For self-pollinating plants to reproduce, male and female organ development must be coordinated as flowers mature. The Arabidopsis transcription factors AUXIN RESPONSE FACTOR 6 (ARF6) and ARF8 regulate this complex process by promoting petal expansion, stamen filament elongation, anther dehiscence, and gynoecium maturation, thereby ensuring that pollen released from the anthers is deposited on the stigma of a receptive gynoecium. ARF6 and ARF8 induce jasmonate production, which in turn triggers expression of MYB21 and MYB24, encoding R2R3 MYB transcription factors that promote petal and stamen growth. To understand the dynamics of this flower maturation regulatory network, we have characterized morphological, chemical, and global gene expression phenotypes of arf, myb, and jasmonate pathway mutant flowers. We found that MYB21 and MYB24 promoted not only petal and stamen development but also gynoecium growth. As well as regulating reproductive competence, both the ARF and MYB factors promoted nectary development or function and volatile sesquiterpene production, which may attract insect pollinators and/or repel pathogens. Mutants lacking jasmonate synthesis or response had decreased MYB21 expression and stamen and petal growth at the stage when flowers normally open, but had increased MYB21 expression in petals of older flowers, resulting in renewed and persistent petal expansion at later stages. Both auxin response and jasmonate synthesis promoted positive feedbacks that may ensure rapid petal and stamen growth as flowers open. MYB21 also fed back negatively on expression of jasmonate biosynthesis pathway genes to decrease flower jasmonate level, which correlated with termination of growth after flowers have opened. These dynamic feedbacks may promote timely, coordinated, and transient growth of flower organs.

When attacked by insects, plants release mixtures of volatile compounds that are beneficial for direct or indirect defense. Natural variation of volatile emissions frequently occurs between and within plant species, but knowledge of the underlying molecular mechanisms is limited. We investigated intraspecific differences of volatile emissions induced from rosette leaves of 27 accessions of Arabidopsis (Arabidopsis thaliana) upon treatment with coronalon, a jasmonate mimic eliciting responses similar to those caused by insect feeding. Quantitative variation was found for the emission of the monoterpene (E)-b-ocimene, the sesquiterpene (E,E)-a-farnesene, the irregular homoterpene 4,8,12-trimethyltridecatetra-1,3,7,11-ene, and the benzenoid compound methyl salicylate. Differences in the relative emissions of (E)-b-ocimene and (E,E)-a-farnesene from accession Wassilewskija (Ws), a high-(E)-b-ocimene emitter, and accession Columbia (Col-0), a trace-(E)-b-ocimene emitter, were attributed to allelic variation of two closely related, tandem-duplicated terpene synthase genes, TPS02 and TPS03. The Ws genome contains a functional allele of TPS02 but not of TPS03, while the opposite is the case for Col-0. Recombinant proteins of the functional Ws TPS02 and Col-0 TPS03 genes both showed (E)-b-ocimene and (E,E)-a-farnesene synthase activities. However, differential subcellular compartmentalization of the two enzymes in plastids and the cytosol was found to be responsible for the ecotype-specific differences in (E)-b-ocimene/(E,E)-a-farnesene emission. Expression of the functional TPS02 and TPS03 alleles is induced in leaves by elicitor and insect treatment and occurs constitutively in floral tissues. Our studies show that both pseudogenization in the TPS family and subcellular segregation of functional TPS enzymes control the variation and plasticity of induced volatile emissions in wild plant species.

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The effect of streptothricin F on macromolecular syntheses in intact cells and cell-free protein synthesis of E. coli was studied. The results indicate that protein synthesis is the primary site of inhibition by streptothricin F in growing E. coli cells. Cell-free polypeptide synthesis from E. coli directed by poly (U) was inhibited, while poly (A) and poly (C) directed polypeptide syntheses were both stimulated by the drug. Furthermore, streptothricin F caused misreading of translation of poly (U), poly (A) and poly (C) directed protein syntheses in E. coli systems. The extent of misreading by streptothricin F increases with increasing drug concentrations.The results are compared with those of other miscoding antibiotics. In rat liver extracts protein synthesis directed by poly (U) or endogenous mRNA was not inhibited.

The effect of streptothricin F on elongation factor-dependent and on elongation factor-free translation systems was studied. Streptothricin F inhibits factor-dependent as well as factorfree polypeptide synthesis. The results suggest that streptothricin F inhibits polypeptide synthesis via interaction with the ribosome. In partial reactions streptothricin F impairs EF-G-dependent translocation and to a lesser extent EF-T.dependent binding of as-RNA to the ribosome, while it does not affect peptide bond formation significantly.We recently examined the effect of streptothricin F (ST-F) on cell-free protein synthesis1). ST-F has been shown to inhibit protein synthesis specifically in intact bacterial cells and in cell-free systems of Escherichia coli, while the antibiotic did not inhibit cell-free protein synthesis in rat liver extracts.Furthermore ST-F induced misreading of synthetic homopolynucleot ides in E. co/i cell-free systems.In the present paper the action of ST-F on the individual reactions of polyphenylalanine formation on E. coli ribosomes is described. Materials and Methods Materials[14C] Phe-tRNA(182 mCi/m Mol) and ac["C]Phe-tRNA (182 mCi/m Mol) were prepared as described by CERNA et a1.2). Ac[14C]Leu-pentanucleotide (CACCA-acLeu, 164 mCi/m Mol) was prepared as described by MONRO et al.'). Radioactivity was determined in a Packard-Tricarb scintillation spectrometer (counting efficiency for 14C was 53 %) and a methane flow counter (Frieseke-Hoepfner, counting efficiency for 14C was 41 %).The antibiotics ST-F, neomycin, turimycin-H, and streptomycin were dissolved in water while oxytetracycline was dissolved in 0.01 N HCI. Antibiotic solutions were prepared immediately before use.Preparation of ribosomes Ribosomes were prepared from E. co/i B by ammonium sulfate precipitation according to GAVRI-LOVA and SPIRIN°) and GAVRILOVA et al.e1. The bacteria were broken by grinding with aluminium oxide powder and the ribosomes were pelleted by centrifugation at 105,000 g in a buffer containing 10 mM Tris-HCl (pH 7.8), 20 mm MgCl2, 5 mm NH4Cl and 1 mm B-mercaptoethanol.The ribosomal pellets were washed 4 times with 1 M NH,Cl in 10 mm Tris-HCl (pH 7.8), 10 mM MgCl2 and 1 mat mercaptoethanol and were precipitated at 0°-4°C by ammonium sulfate adding 49 g of the dry salt per 100 nil of the ribosome suspension containing 2.5 mg ribosomes per ml. The ribosomal precipitate was stored under ammonium sulfate at 4°C. Immediately before use 2 nil of the ribosome suspension were centrifuged for 40 minutes at 15,000 rpm. The pellet was suspended in 10 niM Tris-HCI (pH 7.8), 100 mm KCl and 20 mm MgCl2 and dialysed against the same buffer to complete removal of the ammonium sulfate. Dialysis was continued against a buffer with the MgCl2 concentration required for the experiment.

Resistance to streptothricin was studied in bacteria with different resistance mechanisms. The laboratory-induced streptothricin-resistant mutant E. coli A19 Stcr 2/2/1 showed a high level of cross-resistance to aminoglycosides and other miscoding inducing antibiotics. In contrast, aminoglycosid-resistant E. coli strains with plasmid-determined aminoglycoside modifying enzymes were sensitive to streptothricin. Enzymatic inactivation of streptothricin by acetylation was demonstrated for the streptothricin producing Streptomyces noursei, strain NG13. This strain showed no cross-resistance to miscoding inducing aminoglycosides.

Resistomycin preferentially inhibits RNA synthesis in comparison to DNA and protein synthesis in intact bacterial cells. Studies with cell-free systems have shown that the antibiotic interferes with DNA and RNA synthesis, while protein synthesis is inhibited to a much lesser extent. Detailed studies in cell-free systems indicate an interaction of resistomycin with DNA- and RNA polymerase. In the case of RNA polymerase this was proved by CD measurements, whereas no interaction of the antibiotic with DNA, RNA, and homopolynucleotides could be found. One can conclude that the binding of the antibiotic to RNA polymerase is the basis for its interference with RNA synthesis.

The nourseothricin producer Streptomyces noursei is resistant to its own antibiotic in submerged as well as in surface culture. The strain shows no cross-resistance to miscoding inducing aminoglycoside antibiotics. Cell free extracts of Streptomyces noursei inactivate nourseothricin by enzymatic acetylation. The pattern of cross-resistance of Streptomyces noursei correlates well with the substrate specificity of the nourseothricin acetyltransferase. Furthermore, the acetyltransferase activity parallels the resistance level in nourseothricin-producing strains and nonproducing mutants. The results suggest that the nourseothricin acetyltransferase is important in the self-defence strategy of the nourseothricin-producing strain.