Roman A. Sidorov

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.

Occurrence of fatty acid lower-alkyl esters in euonymus fruits

Small amounts of a mixture of fatty acid lower-alkyl esters (FALAEs) were obtained from chloroform extracts of the fruit arils and seeds of four euonymus species (Euonymus sp., Celastraceae). The FALAEs were the products of biosyntheses in the cell rather than experimental artifacts. By using GC-MS, this mixture was shown to contain a total of 19 individual FALAE species comprising four separate fractions, viz. methyl (FAMEs), ethyl (FAEEs), n-propyl, and n-butyl FA esters. Fruit FALAEs included mainly FAEEs and, to a lesser extent, FAMEs, while the n-propyl and n-butyl FA esters, which occurred less frequently, were found here for the first time as the plant products. The FALAE acid components included C14-C18 saturated, mono-, di-, and trienoic FAs with the predominance of ubiquitous linoleic, oleic, palmitic, and, in some cases, also α-linolenic acid. The indices of qualitative and quantitative composition of separate FALAE fractions varied considerably depending on the plant species, fruit part (aril or seed), and the extent of fruit maturity. It can be supposed that, in some euonymus species, FAMEs and FAEEs are formed at the expense of the same FA pool characteristic for a given species. As a whole, euonymus FALAEs and triacylglycerols seem to be synthesized from different FA pools. Discussed is the physiological significance of FALAE biosynthesis in plant metabolism, possible pathways of this biosynthesis, as well as the perspectives of further investigations of FALAEs of plant origin.

Cold-induced gene expression and ω3 fatty acid unsaturation is controlled by red light in Synechocystis

The expression of cold-induced genes, which are controlled by the cold sensor histidine kinase Hik33, and the formation of ω(3) polyunsaturated fatty acids are controlled by light in the cyanobacterium Synechocystis sp. PCC 6803. Cold-induced Hik33-dependent gene expression is initiated by red light (∼700nm), but not by blue or green light. Red light also turns on the ω(3) fatty acid desaturation. Different combinations of other wavelengths in red spectral region (635 and 726nm) had no effect on the red-light-activated cold-induced transcription or fatty acid desaturation. Therefore, the involvement of phytochrome-like photoreceptor(s), similar to phytochromes of higher plants, in this regulation was not confirmed. The absence of light-dependence of gene expression in the mutant cells deficient in Hik33 suggests the involvement of this histidine kinase in direct or mediated with red light regulation of cold responses in Synechocystis.

Biosynthesis of fatty oils in higher plants

Triacylglycerols (TAGs) are one of the most important storage compounds of higher plants; they are the basis for essentially all plant oils and are used by the cell as a reserve source of energy and carbon. Therefore, as a rule, plants store oils almost exclusively in their seeds. Plant oils are not only a major food and feed products, but also the raw material for obtaining many nonfood products from drying oils and lubricants to biofuel. TAGs differ from other storage compounds in that in the course of fruit ripening their quantitative and qualitative composition does not remain constant, but undergoes significant changes. Therefore, the biosynthesis pathways of TAGs in living organisms have been actively studied for the past several decades, and today enough data can be presented to outline as how and where these processes occur in the plant cell. The present review is devoted to a brief description of current ideas about the ways and mechanisms of TAG formation and accumulation in higher plants.

Positional-Species Composition of Diacylglycerol Acetates from Mature Euonymus Seeds.

The positional‐species composition (PSC) of 3‐acetyl‐1,2‐diacyl‐sn‐glycerols (AcDAGs) from the seeds of mature fruits of 14 species of the genus Euonymus L. was established. The residues of six major fatty acids (FAs), palmitic (P), stearic (St), hexadecenoic (H), octadecenoic (O), linoleic (L), and linolenic (Ln), were present in the AcDAGs. Here, we demonstrated that the profile of PSC of AcDAGs could serve as chemotaxonomic factor to divide euonymus species studied here into groups which completely correlate with the present day systematic of the genus. In particular, the Euonymus section greatly exceeded other sections of the Euonymus subgenus as well as the Kalonymus one in the total levels of AcDAGs positional species having one and two O residues and was characterized by significantly lesser concentrations of species with one and two L residues. Moreover, in seed, AcDAGs of almost all Euonymus species EFL values were slightly higher than EFO ones, but all EFL and EFO values were higher than 1.0, and therefore, it can be concluded that both FAs mainly esterified sn‐2‐position of the glycerol moiety and saturated FAs residues were always virtually absent in the sn‐2 position of Euonymus seed AcDAGs, as it is also the case in nearly all TAGs molecules of plant origin.

Accumulation of neutral acylglycerols during the formation of morphologo-anatomical structure of euonymus Fruits

At three stages of fruit ripening of three euonymus species (Euonymus sp.), growth parameters, the development of morphologo-anatomical structure, and the accumulation of neutral acylglycerols (NAG) of fatty acids were studied. It was established that, in all species studied, in the cells of endosperm and cotyledons, as well as in arillus cells, small oleosomes of similar size were formed, whereas in Euonymus europaeus and E. maximowiczianus large oleosomes differing in their sizes also appeared. Independently of fruit age, dry weight of seeds exceeded that of arils by several times. At the determination of separate NAG classes: TAG (1,2,3-triacyl-sn-glycerols) and acDAG (3-acetyl-1,2-diacyl-sn-glycerols), it was shown that the absolute content of acDAG in seeds was 1.5 orders of magnitude higher than that of TAG; in contrast, in arils TAG were much more abundant than acDAG. Euonymus species differed markedly in the growth pattern and NAG accumulation in seeds and arils.

Dynamics of Fatty‐Acid Composition of Neutral Acylglycerols in Maturing Euonymus Fruits

The dynamics of the fatty‐acid (FA) composition of neutral acylglycerols (NAGs) composed of 1,2,3‐triacyl‐sn‐glycerols (TAGs) and 3‐acetyl‐1,2‐diacyl‐sn‐glycerols (acDAGs) was determined in the fruit seeds and arils of three Euonymus L. species at three stages of their maturity. The NAG composition comprised 29 FAs, linoleic, oleic, palmitic, and α‐linolenic acids being predominant. Noticeable amounts of other FAs, such as lauric, myristic, hexadec‐9‐enoic, stearic, (Z)‐vaccenic, and arachidic acid, etc., could also be present. In the course of maturation, the qualitative composition of major FAs remained nearly unchanged, while the unsaturation index of FAs in seeds and in TAGs, as well as, but to a lesser extent, in arils and in acDAGs, respectively, always decreased. This decline was brought about by a sharp fall of the α‐linolenate level, a decrease of the linoleate content, and a corresponding rise in the oleate content. It is suggested that, in both seeds and arils, both classes of NAGs were formed at the expense of the same FA pool; the quantitative composition of this pool was characteristic of a given fruit part and strongly changed during maturation. The accumulation of TAGs in E. europaeus fruits was accompanied by a conversion of hexadec‐9‐enoic acid into (Z)‐vaccenic acid via the C2‐elongation reaction.

Evidence of Strict Stereospecificity in the Structure of sn-1,2-Diacyl-3-Acetyl-Glycerols from Euonymus maximowiczianus Seeds Using Nuclear Magnetic Resonance Spectroscopy

Asymmetric, optically active sn-1,2-diacyl-3-acetyl-glycerols (AcDAG) have been known to scientists for several decades. However, to date, the problem of their structure has not been definitely resolved, which has led to a vast diversity of terms used for their designation in the literature. Using two-dimensional nuclear magnetic resonance, we have investigated AcDAG from the mature seeds of Euonymus maximowiczianus, from which we have been able to both identify a correlation of the methyl group in acetic acid residue with protons at the carbon atom at sn-3 position in the glycerol residue of the AcDAG molecule and, for the first time, demonstrate that this correlation is observed exclusively with one carbon atom at the α-position, but not with two as would have been expected in case of a racemic mixture. Moreover, results of our analysis of AcDAG isolated from the seeds of E. maximowiczianus directly confirm that diacylglycerol-3-acetyl-transferase is responsible for their biosynthesis, which reveals a strict specificity not only to acetyl-CoA as one of the substrates but also to the sn-3-position of the glycerol residue in sn-1,2-diacylglycerol during their biosynthesis.

Structural and functional characteristics of photosynthetic apparatus of chlorophyll-containing grape vine tissue

Photosynthesis in tissues under periderm of woody stems and shoots of perennial plants occurs in environment that is very different from the internal environment of leaf chloroplasts. These tissues are characterized by high CO2 and low O2 concentrations, more acidic surroundings, besides that only light which have passed through periderm reaches photosynthetic antennas. In contrast to leaves of deciduous plants chlorenchyma tissues of wintering plant organs are exposed to temperature fluctuations during all seasons, that is why the photosynthetic apparatus of woody stems has to be able to adapt to a wide range of environmental temperatures. In order to reveal unique features, which enable photosynthetic apparatus of chlorenchyma cells in woody plant organs to implement biological functions under different light and temperature conditions, we studied photosynthetic tissues of stem cortex in grapevine (Vitis vinifera L.) under normal conditions and after exposure to suboptimal temperatures and high light intensity. Comparative analysis of photosynthetic pigment composition and low-temperature chlorophyll fluorescence emission spectrum of leaves, young shoots and chlorenchyma of lignified shoots revealed relatively high level of chlorophyll b and carotenoids, and high photosystem II (PSII) to photosystem I (PSI) ratio in woody shoots. Analysis of parameters of variable chlorophyll fluorescence revealed high PSII activity in grapevine shoot cortex and demonstrated improved freeze tolerance and higher sensitivity to light of photosynthetic apparatus in grape vine in comparison to leaves. It was shown for the first time that photosynthetic apparatus in chlorenchyma cells of vine undergoes so-called “state-transition”–fast rearrangements leading to redistribution of energy between photosystems. Analysis of fatty acid (FA) compositions of lipids in examined tissues showed that the FA unsaturation index in green tissue of vine is lower than in leaves. A distinct feature of FA compositions of lipids in vine cortex was relatively high level of linoleic acid.

Polyphasic characterization of the thermotolerant cyanobacterium Desertifilum sp. strain IPPAS B-1220

Abstract A cyanobacterial strain from Lake Shar‐Nuur, a freshwater lake in Mongolia, was isolated and characterized by a polyphasic approach. According to the 16S ribosomal RNA gene sequence, this strain (IPPAS B‐1220) belongs to a newly described genus Desertifilum. In general, strains of Desertifilum maintain their genetic stability, as seen from the analysis of the 16S rRNA gene and 16S‐23S rRNA internal transcribed spacer sequences from strains collected at distant locations. The newly discovered strain is characterized by an unusual fatty acid composition (16:1&Dgr;7 and 16:2&Dgr;7,10). Analysis of its draft genomic sequence reveals the presence of six genes for the acyl‐lipid desaturases: two &Dgr;9‐desaturases, desC1 and desC2; two &Dgr;12‐desaturases, desA1 and desA2; one desaturase of unknown specificity, desX; and one gene for the bacillary‐type desaturase, desG, which supposedly encodes an ω9‐desaturase. A scheme for a fatty acid desaturation pathway that describes the biosynthesis of 16:1&Dgr;7 and 16:2&Dgr;7,10 fatty acids in Desertifilum is proposed.