Trienoic fatty acids and plant tolerance of temperature

Abstract

Résumé : Les membranes des chloroplastes, siège de la photosynthèse, sont très riches en acides gras tri-insaturés. La proportion de ces acides gras dans les membranes végétales peut être modifiée lors de changements de température. Pour cette raison, il a été postulé que ces acides gras sont impliqués dans les mécanismes de résistance à la chaleur ou au froid des fonctions membranaires, en particulier de la photosynthèse qui est une des fonctions de la cellule les plus sensibles à la température. Afin de tester cette hypothèse, nous avons obtenu un triple mutant d'Arabidopsis qui ne contient pas d'acides gras tri-insaturés et mesuré les effets de la température sur cette lignée. Nous montrons que les acides gras tri-insaturés ne sont pas nécessaires pour la croissance et la photosynthèse dans des conditions normales de température et de lumière. En revanche, ils sont importants pour assurer la biogenèse et le maintien des chloroplastes de plantes cultivées à 4 °C, ou pour la survie de la plante cultivée à 33 °C. La présence de seulement un tiers de ces acides gras est suffisante au maintien d'une croissance et d'une photosynthèse normale si la plante est transférée à une température en dessus ou au-dessous de la normale.Mots-clés : résistance au froid, thermorésistance, acides gras, lipides, photosynthèse. Summary :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].Article disponible sur le site http://www.ocl-journal.org ou http://dx.doi.org/10.1051/ocl.2002.0000 ARTICLE Do plants adapt to temperature by changing the fatty acid composition of their membrane lipids?In some desert and evergreen plants, the proportion of trienoic fatty acids in the membrane glycerolipids decreases when plants acclimate to high temperatures [6]. Conversely, cold acclimation in higher plants induces increases in trienoic fatty acid level in leaves [7]. These...

Trienoic fatty acids and stress responses in higher plants

“…Similar results were obtained with the Arabidopsis fad7fad8 double mutant, which lacks the activity of plastidial w-3 desaturase (Murakami et al 2000). In this mutant, higher growth rates (Routaboul and Browse 2002;Falcone et al 2004) and stability of the photosynthetic machinery (Kim and Portis 2005) at high temperatures have been confirmed by several labs. These results support the concept that TAs in membrane lipids need to be diminished to allow plant survival at unusually high temperatures.…”

“…Because an excess amount of TAs had detrimental effects on photosynthesis at high temperatures, it appears rather consistent that a reduction of TAs in the chloroplast lipids, but not in the extrachloroplast lipids, made a positive contribution to the tolerance for high temperatures. On the other hand, the nearly complete depletion of TAs in the fad3fad7fad8 triple mutant resulted in a severe inhibition of growth and photosynthesis at high temperatures (Routaboul and Browse 2002). This apparently discrepant phenotype of the mutant could not be ascribed to changes in physicochemical membrane properties, but rather to the impairment of signaling processes mediated by TAs or their derivatives such as jasmonic acid (JA).…”

Thermotolerant cyclamen with reduced acrolein and methyl vinyl ketone

“…In the A. thaliana fad3fad7fad8 mutant which lacks plastidial TAs altogether, a reduction of photosynthetic activity and retardation of growth under heat stress have been observed. The growth inhibition was ascribed to a deficiency of TA-derived jasmonates and their derivatives ( Routaboul and Browse, 2002 ; Wallis and Browse, 2002 ). In contrast, transgenic cyclamen containing 1.4–2.8 mol% of TA may still be able to produce sufficient essential TA derivatives to survive under heat stress and acquire thermotolerance.…”

Antisense‐mediated Depletion of Tomato Endoplasmic Reticulum Omega‐3 Fatty Acid Desaturase Enhances Thermal Tolerance

“…However, there are few data reporting changes in membrane lipid composition in response to high temperature stress. Most studies that have proposed the heat tolerance of the TAs levels have focused on events in plastid omega‐3 fatty acid desaturase (Routaboul and Browse 2002; Falcone et al 2004), but few focused on the extraplastid omega‐3 fatty acid desaturase. The mainly 18:3 in non‐photosynthetic tissues is synthesized by FAD3 in higher plants.…”