The kinetics of [1-14C]acetate incorporation in Arabidopsis thaliana L. (Heyn) showed almost equal labelling of phosphatidylcholine (PC) and diacylgalactosylglycerol (DGG) at early times and the transfer of radioactivity from PC to DGG and diacyldigalactosylglycerol (DDG) at longer times. These kinetics demonstrated the parallel operation of the prokaryotic and eukaryotic pathways of lipid synthesis [Roughan & Slack (1982) Annu. Rev. Plant Physiol. 33, 97-132] in this tissue. At 2 h after the application of [1-14C]acetate, more than 85% of the radioactivity at the sn-2 position of each chloroplast lipid was in 16-carbon fatty acids. However, after 60 h, molecular species containing labelled C18 fatty acids at position sn-2 and presumably derived from microsomal PC made a large contribution (20-70%) to each chloroplast lipid except phosphatidylglycerol. These findings are consistent with the contention that the chain length of the fatty acid at the sn-2 position of glycerol is an accurate predictor of whether a particular lipid molecule has been synthesized by the prokaryotic or eukaryotic pathway. At 30 min after the start of [1-14C]acetate labelling, only 12.3% of the radioactivity in PC was in saturated fatty acids, but the proportion increased steadily to 24.3% after 142 h. It is suggested that steps involved in the conversion of PC to chloroplast lipids on the eukaryotic pathway discriminate against palmitate-containing species. The step involved does not appear to be transfer of PC to the chloroplast because extrachloroplastic and chloroplast membranes purified from Arabidopsis mesophyll protoplasts each contained PC with a fatty acid composition similar to that of the same lipid from leaves. Positional analysis of unlabelled lipids, together with the information summarized above, is used to construct a quantitative scheme of the fluxes through the prokaryotic and eukaryotic pathways during lipid synthesis in Arabidopsis. This scheme shows that 38% of the fatty acids synthesized de novo in the chloroplast enter the prokaryotic pathway in the chloroplast envelope. Of the 62% which are exported as acyl-CoA species to enter the eukaryotic pathway, 56% (34% of the total) are returned to complete synthesis of the chloroplast's complement of glycerolipids.
The fabl mutant of Arabidopsis tbaliana, which contains increased levels of saturated fatty acids, was indistinguishable from the wild type when it was grown at 22 or 12°C. During the first 7 to 10 d after transfer to 2"C, the growth and photosynthetic characteristics of the fabl plants remained indistinguishable from the wild type, with values for the potential quantum efficiency of photosystem II decreasing from 0.8 to 0.7 in plants of both lines. Whereas wild-type plants maintained quantum efficiency of photosystem II at approximately 0.7 for at least 35 d at 2"C, this parameter declined rapidly in the mutant after 7 d and reached a value of less than 0.1 after 28 d at 2°C. This decline in photosynthetic capacity was accompanied by reductions in chlorophyll content and the amount of chloroplast glycerolipids per gram of leaf. Electron microscopic examination of leaf samples revealed a rapid and extensive disruption of the thylakoid and chloroplast structure in the mutant, which is interpreted here as a form of selective autophagy. Despite the almost complete loss of photosynthetic function and the destruction of photosynthetic machinery, fabl plants retained a substantial capacity for recovery following transfer to 22°C. These results provide a further demonstration of the importance of chloroplast membrane unsaturation to the proper growth and development of plants at low temperature.A remarkable feature of the chloroplast membranes of higher plants is the high number of double bonds that are found in the lipid acyl chains. Typically, only about 10% of the fatty acids that compose the hydrophobic mid-portion of the thylakoid bilayer lack double bonds altogether, whereas more than 80% have two or more double bonds (Harwood, 1982). The relevance of thylakoid lipid composition to the correct functioning of these membranes in photosynthesis has been the subject of considerable speculation and experimentation, but it is still not well understood (Quinn et al., 1989;Murata and Wada, 1995). 347To investigate the functional significance of chloroplast lipid composition, we have isolated a series of Arabidopsis mutants with specific alterations in leaf lipid composition (Browse and Somerville, 1991;Somerville and Browse, 1991). Five genetic loci have been identified that encode the genes that are involved in lipid-linked fatty acid desaturation of chloroplast lipids (fad4, fad5, fad6, fad7, and fad8).(The first four of these were previously known as f a d A , fadB, fadC, and fadD, respectively.) The actl mutants are deficient in the chloroplast glycerol-3-phosphate acyltransferase. Each of these mutants exhibits substantial changes in chloroplast fatty acid composition. For example, thefad5 mutant lacks cis-unsaturated 16-carbon fatty acids because of a deficiency in the desaturation of 16:O on MGD (Kunst et al., 1989a), whereas the fad6 mutant has increased levels of monoenoic fatty acids as a result of a mutation in the chloroplast 16:1/ 18:l desaturase (Browse et al., 1989). However, the m u t a n t s do not exh...
We introduce the AusTraits database - a compilation of values of plant traits for taxa in the Australian flora (hereafter AusTraits). AusTraits synthesises data on 448 traits across 28,640 taxa from field campaigns, published literature, taxonomic monographs, and individual taxon descriptions. Traits vary in scope from physiological measures of performance (e.g. photosynthetic gas exchange, water-use efficiency) to morphological attributes (e.g. leaf area, seed mass, plant height) which link to aspects of ecological variation. AusTraits contains curated and harmonised individual- and species-level measurements coupled to, where available, contextual information on site properties and experimental conditions. This article provides information on version 3.0.2 of AusTraits which contains data for 997,808 trait-by-taxon combinations. We envision AusTraits as an ongoing collaborative initiative for easily archiving and sharing trait data, which also provides a template for other national or regional initiatives globally to fill persistent gaps in trait knowledge.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.