Hexadecatrienoic acid

JAs are derived from linolenic acid via an octadecanoid pathway consisting of several enzymatic steps (Figure 36). Multiple compartments in plant cells participate in JA synthesis. The early steps of this pathway occur in chloroplasts, where linolenic acid is converted to OPDA by means of the three enzymes lipoxygenase (LOX), allene oxide synthase (AOS), and allene oxide cyclase (AOC).867-869 Linolenic acid is oxygenated by 13-LOX producing a peroxidized fatty acid 13-hydroperoxylinolenic acid. The product is subsequently metabolized by AOS to an unstable compound allene oxide. Allene oxide is sequentially converted by AOC to produce OPDA. An alternative pathway from another trienoic fatty acid, hexadecatrienoic acid (16 3), is present in chloroplasts.870 In this pathway, dinor OPDA is produced instead of OPDA. OPDA and dinor OPDA are transported into the peroxisome. An ABC transporter involved in this transport was identified in... 

Hexadecatrienoic acid Hexadecatrienoic acid. (Z,Z,Z)-Hexadecenoic acid Hexadecenoic acid, (Z)-... 

The overall reaction sequence can also be carried through, starting from hexadecatrienoic acid (16 3), which is two carbon atoms shorter. Here, the fatty... 

Both the lipid and the fatty acid compositions of plant leaves show a remarkable consistency between species. Furthermore, these compositions are only slightly altered by external factors and developmental period (Hitchcock and Nichols, 1971). The only small exception to these comments is the division of plants into the so-called T6 3-plants (those containing hexadecatrienoic acid mainly esterified in diacyl-galactosylglycerol) and T8 3-plants (which contain little, if any, hexadecatrienoic acid) (Heinz, 1977). These differences are also reflected in similar variations in lipid metabolism in 16 3-plants (prokaryotic-like) and 18 3-plants (Heinz and Roughan, 1982). 

This change in the fatty acid composition of the lipids bound to the protein, that is the increase of Cig-acids and of saturated fatty acids refers in the LHCP-complex to monogalactosyldiglyceride and phosphatidylglycerol and in the D1-peptide besides these lipids also to sulfoquinovosyldiglyceride. Whereas the anionic lipids of the thylakoid membrane contain up to 50% saturated fatty acids and as unsaturated acids linoleic and linolenic acid [8, 17-18], the monogalactolipid of the thylakoid membrane contains linolenic and hexadecatrienoic acid which makes up for 95% of total fatty acids [14-17]. For the... 

Oxygenic photosynthesis occurs in a uniquely constructed bilayer membrane known as thylakoid. The glycerolipid molecules that form the thylakoid membranes are characterized by their sugar head groups and a very high level of unsaturation in the fatty acid chains. In Arabidopsis, trienoic fatty acids - a-linolenic (18 3) and hexadecatrienoic acids (16 3) - account for more than 70% of the total fatty acids in thylakoid lipids. Therefore, this fatty acids might have some crucial role in maintaining photosynthetic functions. 

Poly-unsaturated fatty acids (mainly linoleic (18 2), linolenic (18 3) and hexadecatrienoic (16 3) acids) are major constituents of plant membrane lipids. In green leaves, the C g polyunsaturated fatty acids usually esterify the hydroxyl groups found either in position 1 or position 2. of the sn glycerol backbones of membranous phospholipids or galactolipids in contrast, hexadecatrienoic acid is always found esterified in position 2 of galactolipids. 

The lipids which contain either saturated or unsaturated fatty acids at the n-2 position of their glycerol moieties are derived from phosphatidic acid synthesized within the chloroplast. The biosynthesis of lipids containing such a configuration is referred to as the prokaryotic pathway. The desaturation of palmitic acid to hexadecatrienoic acid is only observed in the prokaryotic pathway of the so-called plants. 

DGDG, digalactosyldiacylglycerol MGDG, monogalactosyldiacyl-glycerol 16 0, palmitic acid 16 3, hexadecatrienoic acid 18 0, stearic acid 18 1, oleic acid 18 2, linoleic acid 18 3, linolenic acid. 

Independently of stress degree, the percentages of saturated fatty acids, such as palmitate, stearate, oleate and linoleate decrease, while those of triunsaturated acids increased. Under salt stress and at all plant ages, linolenic acid rate was reduced weakly and that of hexadecatrienoic acid decreased significantly, in parallel levels of saturated fatty acids increased. 

Plants are defined as those which have hexadecatrienoic acid esterified in their MGDG fraction while 18 3 plants have a-linolenic acid. These differences arise from differences in the fatty acid metabolism of such plants. Because 16 3 plants resemble cyanobacteria in their metabolism of fatty acids, such species are said to have procaryotic metabolism while 18 3 plants have eucaryotic metabolism. ... 

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