Biosynthesis and Intracellular Transport of 11S Globulin in Developing Pumpkin Cotyledons

In vitro studies to explore the biosynthesis of 11S globulin developing cotyledons of pumpkin (Cucurbita sp.) demonstrated that 11S globulin is synthesized on membrane-bound polysomes. M_r of the translation products (preproglobulin) synthesized by the poly(A)⁺-RNA isolated from developing cotyledons were determined to be 64,000 and 59,000, which are larger than those of the mature globulin subunit (62,000 and 57,000). Preproglobulin is then cotranslationally processed by cleavage of the signal peptide to produce proglobulin. In vivo pulse-chase experiments showed the sequential transformation of the single-chain proglobulin to mature globulin subunit (disulfide-linked doublet polypeptides) indicating posttranslational modification of the proglobulin.

Subcellular fractionation of the pulse-chased intact cotyledons showed that the [³⁵S]methionine label is detectable in proglobulin in rough endoplasmic reticulum shortly after the pulse label. With time, the labeled proteins move into other cellular fractions: proglobulin in the density = 1.24 grams per cubic centimeter fractions after 30 minutes and mature globulin subunit associated with protein bodies after 1 to 2 hours. The distribution of proglobulin in sucrose density gradients did not correspond with those of catalase (microbody marker) or fumarase (mitochondria marker). An accumulation of proglobulin occurred in the density = 1.24 grams per cubic centimeter fractions, whereas the mature globulin was scarcely detectable in this fraction. In contrast, proglobulin was not detected by immunochemical blotting analysis in the protein bodies prepared under the mild conditions from cotyledon protoplasts. The results suggest that the d = 1.24 grams per cubic centimeter fractions are engaged in the translocation of proglobulin into the protein bodies.

     

Immunocytochemical localization of concanavalin A in developing jack-bean cotyledons

The lectin, concanavalin A (Con A), was localized in the cotyledon of developing jack beans (Canavalia ensiformis (L.) DC) by electron-microscope immunocytochemistry. In mature seeds, Con A was present in protein-storage vacuoles (protein bodies) of storage-parenchyma cells. Although protein bodies could be seen in other cell types, only protein bodies in storage-parenchyma cells contained Con A. During seed development, Con A was also localized on the endoplasmic reticulum and Golgi apparatus, presumably en route toward deposition within the protein bodies. The intensity of labeling of the endoplasmic reticulum was much greater during the developmental stage of protein-body filling (66% final seed weight) than in mature seeds.Abbreviations Con A concanavalin A - ER endoplasmic reticulum - IgG immunoglobulin G     

Immunolocalization of avenin and globulin storage proteins in developing endosperm of Avena sativa L.

The seed storage proteins of oats (Avena sativa L.) are synthesized and assembled into vacuolar protein bodies in developing endosperm tissue. We used double-label immunolocalization to study the distribution of these proteins within protein bodies of the starchy endosperm. When sections of developing oat endosperm sampled 8 d after anthesis were stained with uranyl acetate and lead citrate, the vacuolar protein bodies consisted of light-staining regions which were usually surrounded by a darker-staining matrix. Immunogold staining of this tissue demonstrated a distinct segregation of proteins within protein bodies; globulins were localized in the dark-staining regions and prolamines were localized in the light-staining regions. We observed two additional components of vacuolar protein bodies: a membranous component which was often appressed to the outside of the globulin, and a granular, dark-staining region which resembled tightly clustered ribosomes. Neither antibody immunostained the membranous component, but the granular region was lightly labelled with the anti-globulin antibody. Anti-globulin immunostaining was also observed adjacent to cell walls and appeared to be associated with plasmodesmata. Immunostaining for both antigens was also observed within the rough endoplasmic reticulum. Based on the immunostaining patterns, the prolamine proteins appeared to aggregate within the rough endoplasmic reticulum while most of the globulin appeared to aggregate in the vacuole.Abbreviations DAA days after anthesis - IgG immunoglobulin G - M_r apparent molecular mass - RER rough endoplasmic reticulum - SDS-PAGE sodium dodecyl sulfate — polyacrylamide gel electrophoresis     

Sugar uptake by cotton tissues: leaf disc versus cultured roots

The synthesis, transport, and posttranslational processing of reserve globulin in Avena sativa L. seeds were studied by pulse-chase labeling. Developing oat seeds were labeled with radioactive sulfate and tissue homogenates were used for globulin extraction.

Two globulin precursors (58-62 kilodaltons) were labeled after 1 hour pulse. The α and β globulin subunits appeared between 2 and 10 hours later, while simultaneously the 58 to 62 kilodaltons polypeptides gradually disappeared. This confirmed a precursor-product relationship. In a second pulse-chase experiment, the tissue extracts were fractionated on a sucrose gradient. The major portion of radioactivity was initially (1 hour pulse) associated with the endoplasmic reticulum. However, a significant amount of radioactivity shifted from the endoplasmic reticulum to protein bodies after 20 hours chase, suggesting the transport of the newly synthesized proteins. Protein bodies isolated from pulse-chased seeds were analyzed for the arrival of the newly synthesized globulin. Labeled precursors were detected after 2 hours chase and gradually disappeared. The α and β subunits appeared during the same chase period and assembled into a 12S oligomer.

The data indicated that oat globulin was synthesized as two large precursors which were transported from endoplasmic reticulum into protein bodies where they were processed to the α and β subunits forming a 12S oligomer.

     

Role of endoplasmic reticulum in biosynthesis of oat globulin precursors

Oat (Avena sativa L.) groats were labeled with radioactive leucine and salt-soluble proteins were extracted and analyzed. Polyacrylamide gel electrophoresis followed by fluorography indicated two radioactive polypeptides with molecular weight 58 to 62 kilodaltons which were similar in size to unreduced globulin α-β dimers. The role of endoplasmic reticulum in the synthesis of these globulin polypeptides was investigated by in vivo and in vitro protein synthesis studies. Labeled tissue was fractionated by centrifugation and rough endoplasmic reticulum was isolated. Two polypeptides which had molecular weights of 58 to 62 kilodaltons and were immunoprecipitable with antiglobulin immunoglobulin G were found to be transiently associated with the endoplasmic reticulum. Rough endoplasmic reticulum, as well as membrane-bound polysomes, directed the in vitro synthesis of two polypeptides with molecular weight 58 to 62 kilodaltons corresponding in size to unreduced α-β dimers and could be immunoprecipitated with antiglobulin immunoglobulin G. The translation products of free polysomes did not show this. In pulse-labeling, globulin polypeptides with molecular weight 58 to 62 kilodaltons, as well as the α + β subunits, were labeled in protein bodies.

The data suggest that oat globulin polypeptides are synthesized as higher molecular weight precursors on ER-associated polysomes. These precursors are probably transported into protein bodies and cleaved into smaller α and β subunits.

     

Rice protein-body formation: all types are initiated by dilation of the endoplasmic reticulum

The ultrastructure of protein deposition in the starchy endosperm of developing rice (Oryza sativa L.) grains was examined in conventionally fixed (glutaraldehyde and osmium tetroxide) tissues and also in thick sections (0.3 m) of zinc iodide-osmium tetroxide post-fixed tissue. Three types of previously characterised protein body were observed and it was shown that each type was initiated by dilations of the endoplasmic reticulum. Crystalline type protein bodies were initiated by a ribosome-free dilation from rough cisternal endoplasmic reticulum and developed by inclusion of protein from dictyosome-derived vesicles. The large spherical and small spherical protein bodies developed within the cisternae of the rough endoplasmic reticulum.Abbreviations Cr crystalline protein body - DAF days after fertilization - ER endoplasmic reticulum - Ls large spherical protein body - Ss small spherical protein body - ZIO zinc iodide-osmium tetroxide     

Synthesis and deposition of zein in protein bodies of maize endosperm

The origin of protein bodies in maize (Zea mays L.) endosperm was investigated to determine whether they are formed as highly differentiated organelles or as protein deposits within the rough endoplasmic reticulum. Electron microscopy of developing maize endosperm cells showed that membranes surrounding protein bodies were continuous with rough endoplasmic reticulum membranes. Membranes of protein bodies and rough endoplasmic reticulum both contained cytochrome c reductase activity indicating a similarity between these membranes. Furthermore, the proportion of alcohol-soluble protein synthesized by polyribosomes isolated from protein body or rough endoplasmic reticulum membranes was similar, and the alcohol-soluble or -insoluble proteins showed identical [¹⁴C]leucine labeling. These results demonstrated that protein bodies form simply as deposits within the rough endoplasmic reticulum.

Messenger RNA that directed synthesis of only the smaller molecular weight zein subunit was separated from mRNA that synthesized both subunits by sucrose gradient centrifugation. This result demonstrated that separate but similar sized mRNAs synthesize the major zein components. In vitro translation products of purified mRNAs or polyribosomes were approximately 2,000 daltons larger than native zein proteins, suggesting that the proteins are synthesized as zein precursors. When intact rough endoplasmic reticulum was placed in the in vitro protein synthesis system, proteins corresponding in molecular weight to the native zein proteins were obtained.

     

Formation of protein storage bodies during embryogenesis in cotyledons of Sinapis alba L.

An electron microscopic investigation of fine structural changes in post-meristematic cotyledon mesophyll cells during the period of storage protein accumulation (16–32 d after pollination) showed that the rough ER, the Golgi apparatus and the developing vacuome are intimately involved in the formation of storage protein bodies (aleurone bodies). At the onset of storage protein accumulation (16–18 d after pollination) storage protein-like material appears within Golgi vesicles and preformed vacuoles. At a later stage (24 d after pollination) similar material can also be detected within vesicles formed directly by the rough endoplasmic reticulum (ER). It is concluded that there are two routes for storage protein transport from its site of synthesis at the ER to its site of accumulation in the vacuome. The first route involves the participation of dictyosomes while the second route bypasses the Golgi apparatus. It appears that the normal pathways of membrane flow in the development of central vacuoles in post-meristematic cells are used to deposit the storage protein within the protein bodies. Thus, the protein body can be regarded as a transient stage in the process of vacuome development of these storage cells.Abbreviation ER endoplasmic reticulum     

Immunogold-localization and synthesis of an oil-body membrane protein in developing soybean seeds

The synthesis of a major oil-body membrane brotein was studied in maturing soybean (Glycine max (L.) Merr.) cotyledons. The membrane contained four abundant proteins with apparent molecular mass (M_r) of 34000, 24000, 18000 and 17000. The M_r=24000 protein (mP 24) was selected for more detailed analysis. The protein was purified to apparent homogeneity by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and isolated from the gel by electroelution or chemical hydrolysis of gel crosslinks. It was then used to elicit rabbit antibodies which were judged to be specific when assayed by SDS-PAGE-immunoblot procedures. The mP 24 was localized in immature soybean cotyledon cells by indirect immunogold procedures on thin sections of Lowicryl- and LR-White-embedded tissue. Indirect labeling with the primary antiserum followed by colloidal gold-protein A showed specific labeling of the oil-body membrane and an absence of label on the other subcellular organelles including the endoplasmic reticulum (ER). Parallel tissue samples were studied by conventional transmission electron microscopy. Although segments of the ER were observed to be closely juxtaposed to the oil bodies, continuity between the two organelles was not observed. The synthesis of mP 24 was studied by in-vitro translation and in-vivo labeling with [³H]leucine followed by indirect immunoaffinity isolation of the labeled products. The SDS-PAGE fluorography results indicated that the primary translation product and the in-vivo synthesized protein have the same M_r, and this is also the same M_r as the protein in the mature membrane.Abbreviations and symbols DATD N N'-diallyltartardiamide - EM electron microscopy/scopic - ER endoplasmic reticulum - IgG immunoglobulin G - M_r apparent molecular mass - PBS phosphate-buffered saline - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis - TBS Trisbuffered saline     

Functional specialization of <Emphasis Type="Italic">Medicago truncatula</Emphasis> leaves and seeds does not affect the subcellular localization of a recombinant protein

A number of recent reports suggest that the functional specialization of plant cells in storage organs can influence subcellular protein sorting, so that the fate of a recombinant protein tends to differ between seeds and leaves. In order to test the general applicability of this hypothesis, we investigated the fate of a model recombinant glycoprotein in the leaves and seeds of a leguminous plant, Medicago truncatula. Detailed analysis of immature seeds by immunofluorescence and electron microscopy showed that recombinant phytase carrying a signal peptide for entry into the endoplasmic reticulum was efficiently secreted from storage cotyledon cells. A second version of the protein carrying a C-terminal KDEL tag for retention in the endoplasmic reticulum was predominantly retained in the ER of seed cotyledon cells, but some of the protein was secreted to the apoplast and some was deposited in storage vacuoles. Importantly, the fate of the recombinant protein in the leaves was nearly identical to that in the seeds from the same plant. This shows that in M. truncatula, the unanticipated partial vacuolar delivery and secretion is not a special feature of seed cotyledon tissue, but are conserved in different specialized tissues. Further investigation revealed that the unexpected fate of the tagged variant of phytase likely resulted from partial loss of the KDEL tag in both leaves and seeds. Our results indicate that the previously observed aberrant deposition of recombinant proteins into storage organelles of seed tissue is not a general reflection of functional specialization, but also depends on the species of plant under investigation. This discovery will have an impact on the production of recombinant pharmaceutical proteins in plants. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis of an integral protein of the protein-body membrane in Phaseolus vulgaris cotyledons

Protein-body membranes (PBMs) were isolated from cotyledons of Phaseolus vulgaris L. by a procedure involving osmotic shock of purified protein bodies. The purified PBMs have a characteristic density of 1.16 g cm^-3. Treatment of the membranes with increasing concentrations of detergent (Triton X-100) or with a solution at pH 12.0 showed that the membranes contained a characteristic integral protein (IMP) with a relative molecular mass of 25,000. This IMP is not a glycoprotein. When developing cotyledons were labeled with ³H-amino acids for 2–3 h, a radioactive polypeptide with the same mobility on denaturing polyacrylamide gels as IMP was found to be associated with the rough endoplasmic reticulum (ER). During a 24-h chase, a considerable portion of the radioactivity slowly transferred into the IMP associated with more rapidly sedimenting organelles, which sedimented in the same region of the sucrose gradients as the PBMs. Antibodies prepared against purified IMP crossreacted with an ER-associated protein which had the same mobility on denaturing acrylamide gels as authentic IMP. Synthesis of IMP occurred at all stages of cotyledon development examined, but not during seed germination. The results show that a newly synthesized protein of the PBM is associated with the rough ER, just like the soluble matrix proteins, phaseolin (R. Bollini, W. Van der Wilden and M.J. Chrispeels, 1983, J. Cell Biol. 96,999–1007) and phytohemagglutinin (M.J. Chrispeels and R. Bollini, 1982, Plant Physiol. 70, 1425–1428), but that the chase-out from the ER is much slower for IMP than for the matrix proteins.Abbreviations EDTA ethylenediamino-tetraacetic acid - ER endoplasmic reticulum - IMP integral membrane protein - PB protein body - PBM protein-body membrane - PHA phytohemagglutinin - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis     

Extracellular matrix metabolism by chondrocytes: VI. Concomitant depression by exogenous levels of proteoglycan of collagen and proteoglycan synthesis by chondrocytes

The synthesis of collagen and proteoglycans by cultured chondrocytes, as measured by the incorporation of L-[³H]proline into hydroxyproline and [³H]acetate into glycosaminoglycans, was shown to be depressed by 59% and 39%, respectively, by the addition of exogenous proteoglycan at a concetration of 10 mg/ml growth media. The incorporation of L-[³H]proline into acid-in-soluble protein remained unaltered in the presence of the proteoglycan. It was concluded that the effect was depressing the activity of the enzymatic steps, associated with the endoplasmic reticulum, which are responsible for the post-traslational modification of collagen and proteoglycan.     

The role of glycosylation in storage-protein synthesis in developing pea seeds

Intact pea (Pisum sativum L.) cotyledons were incubated with [¹⁴C]glucosamine at several stages of seed development and the resultant radioactive proteins were analysed by gel electrophoresis combined with immunoaffinity chromatography and sucrose gradient fractionation. Glucosamine was incorporated into at least five vicilin polypeptides (approx. molecular weight 70,000; 50,000, two components; 14,000, two components). No incorporation was detected into the subunits of legumin. Tunicamycin at 50 g/ml largely inhibited glucosamine incorporation but had little effect on the incorporation of ¹⁴C-labelled amino acids into cotyledon proteins, including vicilin. The assembly of vicilin polypeptides into full-sized protein oligomers (7–9 S) was also unaffected by tunicamycin. Chromatography on concanavalin A confirmed that glycosylation of cotyledon proteins was inhibited by tunicamycin. It is concluded that glycosylation of most cotyledonary proteins involves lipid-linked sugar intermediates, but that glycosylation itself is not an essential step in the synthesis of vicilin polypeptides nor in their assembly into oligomers.Abbreviations IgG immunoglobulin G - M W_t approximate molecular weight based on electrophoretic mobility relative to that of protein standards - SDS-PAGE Na-dodecyl sulfate-polyacrylamide gel electrophoresis     

Intracellular distribution of the hydrophobic triterpene,bryonolic acid,in cultured cells of Luffa cylindrica L.

Summary Intracellular localization of bryonolic acid, an antiallergic pentacyclic triterpene, in cultured cells of Luffa cylindrica was investigated with reference to the sites of its biosynthesis and accumulation. The results of cell fractionation showed that bryonolic acid was mostly located in the cell wall fraction. The addition of FC-43 emulsion to the culture medium was found to cause the release of bryonolic acid from the cell wall into the medium without affecting cell growth and bryonolic acid production. Under this culture condition, ¹⁴C-labeled sodium acetate administered to the cells was rapidly incorporated into bryonolic acid which was then excreted into the medium within 10 min after administration. Electron microscopic observations suggested that spherical vesicles (ca 0.1 m in diameter) derived from the rough endoplasmic reticulum may be associated with the biosynthesis and excretion of this compound into the cell wall. Furthermore, the activity of 2,3-oxidosqualene cyclase, a key enzyme involved in the biosynthesis of bryonolic acid, was detected in the microsomal fraction containing the endoplasmic reticulum.Abbreviations BA bryonolic acid - ER endoplasmic reticulum - LS Linsmaier-Skoog - NAA 1-naphthaleneacetic acid - MES 2-(N-morpholino)ethanesulfonic acid - PVPP polyvinyl polypyrrolidone     

Functional interaction of free polyribosomes with the membrane of the endoplasmic reticulum in a cell-free protein-synthesizing system from plasmacytoma X5563

In cell-free protein synthesis by the murine plasmacytoma X5563, which had become a nonproducing mutant, mixed systems with free polyribosomes and mirosomes incorporated ¹⁴C-amino-acid into protein 3–8 times greater than the sum of the incorporations in the individual system irrespective of S-100 concentrations. This enhancement was inhibited by lecithinase A and was markedly reduced at high KCl concentrations. Smooth endoplasmic membranes had more stimulatory activity than rough endoplasmic membranes. The results indicate that the membrane of the endoplasmic reticulum and free polyribosomes interact in the cell-free protein-synthesizing system, resulting in the enhancement of protein synthesis.     

DIFFERENCES IN THE SUBCELLULAR AND SUBSYNAPTOSOMAL DISTRIBUTION OF THE PUTATIVE ENDOPLASMIC RETICULUM MARKERS, NADPH-CYTOCHROME c REDUCTASE, ESTRONE SULFATE SULFOHYDROLASE AND CDP-CHOLINE DIACYLGLYCEROL CHOLINEPHOSPHOTRANSFERASE IN RAT BRAIN

Abstract— A comprehensive study has been undertaken on the subcellular and subsynaptosomal distribution of a number of markers for subcellular organelles in preparations from rat brain. Although the activity of most enzymatic markers was decreased by freezing and storage at - 70^oC, no significant changes were noted in the distribution of these activities. This demonstrates that contamination of brain fractions by subcellular organelles can be accurately assessed after freezing and thawing. A marked discrepancy was noted between the distribution of three putative markers for endoplasmic reticulum. CDP-choline-diacylglycerol cholinephosphotransferase (EC 2.7.8.1) activity was mainly limited to the microsomal fraction and was present to a lesser extent in the synaptosomal fraction than the other putative markers for endoplasmic reticulum. Estrone sulfate sulfohydrolase (EC 3.1.6.2) activity demonstrated a bimodal distribution between the crude nuclear and microsomal fractions. However, considerable activity was associated with the synaptosomal fraction. NADPH-cytochrome c reductase (EC 2.3.1.15) activity sedimented in the microsomal and the synaptosomal fractions. Calculations based on the relative specific activities of the microsomal and synaptic plasma membrane fraction indicated that the contamination of the synaptic plasma membranes by endoplasmic reticulum was 44.5% (NADPH-cytochrome c reductase), 38.0% (estrone sulfatase) and 9.0% (cholinephosphotransferase). Since it is believed that virtually all of the synthesis of phosphatidylcholine by cholinephosphotransferase occurs in the neuronal and glial cell bodies, it was concluded that cholinephosphotransferase is a satisfactory marker for the endoplasmic reticulum derived from these sources. The results suggest that NADPH-cytochrome c reductase and estrone sulfatase may be present in the smooth endoplasmic reticulum system responsible for the fast transport of macromolecules along the axon to the nerve endings as well as in the endoplasmic reticulum of the cell bodies. The possible relation between that portion of the smooth endoplasmic reticulum involved in fast axonal transport and the GERL (Golgi, Endoplasmic Reticulum, Lysosomes) complex discovered by Novikoff and his coworkers (Novikoff , 1976) is discussed.     

Subcellular targets of the soluble SiO2-liberated macrophage factors in experimental granulation tissue.

The supernatant from SiO2-treated macrophages increased the incorporated radioactivity of collagen in the incubated experimental granulation tissue slices, especially in the rough endoplasmic reticulum fraction, markedly over that in the respective control preparation. The effect was observed after a 20 min incubation and increases linearly at least up to 3 h. The amount of RNA and phospholipids in the rough endoplasmic reticulum, calculated per protein, increased simultaneously in the incubated slices. The incorporation of the radioactive precursors into DNA in the slices and in the nuclei from proliferating granulation tissue was enhanced significantly by the soluble fraction from SiO2-treated macrophages. This effect could be seen after a 40 min incubation in the slices and after 5 min in the nuclei, when the incorporated radioactivity in DNA began to decrease in the control experiments.     

Incorporation of D-[14C]galactose into organelle glycoprotein in castor bean endosperm

Excised casto bean (Ricinus communis L.) endosperm tissue supplied with [¹⁴C]galactose incorporates radioactivity into particulate cell components. Fractionation of homogenates established that ¹⁴C-labeled trichloroacetic acid-insoluble material was located primarily in the microsomal and glyoxysomal fractions. The capacity of the tissue to incorporate [¹⁴C]galactose into organelle glycoprotein varied during seedling development, increasing during the first 3 days of germination and subsequently declining. The kinetics of incorporation into the major organelle fractions of 2-day old endosperm tissue showed that the endoplasmic reticulum was immediately labeled whereas a lag period preceded the labeling of glyoxysomes. Sub-fractionation of the isolated organelles established that the greatest proportion of the [¹⁴C]-galactose labeled glycoprotein was located in the membrane, although a significant incorporation into the matrix protein was also observed.The results indicate that the addition of the carbohydrate moiety to the polypeptide cores occurs in the endoplasmic reticulum during or immediately after their synthesis on membrane-bound ribosomes.Abbreviations ER endoplasmic reticulum - SDS sodium dodecyl sulphate - TCA trichloroacetic acid     

Ultrastructure and Lipase Activity of Cotyledon cell During Pod Development in Peanut

A series of significant changes of the ultrastructure and lipase activity of cotyledon cell were found in peanut (Arachis hypogaea) during pod development. In he initial stage of cotyledon development there were many plastids which kept producing starch grain and there were low lipase activity and very few lipid and protein bodies in the cell. In the middle stage of cotyledon development, a great number of larger lipid bodies were seen in the cell and a lot of protein bodies formed in the vacuoles and continued to increase in size. Lipase activity increased in the cytoplasm, endoplasmic reticulum, protein bodies, plasmalemma and intercellular space. In the later stage of cotyledon development, the lipid bodies did not increase in number but became slightly larger. The protein bodies continued to increase both in number and in size. Lipase acttvity was even hegher in the cytoplasm. In the final stage the protein bodies became irregular in shape and some of them tended to disintegrate with their content entered into the space around the lipid bodies. The lipase activity in the cell declined. The results indicated that the lipid body originated in the cytoplasm and the protein body originated in the vacuole; that the accumulation of oil and protein in peanut cotyledon resulted from the formation and development of lipid and protein bodies in the cell, and that the changes of plasmid and lipase activity in the cell played a role in the development of lipid body during the development of cotyledon.     

THE SECRETORY PATHWAYS OF RAT SERUM GLYCOPROTEINS AND ALBUMIN : Localization of Newly Formed Proteins within the Endoplasmic Reticulum

These studies compare the secretory pathways of newly formed rat serum glycoproteins and albumin by studying their submicrosomal localization at early times after the beginning of their synthesis and also by determining the submicrosomal site of incorporation of N-acetylglucosamine, mannose, galactose, and leucine into protein. N-acetylglucosamine, mannose, and galactose were only incorporated in vitro into proteins from membrane-attached polysomes and not into proteins from free polysomes. Mannose incorporation occurred in the rough endoplasmic reticulum, was stimulated by puromycin but not by cycloheximide, and 90% of the mannose-labeled protein was bound to the membranes. Galactose incorporation, by contrast, occurred in the smooth microsome fraction and 89% of the radioactive protein was in the cisternae. Albumin was mostly recovered (98%) in the cisternae, with negligible amounts in the membranes. To determine whether the radio-active sugars were being incorporated into serum proteins or into membrane protein, the solubilized in vivo-labeled proteins were treated with specific antisera to rat serum proteins or to albumin. Immunoelectrophoresis of the ¹⁴C-labeled leucine membrane and cisternal proteins showed that the membranes contained radioactive serum glycoprotein but no albumin, while the cisternal fraction contained all of the radioactive albumin and some glycoproteins. The results indicate that newly formed serum glycoproteins remain attached to the membranes of the rough endoplasmic reticulum after they are released from the membrane-attached polysomes, while albumin passes directly into the cisternae.