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Plastid membranes

Understanding mechanisms controlling metabolon localization in plastids of different membrane architectures Little is known about metabolon structure, assembly, and membrane targeting. The carotenoid biosynthetic pathway exists on plastid membranes. However, plastids have different membrane architectures and therefore tissue- and plastid-specific differences in membrane targeting of the biosynthetic metabolon can be expected. Localization in chloroplasts that harbor both thylakoid and envelope membranes differs from the envelope membranes in endosperm amy-loplasts. In fact, localization on both thylakoid and envelope membranes implies that the carotenoid pathway is really not a single pathway, but a duplicated pathway that may very well have membrane-specific roles with regard to functions in primary and secondary metabolism. [Pg.383]

Plants must be especially versatile in their handling of carbohydrates, for several reasons. First, plants are autotrophs, able to convert inorganic carbon (as C02) into organic compounds. Second, biosynthesis occurs primarily in plastids, membrane-bounded organelles unique to plants, and the movement of intermediates between cellular compartments is an important aspect of metabolism. Third, plants are not motile they cannot move to find better supplies of water, sunlight, or nutrients. They must have sufficient metabolic flexibility to allow them to adapt to changing conditions in the place where they are rooted. Finally, plants have thick cell walls made of carbohydrate polymers, which must be assembled outside the plasma membrane and which constitute a significant proportion of the cell s carbohydrate. [Pg.751]

Review of the transporters that carry P, and various sugar phosphates across plastid membranes. [Pg.783]

One response under phytochrome control is the closing of leaflets of Mimosa at the onset of darkness. The response occurs within 5 min, too short a time to be the result of transcriptional control. This and the finding that some phytochrome is tightly bound to membranes have led to the proposal that one primary effect of phytochrome is to alter membrane properties. It is not certain whether it is Pr or Pfl. that is active in causing a response, but Pfl. seems to be the most likely candidate for the "active" form. According to one suggestion, phytochrome in plastid membranes may mediate the release of gibberelins stored within the plastids.629... [Pg.1338]

The use of Triton X-100 to disperse Triticum chloroplast membranes has been reported to increase the recoverable yield of GAg by 1000 as compared with methanol extraction. The authors suggest that the methanol causes irreversible binding of GAS to the plastid membrane (72). However, the enhanced recovery using Triton X-100 has been disputed (73) and was not beneficial in the extraction of chloroplasts of Pisum. Now that physico-chemical procedures are available for many of the PGS, more attention should be directed at improving the extraction procedures for PGS. [Pg.235]

Simpson, D.J. 1979. Freeze-fracture studies on barley plastid membranes. III. Location of the light-harvesting chlorophyll-protein. Carlsberg Res. Commun. 44, 305-336. [Pg.165]

Fig. 1. Composition of plastid membranes. Figures given are percentages (percentage of total lipid) of the pictured lipid in the membranes specified. Data from Refs. [34,35]. Fig. 1. Composition of plastid membranes. Figures given are percentages (percentage of total lipid) of the pictured lipid in the membranes specified. Data from Refs. [34,35].
Since phosphatidic acid serves as a precursor of phospholipids, galactolipids, and TGs, it is not surprising that its own synthesis has been reported in four plant compartments plastids, ER, mitochondria, and Golgi bodies. In each case, esterification of the first acyl group to the in-1 position of glycerol-3-phosphate is catalyzed by glycerol-3-phosphate acyltransferase. Lysophosphatidic acid acyltransferase then completes the synthesis by acylating the sn-2 position. However, plastidial and extraplastidial acyltransferases show distinct differences in structure and specificity. Analysis of these differences and the different compositions of plastid and non-plastid membranes led to the prokaryotic/ eukaryotic two-pathway scheme for plant lipid synthesis shown in Fig. 3. [Pg.104]

Frosch et al. (10) also concluded that the pyridazinone effect on the lipid composition of the plastid membrane did not result from photooxidation. They demonstrated that both BASF 13 338 and San 9789 caused changes in membrane lipid composition, but neither compound structurally altered the plastid membrane system, visualized with the electron microscope, under conditions excluding photodestruction of chlorophyll. When treated seedlings were transferred to white light, the thylakoids and plastid ribosomes disappeared only in the San 9789 -treated seedlings. [Pg.102]

The effectiveness of the light in causing structural disturbances correlated with the effectiveness of light in mediating the photodestruction of chlorophyll. The structural disintegration was not related to the effect of the pyridazinones on the lipid composition of the plastid membrane si.nce structural changes did not occur in the presence of BASF 13 338 even though the lipid compositional effects had occurred. [Pg.102]

The termination of elongation is catalyzed by ACP-thioesterases (enzymes belonging to the class of acyl-ACP hydrolases). These enzymes hydrolyze acyl-ACP with the formation of free FA, whieh ean eross the plastid membrane to be reactivated outside the organelle [11]. [Pg.127]

As an alternative to the Kennedy s pathway, FAs arising de novo in a course of FA biosynthesis may be first integrated into the lipids of plastid membrane and/or those of the ER and are only later accumulated as TAGs (Figure 5) [7]. [Pg.136]

Changes in plastid membrane permeability during development also have been noted [13]. General, there is more rapid uptake of amino adds early followed by a decline as tissues mature this in turn could influence p C]aspartate incorporation rates seen in intact plastids. Again, this appears unlikely, since amino add production by Triton X-100 disrupted plastids (which would not be subject to permeability effects) varies in a similar fashion to light-driven activity (Fig. 2). [Pg.3042]

Leaves Neutral fats and /or Phospholipids of Plastid membrane... [Pg.247]

In plants phosphatidylcholine is the major phospholipid in extra-plastid membranes and is synthesised mainly by the CDP-choline pathway. There are three steps in the pathway catalysed by the enzymes choline kinase, cholinephosphate cytidylyltransferase (CPCT) and cholinephosphotransferase (Harwood, 1989). Evidence from studies in animals (Pelech and Vance, 1984) and in plants (Price-Jones and Harwood, 1983) suggests that the intermediate step catalysed by CPCT is the main regulatory step. The cloning of a full length and partial cDNA clones for pea cholinephosphate cytidylyltransferase is described. [Pg.398]

Operation of the FAS system involves an enzyme-catalyzed cycle of condensation, reduction, dehydration and a second reduction (Figure 3.2), and is dependent upon the supply of a carbon source and energy provision in the forms of ATP, NADH and NADPH. The extreme importance of acetyl-CoA carboxylase activity to the functioning of FAS may be deduced from the observed close proximity of each system to each other in plastidic membranes of maturing rape seed (Slabas and Smith, 1988). [Pg.62]

Further desaturation and acyl chain elongation of fatty acids are generally accepted to involve cytosolic membranous systems associated with the endoplasmic reticulum (Stumpf, 1989). A critical importance, therefore, would appear to exist for a detailed understanding of the mechanics by which the fatty acids are exported from the plastid. At present, there is little available information on the precise transport system or its regulation. Although fatty acids are presumed to be released on hydrolysis of acyl-ACPs by specific thioesterases, it is not known whether an initial formation of acyl-CoA is required prior to transport across the plastidic membrane in association with carnitine or some other system. A direct transacylation between ACP and CoA or some carrier system would be less expensive energetically than a process involving hydrolysis and synthesis. [Pg.66]

Fig. 3.3. A three-dimensional diagram illustrating the structure of the developing wheat endosperm amyloplast. S starch, 0PM outer plastid membrane, IPM inner plastid membrane, T tubular invaginations of IPM. From Buttrose, 1963 [37]... Fig. 3.3. A three-dimensional diagram illustrating the structure of the developing wheat endosperm amyloplast. S starch, 0PM outer plastid membrane, IPM inner plastid membrane, T tubular invaginations of IPM. From Buttrose, 1963 [37]...

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