are associated with the biosynthesis and degradation of the acyl lipids mentioned above. These pathways, enzymes, and genes are also presented in detail in an associated website (ARALIP: http://aralip.plantbiology.msu.edu/). Protocols and methods used for analysis of Arabidopsis lipids are provided. Finally, a detailed summary of the composition of Arabidopsis lipids is provided in three figures and 15 tables.

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Acyl-Lipid Metabolism

Revue bibliographique sur la biosynthese, la degradation et les aspects specialises recents du metabolisme des acides gras

Fatty Acid Metabolism

Lipids of mitochondria.

Biochemical and biophysical properties of thylakoid acyl lipids

Lipides acyle dans Arabidopsis et toutes les autres plantes ont une myriade de fonctions diverses. Il s'agit notamment de fournir la barriere de diffusion de base des membranes qui separe les cellules et les organites subcellulaires. Cette fonction implique seuls plus de 10 classes de lipides membranaires, y compris les phospholipides, galactolipides, et sphingolipides, et au sein de chaque classe, les variations dans la composition de la chaine acyle augmenter le nombre de structures a plusieurs centaines de possibles especes moleculaires. Lipides acyle dans le sous forme de compte triacylglycerol de 35% du poids de graines d'Arabidopsis et representent leur forme majeure de carbone et de stockage d'energie. Une couche de cutine et les cires cuticulaires qui limite la perte d'eau et offre une protection contre les invasions par des agents pathogenes et autres stress recouvre toute la surface aerienne d'Arabidopsis. Des fonctions similaires sont fournis par la suberine et des cires associes qui sont localisees dans les racines, les teguments et les zones d'abscission et sont produites en reponse a une blessure. Ce chapitre se concentre sur les voies metaboliques qui sont associes a la biosynthese et la degradation des lipides acyle mentionnes ci-dessus. Ces voies, les enzymes et les genes sont egalement presentes en detail dans un site Web associe (ARALIP: http://aralip.plantbiology.msu.edu/ ). Protocoles et methodes utilises pour l'analyse des lipides Arabidopsis sont fournis. Enfin, un resume detaille de la composition des lipides Arabidopsis est fourni en trois chiffres et 15 tables.

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Acyl-métabolisme des lipides

1. The incorporation of radioactivity from [1-14C]acetate into the leaf lipids of barley, pea and wheat has been studied in pulse-labelling experiments. 2. There was little increase in the total labelling of lipids after the leaves were transferred to non-radioactive medium. However, there was an increase in the relative labelling of unsaturated fatty acids. In addition, there was an increase in the relative labelling of diacylgalactosylglycerol. 3. The principal radioactively labelled acyl lipids were diacylgalactosylglycerol and phosphatidylcholine. Phosphatidylcholine showed a decreasing proportion of [14C]oleate and an increasing amount of [14C]linoleate with time. Diacylgalactosylglycerol also had decreasing amounts of [14C]oleate but, in addition, had an increasing proportion of [14C]linolenate with time. 4. The absence of significant amounts of [14C]linolenate in phosphatidylcholine appeared to exclude a role for this phospholipid in linoleate desaturation. 5. The specific radioactivities of oleate and linoleate in phosphatidylcholine, diacylgalactosylglycerol and diacylgalabiosylglycerol were very similar in any single experiment. It was concluded that these fatty acids can rapidly exchange between the three intact lipids.

Fatty acid biosynthesis in the leaves of barley, wheat and pea.

The acyl-lipid composition of a barley mutant that contained no detectable chlorophyll b was studied. This mutant contained chloroplasts that were much less organized than chloroplasts of normal barley. The mutant contained all the normal acyl lipids, with small increases in the relative concentration of phosphatidylglycerol and diacylsulphoquinoglycerides was unchanged, but most other lipids of the mutant barley contained lower amounts of alpha-linolenic acid compared with normal. There was no difference in the transhexadec-3-enoic acid content of phosphatidylglycerol, which was evidence against this lipid being involved in grana stacking.

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Jane Wharfe

Papers

Fatty acid biosynthesis in the leaves of barley, wheat and pea.

The lipid composition of a barley mutant lacking chlorophyll b.

Lipid metabolism in germinating seeds: Purification of ethanolamine kinase from soya bean