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

Gene activity during germination of spores of the fern, Onoclea sensibilis. Cell-free translation analysis of mRNA of spores and the effect of alpha-amanitin on spore germination

Poly(A)-RNA fractions of dormant, dark-imbibed (non-germinating) and photoinduced (germinating) spores of Onoclea sensibilis were poor templates in the rabbit reticulocyte lysate protein synthesizing system, but the translational efficiency of poly(A)+RNA was considerably higher than that of unfractionated RNA. Poly(A)+RNA isolated from photoinduced spores had a consistently higher translational efficiency than poly(A)+RNA from dark-imbibed spores. Analysis of the translation products by one-dimensional polyacrylamide gel electrophoresis showed no qualitative differences in the mRNA populations of dormant, dark-imbibed, and photoinduced spores. However, poly(A)+RNA from dark-imbibed spores appeared to encode in vitro fewer detectable polypeptides at a reduced intensity than photoinduced spores. A DNA clone encoding the large subunit of maize ribulose bisphosphate carboxylase hybridized at strong to moderate intensity to RNA isolated from dark-imbibed spores, indicating the absence of mRNA degradation. Although alpha-amanitin did not inhibit the germination of spores, the drug prevented the elongation of the rhizoid and protonemal initial with a concomitant effect on the synthesis of poly(A)+RNA. These results are consistent with the view that some form of translational control involving stored mRNA operates during dark-imbibition and photoinduced germination of spores.

Phytin is synthesized in the cotyledons of germinated castor-bean seeds in response to exogenously supplied phosphate

Following germination of the castor bean (Ricinus communis L.) seed, levels of phytin decline in both the endosperm and the embryo. However, as seedling growth continues, phytin increase in the latter to a level exceeding that present in the mature dry embryo, while phytin declines concomitantly in the endosperm. It is likely that phosphate mobilized from phytin in the endosperm acts as a substrate for phytin synthesis in the embryo. This is supported by the observation that isolated embryos supplied with phosphate accumulate phytin, particularly in the cotyledons. This increase is enhanced whenmyo-inositol is provided concurrently as a carbon source. Phytin synthesis in the cotyledons of the isolated embryos can occur without the attached axis. Whether initially exposed to exogenous phosphate or not, the isolated cotyledons remain competent in their ability to synthesize phytin for an extended post-germinative period, even though the major reserves are being mobilized at this time.

Identification and characterization of the mRNA for major storage proteins from radish

Precursors for radish storage proteins were identified by immunoprecipitation of cell-free protein-synthesis products. The 12S globulin polypeptides (21,000-33,000 Mr) are made from four larger precursors (47,500-60,000 Mr) and the 1.7 S albumin polypeptides (7,000-12,000 Mr) are synthesized as eight products of Mr about 20,000. From a cDNA library, several clones have been identified, using heterologous cDNA probes for rapeseed cruciferin and napin, and two of them (pAE10 and pBA3) used to hybrid-select the corresponding mRNA. The napin cDNA clone selects all translation products immunoprecipitated by anti-napin antibodies whereas the cruciferin clone selects only one polypeptide among the four recognized by 12S antibodies. The 12S globulin and the 1.7S albumin message sizes were estimated to be 1950 and 800 nucleotides respectively. Experiments carried out with mRNA populations from different maturation stages suggest a sequential gene expression for the two major storage protein families. In addition two napin subfamilies can be distinguished by their expression pattern. In dry seed, napin mRNA is not detectable and the amount of cruciferin mRNA decreased considerably so that it no longer represents a major fraction of dry seed mRNA.

Lectin synthesis in developing and germinating wheat and rye embryos

Wheat (Triticum aestivum L.) and rye (Secale cereale L.) lectins are specifically synthesized during seed formation. They accumulate exponentially in the primary axes in a period coinciding with the development of this complex organ. Since the specific lectin content also increases dramatically, there is apparently an outburst of lectin synthesis during the development of the primary axes. Germinating embryos also synthesize some lectin. The fortunate availability of a highly specific procedure for the isolation of cereal lectins enabled us to follow the kinetics of their synthesis during early germination. Stored mRNAs appear to be involved in this residual lectin synthesis.

Efficient translation of long-lived messengers in extracts from dry pea primary axes : Evidence for the presence of lectin mRNA

Extracts prepared from dry pea (Pisum sativum, L; cv oberon) primary axes translate efficiently their endogenous messengers in an in vitro protein synthesizing system. The native long-lived messengers are biologically fully active and direct the synthesis of a whole range of polypeptides with MW ranging up to 130,000. About 0.5% of the total in vitro synthesized polypeptides are recovered in the immunoprecipitate obtained with pea lectin antiserum. Since about one-fourth of the radioactivity in the immunoprecipitate comigrates with authentic pea lectin it is concluded that about 0.1% of the long-lived messengers code for the lectin.

Isolation and function of a low molecular weight protein of mung bean embryonic axes

A low molecular weight protein from dry mung bean (Vigna radiata) embryonic axes has been purified to near homogeneity by chromatography on DEAE-cellulose and hydroxylapatite. It shows a molecular weight of about 12,000 in sodium dodecyl sulfate-polyacrylamide gels and a sedimentation coefficient of about 2 S in sucrose gradients. This protein occurs in greater amounts in dry axes than in dry cotyledons, and it dramatically disappears during early germination of the seed. Affinity chromatography tests do not indicate it as a trypsin inhibitor or as a glycoprotein. It is a water-soluble cytoplasmic protein exhibiting an amino acid composition characteristic of storage proteins with a high content of glutamic acid/glutamine. We suggest that it is a low molecular weight storage albumin.