Abstract
The biophysical reactions of light harvesting and electron transport during photosynthesis take place in a uniquely constructed bilayer, the thylakoid. In all photosynthetic eukaryotes, the complement of atypical glycerolipid molecules that form the foundation of this membrane are characterised by sugar head-groups and a very high level of unsaturation in the fatty acids that occupy the central portion of the thylakoid bilayer. alpha-linolenic (18:3) or a combination of 18:3 and hexadecatrienoic (16:3) acids typically account for approximately two-thirds of all thylakoid membrane fatty acids and over 90% of the fatty acids of monogalactosyl diacylglycerol, the major thylakoid lipid [1, 2]. The occurrence of trienoic fatty acids as a major component of the thylakoid membrane is especially remarkable since these fatty acids form highly reactive targets for active oxygen species and free radicals, which are often the by-products of oxygenic photosynthesis. Photosynthesis is one of the most temperature-sensitive functions of plant [3, 4]. There remains a widespread belief that these trienoic fatty acids might have some crucial role in plants to be of such universal occurrence, especially in photosynthesis tolerance of temperature [5].
Highlights
Résumé : Les membranes des chloroplastes, siège de la photosynthèse, sont très riches en acides gras tri-insaturés
Photosynthesis and growth are affected by low temperature only when dienoic fatty acids as well as trienoic fatty acids are eliminated from organisms [14]
A surprising finding during the initial isolation and characterisation of the fad3-2 fad7-2 fad8 line was that triple mutant plants lacking trienoic fatty acids were indistinguishable from wild type in vegetative growth and development at 22°C [20]
Summary
Mutant photosynthesis activity was higher after brief high temperature treatments and mutant plants adapted better to high temperature compared to the non-transformed wild type tobacco These observations led to the proposal that plants may adapt to temperature changes by altering the fatty acid composition of their membrane lipids. There was no significant difference in either the membrane lipid content (measured as fatty acids per gram fresh weight) or the protein content of mutant leaves compared with the wild type. Trienoic fatty acids are required to maintain chloroplast function at low temperature To compare the in vivo behaviour of the wild-type and fad fad fad photosynthetic membranes at low temperatures, we recorded the fluorescence characteristics of detached leaves during short exposure to a range of temperatures from 25°C to 5°C. Our data suggest that PHIII (as well as the visual appearance of plants growing at 4°C) can be maintained at wild-type levels by 15 to 20% trienoic fatty acids in the leaf membranes even though leaves of wild-type plants contain more than 60% of these fatty acids
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