NH(4)-Excreting Azospirillum brasilense Mutants Enhance the Nitrogen Supply of a Wheat Host

Spontaneous ethylenediamine-resistant mutants of Azospirillum brasilense were selected on the basis of their excretion of NH(4). Two mutants exhibited no repression of their nitrogenase enzyme systems in the presence of high (20 mM) concentrations of NH(4). The nitrogenase activities of these mutants on nitrogen-free minimal medium were two to three times higher than the nitrogenase activity of the wild type. The mutants excreted substantial amounts of ammonia when they were grown either under oxygen-limiting conditions (1 kPa of O(2)) or aerobically on nitrate or glutamate. The mutants grew well on glutamate as a sole nitrogen source but only poorly on NH(4)Cl. Both mutants failed to incorporate [C]methylamine. We demonstrated that nitrite ammonification occurs in the mutants. Wild-type A. brasilense, as well as the mutants, became established in the rhizospheres of axenically grown wheat plants at levels of > 10 cells per g of root. The rhizosphere acetylene reduction activity was highest in the preparations containing the mutants. When plants were grown on a nitrogen-free nutritional medium, both mutants were responsible for significant increases in root and shoot dry matter compared with wild-type-treated plants or with noninoculated controls. Total plant nitrogen accumulation increased as well. When they were exposed to a N(2)-enriched atmosphere, both A. brasilense mutants incorporated significantly higher amounts of N inside root and shoot material than the wild type did. The results of our nitrogen balance and N enrichment studies indicated that NH(4)-excreting A. brasilense strains potentially support the nitrogen supply of the host plants.     

Metabolic regulation of rice α-amylase and sucrose synthase genes in planta

Isolated rice embryos were used to investigate the regulatory effects of endosperm extracts and pure sugars on the expression of alpha-amylase gene RAmy3D and a sucrose synthase gene homologous to the maize isozyme Ss2. The high-level expression of RAmy3D in the scutella of isolated embryos could be inhibited by a variety of sugars as well as endosperm extracts from germinated rice grains. Glucose, at a concentration of 250 mM, was most effective in repressing RAmy3D mRNA accumulation. Furthermore, this repression was reversible. Interestingly, RAmy3D repression was always accompanied by the induction of sucrose synthase gene expression. These results support a model in which the expression of alpha-amylase and sucrose synthase genes in the rice scutellum are counter-regulated by the influx of sugars from the endosperm.     

Tumour invasion: effects of cell adhesion and motility

Metastasis is the major cause of failure in cancer therapy. Recent studies of the molecular cell biology of the metastatic process have provided new insights into the mechanisms of cell-cell adhesion, cell-substrate adhesion and cell motility that underly invasion by tumour cells. In this review, Van Roy and Mareel discuss the role of proteins with invasion-promoting and invasion-suppressing functions in metastasis.     

A goal programming network for linear programming

Tank and Hopfield have shown that networks of analog neurons can be used to solve linear programming (LP) problems. We have re-examined their approach and found that their network model frequently computes solutions that are only suboptimal or that violate the LP problem's constraints. As their approach has proven unreliable, we have developed a new network model: the goal programming network. To this end, a network model was first developed for goal programming problems, a particular type of LP problems. From the manner the network operates on such problems, it was concluded that overconstrainedness, which is possibly present in an LP formulation, should be removed, and we have provided a simple procedure to accomplish this.     

Sex pheromone perception in male pine sawflies,Neodiprion sertifer (Hymenoptera; Diprionidae)

Summary Electroantennographic and single sensillum recordings were performed on male pine sawfly, Neodiprion sertifer, antennae. Responses to the sex pheromone component (2S, 3S, 7S)- 3,7-dimethyl-2-pentadecenyl (diprionyl) acetate (SSS:OAc), to the behavioral inhibitor (2S, 3R, 7R)-diprionyl acetate (SRR:OAc), to the six other enantiomers of diprionyl acetate, and to the biosynthetic precursor diprionol were recorded. Responses to trans-perillenal, a monoterpene identified in female gland extracts and to (2S, 3S, 7S)-diprionyl propionate (SSS:OPr), a field attractant for N. sertifer and some related sawfly species were also recorded.EAG recordings demonstrated a high antennal sensitivity to SSS:OAc and to SSS:OPr. A somewhat lower response was elicited by SRR:OAc.Single sensillum recordings revealed 8–12 different cells firing in each sensillum, corresponding to the number of cells observed in earlier morphological investigations. Out of these cells all, except one, responded to SSS:OAc and to SSS:OPr. No differences in the response to the two components could be observed. The largest amplitude cell in each sensillum was specifically tuned to the behavioral antagonist, SRR:OAc. The pheromone perception system encountered in male pine sawflies thus differs clearly from that observed in moths.Abbreviation EAG electroantennogram - OAc acetate - OPr propionate     

Interconversion of F430 derivatives of methanogenic bacteria

F₄₃₀ is the prosthetic group of the methylcoenzyme M reductase of methanogenic bacteria. The compound isolated from Methanosarcina barkeri appears to be identical to the one obtained from the only distinctly related Methanobacterium thermoautotrophicum. F₄₃₀ is thermolabile and in the presence of acetonitrile or C10 _in4 ^sup- two epimerization products are obtained upon heating; in the absence of these compounds F₄₃₀ is oxidized to 12, 13-didehydro-F₄₃₀. The latter is stereoselectively reduced under H₂ atmosphere to F₄₃₀ by cell-free extracts of M. barkeri or M. thermoautotrophicum. H₂ may be replaced by the reduced methanogenic electron carrier coenzyme F₄₂₀.Abbreviations CH₃S-CoM methylcoenzyme M, 2-methylthioethanesulfonic acid - HS-CoM coenzyme M, 2-mercaptoethanesulfonic acid - F₄₃₀ Ni(II) tetrahydro-(12, 13)-corphin with a uroporphinoid (III) ligand skeleton - 13-epi-F₄₃₀ and 12,13-di-epi-F₄₃₀ the 12, 13- and 12, 13-derivatives of F₄₃₀ - 12, 13-didehydro-F₄₃₀ F₄₃₀ oxidized at C-12 and C-13 - coenzyme F₄₂₀ 7,8-didemethyl-8-hydroxy-5-deazaflavin derivative - coenzyme F₄₂₀H₂ reduced coenzyme F₄₂₀ - MV⁺ methylviologen semiquinone - HPLC high-performance liquid chromatography     

Book reviews

Book reviewed in this article: Ecological theory and integrated pest management in practice. M. Kogan, editor World crop pests , Vol. 2. Aphids; their biology, natural enemies and control, PART A (Eds. A. K. Minks and P. Harrewijn)     

Heterogeneity of human tissue-type plasminogen activator

Tissue-type plasminogen activator (t-PA) from human melanoma cells (Bowes) was purified by immunosorbent chromatography on affinospecific polyclonal antibodies and gel filtration in the presence of KSCN. The immunosorbent eluate contained three major components of greater than 200, 85 and 65 kDa, respectively. The 65 kDa t-PA component could be separated by gel filtration on Ultrogel AcA44 in the presence of KSCN to a pure preparation yielding a unique N-terminal amino acid sequence. Immunoblot analysis, using affinospecific antibodies against t-PA, was a specific and sensitive method to identify different types of t-PA (I-IV), as well as t-PA-inhibitor complexes and degradation products in unstimulated melanoma cell culture fluids. Furthermore, the t-PA preparations, produced by phorbol ester-treated melanoma cells, were free of type IV and thus differed physiochemically from the constitutively produced t-PA preparations. The composition of t-PA from mammalian cell cultures is thus more complex than hitherto described.     

Purification of a form of protease nexin 1 that binds heparin with a low affinity

A form of protease nexin 1 (PN-1) that binds heparin with a low affinity (L-PN-1) was purified and studies since altered interactions with glycosaminoglycans could affect its inhibition of certain serine proteases. Purification of L-PN-1 and PN-1 was achieved by fractionating serum-free conditioned culture medium from human fibroblasts over dextran sulfate-Sepharose followed by immunoaffinity fractionation over a PN-1 monoclonal antibody-Sepharose column. The first step separated L-PN-1 from PN-1, and the second step resulted in apparently homogeneous L-PN-1 and PN-1. Comparisons of the two proteins showed that they could not be distinguished by the following properties: (a) molecular weight; (b) proteases complexed; (c) molecular weights of protease-L-PN-1 and protease-PN-1 complexes; (d) CNBr peptide maps; and (e) immunological cross-reactivity. Studies on activities that depend on the heparin binding domain revealed that heparin equally accelerated the rate of formation of 125I-thrombin-L-PN-1 and 125I-thrombin-PN-1 complexes even when the ratio of heparin to L-PN-1 or PN-1 was varied from 0.01 to 100. A functional difference, however, between L-PN-1 and PN-1 was observed in studies on the ability of the fibroblast surface to accelerate their reactions. Fixed fibroblasts accelerated the formation of 125I-thrombin-L-PN-1 complexes 2-fold, whereas they accelerated the formation of 125I-thrombin-PN-1 complexes 5-fold. The availability of purified L-PN-1 will permit studies on its functional relationship to PN-1.