Preformed messenger of quiescent wheat embryos

Synthesis of the peptide-transport carrier of barley scutellum during the early stages of germination

Development of peptide-transport activity in the scutella of isolated barley (Hordeum vulgare l. cv. Maris Otter, Winter) embryos is shown to increase rapidly after about 15 h of imbibition, with the bulk of the transport activity being expressed by 24 h. This development is prevented by treatment of 15 h embryos with cycloheximide. Protein synthesis is found to increase in a closely related manner and also to be abolished by cycloheximide. Measurement of the incorporation of bound [(35)S]methionine by 15 to 21-h embryos indicates that de-novo protein synthesis during this period is greater in the scutellum than in the embryonic axis. Previous studies have shown that the peptide-transport system possesses essential dithiol groups, probably located at the substrate-binding site (Walker-Smith and Payne 1983 b, 1984b). Treatment of 15-h embryos with the non-penetrant thiol reagent p-chloromercuribenzene sulphonic acid did not affect development of peptide-transport activity during the following 6 h, whereas with 3-d embryos identical treatment inhibited uptake almost completely during a subsequent 6-h period. Radioautography revealed that amongst the proteins synthesised during this early phase of germination and labelled in vitro with [(35)S]methionine some are found within the epithelial plasmalemmae of the scutellum, which is the location of the peptide-transport carrier identified previously by externally labelling with a radioactive thiol reagent. The results provide evidence that protein(s) of the peptide-transport system are synthesised and inserted into the scutellum during early germination, allowing the system to play a major role in the nitrogen nutrition of the embryo.

Comparative study of levels of secondary processing in bulk mRNA from dry and germinating wheat embryos

There has been no previous study of levels of secondary processing in the template-active RNA of dry seeds and embryos. Such information is needed to evaluate the role of transcription in changing the cell-free translational capacity of bulk RNA during early imbibition of water by dry wheat embryos [J. Biol. Chem. 255, 5969-5970 (1980)]. Although it probably contains a higher proportion of "hidden breaks' than bulk mRNA from imbibing embryos, bulk mRNA in dry wheat embryos is also "capped' by 7-methylguanosine at 5' termini, devoid of unmethylated "caps', methylated internally (N6-methyladenosine) and polyadenylated at 3' termini. In contrast to other developing systems, there is no evidence that there are signal changes in levels of secondary processing in the bulk mRNA populations which support change in cell-free translational capacity of RNA 1-5 h postimbibition of dry wheat embryos. Change in the pattern of protein synthesis 5-24 h postimbibition also takes place without signal changes in levels of secondary processing in template-active RNA. The analytical data are evaluated and discussed in terms of difficulties allied with comparative analyses of poly(A)-rich RNA from dry and imbibing embryos, the former being refractory to, and the latter being most easily analyzed by, labeling in vivo.

Characterization of a maturation-specific mRNA in dry mung bean embryonic axes

The poly(A)-rich RNA from dry mung bean (Vigna radiata [L.] Wilczek) embryonic axes has been isolated and translated in a wheat embryo cell-free system, and the products were analyzed on sodium dodecyl sulfate-polyacrylamide gels. The fluorographyic patterns showed a heavy band at approximately MW 12,000. The messenger RNA coding for this polypeptide disappeared in the course of early germination. This messenger is translated in vivo but simultaneously degrades when the axes imbibe. The poly(A)-rich RNA from dry axes has been fractionated on sucrose-dimethyl sulfoxide gradients, and this messenger has been found to be distributed largely in the 9-14 S region. The polypeptide synthesized in vitro has been immunoprecipitated, using the antiserum raised against this protein purified from dry axes.

Sedimentation properties of preformed messenger particles in dry rye embryo extracts

Two classes of messenger containing particles can be distinguished in cell-free extracts from dry rye (Secale cereale, L.; var. Celestijner) embryos. A part of the endogenous template activity is associated with large structures, even during in vitro translation. Treatment with detergents results in a partial solubilization of the messenger particles from the large, presumably membranous structures. The sedimentation behavior of the "soluble" mRNP particles (about 75% of the total endogenous template activity) is strongly influenced by the composition of the homogenization medium. At high Mg(2+) or Ca(2+) concentrations, and at low pH, the soluble mRNP particles form aggregates sedimenting at low centrifugal forces. This peculiar behavior is of partical interest with respect to the preparation of cell-free extracts with low endogenous template activity.

Decline in ribonucleic acid and protein synthesis with loss of viability during the early hours of imbibition of rye (Secale cereale L.) embryos

A decline in protein synthesis and slow germination accompanies loss of viability in embryos of rye (Secale cereale L.) grains. Associated with this, incorporation of precursors into all the major classes of RNA is decreased and the processing of precursor rRNA to 25S and 18S RNA is retarded. Embryos that just reach 0% viability still synthesize some low-molecular-weight non-nucleolar material, although they do not synthesize protein. It is suggested that early-synthesized RNA could play a major part in determining the extent of protein synthesis at early germination, and thereby regulate the rate at which germination can proceed.

Messenger ribonucleoprotein particles in dry wheat and rye embryos : In vitro translation and size distribution

Extracts prepared from dry wheat (Triticum aestivum L.; var. Cama) and rye (Secale cereale L.; var. Celestijner) embryos exhibit relatively high endogenous messenger activities in an in vitro protein synthesizing system: up to 400 pmol leucine are incorporated per 50 μl reaction mixture; the messenger/ribosome ratio is estimated at about 0.03. Sucrose gradient analysis of the incubation mixture during cellfree protein synthesis shows a progressive in vitro polysome formation with the native endogenous mRNPs. The translation of these messengers, although dependent on initiation, follows linear kinetics. The native mRNP particles can be separated on sucrose gradients in 6 distinct size classes with sedimentation values varying from 25 S to 104 S. Their size is strongly reduced after deproteinization so that the naked mRNAs sediment in a range between 8 S and 35 S. The molecular weights of the proteins synthesized under direction of the native RNA particles range from 12,000 to 70,000 as estimated by polyacrylamide gel electrophoresis.

Evidence for the presence of mRNA in the post-ribosomal cytoplasm of sheep lymphocytes

Several fractions of RNA prepared from the post-ribosomal cytosol of sheep lymphoid cells were found to include messenger-like RNA as defined by the following criteria: a, template activity, i.e. the ability to promote the incorporation of radioactive amino acids into protein in cell-free protein-synthesising systems derived from wheat embryos or ascites tumour cells; b, a low magnesium optimum (1-2.5 mM) for template activity which is characteristic of many natural mRNAs; c, sensitivity of the template response to aurintricarboxylic acid, a specific inhibitor of the initiation of protein synthesis. The lymphoid post-ribosomal RNA fractions, however, were translated less efficiently than were rabbit reticulocyte globin mRNA or tobacco mosaic viral (TMV) RNA; no explanation for this relatively poor template activity was found. The major fraction of messenger-like RNA had an average sedimentation coefficient of 12 S; this fraction directed the translation of several discrete polypeptides in the molecular weight range 10 000-25 000. On average the products of 12 S RNA-directed protein synthesis appeared lysine rich compared with TMV RNA-directed products. It is suggested that the apparent pool of uncommitted mRNA in resting lymphocytes may be utilised during the early stages of lymphocyte activation, and that the mRNAs could be stored in forms similar to those evident in other dormant tissues.

[Studies on stable and during early imbibition phases synthesized poly(A)-RNA of Agrostemma githago embryos (author's transl)]

RNA isolated from dry embryos of Agrostemma githago seeds contains poly(A)-sequences, but in very small amounts. In the early phase of imbibition, an intensive synthesis of poly(A)-containing RNA is brought about. The importance of this synthesis of poly(A)-RNA is discussed.

Translation of nonpolyadenylylated messenger RNA of sea urchin embryos

A large proportion of newly synthesized polyribosomal RNA of sea urchin blastulae is not polyadenylylated. The size distributions of the polyadenylylated and nonpolyadenylylated RNA are indistinguishable (mean size of 26 S). Upon translation of sea urchin polyribosomal RNA containing poly(A) and that without poly(A) in a wheat embryo cell-free protein-synthesizing system, where polypeptide synthesis is dependent on added messenger, both classes of RNA support peptide synthesis to the same extent. A preliminary analysis of the proteins synthesized in response to added mRNA (polyadenylylated and nonpolyadenylylated) indicates that these classes of mRNA molecules may code for different populations of proteins.

Ribonucleic acid synthesis and loss of viability in pea seed

RNA synthesis and protein synthesis in embryonic axis tissue of viable pea (Pisum arvense L. var. N.Z. maple) seed commences during the first hour of germination. Protein synthesis in axis tissue of non-viable pea seed is barely detectable during the first 24 h after the start of imbibition. Nonviable axis tissue incorporates significant levels of [(3)H]uridine into RNA during this period but the level of incorporation does not increase significantly over the first 24 h of imbibition. In axis tissue of non-viable seed during the first hour of imbibition most of the [(3)H]uridine was incorporated into low molecular weight material migrating in advance of the 4S and 5S RNA species in polyacrylamide gels but some radioactivity was incorporated into a discrete species of RNA having a molecular weight of 2.7×10(6). After 24 h, non-viable axis tissue incorporates [(3)H]uridine into ribosomal RNA, the low molecular weight material migrating in advance of the 4S and 5S RNA peak in polyacrylamide gels and a heterogeneous RNA species of molecular weight ranging from 2.2×10(6) to 2.7×10(6). No 4S or 5S RNA synthesis is detectable after 24 h of imbibition in non-viable axis tissue. Axis tissue of viable pea seed synthesises rRNA, 4S and 5S RNA, the low molecular weight material migrating in advance of the 4S and 5S RNA peak in polyacrylamide gels and the rRNA precursor species at both periods of germination studied. Loss of viability in pea seed appears to be accompanied by the appearance of lesions in the processing of rRNA precursor species and a significant loss of RNA synthesising activity.

In vitro translation of the long-lived messenger ribonucleic acid of dry seeds

The total RNA extracted from rye embryos (Secale cereale) and seed of the broad bean (Vicia faba), pea (Pisum sativum) and oil-seed rape (Brassica napus) exhibits low levels of template activity when incubated in a wheat-germ cell-free protein-synthesising system. The RNA from pea, rapeseed and rye embryos was fractionated by chromatography on oligo dT-cellulose columns. Most of the template-active RNA bound to the column at high ionic strength, indicating that it is polyadenylated. The remainder would not bind, even when passed through the column several times. The proteins synthesised in vitro from the template-active RNA migrated as numerous bands in polyacrylamide gels and ranged in molecular weight from 10,000 to 70,000. The banding patterns obtained were quite different for the three species of seed tested. It is concluded that dry seeds contain a store of intact, long-lived mRNA.

Poly(A)-containing RNA from Petroselinum hortense: isolation, properties and messenger function in vitro

Cell suspension cultures from parsley (Petroselinum hortense Hoffm.) were labelled in vivo with [2-3H] adenosine. The RNA isolated from the ribosomal pellet was fractionated on an oligo(dT)-cellulose column. Approximately 1.5% of the RNA, representing about 15% of the total radioactivity, was retained at high salt concentrations and eluted at low ionic strength. As determined by two independent methods, this fraction contained poly(A) segments with an average length of about 80 nucleotides. It was active as template in a cell-free system from wheat germ, directing the synthesis of peptides ranging in molecular weight from about 4000-40000 daltons.

Early ribonucleic acid synthesis during the germination of rye (Secale cereale) embryos and the relationship to early protein synthesis

Incorporation studies with radioactive precursors showed that synthesis of protein and RNA is initiated in germinating embryos of rye within the first hour of imbibition of water. By polyacrylamide-gel fractionations of radioactive nucleic acid components, the appearance of products of transcription of the genome was shown to follow the sequence: heterogeneous (ribonuclease-sensitive) RNA, 4S and 5S RNA by 20min, 31S and 25S rRNA by 40min, and 18S RNA by 60min. "Fingerprint' analysis of T1-ribonuclease digests show that all the large oligonucleotides present in 25S and 18S RNA are present in the 31S species, indicating that 31S RNA is the precursor rRNA molecule to both 25S and 18S RNA. The importance of these early RNA syntheses and in particular the possible template function of the heterogeneous RNA is discussed in relation to the concept of long-lived mRNA and the coding for protein synthesis in the first hours of germination.

Poly (A)-containing polyribosomal RNA in sea urchin embryos: changes in proportion during development

Evidence is described which suggests that a large fraction of sea urchin embryo polyribosomal RNA is not polyadenylated, and that the proportion of poly(A)-containing RNA increases during embryological development. Cleavage, early blastula, and mesenchyme blastula stage embryos were treated with cordycepin, and the effects of the drug on polyribosome appearance were determined. Polyribosomes in cleaving embryos and early blastulae were unaffected by the drug. However, there was a significant reduction in the amount of polyribosomes present and in the amount of newly synthesized RNA entering polyribosomes in mesenchyme blastulae after cordycepin treatment. Polyribosomal RNA was isolated from cleavage, early blastula, and mesenchyme blastula stage embryos, and the RNA was characterized by sucrose gradient centrifugation. Cleaving embryo polyribosomal RNA has a prominent 9 S peak and a smaller 20 S peak, and the larger RNA is heterodisperse. There is no poly(A) associated with the 9 S and 20 S material, but there is poly(A) associated with the RNA sedimenting faster than 20 S. Early blastula and mesenchyme blastula polyribosomal RNA have 22 S and 26 S peaks, respectively. This later stage RNA is quite heterodisperse and poly(A) is associated with RNA in all size classes larger than 9 S. Finally, the proportion of polyadenylated light and heavy polyribosome RNA was determined for cleavage, early blastula, and mesenchyme blastula stage embryos. Approximately 20-25% of newly synthesized light polyribosome RNA is polyadenylated and this amount is relatively constant during early development. However, the proportion of newly synthesized RNA in heavy polyribosomes that is polyadenylated increases during development: 25% at cleavage, 33% at early blastula, and 48% at mesenchyme blastula stages.

Messenger RNA metabolism of animal cells. Possible involvement of untranslated sequences and mRNA-associated proteins

The past several years have seen a virtual revolution in the study of eukaryotic mRNA. Among the notable recent achievements are the positive identification of mRNA precursors in HnRNA, the enumeration of the DNA sequences from which mRNA is transcribed, and the finding that mRNA in cultured cells is much more stable than was previously believed. One of most far-reaching discoveries has been the finding that mRNA in eukaryotes contains poly A. This discovery, aside from providing a powerful tool for mRNA isolation, has generated a large body of research into the properties and metabolism of poly A itself. In addition, the finding of a poly A-associated protein has given a renewed stimulus to the study of proteins associated with mRNA. This review is devoted to a discussion of these and related achievements, and some of their implications

Studies on messenger and ribosomal RNA synthesis in plant tissue cultures induced to undergo synchronus cell division

Messenger and ribosomal RNA metabolism was tudied in a plant tissue culture system: cells from the quiescent tubers of Helianthus tuberosus (Jerusalem artichoke) were induced to divide synchronously and dedeifferentiate by excision and culture of explants in nutrient medium. Large accumulations of ribosomal RNA and protein started early in the 20-h lag-period preceding the first division. In pulse-labelling experiments, two types of polydisperse messenger-like RNAs were detected one with and one without a poly(adenylic acid) sequence. In the first 2 h of culture the two polydisperse RNA fractions were the predominant types of RNA synthesised. Ribosomal RNA synthesis was very low during the first 2 h, but acclerated later. Low concentrations of actinomycin-D strongly inhibited ribosomal RNA synthesis, but had little effect on the synthesis of transfer RNA or either type of polydisperse messenger-like RNA. In explants cultured with low concentrations of actinomycin-D ribosomal RNA accumulation was completely inhibited, but cell division and protein accumulation occurred, though at a reduced rate. It is concluded that the synthesis and accumulation of new ribosomal RNA which normally occur during culture are not required for the induction of cell division or for protein accumulation, i.e. the ribosomal RNA existing in the quiescent tuver cells can support protein accumulation and cell division induced by excision and culture. The quiescent tuber tissue is also shown to contain significant amounts of messenger-like RNA.

Preformed mRNA and the programming of early embryo development

A significant feature of the early development of fertilized echinoderm and amphibian eggs and germinating seed embryos is the utilization of genetic information that has been previously transcribed during oogenesis and seed ripening. When RNA synthesis is suppressed in the early developing embryos by actinomycin D, cordycepin, or alpha-amanitin, there is no effect on the translation of the "preformed mRNA", only a limited number have been thus far identified; microtubule and histone proteins in the fertilized sea urchin egg and carboxypeptidase and isocritric lyase in germinating cottonseed. Data obtained on the protein synthetic pattern at different times after the onset of development suggest that preformed mRNAs are made available to the translational system in a gradual process, thereby providing a molecular basis for the regulation of development. The possibility is considered that polyadenylation of mRNA, a reaction known to occur early after sea urchin fertilization, is responsible for regulating the release of preformed mRNA. It is shown that this reaction (polyadenylation) can be completely suppressed with little effect on the function of preformed mRNA. Finally, it is suggested, at least for the seed embryo system, that the formation of ATP may be a prerequisite for the activation of protein synthesis.

Embryogenesis and germination in rye (Secale cereale L.) : II. Biochemical and fine structural changes during germination

When rye embryos imbibe water they rapidly return to a condition of biochemical and structural complexity. Three stages of imbibition can be recognised: Phase I a short period (10 min) of physical wetting; Phase II a longer period (1 h) when little further imbibition occurs, followed by Phase III a continuous phase of active water uptake. The latter coincides with an increase in respiration rate and an increase both in the number of mitochondria and of cristae within them. Changes in fine structure become evident in all organelles in Phase III, after 2 h of imbibition. In the unimbibed embryo endoplasmic reticulum is present only as short crescents associated with electron lucent bodies, but in Phase III the endoplasmic reticulum proliferates to form many surrounding cirlets. After 6 h these circlets become fewer and instead the endoplasmic reticulum is seen in close association with the nuclear membrane. Concurrently incorporation of radioactive uridine and thymidine is first detectible. This suggests that the large increase in protein synthesis occurs on new ribosomes present on the reticulum associated with the nuclear membrane. For the first 6 h protein synthesis must occur either on polysomes within the dense packing of ribosomes or on these circlets of endoplasmic reticulum associated with electron lucent bodies.

Gas exchange in dry seeds: circadian rhythmicity in the absence of DNA replication, transcription, and translation

A 24-hour rhythm of gas exchange has been detected in dry onion seeds. The rhythm persists in constant conditions, and its period appears to be independent of temperature. Since DNA replication, transcription, and perhaps translation do not occur in this quiescent state, it is concluded that the basic oscillation that defines circadian rhythmicity does not derive directly from these processes.

Rate of RNA synthesis and tRNA end-labeling during early development of Phaseolus

Axes of Phaseolus vulgaris cease synthesis of RNA during the maturation stage of embryogeny. During the imbibition phase of germination RNA synthesis resumes after the axes reach a normal water content. In the first hour of inbibition a very low rate of incorporation of (3)H-adenosine into is RNA found, and the primary site of incorporation is the-CCA end of tRNA. At later stages of germination tRNA end-labeling accounts for a minor fraction of adenosine incorporation. The rate of RNA synthesis increases after initiation of axis elongation to a maximal rate at 18 h of germination. ATP pool-size and specific activity vary over a several-fold range during development, an important consideration in determining the rate of RNA synthesis.

Some observations on coleoptile cell ultrastructure in ungerminated grains of rice (Oryza sativa L)

The ultrastructure of coleoptile cells of ungerminated rice grains has been examined following fixation in glutaraldehyde and osmium tetroxide. In many respects the cell structure resembles that reported for other dormant seed tissues: the cells contain protein bodies and lipid droplets, mitochondria and plastids show little internal structure but cytoplasm invaginates into many plastids; golgi cisternae cannot be discerned. Rough ER is present as cisternae surrounding protein bodies, as occasional regions of parallel layers, and in concentric whorls where it alternates with smooth paired membranes of an unknown nature. The ribosomes on the ER are at least partly arranged into regular rows. Various crystalline, presumably proteinaceous, inclusions lie in the groundplasm, plastids and nuclei.