Evidence for Cytokinin Involvement in Rhizobium (IC3342)-Induced Leaf Curl Syndrome of Pigeonpea (Cajanus cajan Millsp.)

A uniquely abnormal shoot development (shoot tip-bending, leaf curling, release from apical dominance, and stunted growth) in pigeonpea (Cajanus cajan Millsp) induced by a nodulating Rhizobium strain, IC3342, is thought to be due to a hormonal imbalance. Amaranthus betacyanin bioassay indicated that xylem exudate and leaf extracts from pigeonpea plants with Rhizobium-induced leaf curl symptoms contained high concentrations of cytokinin relative to those in normal plants. Radioimmunoassay (RIA) of samples purified with high performance liquid chromatography revealed that zeatin riboside (ZR) and dihydrozeatin riboside (DZR) concentrations in xylem sap from plants with leaf curl symptoms were 7 to 9 times higher than those in the sap from symptomless, nodulated plants. The sap from symptomless plants nodulated by a Curl⁻ mutant had ZR and DZR concentrations comparable to those in the normal plant sap. RIA indicated that the respective concentrations of zeatin and N⁶-isopenteny-ladenine in culture filtrates of the curl-inducing strain IC3342 were 26 and 8 times higher than those in filtrates of a related normal nodulating strain (ANU240). Gas chromatographic-mass spectrometric analyses revealed similar differences. Gene-specific hybridization and sequence comparisons failed to detect any homology of IC3342 DNA to Agrobacterium tumefaciens or Pseudomonas savastanoi genetic loci encoding enzymes involved in cytokinin biosynthesis.     

Metabolism of 13-cis-retinoic acid: Identification of 13-cis-retinoyl-and 13-cis-4-oxoretinoyl-β-glucuronides in the bile of vitamin A-normal rats

The metabolism of 13-cis-[11-³H]retinoic acid has been examined in vitamin A-normal rats. Within 24 h after intravenous administration of the parent retinoid (15 μg/kg) to animals with biliary fistulas, 69 ± 9% of the dose was detected in the bile with 9 ± 6% being found in the urine. Analysis of the bile by reverse-phase high-pressure liquid chromatography demonstrated that the retinoic acid was being metabolized to several more polar compounds. A number of these compounds were sensitive to incubation with β-glucuronidase as evidenced by a change in their chromatographic behavior after treatment with the enzyme. Two of the metabolites have been identified as 13-cis-4-oxoretinoyl-β-glucuronide (8.1 ± 1.0% of the dose during the first 4 h after administration of the parent compound) and 13-cis-retinoyl-β-glucuronide (7.0 ± 4.4% of the dose). A comparison of the chromatographic profiles of bile from 13-cis- versus all-trans-retinoic acid-treated rats indicated a difference in their metabolism, with a greater proportion of the all-trans-retinoic acid being converted to compounds that eluted in the more polar regions of the column effluent.     

Some effects of environmental stress on seed yield of cowpea (Vigna unguiculata (L.) walp.) cv. Prima

Summary Separate experiments examined nodulation and seed yield of cowpea cv. Prima after (a) changes in the level of combined nitrogen from 25 to 0 or 60 ppm N, (b) cycles of wilting and rehydration, and (c) shading to ca 50% full daylight. Plants were grown in the simulated tropical environment of a plastics bubble house and experienced these changes over the growth stages: emergence to first flower, first flower to mid pod-fill or mid pod-fill to maturity.Seed yields of nodulated plants were unaffected by combined nitrogen supply and almost double those of non-nodulated plants (100 g cf 56 g per plant)-due mainly to increases in pod number per plant and mean seed weight. Reducing the nitrogen level from 25 to 0 ppm N, especially between mid pod-fill and maturity, reduced seed yields of non-nodulated plants to 36 g per plant. At the first flowering stage, plants grown without combined nitrogen had nitrogenase activities less than 10% of those supplied with 25 ppm N; 60 ppm N at any stage of development more than halved nitrogenase activity when compared with plants supplied with 25 ppm.Repeated wilting prior to flowering markedly reduced seed yields compared with the unstressed controls (41 g cf 76 g per plant)-mainly by decreasing subsequent pod production. Nodule weight and nitrogenase activity per plant were also much reduced. Wilting after flowering did not reduce yield, and nitrogenase activity was less affected.Shading throughout, or from first flower onwards, reduced seed yield by about 25% because fewer pods were produced. All shading treatments significantly increased mean seed weight compared with unshaded controls (116–121 mg cf 105 mg).One of a series of papers describing work undertaken in a collaborative project with the International Institute of Tropical Agriculture, Nigeria, sponsored by the U.K. Ministry of Overseas Development.Soil Microbiology Department, Rothamsted Experimental Station, Harpenden, Herts.Soil Microbiology Department, Rothamsted Experimental Station, Harpenden, Herts.     

The PSD95-nNOS interface: a target for inhibition of excitotoxic p38 stress-activated protein kinase activation and cell death

The stress-activated protein kinase p38 and nitric oxide (NO) are proposed downstream effectors of excitotoxic cell death. Although the postsynaptic density protein PSD95 can recruit the calcium-dependent neuronal NO synthase (nNOS) to the mouth of the calcium-permeable NMDA receptor, and depletion of PSD95 inhibits excitotoxicity, the possibility that selective uncoupling of nNOS from PSD95 might be neuroprotective is unexplored. The relationship between excitotoxic stress-generated NO and activation of p38, and the significance of the PSD95-nNOS interaction to p38 activation also remain unclear. We find that NOS inhibitors reduce both glutamate-induced p38 activation and the resulting neuronal death, whereas NO donor has effects consistent with NO as an upstream regulator of p38 in glutamate-induced cell death. Experiments using a panel of decoy constructs targeting the PSD95-nNOS interaction suggest that this interaction and subsequent NO production are critical for glutamate-induced p38 activation and the ensuing cell death, and demonstrate that the PSD95-nNOS interface provides a genuine possibility for design of neuroprotective drugs with increased selectivity.     

The European Renal Genome Project: An Integrated Approach Towards Understanding the Genetics of Kidney Development and Disease

Rapid progress in genome research creates a wealth of information on the functional annotation of mammalian genome sequences. However, as we accumulate large amounts of scientific information we are facing problems of how to integrate and relate the data produced by various genomic approaches. Here, we propose the novel concept of an organ atlas where diverse data from expression maps to histological findings to mutant phenotypes can be queried, compared and visualized in the context of a three-dimensional reconstruction of the organ. We will seek proof of concept for the organ atlas by elucidating genetic pathways involved in development and pathophysiology of the kidney. Such a kidney atlas may provide a paradigm for a new systems-biology approach in functional genome research aimed at understanding the genetic bases of organ development, physiology and disease.Key Words: EuReGene, kidney, genome, development, pathophysiology, genetics     

Reduction of acetylene by nodules of Trifolium subterraneum as affected by root temperature,Rhizobium strain and host cultivar

Summary The nitrogenase activity (measured by reduction of C₂H₂ to C₂H₄) of nodules of Trifolium subterraneum grown at root temperatures from 7°C–19°C was broadly correlated with nitrogen fixation. Root temperature did not affect enzyme activity per se but did affect the amount of enzyme formed. Exposure of nodules to 7°C for 24 h did not decrease activity cf. 19°C. Activity was greatest when nodules were about 4 days old, before swollen bacteroid forms were produced, and then declined. The effectiveness of a bacterial strain at a given temperature was related to the amount of enzyme produced and to its persistence. Nitrogenase activity should be measured throughout the plant growth cycle for valid comparisons of strain effectiveness.     

Widespread and ancient distribution of a noncanonical genetic code in diplomonads

Recently, a group of diplomonads has been found to use a genetic code in which TAA and TAG encode glutamine rather than termination. To survey the distribution of this characteristic in diplomonads, we sought to identify TAA and TAG codons at positions where glutamine is expected in genes for alpha-tubulin, elongation factor-1 alpha, and the gamma subunit of eukaryotic translation initiation factor-2. These sequences show that the variant genetic code is utilized by almost all diplomonads, with the genus Giardia alone using the universal genetic code. Comparative phylogenetic analysis reveals that the switch to this genetic code took place very early in the evolution of diplomonads and was likely a single event. Termination signals and downstream untranslated regions were also cloned from three Hexamita genes. In all three of these genes, the predicted TGA termination codon was found at the expected position. Interestingly, the untranslated regions of these genes are high in AT. This is incongruent with the coding regions, which are comparatively GC-rich.      

Nodulation studies in legumes

Summary The influence of combined nitrogen (as ammonium nitrate) on the symbiotic performances of selected bacterial associations of four legumes was examined using sand culture.In barrel medic (Medicago tribuloides Desr.) and vetch (Vicia sativa L. andV. atropurpurea Desf.) bacterial partnerships of a host plant varied greatly in their nodulation responses to a range of amounts of nitrogen applied at sowing. Some bacterial strains exhibited varying degrees of stimulation of nodule number, growth and fixation by low or medium amounts of nitrogen. Higher levels of combined nitrogen depressed symbiosis. Other strain responses showed a severe restriction of symbiosis with any amount of added nitrogen.Seasonal influences conditioned symbiotic responses to combined nitrogen in an association of cowpea (Vigna sinensis End.) With a summer sowing small amounts of ammonium nitrate added at sowing benefited later symbiotic development. No such stimulation was evident in an autumn sowing and symbiotic injury from high levels of nitrogen was greater than in the summer sowing.The developing association of cowpea was found to be most sensitive to ammonium nitrate added just as the first leaves unfolded. Here damage was manifest in a permanent elevation of the top: root ratio with subnormal growth and functioning of nodules. Greatest benefit from added inorganic nitrogen followed applications made as the first nodules appeared on the primary root. In this case added combined nitrogen acted as an investment providing returns in additional fixation equivalent to 5–10 times the amount of nitrogen originally fed to the seedling and representing some 50 per cent greater total fixation than in minus-nitrogen controls.