Occurrence of Fatty Acid Short‐Chain‐Alkyl Esters in Fruits of Celastraceae Plants

Small amounts of a mixture of fatty acid short‐chain‐alkyl esters (FASCAEs) were obtained from the fruits of twelve plant species of Celastraceae family, and in five of them the FASCAEs were present not only in the arils but also in the seeds. These mixtures contained 32 individual FASCAE species, which formed four separate fractions, viz. FA methyl, ethyl, isopropyl, and butyl esters (FAMEs, FAEEs, FAIPEs, and FABEs, resp.). The FASCAE acyl components included the residues of 16 individual C₁₄–C₂₄ saturated, mono‐, di‐, and trienoic FAs. Linoleic, oleic, and palmitic acids, and, in some cases, also α‐linolenic acid predominated in FAMEs and FAEEs, while myristic acid was predominant in FAIPEs. It can be suggested that, in the fruit arils of some plant species, FAMEs and FAEEs were formed at the expense of a same FA pool characteristic of a given species and were strongly different from FAIPEs and FABEs esters regarding the mechanism of their biosynthesis. However, as a whole, the qualitative and quantitative composition of various FASCAE fractions, as well as their FA composition, varied considerably depending on various factors. Therefore, separate FASCAE fractions seem to be synthesized from different FA pools other than those used for triacylglycerol formation.     

Cell ultrastructure and fatty acid composition of lipids in vegetative organs of <Emphasis Type="Italic">Chenopodium album</Emphasis> L. under salt stress conditions

White goosefoot plants (Chenopodium album L. of the family Chenopodiaceae) grown at various NaCl concentrations (3–350 mM) in the nutrient solution were used to study the cell ultrastructure as well as the qualitative and quantitative composition of fatty acids in the lipids of vegetative organs. In addition, the biomass of Ch. album vegetative organs, the water content, and the concentrations of K⁺, Na⁺, and Cl^– were determined. The growth rates of plants raised at NaCl concentrations up to 200–250 mM were the same as for the control plants grown at 3 mM NaCl; the growth parameters remained rather high even at NaCl concentrations of 300–350 mM. The water content in Ch. album organs remained high at all NaCl concentrations tested. Analysis of the ionic status of Ch. album revealed a comparatively high K⁺ content in plant organs. At low NaCl concentrations in the nutrient solution, K⁺ ions were the dominant contributors to the osmolarity (the total concentration of osmotically active substances) and, consequently, to the lowered cell water potential in leaves and roots. As the concentration of NaCl was increased, the plant organs accumulated larger amounts of Na⁺ and Cl^–, and the contribution of these ion species to osmolarity became increasingly noticeable. At 300–350 mM NaCl the contribution of Na⁺ and Cl^– to osmolarity was comparable to that of K⁺. An electron microscopy study of Ch. album cells revealed that, apart from the usual response to salinity manifested in typical ultrastructural changes of chloroplasts, mitochondria, and the cytosol, the salinity response comprised the enhanced formation of endocytic structures and exosomes and stimulation of autophagy. It is supposed that activation of these processes is related to the removal from the cytoplasm of toxic substances and the cell structures impaired by salt stress conditions. The qualitative and quantitative composition of fatty acids in the lipids of Ch. album organs was hardly affected by NaCl level. These findings are consistent with the high salt tolerance of Ch. album, manifested specifically in retention of growth functions under wide-range variations of NaCl concentration in the nutrient solution and in maintenance of K⁺, Na⁺, and Cl^– content in organs at a constant level characteristic of untreated plants.     

Transformation of tobacco with a gene for the thermophilic acyl-lipid desaturase enhances the chilling tolerance of plants

The desC gene for the acyl-lipid Delta9-desaturase from the thermophilic cyanobacterium Synechococcus vulcanus was introduced into Nicotiana tabacum under control of the 35S promoter. Expression of the desaturase was confirmed by Western blotting. Lipid analysis revealed that lipid content and the extent of fatty acid unsaturation significantly increased in leaves of transgenic plants. Chilling tolerance of those plants also increased, as estimated by the electrolyte leakage from the tissues damaged by cold treatments. Seeds of plants that expressed the desC gene imbibed at low temperatures demonstrated higher chilling tolerance than those of the control plants. The results demonstrate that the cyanobacterial thermophilic acyl-lipid desaturase was efficiently expressed in tobacco at ambient temperatures, and its expression resulted in the enhanced chilling tolerance of the transgenic plants.     

Comparative expression in Escherichia coli of the native and hybrid genes for acyl-lipid delta(9) desaturase

Expression of the desC gene coding for acyl-lipid delta(9) desaturase of thermophilic cyanobacterium Synechocystis sp. PCC6803 was studied in Escherichia coli cells. In a hybrid gene constructed (desC-licBM3), a sequence of the native acyl-lipid delta(9) desaturase was fused in frame with the reporter gene coding for thermostable lichenase. Lichenase contained in the hybrid protein simplified selection and analysis of the expression of membrane desaturase in the heterologous host. Comparisons of the expression for the native and hybrid genes in bacterial cells showed that lichenase remained active and thermostable in the hybrid protein, while desaturase retains the capability of introducing a double bound in the corresponding position of fatty acids.     

Comparative expression in <Emphasis Type="Italic">Escherichia coli</Emphasis> of the native and hybrid genes for acyl-lipid Δ<Superscript>9</Superscript> desaturase

Expression of the desC gene coding for acyl-lipid Δ⁹ desaturase of thermophilic cyanobacterium Synechocystis sp. PCC6803 was studied in Escherichia coli cells. In a hybrid gene constructed (desC-licBM3), a sequence of the native acyl-lipid Δ⁹ desaturase was fused in frame with the reporter gene coding for thermostable lichenase. Lichenase contained in the hybrid protein simplified selection and analysis of the expression of membrane desaturase in the heterologous host. Comparisons of the expression for the native and hybrid genes in bacterial cells showed that lichenase remained active and thermostable in the hybrid protein, while desaturase retains the capability of introducing a double bound in the corresponding position of fatty acid residues.     

Light-dependent cold-induced fatty acid unsaturation, changes in membrane fluidity, and alterations in gene expression in Synechocystis

Cold stress causes unsaturation of the membrane lipids. This leads to adjustment of the membrane fluidity, which is necessary for cold acclimation of cells. Here we demonstrate that the cold-induced accumulation of PUFAs in the cyanobacterium Synechocystis is light-dependent. The desA(-)/desD(-) mutant, that lacks the genes for Δ12 and Δ6 desaturases, is still able to adjust the fluidity of its membranes in spite of its inability to synthesize PUFAs and modulate the fatty acid composition of the membrane lipids under cold stress. The expression of cold-induced genes, which are controlled by the cold sensor histidine kinase Hik33, depends on the fluidity of cell membranes and it is regulated by light, though it does not require the activity of the photosynthetic apparatus. The expression of cold-induced genes, which are not controlled by Hik33, does not depend on the membrane fluidity or light. Thus, membrane fluidity determines the temperature dependence of the expression of cold-induced genes that are under control of the Hik33, which might be the sensor of changes in the membrane fluidity. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.     

Changes in the content and composition of lipid fatty acids in tobacco leaves and roots at low-temperature hardening

Changes in the fatty acid (FA) composition of leaf and root lipids of heat-loving tobacco (Nicotiana tabacum L., cv. Samsun) plants during low-temperature hardening (8°C for 6 days) were studied. Hardening could improve leaf but not root cold tolerance. As this took place, the relative content of polyunsaturated (18:2n-6 and 18:3n-3) FAs increased and the proportion of saturated and monounsaturated FAs decreased. In contrast, in the roots hardening slightly increased the concentration of saturated FAs (16:0 and 18:0) and reduced the level of unsaturated FAs (18:1n-9, 18:2n-6, and 18:3n-3). At the same time, root lipids contained much C_20–24 FAs, and their content increased during hardening. It was suggested that an increased FA saturation and elevated proportion of C_20–24 FAs in the root lipids resulting in the lower membrane fluidity could be a reason for incapability of heat-loving tobacco plant roots of hardening and plant death at the lowtemperature stress.     

Fatty Acid Composition of Lipids from Leaves and Strobila of Cycas Revoluta (<Emphasis Type="Italic">Cycas revoluta</Emphasis>)

Fatty acid (FA) composition of lipids from leaves and differentiated fleshy strobila tissues and sporangia with spores of Cycas (Cycas revoluta Thumb.) after their step quantitative extraction from plant material was investigated. Quantitative content and qualitative composition of FAs of extractable and nonextractable leaf lipids were determined. It was established that flesh lipids of sporophylls are characterized by a high saturation level and contain a considerable proportion of saturated FAs with the usual chain length (C₁₂–C₁₈, 53–57%). At the same time, total amount of etherified FAs with a very long chain in lipids not extractable by the method of Zhukov and Vereshchagin exceeds several times that found in extractable lipids (~15 and ~4%, respectively). Neutral lipids of Cycas spores were represented by triacylglycerols, the lower-alkyl esters of FAs, free FAs, and sterol esters.     

Changes in Triacylglycerol Composition in Maturing Sea Buckthorn (Hippophaë rhamnoides) Seeds

Sea buckthorn (Hippophaë rhamnoides L.) seeds on the 29th, 53rd, 80th, and 107th day after pollination were used for determining, by lipase hydrolysis, the qualitative and quantitative composition of the triacylglycerol (TAG) positional types, groups, and positional species, as well as the factor of selectivity of incorporation of unsaturated fatty acids, octadecenoic, linoleic, and linolenic, into the sn-2-position of TAGs. Until the 80th day after pollination, there was a predominant formation of triunsaturated TAGs, which included linolenic and linoleic acid residues. After the 80th day, the absolute content of these major components of total TAGs markedly decreased, and an increase in total TAG content was mainly accounted for by the rise in the level of those TAG species, which included saturated fatty acids, palmitic and stearic (monosaturated–diunsaturated and disaturated–monounsaturated), as well as in the level of sn-2-octadecenoyl species belonging to the triunsaturated and palmito–diunsaturated types of TAGs. At each maturation stage, the quantitative dynamics of separate TAG species was determined by the content of fatty acid species available for TAG formation and the factor of selectivity of these species. The decrease in the content of a certain group of triunsaturated TAGs found here seems to be caused by their metabolization during seed maturation.