Fatty acids chloroplast

This study showed that chloroplasts from hemiparasitic plants reveal a trend for low values of chlorophyll and polar lipids while the protein content is less affected. "Tropical chlroroplasts present marked changes in polar lipid composition along with a decrease in unsaturation of fatty acids. Chloroplasts from all hemiparasitic plants are capable of a more or less limited photosynthesis, probably reflecting the degree of dependence on the host. 

Light and photosynthetic electron transport convert DPEs into free radicals of undetermined stmcture. The radicals produced in the presence of the bipyridinium and DPE herbicides decrease leaf chlorophyll and carotenoid content and initiate general destmction of chloroplasts with concomitant formation of short-chain hydrocarbons from polyunsaturated fatty acids (37,97). 

Experiments with chloroplasts showed an apparent inhibition of fatty acid synthesis by PAN (at 72 ppm for 10 min). The result is difficult to interpret the inhibition could be attributed to inactivation of one of the enzymes of the multistep system or to oxidation of the reductant (reduced NADP, or NADPH) required in the chain elongation process. 

The fatty acids are synthesized in chloroplasts or proplastids and moved into the cytoplasm and the endomembrane system for further modification and synthesis of neutral fats, phospholipids, and other compounds... 

Fatty Acid Synthesis Occurs in the Cytosol of Many Organisms but in the Chloroplasts of Plants... 

In the photosynthetic cells of plants, fatty acid synthesis occurs not in the cytosol but in the chloroplast stroma (Fig. 21-8). This makes sense, given that NADPH is produced in chloroplasts by the light reactions of photosynthesis ... 

In plants most biosynthesis occurs in the chloro-plasts or in the protoplastids of seeds.72-75 There are two different synthase systems in chloroplasts, one that forms primarily the 16 0 palmitoyl-ACP and the other the 18 0 stearoyl-ACP. Hydrolysis of the palmitoyl-ACP releases palmitate, one major product of chloroplasts. However, the stearoyl-ACP is desaturat-ed to oleoyl-ACP75a before hydrolysis to free oleate or conversion to oleoyl-CoA. In many species oleic acid is almost the sole fatty acid exported by the chloroplasts. However, it undergoes a variety of modification reactions in the plant cytosol. 

Figure 21-3 Major pathways of synthesis of fatty acids and glycerolipids in the green plant Arabidopsis. The major site of fatty acid synthesis is chloroplasts. Most is exported to the cytosol as oleic acid (18 1). After conversion to its coenzyme A derivative it is converted to phosphatidic acid (PA), diacylglycerol (DAG), and the phospholipids phosphatidylcholine (PC), phosphatidylinositol (PI), phosphatidylglycerol (PG), and phosphatidylethanolamine (PE). Desaturation also occurs, and some linoleic and linolenic acids are returned to the chloroplasts. See text also. From Sommerville and Browse.106 See also Figs. 21-4 and 21-5. Other abbreviations monogalactosyldiacylglycerol (MGD), digalactosyldiacylglycerol (DGD), sulfolipid (SL), glycerol 3-phosphate (G3P), lysophosphatidic acid (LPA), acyl carrier protein (ACP), cytidine diphosphate-DAG (CDP-DAG).

Moreover, there is considerable evidence that PPO is not active as a phenol oxidase in chloroplasts, but is limited as a phenol oxidase by latency or lack of substrate [18]. The latent form of the enzyme can be activated by a wide variety of treatments, including detergents [19], fatty acids [20] trypsin [21] and Ca2+ [22]. The results of Tolbert [21] indicated that light could activate latent PPO because polyphenols can be oxidized photochemically by chloroplast membranes in the absence of other... 

The specific neutral FDPase present in nonphotosynthetic plant tissues resembles that isolated from animal tissues in its sensitivity to AMP. The alkaline FDPase of chloroplasts is not inhibited by AMP, but evidence has been presented which suggests that the enzyme may be inhibited by fatty acids and fatty acid esters 110). These substances also seem to inhibit the conversion of SDP to S7P in chloroplasts the presence of this activity in chloroplasts was reported by Racker and Schroeder 85), but the nature of this enzyme and its possible relation to the FDPase of chloroplasts remains obscure. 

Gemel, J., Saczynska, V. Kaniuga, Z. (1988). Galactolipase activity and free fatty acid levels in chloroplast of domestic and wild tomatoes with different chilling tolerance. Physiologia Plantarum 74, 509-14. 

Several reports of the effects of ozone in vivo are presented in Table XII. It is impossible to decide whether the effects of ozone are primary reactions or the result of a series of reactions initiated by ozone. All results can be rationalized as enzyme inhibition of one sort or another. Effects on membrane structure are harder to observe, and in one case it was reported that the malonaldehyde which would be expected on fatty acid ozonolysis was only observed after symptoms were apparent (74). Results of electron microscope examination showed that the first observable damage was in the stroma of the chloroplasts (70). One can easily argue that earlier damage could not be detected by microscopic techniques. However, recent reports that the chloroplast polyribosomes are much more susceptible to degradation by ozone are important observations which are consistent with the microscopy experiments (76). Chloroplast polysomes are also more susceptible to sulfhydryl reagents than are cytoplasmic polysomes (77). This evidence indicates that ozone itself, or a toxic product from primary oxidation, can pass through the cytoplasm and have its effect in the chloroplast. 

FROELICH, J.E., ITOH, A., HOWE, G.A., Tomato allene oxide synthase and fatty acid hydroperoxide lyase, two cytochrome P450s involved in oxylipin metabolism, are targeted to different membranes of chloroplast envelope., Plant Physiol., 2001,125,306-317. 

R(+) enantiomer is herbicidally active (23.24). Hoppe and Zacher (12) showed that the R(+) enantiomer of diclofop was more effective than the S(-) enantiomer in reducing acetate incorporation into free fatty acids in isolated maize chloroplasts. ACCase activity is inhibited by R(+) (98% enantiomeric excess) haloxyfop acid but not by the S(-) (94% enantiomeric excess) enantiomer (Fig. 5). The inhibition caused by the S(-) enantiomer could be accounted for by the 3% contamination in the S(-) preparation by the R(+) enantiomer. 

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... 

Chloroplast ferredoxin is a small water soluble protein M W 000) containing an Fe-S center [245]. Its midpoint potential ( — 0.42 V [246]) is suitable for acting as an electron acceptor from the PSI Fe-S secondary acceptors (Centers A and B) and as a donor for a variety of functions on the thylakoid membrane surface and in the stroma. Due to its hydrophylicity and its abundance in the stromal space, ferredoxin is generally considered as a diffusable reductant not only for photosynthetic non-cyclic and cyclic electron flow, but also for such processes as nitrite and sulphite reduction, fatty acid desaturation, N2 assimilation and regulation of the Calvin cycle enzyme through the thioredoxin system [245]. Its possible role in cyclic electron flow around PSI has already been discussed. The mobility of ferredoxin along the membrane plane could be an essential feature of this electron transfer process the actual electron acceptor for this function and the pathway of electron to plastoquinone is, however, still undefined. 

The leaves of higher plants contain upto 7% of their dry weight as fats some of which are present as surface lipids, the others as components of leaf cells, especially in the chloroplast membrane. The fatty acid composition of plant membrane lipids is very simple. Six fatty acids- palmitic, palmitoleic, stearic, oleic, linoleic and y-linolenic generally account for over 90% of the total fatty acids. 

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