Regulation of Legumin Levels in Developing Pea Seeds under Conditions of Sulfur Deficiency: Rates of Legumin Synthesis and Levels of Legumin mRNA

It was shown previously that when peas (Pisum sativum L.) are grown with suboptimal sulfur supply the level of legumin (the more S-rich of the two major seed storage proteins) in the mature seed is selectively reduced (Randall, Thomson, Schroeder, 1979 Aust J Plant Physiol 6: 11-24). This paper reports a study of the cellular mechanisms involved in regulating legumin synthesis under these conditions. Pulse and pulse-chase labeling experiments were carried out with excised, immature cotyledons from normal and S-deficient plants. Legumin was isolated from cotyledon extracts by immunochromatography, and the proportion of legumin synthesis relative to total protein synthesis was determined. Results showed that reduced legumin accumulation could largely be accounted for by a greatly reduced level of legumin synthesis (80-88% reduction) rather than by a major increase in legumin breakdown.

Legumin mRNA levels were assayed by two methods. In vitro translation of polysomal RNA from cotyledons of normal and S-deficient plants indicated a reduction of 60 to 70% in synthesis of legumin-related products by preparations from S-deficient plants. A legumin cDNA clone was constructed, characterized, and used to measure the levels of legumin mRNA in polysomal and total RNA preparations from developing cotyledons. Legumin mRNA levels were reduced by 90% in preparations from S-deficient plants.

When restored to an adequate S supply, S-deficient plants (or pods taken from such plants) recovered normal levels of legumin synthesis (in vivo and in vitro) and of legumin mRNA. These results indicate that reduced legumin accumulation under conditions of S deficiency is primarily a consequence of reduced levels of legumin mRNA.

     

Maternal effects and temperature-sensitive period of mutations affecting embryogenesis in Caenorhabditis elegans

We have used standard tests to investigate the nature of gene expression of a new set of temperature-sensitive mutants defining 30 emb genes (essential for embryogenesis) in the nematode Caenorhabditis elegans. The mode of gene expression as determined by progeny tests for parental effects divides the genes into four classes. For 18 genes maternal gene expression is necessary and sufficient for normal embryogenesis; for 2 genes zygotic expression is necessary and sufficient; for 7 genes either maternal or zygotic expression is sufficient; for 3 genes both maternal and zygotic expression are necessary. One mutant displayed partial paternal sufficiency. The results of temperature-shift experiments define two “execution stages,” corresponding to the limits of the temperature-sensitive period (TSP), and indicate the nature and the time of action or synthesis of the gene products. Most of the maternally expressed genes have very early execution stages indicating translation before fertilization, but some are temperature sensitive late in embryogenesis. Early execution stages for 2 zygotically necessary genes demonstrate that the zygotic genome can be active in the earliest stages of embryogenesis. All taken together, the mode of gene expression, TSP, and arrest stage (terminal phenotype) allow us to classify functionally and begin to order the genes essential for embryogenesis. The results indicate a preeminent role for maternal genes and gene products in embryogenesis, in agreement with the results of others.     

Relationship between foliar composition of red-pine and jack-pine seedlings and vulnerability to Lophodermium needle-cast disease

Summary The Mn and Al content of needles from two-year-old jack pine (Pinus banksiana) seedlings was found to be more than twice that of red pine (Pinus resinosa). It is speculated that the high Mn and Al content of jack pine seedlings may impart some degree of resistance to needle cast disease caused byLophodermium pinastri. Contribution from the Soils Dept., Univ. of Wis., Madison, in cooperation with and supported in part by the Wisconsin Dept. of Natural Resources. Publication approved by the Director of the Wisconsin Agricultural Experiment Station.     

Involvement of recA and exr Genes in the In Vivo Inhibition of the recBC Nuclease

When Escherichia coli cells are gamma irradiated they degrade their deoxyribonucleic acid (DNA). The DNA of previously gamma-irradiated T4 phage is also degraded in infected cells. The amount of degradation is not only dependent on the dose but also on the genotype of the cell. The amount of degradation is less in cells carrying a recB or a recC mutation, suggesting that most of the DNA degradation is due to the recB(+) and recC(+) gene product (exonuclease V). In some strains a previous dose of ultraviolet (UV) light followed by incubation renders the cells resistant to DNA degradation after gamma irradiation. We have shown this inhibition to take place for infecting T4 phage also. By using six strains of E. coli selected for mutations in the genes recA, exr (or lex), and uvrB, we have been able to show that the preliminary UV treatment produces no change in recA and exr cells for both endogenous DNA degradation and the degradation of infecting irradiated T4 phage DNA, i.e., inhibition was not detected in these strains. On the other hand, wild-type cells and strains carrying mutations of uvrB show inhibition in both types of experiments. Because the recA gene product and the exr(+) (lex(+)) gene product are necessary for the induction of prophage, it is possible that the phenomenon of inducible inhibition requires recA(+) and exr(+) presence. One interpretation of these results is that an inducible inhibitor may be controlled by the exr gene.     

Genetic Analysis of tox+ and tox? Bacteriophages of Corynebacterium diphtheriae

A series of mutants derived from the temperate corynebacteriophages beta(tox+), gamma(tox-), and L(tox+) was isolated and characterized. In three-factor crosses between mutant beta phages the relative map order of the genetic markers determining extended host ranges (h and h') and loss of ability to lysogenize (c) was found to be h--c--h'. Recombination between markers was observed in matings between phage beta and the heteroimmune corynebacteriophages gamma and L. In such matings between heteroimmune phages the c markers of phages beta and gamma failed to segregate from the imm markers which determine the specificity of lysogenic immunity in these phages. The factor which directs the synthesis of diphtherial toxin during infection of appropriate corynebacterial hosts by toxinogenic corynebacteriophages is designated tox(+). It was possible to show that the tox(+) determinant of phage beta behaves as a single genetic element which occupies a position between the loci h and imm on the genetic map of this phage. Genetic recombination between mutants of phage beta occurred at very low frequencies in biparental matings performed by mixed infection of Corynebacterium diphtheriae C7(s)(-)(tox-). Considerably higher recombination frequencies were observed when lysogenic bacterial strains carrying one parental phage as prophage were induced by ultraviolet irradiation and then superinfected by the second parental phage. Maximal stimulation of genetic recombination between mutant beta phages was detected when superinfection followed ultraviolet irradiation of the lysogenic cells within a limited period of time. In matings between phages with incomplete genetic homology, the stimulation of recombination by ultraviolet radiation was much less effective.     

Preimplantation mammalian aggregation and injection chimeras

The preimplantation embryo is highly resilient to experimental manipulations. A specific manipulation that has revealed many clues to the developmental process is chimera production. Chimeras have been used to describe the importance of developmental characteristics of embryonic cells and how these characteristics are involved with developmental fate. These characteristics have been monopolized in the production of interspecific chimeras and the production of transgenic animals. This review attempts to discuss the major factors affecting preimplantation mammalian embryo chimera production.