Endoplasmic Reticulum as the Site of Lecithin Formation in Castor Bean Endosperm

Lord, J. Michael; Kagawa, T.; Moore, Thomas; Beevers, Harry

doi:10.1083/jcb.57.3.659

Cited by 320 publications

(211 citation statements)

References 34 publications

(51 reference statements)

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“…Apparently, acyltransferase and the majority of Cyt reductase comigrated with the RER. The RER did not appear as a sharp peak but was distributed in many fractions of different densities, as expected (11,17).…”

Section: Methodsmentioning

confidence: 67%

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Diacylglycerol Acyltransferase in Maturing Oil Seeds of Maize and Other Species

Cao

Huang²

1986

Plant Physiol.

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Diacylglycerol acyltransferase (EC 2.3.1.20) activity was detected in the microsomal fractions of maturing maize scutellum, soybean cotyledon, peanut cotyledon, and castor bean endosperm. The activity detected was high enough to account for the in vivo rate of triacylglycerol synthesis. The activity of the maize enzyme was characterized using diolein micelles prepared by sonication in Tween 20 as the substrate. The activity was highest at pH values of 6 to 7. The activity was proportional to the amount of enzyme added, and the reaction rate was linear for about 2 minutes. The enzyme was not inactivated by Tween 20, Zwitterion 3-08, Triton-X 100, and cholate, but was inactivated completely by sodium dodecyl sulfate. The enzyme was active on linoleoyl coenzyme A (CoA), palmitoyl CoA, and oleoyl CoA, although the activity was highest on linoleoyl CoA. Endogenous diacylglycerol was present in the microsomes, and the enzyme activity was only partially dependent on the addition of external diolein. Subcellular fractionation of the total scutellum extract in sucrose density gradients was performed. By comparing the migration of the enzyme between rate and equilibrium centrifugation, and between equilibrium centrifugation in the presence and absence of magnesium ions in the preparative media, the enzyme was shown to be associated with the rough endoplasmic reticulum. Some of the above findings on the maize enzyme were extended to the enzymes from castor bean, soybean, and peanuts.Diacylglycerol acyltransferase (EC 2.3.1.20) catalyzes the final step in the synthesis of triacylglycerols in oil seeds (18,22). It is also the only known enzyme unique to the long biosynthetic pathway of triacylglycerols, since the diacylglycerol produced could also be used to produce phospholipids or galactolipids. In spite of the importance of this enzyme in triacylglycerol biosynthesis in oil seeds, its properties have not been well studied.Diacylglycerol acyltransferase in the microsomal fraction of developing seeds has been assayed directly or together with other enzymes (6,10,20,21). In a recent, and so far the most detailed, study, the general properties of the enzyme in a safflower microsomal fraction were characterized (10). However, the detected level ofactivity was almost a magnitude lower than that required to catalyze the sequence of reaction from glycerol phosphate to triacylglycerol (21, 22). Using an enzyme assay which had been used successfully to study the enzyme in spinach leaves, Martin and Wilson (13) failed to detect enzyme activity in the cotyledon extract of developing soybean.An important but unknown aspect of diacylglycerol acyltransferase is its subcellular location. In general, the microsomal fractions were used to study the enzyme activity, and they 'Supported by National Science Foundation grant DMB 85-15556.presumably contained vesicles of the ER as well as membranes of other subcellular particles, including broken plastids. In a recent detailed analysis of the subcellular location ofthe enzyme in spinach...

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Section: Methodsmentioning

confidence: 67%

“…Cyt reductase at this density in an equilibrium centrifugation should represent the ER (1 1, 17). At this region of the gradient, although one galactosyl- (11,17). In the absence of Mg2", the RER would loose the polysomes and become artifically smooth ER.…”

Section: Methodsmentioning

confidence: 99%

Diacylglycerol Acyltransferase in Maturing Oil Seeds of Maize and Other Species

Cao

Huang²

1986

Plant Physiol.

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“…The plasma membrane and the other membrane fraction were analysed for enzyme activities that serve as markers for various plant membranes, including the plasma membrane, tonoplast, mitochondria, Golgi and endoplasmic reticulum (ER). Speci®c markers include: the VO 4± sensitive Ptype ATPase activity (marker for plasma membrane and ER), NO 3± sensitive V-type ATPase activity (marker for tonoplast) (Gallagher and Leonard, 1982), Mg +2 -depedent inosine diphosphatase (marker for Golgi) (Ray et al, 1969), antimycine A insensitive NADHdependent cytochrome c reductase (marker for ER) (Lord et al, 1973) and cytochrome c oxidase (marker for mitochondria) (Hodges and Leonard, 1972).…”

Section: Membrane Isolation and Fractionationmentioning

confidence: 99%

The spatial expression patterns of a phosphate transporter (MtPT1) from Medicago truncatula indicate a role in phosphate transport at the root/soil interface

Chiou¹,

Liu²,

Harrison³

2001

The Plant Journal

183

145

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SummaryThe movement of phosphate from the soil into plant root cells is the ®rst of many crucial transport events required to supply phosphorous (P) to cells throughout the plant. In addition to the ability to acquire phosphate from the soil, the majority of the vascular plants are able to form arbuscular mycorrhizal associations in which phosphate may be delivered to the cortex via a fungus. Previously, we cloned two phosphate transporter genes, MtPT1 and MtPT2 from Medicago truncatula roots. Complementation of a yeast phosphate transport mutant revealed that MtPT1 is a functional phosphate transporter and Northern analyses revealed that MtPT1 is expressed exclusively in roots (Liu et al., 1998, Mol. Plant-Microbe Interact. 11, 14±22). Utilising an antibody speci®c for MtPT1, we have analysed the accumulation and spatial expression patterns of the MtPT1 transporter. MtPT1 transcript and protein levels show close correlation and increase dramatically in the roots in response to phosphate starvation. MtPT1 protein levels decrease in roots during development of a symbiosis with arbuscular mycorrhizal (AM) fungi, indicating that this transporter is not involved in symbiotic phosphate transport. Membrane fractionation and analysis of a MtPT1/GFP fusion protein revealed that MtPT1 is located in the plasma membrane, while in situ hybridisation and immunolocalisation demonstrate the presence of MtPT1 transcripts and protein in the epidermal cells and root hairs of M. truncatula roots. MtPT1 shows expression patterns consistent with a role speci®cally in the acquisition of phosphate from the soil and is distinct from the other phosphate transporter of this class described to date.

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“…Gradient fractions were assayed for ATPase, pH 6.5 and 9, Cyt c oxidase, latent IDPase, and NADH-Cyt c reductase activities. Latent IDPase activity is believed to be a marker for Golgi apparatus membranes (27), and NADH-Cyt c reductase activity that is insensitive to Antimycin A appears to be a marker for the endoplasmic reticulum (20). However, NADH-Cyt c reductase activity has also been shown to be associated with the outer mitochondrial membrane and microbodies, and in the latter case the activity is Antimycin A insensitive (4).…”

mentioning

confidence: 99%

“…NADH-Cyt c reductase activity in this area of the gradient was not sensitive to I ,UM antimycin A, a concentration which strongly inhibited the activity of this enzyme in mitochondria. Endoplasmic reticulum from endosperm and cotyledon of a variety of fatty seedlings equilibrates at a density of about 1.12 g/cc in sucrose gradients (13,20).…”

mentioning

confidence: 99%

Isolation of Plasma Membranes from Corn Roots by Sucrose Density Gradient Centrifugation

Leonard¹,

VanDerWoude²

1976

Plant Physiol.

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An investigation was conducted into the isolation of plasma membrane vesicles from primary roots of corn (Zea mays L., WF9 x M14) by sucrose density gradient centrifugation. Identification of plasma membranes in cell fractions was by specific staining with the periodic-chromic-phosphotungstic acid procedure. Plasma membrane vescles were rich in K+-stimulated ATPase activity at pH 6.5, and equilibrated in linear gradients of sucrose at a peak density of about 1.165 g/cc. It was necessary to remove mitochondria (equilibrium density of 1.18 g/cc) from the homogenate before density gradient centrifugation to minimize mitochondrial contamination of the plasma membrane fraction. Endoplasmic reticulum (NADH-cytochrome c reductase) and Golgi apparatus (latent IDPase) had equilibrium densities in sucrose of about 1.10 g/cc and 1.12 to 1.15 g/cc, respectively. A correlation (r = 0.975) was observed between K+-stimulated ATPase activity at pH 6.5 and the content of plasma membranes in various cell fractions. ATPase activity at pH 9 and cytochrome c oxidase activity were also correlated.A major peak of ATPase activity at pH 6.5 was observed at low density in Ficoll after nonequilibrium centrifugation in a combination Ficollsucrose gradient. Twenty to forty percent of the vesicles in this ATPase fraction stained positively for plasma membranes, and with equilibrium centrifugation the major portion of the ATPase activity shifted to densities in sucrose which were characteristic of plasma membranes. All major vesicular ATPase activities observed in Ficoll or sucrose contained substantial amounts of plasma membranes. For unknown reasons, mitochondria and plasma membranes equilibrated over a broader density range and at lower peak densities in sucrose as a result of equilibrium centrifugation through Ficoll.

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Endoplasmic Reticulum as the Site of Lecithin Formation in Castor Bean Endosperm

Cited by 320 publications

References 34 publications

Diacylglycerol Acyltransferase in Maturing Oil Seeds of Maize and Other Species

Diacylglycerol Acyltransferase in Maturing Oil Seeds of Maize and Other Species

The spatial expression patterns of a phosphate transporter (MtPT1) from Medicago truncatula indicate a role in phosphate transport at the root/soil interface

Isolation of Plasma Membranes from Corn Roots by Sucrose Density Gradient Centrifugation

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