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Glycerolipid synthesis in leaves - ScienceDirect

Expression of lauroyl-acyl carrier protein thioesterase in Brassica napus seeds induces pathways for both fatty acid oxidation and biosynthesis and implies a set point for triacylglycerol accumulation.

: Monocots and dicot plastidic are fundamentally different, and these differences create the basis for herbicide . The multidomain form of ACCase found only in graminaceous monocots is the only one completely inhibited by the ACCase-inhibiting herbicides, which allows them to specifically control certain weedy members of the Poacea, mostly in dicot crops. Further subtle differences between the ACCase enzymes from small grain crops (wheat and barley) and grassy weeds allow the use of herbicides like diclofop to control wild oats in these crops.
Much of our knowledge about plant ACCases derives from studies of their herbicide inhibitors, their mechanism of toxicity, and the mechanisms of evolved . For example, investigations on the sensitivity of ACCases from certain grass families have provided detailed information on the different ACCase isoforms and their relative contributions to lipid biosynthesis. The ability of herbicides to specifically inhibit certain isoforms indicates that the plastidic form of the provides most of the lipids for membranes and cellular in the Poacea, as well as other plant families.

Isoforms of acyl carrier protein involved in seed-specific fatty acid synthesis.

Glycerolipid synthesis in leaves

WRINKLED1 encodes an AP2/EREB domain protein involved in the control of storage compound biosynthesis in Arabidopsis.

All organisms synthesize , which are long-chain aliphatic carboxylic acids. Fatty acids are used primarily as precursors for , a family of lipids containing a glycerol backbone that are essential components of cellular membranes. In plants, this is additionally important because some fatty acids are elongated in a related series of reactions to produce and cuticular waxes. These are critical protective compounds on leaf and stem surfaces. Breakdown products of fatty acids are also widely used as intracellular signaling molecules as part of cellular responses to external stimuli. inhibition of either fatty synthesis or elongation prevents the production of these important molecules and thus is lethal to plants.

This discussion of plant fatty acid synthesis and its herbicide inhibitors is divided into two sections:


: The first of fatty acid synthesis is acetyl CoA-carboxylase (ACCase; EC 6.3.4.14), which the ATP-dependent carboxylation of acetyl-CoA to form malonyl-CoA . ACCase carries out the first committed step and is thus the regulatory site for the whole . The enzyme is composed of two monomers with different functions: a biotin carboxylase complex and a carboxyltransferase complex. Higher plants have two forms of ACCase: a eukaryotic, cytosolic form that is mostly to herbicides and a prokaryotic, plastidic form that is to herbicides. The plastidic enzyme is further subdivided into two isoforms: a dimeric form found in most monocots and all , and an unusual multidomain form found only in graminaceous monocots. Biochemical investigations on the for ACCase-inhibiting herbicides show that they interact with a 400-amino acid region of the carboxyltransferase of the enzyme.
In plants, are synthesized in . According to the , plastids are the modern, evolutionary descendents of free-living prokaryotes that were engulfed and retained by larger bacteria. These endosymbionts gradually evolved into chloroplasts and mitochondria. The fatty acid biosynthetic pathway in plant plastids is very similar to the pathway in modern prokaryotes, providing support for this theory. The pathway begins with the of two-carbon units to acetyl-CoA (from glycolysis) to create 16- or 18-carbon fatty acids. These molecules are either exported into the where they are integrated into membranes or other cellular components, or are further elongated into waxes, , or .

: Malonyl-CoA is elongated into fatty acids by the stepwise addition of two-carbon acetyl units by the enzyme fatty acid synthase. Synthesis by this process continues to produce 16:0-acyl carrier (ACP) or 18:0-ACP saturated fatty acids. Terminal reactions of fatty acid synthesis include thioester bond , acyl desaturation, and transfer of the acyl group to a glycerolipid. Of these reactions, glycerolipid synthesis deserves special mention since these are the main structural lipids of all cellular membranes except those of the . Briefly, 16:0 and 18:1 fatty acids are exported from the chloroplast to the endoplasmic reticulum (ER) as their acyl-CoA moieties, where they are incorporated into and other phospholipids. The diversity of fatty acids is immense, with over 200 different fatty acids identified in higher plants.

: In plants, very long-chain fatty acids (VLCFAs) are particularly important as membrane components and as cuticular and epicuticular waxes. Fatty acids from the chloroplast are exported into the endoplasmic reticulum, where a family of elongase enzymes first convert free long-chain fatty acids into fatty acyl-CoA esters. The same enzymes subsequently elongate these molecules up to 34 carbons to create waxes and suberin.

(G3P) during the de novo synthesis of glycerolipid and (2) ..

All organisms synthesize , which are long-chain aliphatic carboxylic acids. Fatty acids are used primarily as precursors for , a family of lipids containing a glycerol backbone that are essential components of cellular membranes. In plants, this is additionally important because some fatty acids are elongated in a related series of reactions to produce and cuticular waxes. These are critical protective compounds on leaf and stem surfaces. Breakdown products of fatty acids are also widely used as intracellular signaling molecules as part of cellular responses to external stimuli. inhibition of either fatty synthesis or elongation prevents the production of these important molecules and thus is lethal to plants.

This discussion of plant fatty acid synthesis and its herbicide inhibitors is divided into two sections:

Metabolic flux maps comparing the effect of temperature on protein and oil biosynthesis in developing soybean cotyledons.

Herbicides inhibit several different elongases, each with different enzymatic functions. Long-chain fatty acid:CoA (EC 6.2.1.3) is inhibited by the carbamothioate herbicides EPTC and triallate. However, details about other elongases inhibited by these herbicides are unknown.
: These soil-applied herbicides inhibit early development, primarily the emergence and elongation of primary . One of the first documented injury symptoms of EPTC was a in cuticular wax deposition. Other severe injury symptoms include the failure of leaf emergence from the coleoptile and a general stunting of seedling growth, indicating that inhibition of VLCFA synthesis has many, widespread effects on normal plant growth. This observation also supports the idea that there may be other functions for elongation in plants.
Carbamothioate herbicides are actually , in that the form of the herbicide applied to plants (the parent molecule) is not toxic. Once the parent molecule is absorbed into plant tissues, it must be cleaved and metabolically activated by in order to become .
Carbamothioates are soil applied and can be applied as pre-plant incorporated or pre-emergence herbicides. Crop selectivity depends upon planting crop seeds below the treated soil. Such manipulations are sometimes hard to achieve with precision, and so crop injury from these herbicides is a recurring problem. The potential for crop injury led to early research on compounds known as , antidotes, or protectants. The first safeners thus identified were used to protect corn from EPTC injury, and include the compounds naphthalic anhydride, benoxacor, fenclorim, and fluxofenim. Safeners are coated onto crop seeds or may be mixed with some commercial herbicide formulations. They commonly induce one or more plant defense mechanisms, including increased production, and enhanced and activity. The result is that crop plants are better able to metabolize and the herbicide. Interestingly, these compounds protect monocot but not dicot crops from herbicide injury, for reasons that are not entirely clear.
Carbamothioate herbicides have been shown to cause changes in the makeup of soil microbial communities. In particular, continuous usage in the same field selects for bacteria and actinomycetes that rapidly degrade these herbicides, to the extent that they are essentially ineffective for weed control. This phenomenon of rapid herbicide has been termed ‘enhanced degradation’ and ‘preconditioned soil’.

: The chloroacetamide family is one of the most widely used groups of herbicides in the world, primarily due to the use of metolachlor. The first member of this family to be commercialized was alachlor by the Monsanto Company in 1969. They are extensively used in corn and soybeans to control a broad spectrum of annual grasses and some broadleaf weeds. They are soil applied and usually do not require soil incorporation for activity. Herbicides in this family inhibit plastidic VLCFA synthesis, although the precise enzymatic step(s) are not known.




to the carbamothioate herbicide triallate did not evolve until it had been used for more than 25 years. Wild oat (Avena fatua) populations to triallate were first documented in 1990 in Alberta and subsequently reported in Montana. The resistant biotypes are unusual, because they represent metabolic . Carbamothioate herbicides are actually pro-herbicides, in that they require metabolic activation by sulfoxidase enzymes to become phytotoxic. In Montana, the resistant was 10- to 15-fold slower at converting the triallate into the phytotoxic triallate sulfoxide. Both biotypes were equally susceptible to synthetic triallate sulfoxide, and the rates of this toxic form were equivalent. Resistance was conferred by two nuclear , which may encode the enzymes responsible for triallate sulfoxidation. The mechanism of resistance in the Canadian biotype appears to involve alterations in gibberellin biosynthesis. Interestingly, both biotypes are cross-resistant to difenzoquat, an unrelated pyrazolium herbicide.
Triallate was used for about 30 years before resistant biotypes appeared in agricultural fields. This unusually long, resistance-free usage period illustrates several important concepts about plant responses to herbicide . First, even though triallate has a reasonably long soil , its precise application requirements rarely allow it to achieve greater than about 85% wild oat control, and so it exerts less pressure compared to some other herbicides. Second, the target (wild oat) has relatively low seed production and poor seed dispersal, traits that tend to limit population sizes and thus reduce the of potentially resistant individuals. And third, the necessity of accumulating two separate recessive to achieve resistance in self-pollinating wild oats would require a large number of individuals and generations. If carbamothioate herbicides in fact inhibit several elongases, the accumulation of additional alleles would require even more . It might be expected that the loss of two sulfoxidase-like activities would be associated with a fitness cost in the resistant biotype. While fitness comparisons have not been done for the Montana biotypes, studies of the Canadian biotypes did not support this idea, and in fact seed was higher in the resistant .
Resistance to chloroacetamide herbicides has only been verified for barnyardgrass (China) and rigid ryegrass (Australia), and in both cases is based on enhanced metabolism. The scarcity of resistant species is surprising, considering the long history and widespread use patterns of these herbicides.

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Plant Fatty Acid Synthesis - AOCS Lipid Library


Glycerolipid Structure, Function, and Synthesis in ..

Thus, thromboxane synthetase generates MDA, with thromboxane A2, from prostaglandin endoperoxides during human platelet activation (Hecker M et al., J Biol Chem 1989, 264, 141).
As 4-HNE, MDA is able to form adducts with free amino acids and many more with proteins.

The inititation of glycerolipid synthesis begins at a branchpoint ..

Herbicides inhibit several different elongases, each with different enzymatic functions. Long-chain fatty acid:CoA (EC 6.2.1.3) is inhibited by the carbamothioate herbicides EPTC and triallate. However, details about other elongases inhibited by these herbicides are unknown.
: These soil-applied herbicides inhibit early development, primarily the emergence and elongation of primary . One of the first documented injury symptoms of EPTC was a in cuticular wax deposition. Other severe injury symptoms include the failure of leaf emergence from the coleoptile and a general stunting of seedling growth, indicating that inhibition of VLCFA synthesis has many, widespread effects on normal plant growth. This observation also supports the idea that there may be other functions for elongation in plants.
Carbamothioate herbicides are actually , in that the form of the herbicide applied to plants (the parent molecule) is not toxic. Once the parent molecule is absorbed into plant tissues, it must be cleaved and metabolically activated by in order to become .
Carbamothioates are soil applied and can be applied as pre-plant incorporated or pre-emergence herbicides. Crop selectivity depends upon planting crop seeds below the treated soil. Such manipulations are sometimes hard to achieve with precision, and so crop injury from these herbicides is a recurring problem. The potential for crop injury led to early research on compounds known as , antidotes, or protectants. The first safeners thus identified were used to protect corn from EPTC injury, and include the compounds naphthalic anhydride, benoxacor, fenclorim, and fluxofenim. Safeners are coated onto crop seeds or may be mixed with some commercial herbicide formulations. They commonly induce one or more plant defense mechanisms, including increased production, and enhanced and activity. The result is that crop plants are better able to metabolize and the herbicide. Interestingly, these compounds protect monocot but not dicot crops from herbicide injury, for reasons that are not entirely clear.
Carbamothioate herbicides have been shown to cause changes in the makeup of soil microbial communities. In particular, continuous usage in the same field selects for bacteria and actinomycetes that rapidly degrade these herbicides, to the extent that they are essentially ineffective for weed control. This phenomenon of rapid herbicide has been termed ‘enhanced degradation’ and ‘preconditioned soil’.

Glycerolipid Biosynthesis - ResearchGate

At higher concentrations (1 to 20 mM), 4-HNEinhibits DNA and protein synthesis and activates phospholipase A2 confirmingsimilar observations in tissue in response to oxidative stress.

In plants, approximately one ..

29-70).

The first component protein of an enzyme of fatty acid biosynthesis, fatty acidsynthase, was purified ().

Polyprenol diphosphates were shown to be involved in the biosynthesis ofpolysaccharides in () and in the biosynthesis of peptidoglycans in ().

The structure of juvenile hormone of insects was elucidated by Roller H ().

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