Evaluation of N2-fixation and nitrogen economy of a maize/cowpea intercrop system using15N dilution methods

Yields of above ground biomass and total N were determined in summer-grown maize and cowpea as sole crops or intercrops, with or without supplementary N fertilizer (25 kg N ha⁻¹, urea) at an irrigated site in Waroona, Western Australia over the period 1982–1985. Good agreement was obtained between estimates of N₂ fixation of sole or intercrop cowpea (1984/85 season) based on the¹⁵N natural abundance and¹⁵N fertilizer dilution techniques, both in the field and in a glasshouse pot study. Field-grown cowpea was estimated to have received 53–69% of its N supply from N₂-fixation, with N₂-fixation onlyslightly affected by intercropping or N fertilizer application. Proportional reliance on N₂-fixation of cowpea in glasshouse culture was lower (36–66%) than in the field study and more affected by applied N. Budgets for N were drawn up for the field intercrops, based on above-ground seed yields, return of crop residues, inputs of fixed N and fertilizer N. No account was taken of possible losses of N through volatilization, denitrification and leaching or gains of N in the soil from root biomass. N₂-fixation was estimated tobe 59 kg N ha⁻¹ in the plots receiving no fertilizer N, and 73 kg N ha⁻¹ in plots receiving 25 kg N ha⁻¹ as urea. Comparable fixation by sole cowpea was higher (87 and 82 kg N ha⁻¹ respectively) but this advantage was outweighed by greater land use efficiency by the intercrop than sole crops.     

Detergent solubilization of the interleukin 1 receptor

Interleukin 1 (IL 1) receptors were solubilized from membranes prepared from murine EL-4 thymoma cells with the zwitterionic detergent 3[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate (CHAPS). Binding of IL 1 to the solubilized receptor was detected by a polyethylene glycol (PEG) precipitation procedure. Concentrations of CHAPS from 4 to 8 mM were effective in solubilizing the IL 1 receptor. At 10 mM CHAPS, there was some loss in binding activity, whereas 2 mM CHAPS was completely ineffective in solubilizing the receptor. Detergent concentrations of 4 mM were routinely used. The solubilized receptor retains the ability to bind 125I-IL 1 in a specific and saturable manner. Scatchard analysis reveals a single type of high affinity binding site having an apparent dissociation constant (KD) of approximately 1.2 X 10(-10) M. Nearly identical KD values are observed for membrane fractions. There are approximately 400 to 500 fmol receptor/mg protein in the detergent extract, corresponding to a two- to threefold enrichment in the Bmax observed for membranes. There is no loss in receptor activity as determined by complete recovery of the total number of binding sites from membranes after solubilization. Binding kinetics show that apparent steady state for the solubilized receptor is reached after 60 min at 37 degrees C. The binding of 125I-IL 1 is essentially irreversible because relatively little bound ligand can be dissociated from the receptor on the addition of excess unlabeled IL 1 at 37 degrees C. Both human IL 1 alpha and IL 1 beta compete for binding of 125I-IL 1 to the soluble receptor, confirming that IL 1 alpha and IL 1 beta bind to the same receptor. Other recombinant proteins, including interferon-alpha A, interferon-gamma, and interleukin 2 have no inhibitory effect.     

Class I-like MHC molecules expressed by baboon placental syncytiotrophoblast

Human placental villous trophoblast is known to be unreactive with W6/32 and other monoclonal antibodies recognizing monomorphic determinants of human class I MHC heavy chains, whereas extravillous cytotrophoblast in the placental bed is W6/32-reactive by immunohistology. We have now demonstrated, in contrast, that syncytiotrophoblast is the only cellular component of baboon early placental villous tissue which is reactive with any of these antibodies. Radioimmunoprecipitation of detergent-solubilized baboon placental membrane preparations, and subsequent SDS-PAGE, has shown the W6/32-reactive component to have an m.w. of 41,000 and to be associated with beta 2-microglobulin, whereas baboon peripheral lymphocytes express 45,000 m.w. W6/32-reactive antigens comparable with the HLA-A,B,C heavy chains of human lymphocytes.     

Free-flap reconstruction of large defects of the scalp and calvarium

Beyond a certain size, full-thickness defects of scalp are not amenable to local flap repair. Staged distant flaps have now been virtually eliminated by free-flap reconstruction. The authors present 12 patients in whom full-thickness scalp defects with an average area of 275 cm2 were reconstructed utilizing free flaps. Nine patients had corresponding large calvarial defects. Ten patients had reconstruction with free latissimus dorsi muscle flaps and overlying skin grafts, and one patient had reconstruction with a scapular free flap. Of the 12 patients, 8 had extirpative surgery for tumor with immediate reconstruction and the remaining 4 had reconstruction for chronic radionecrosis of the scalp, usually associated with infected osteoradionecrosis of the calvarium. Of this latter group, 2 patients underwent simultaneous acrylic cranioplasty. The technique and results are discussed.     

Regulation of transplasmalemma electron transport in oat mesophyll cells by sphingoid bases and blue light

Long-chain sphingoid bases inhibit transplasmalemma electron transport in certain animal cells in part by inhibiting protein phosphorylation. As a first step in determining whether similar regulatory processes exist for cell surface redox activity in plants, peeled leaf segments of Avena sativa L. cv Garry were exposed to sphingoid bases and other long chain lipids. Sphingoid bases which are the most active inhibitors of protein kinase C in animal cells inhibit transplasmalemma electron transport by mesophyll cells in the dark as measured by reduction of exogenous ferricyanide. In white light, however, the same compounds markedly stimulate redox activity. The stimulation by sphingoid bases in the light is not eliminated by the inhibitor of photosynthesis, 3-(3,4-dichlorophenyl)-1,1 dimethylurea (DCMU). Redox activity remaining in the presence of DCMU and sphingoid bases can be observed in blue but not red light. A tentative hypothesis considering the involvement of two separate redox systems is presented in an attempt of explain the disparate action of sphingoid bases on electron transport across the plasmalemma.     

Interaction of cyclosporine A and calcitonin on bone resorption in vitro

Cyclosporine A (CsA), which is a potent immunosuppressive agent, inhibits bone resorption in vitro. The inhibition of bone resorption by CsA is sustained, unlike the transient inhibition of bone resorption produced by calcitonin (CT). These different patterns of inhibition were studied by examining the interaction between CsA and CT on stimulated bone resorption in the neonatal mouse calvarial resorptive system. "Escape" from the CT inhibition of PTH stimulated bone resorption occurred after 24 hr of organ culture. Coincubation with CsA (1 micrograms/ml) delayed the "escape" response of CT + PTH treated bones, so that the full "escape" response did not occur until after 48 hr of organ culture. Likewise, a pretreatment of 24 hr with CsA (1 micrograms/ml) was sufficient to delay "escape" from CT inhibition of PTH stimulated bone resorption until after 48 hr of organ culture. A higher concentration of CsA (10 micrograms/ml) completely prevented the "escape" response. Our data could indicate an interaction between the CsA and CT inhibitory effects on resorption.     

EGF-stimulated tyrosine phosphorylation of p185neu: a potential model for receptor interactions.

p185neu is a receptor-like protein encoded by the neu/erbB-2 proto-oncogene. This protein is closely related to the epidermal growth factor (EGF) receptor, but does not bind EGF. We report here that incubation of Rat-1 cells with EGF stimulates tyrosine phosphorylation of p185. This effect is specific to EGF since neither platelet derived growth factor (PDGF) nor insulin, which also bind to receptors with ligand-stimulated tyrosine kinase activity, induced tyrosine phosphorylation of p185. The EGF-stimulated tyrosine phosphorylation of p185 and of the EGF receptor occurred with similar kinetics and EGF dose-responses, and both phosphorylations were prevented by down-regulation of the EGF receptor with EGF. Since p185 does not bind EGF, these results suggested that p185 is a substrate for the EGF receptor kinase. Incubation of cells with EGF before lysis stimulated the tyrosine phosphorylation of p185 in immune complexes. This suggested that EGF, acting through the EGF receptor, can regulate the intrinsic kinase activity of p185.     

Molecular characterization of ataxia telangiectasia T cell clones

Summary To delimit the 14q32.1 recurrent breakpoint of ataxia telangiectasia clones, we performed an in situ hybridization study with various probes located on the 14q32 band. We thus mapped this breakpoint between the D14S1 and Pi loci. Furthermore, an interstitial duplication including D14S1 and a part of the IgH locus was demonstrated on a t(14;14) clone.