Hormonal regulation of translation inhibition requiring RNA synthesis

Sequence and characterization of 6 Lea proteins and their genes from cotton

Lea genes code for mRNAs and proteins that are late embryogenesis abundant in higher plant seed embryos. They appear to be ubiquitous in higher plants and may be induced to high levels of expression in other tissues and at other times of ontogeny by ABA and/or desiccation. Presented here are the genomic and cDNA sequences for 6 of these genes from cotton seed embryos and the derived amino acid sequences of the corresponding proteins.The Lea genes contain the standard sequence features of eucaryotic genes (TATA box and poly (A) addition sequences) and have 1 or more introns. Sequences differences between cDNA and genomic DNA confirm the existence of small multigene families for several Lea genes. The amino acid composition and sequence for the Lea proteins are unusual. Five are extremely hydrophilic, four contain no cys or trp and 4 have sequence domains that suggest amphiphilic helical structures. Hypothetical functions in desiccation survival, based on amino acid sequence, are discussed.

Effect of abscisic and gibberellic acids on malate synthase transcripts in germinating castor bean seeds

Several clones complementary to malate synthase mRNA have been identified in a complementary-DNA library to mRNA from castor bean endosperm. One of these clones has been used as a probe to measure levels of transcripts during seed germination and the effects of gibberellic acid and abscisic acid on these levels have been examined.Malate synthase transcripts increased during germination and GA3 advanced their appearance in the endosperm. Exogenously applied ABA inhibited the accumulation of transcripts over a time course of germination but the addition of GA3 counteracted its inhibitory effects. The data confirmed previous reports which indicated that the action of both growth regulators was on transcript accumulation and that there is a coordinated induction of the enzymes involved in the lipid metabolism in oil seeds.

Em polypeptide and its messenger RNA levels are modulated by abscisic acid during embryogenesis in wheat

The effect of abscisic acid (ABA) on the expression of the 'early-methionine-labeled' (Em) polypeptide was examined in cultured, immature wheat (Triticum aestivum, L.) embryos and in developing embryos in planta. A complementary DNA (cDNA) library was constructed from poly(A)-rich RNA from immature embryos cultured in the presence of ABA. ABA-enhanced sequences were first identified by differential colony-blot hybridization, and then verified using RNA slot-blot analysis. Dot-blot hybridization showed that one clone, p1015, was homologous to the previously isolated Em cDNA, pWG432. Electrophoretic analysis of the hybrid-select translation product of p1015 confirmed its identity as an Em sequence. Comparison of the p1015 cDNA insert size and the Em message size, from northern blot analysis, showed that p1015 contained about 87% of the Em sequence. RNA slot-blot analysis and protein electrophoresis showed that Em message, but not Em protein, accumulated at a low, basal level in immature embryos in the absence of ABA. Neither Em message nor Em protein was seen in three-day germinated seedlings. Steady-state levels of Em message and protein increased in immature embryos in the presence of ABA, both in culture and in planta. Regulation appeared to be primarily at the level of transcription or specific message stability. Regulation may also involve specific protein stability, since synthesis of Em protein continued in immature embryos in the absence of ABA, but Em protein did not accumulate in detectable amounts. We conclude that ABA specifically modulates Em message and protein levels in immature embryos, but is probably not responsible for the embryogenic specificity of Em expression.

Developmental biochemistry of cottonseed embryogenesis and germination: changing messenger ribonucleic acid populations as shown by in vitro and in vivo protein synthesis

Changes in messenger ribonucleic acid (mRNA) populations during embryogenesis of cottonseed have been followed by cataloging (a) extant proteins, (b) proteins synthesized in vivo, and (c) proteins synthesized in vitro from extracted RNA, all at specific stages of embryogenesis. Evidence is presented for the existence of five mRNA subsets, all apparently under different regulatory regimes, that produce the abundant proteins of embryogenesis. One of these functions principally during the cell division phase of embryogenesis and encodes among its products the seed storage proteins whose mRNA is superabundant during this period. This subset has disappeared from the abundant group by the mature seed stage. Two other subsets appear in late embryogenesis, one of which may result from the removal of the embryo from the maternal environment, since it is inducible by excision of the young embryo from the seed. The other appears to be induced by the plant growth regulator abscisic acid, whose endogenous concentration increases at this stage. It can be induced by incubating excised young embryos in abscisic acid. The last two subsets exist throughout embryogenesis, but only one of them appears to function in germination.

Qualitative and quantitative changes in mRNA of castor beans during the initial stages of germination

The increase in extractable RNA during the initial germination stages of castor bean was measured, for both the embryonic axis and the storage endsperm. The extractable rRNA increased between 24 and 72 h after initial imbibition in the embryo and 48-72 h in the endosperm. The mRNA species present over the first 6 days of germination were identified by the products from in vitro translation. The mRNA from dry seeds gave predominantly low molecular weight polypeptide products. Between 0.5 and 1 h of initial imbibition new mRNA species were detectable and the qualitative changes were largely complete by 8 h, some 16 h-40 h before the detectable quantitative changes. Despite the large variations in enzyme activity occurring 48 h-192 h after imbibition, the mRNA species qualitatively varied very little, after this initial change, up to 144 h after imbibition. In the light of this large, early, qualitative change in mRNA, the possible importance of long-lived mRNA in seed germination is discussed.

Developmental regulation in cotton seed germination: polyadenylation of stored messenger RNA

Evidence that RNA preexisting in the cotyledons of mature cotton seed (stored mRNA) is polyadenylated during the first day of germination is presented, based on three different experimental data sets. First, actinomycin D is found to inhibit 32PO4 incorporation into mRNA-poly(A) by 62%, into mRNA by 70%, but into poly(A) only 30%. Second, far more 32PO4 and [2-3H]adenosine are incorporated into the poly(A) portion of mRNA-poly(A) than into the mRNA portion as would be expected from their relative sizes and base composition. This underlabeling of the mRNA moiety is enhanced when cotyledons are germinated in actinomycin D. However, an expected distribution of the isotopes between the mRNA and poly(A) moieties is found in cotyledons labeled later in germination. Third, spectral measurements of the absolute amount of mRNA-poly(A) accumulated during the first day of germination in cotyledons germinated in actinomycin D are larger than would be expected from the 70% inhibition of mRNA labeling caused by the drug. The three sets of data suggest that over 50% of the total mass of mRNA polyadenylated during early germination exists in the mature seed. Its complexity, however, has not been measured. These data may explain the sensitivity of much of germination enzyme synthesis to inhibition by 3'dAdo during early germination and its insensitivity to actinomycin D during this period.

[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.

The developmental biochemistry of cotton seed embryogenesis and germination. VI. Levels of cytosol and chloroplast aminoacyl-tRNA synthetases during cotyledon development

The separation of isotransferring aminoacyl-tRNA synthetase activities (amino acid: tRNA ligases, EC 6.1.1.x) for several amino acids extracted from tissues of embryonic and germinating cotton seeds was carried out by DEAE-cellulose column chromatography. Evidence was obrained that the separated activities represent discrete enzymes, and could be defined as cytosol or chloroplast enzymes by several criteria. The levels of the cytosol enzymes per cell were found to be constant in germinated and ungerminated cotyledons. Chloroplast enzymes were found to be present in immature embryonic cotyledons and in roots at constant levels relative to the cytosol enzymes, but found to increase markedly in germinating cotyledons. This increase takes place to the same extent in etiolated cotyledons as in greened cotyledons indicating that the chloroplast synthetase increase is analogous to the simultaneous increase in chloroplast tRNA and rRNA which also is not light dependent. The separated cytosol and chloroplast enzymes show varying degrees of specificity for isoaccepting tRNA species from homologous and heterologous sources.

Effect of actinomycin D on the formation of enzymes in Jerusalem artichoke tuber slices

The formation of both peroxidase and phenol oxidase was induced by culturing slices of Jerusalem artichoke tubers. Actinomycin D inhibited the formation of enzymes only when added before the termination of the lag phase (10 h after slicing). The data suggest that 4 to 6 h after slicing, tissues produce a mRNA which does not become fully operative until a translation mechanism has been activated.

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.