Evidence for translational control of storage protein biosynthesis during embryogenesis ofAvena sativa L. (oat endosperm)

Abscisic acid and ethephon regulation of cellulase in the endosperm cap and radicle during lettuce seed germination

The purpose of this study was to investigate the role of cellulase in endosperm cap weakening and radicle elongation during lettuce (Lactuca sativa L.) seed germination. The application of abscisic acid (ABA) or ethephon inhibits or promotes germination, respectively, by affecting endosperm cap weakening and radicle elongation. Cellulase activities, and related protein and transcript abundances of two lettuce cellulase genes, LsCEL1 and LsCEL2, increase in the endosperm cap and radicle prior to radicle protrusion following imbibition in water. ABA or ethephon reduce or elevate, respectively, cellulase activity, and related protein and transcript abundances in the endosperm cap. Taken together, these observations suggest that cellulase plays a role in endosperm cap weakening and radicle elongation during lettuce seed germination, and that the regulation of cellulase in the endosperm cap by ABA and ethephon play a role in endosperm cap weakening. However, the influence of ABA and ethephon on radicle elongation may not be through their effects on cellulase.

Glutamate dehydrogenase (NADP-dependent) mRNA in relation to enzyme synthesis in Euglena gracilis. Evidence for post-transcriptional control

Cells of Euglena gracilis Klebs strain z Pringsheim had high NADP-dependent glutamate dehydrogenase activity when grown on glutamate as nitrogen source but activity was completely repressed in cells grown on ammonium (NH4+). A 120-fold purification of NADPH-glutamate dehydrogenase (subunit Mr = 45 000) was achieved from glutamate-grown cells by affinity chromatography on blue Sepharose CL-6B. Antisera raised against the homogeneously pure protein were used to demonstrate that increase in NADPH-glutamate dehydrogenase activity on transfer from NH4+ to glutamate medium resulted from an increase in the amount of protein. Glutamate NH4+-grown cells were labelled with L-[35S]methionine and anti-(NADPH-glutamate dehydrogenase) used to immunoprecipitate the dehydrogenase from cell extracts. NADPH-glutamate dehydrogenase protein was detected in glutamate-grown but not NH4+-grown cells. Anti-(NADPH-glutamate dehydrogenase) was used to detect NADPH-glutamate dehydrogenase resulting from the translation of total polyadenylated RNA from Euglena in a cell-free rabbit reticulocyte lysate system. NADPH-glutamate dehydrogenase mRNA was present in glutamate NH4+-grown cells, there being no apparent difference in mRNA abundance between cells showing a tenfold difference in NADPH-glutamate dehydrogenase specific activity. These results indicate that the synthesis of this dehydrogenase is regulated primarily at the post-transcriptional level.

Characterization of developing oat seed mRNA: evidence for many globulin mRNAs

Polyadenylated mRNA from developing oat (Avena sativa L.) seeds was isolated and analyzed. Prominent mRNA species of 18S, 15S and 12S were observed; the 18S mRNA was judged to be esentially free of ribosomal RNA by hybridization analysis. Size fractionation andin vitro translation of this mRNA was performed. SDS, IEF-SDS gel electrophoresis and immunoprecipitation were used to analyze the translation products. It is shown that globulin mRNA (18S) accounts for roughly 30% of the total mRNA in developing seeds, the 12S and 15S mRNAs accounting for the remainder. The 18S mRNA directs the synthesis of a series of distinct but related polypeptides, suggesting that some of the heterogeneity seen in the oat globulins is at the amino acid sequence level.