Genotypic variation in biological nitrogen fixation by common bean

Field experiments were performed in Austria, Brazil, Chile, Colombia, Guatemala, Mexico and Peru as part of an FAO/IAEA Co-ordinated Research Programme to investigate the nitrogen fixing potential of cultivars and breeding lines of common bean (Phaseolus vulgaris L.). Each experiment included approximately 20 bean genotypes which were compared using the ¹⁵N isotope dilution method. Great differences in nitrogen fixation were observed between and within experiments, with average values of 35% N derived from atmosphere (% Ndfa) and highest values of 70% Ndfa being observed. These values which were larger than had been reported previously for common bean, were observed only when environmental factors were favorable. Therefore, common bean lines are available, which can support high biological nitrogen fixation. These can be used either directly as cultivars for production or in breeding programmes to enhance nitrogen fixation in other cultivars.     

Minimizing the effect of mineral nitrogen on biological nitrogen fixation in common bean by increasing nutrient levels

Although common bean (Phaseolus vulgaris L.) has good potential for N₂ fixation, some additional N provided through fertilizer usually is required for a maximum yield. In this study the suppressive effect of N on nodulation and N₂ fixation was evaluated in an unfertile soil under greenhouse conditions with different levels of soil fertility (low=no P, K and S additions; medium = 50, 63 and 10 mg kg^–1 soil and high = 200, 256 and 40 mg kg^–1 soil, respectively) and combined with 5, 15, 60 and 120 mg N kg^–1 soil of ¹⁵N-labelled urea. The overall average nodule number and weight increased under high fertility levels. At low N applications, nitrogen had a synergistic effect on N₂ fixation, by stimulating nodule formation, nitrogenase activity and plant growth. At high fertility and at the highest N rate (120 mg kg^–1 soil), the stimulatory effect of N fertilizer on N₂ fixation was still observed, increasing the amounts of N₂ fixed from 88 up to 375 mg N plant^–1. These results indicate that a suitable balance of soil nutrients is essential to obtain high N₂ fixation rates and yield in common beans.     

Detection of serum antibodies in Ethiopian baboons that cross-react with SIV,HTLV-I,and type D retroviral antigens

Baboons (Papio cynocephalus) imported from Ethiopia were screened for antibodies to various primate retroviruses by immunoblotting. Antibodies that cross-reacted with SIV/Mne or with type D viral antigens were detected in approximately one-third of these animals. In addition, 20% of these baboons had antibodies that cross-reacted with HTLV-I viral antigens. These data suggest that wild-caught baboons are infected with retroviruses only partially related to known primate viral isolates.     

A common allergenic epitope of Bermuda grass pollen shared by other grass pollens

The present study disclosed the cross-reactivity between Bermuda grass pollen (BGP) and other grass pollens using monoclonal antibodies (MAbs) and polyclonal antiserum. MAb 9–13, directed against a group of minor allergens of BGP (Cyn d Bd68K, 48K, 38K) was found to cross-react with extracts of ten other grass pollens. Immunoblotting assays illustrated that MAb 9–13 cross-reacted with multiple components of most of these pollens, and the major cross-reactive components had molecular weights of 29–36 kD. The cross-reactivity between BGP andLol pI, the group I allergen of rye grass pollen, was further evaluated;Lol pI was recognized by MAb 9–13, but not by our MAbs/polyclonal antiserum againstCyn dI, the major allergen of BGP. These results suggest that the epitope recognized by MAb 9–13 is a common (C) epitope shared byLol pI andCyn d Bd68K, 48K, 38K, andCyn dI does not share significant antigenicity withLol pI. In a modified radio-allergosorbent test, IgE antibodies in the serum of BGP-allergic patients reacted mildly with C-epitope-bearing components of both BGP and rye grass pollens, and this binding could be blocked specifically by MAb 9–13. This suggests that in addition to an antigenic cross-reaction, the C epitope can also lead to an allergenic cross-reaction.     

Fibroblasts isolated from human pterygia exhibit transformed cell characteristics

Summary Pterygium is a degenerative corneal limbal process and UV irradiation has been suggested as being a major environmental predisposing factor. The invasive nature of the fibroblasts associated with pterygia raises the question as to whether these cells are transformed. To test this hypothesis, we established fibroblast strains from autologous and heterologous pterygial and conjunctival specimens, respectively, from subjects between 40 to 50 yr of age, and compared their growth characteristics in culture. All pterygial fibroblast strains exhibited a reduced dependence on serum and exogenous growth factors for growth and reached a saturation population density that was threefold higher than conjunctival fibroblasts cultured under the same conditions. In addition, all pterygial fibroblast strains were able to form colonies in soft agar in 5% fetal bovine serum at a 6.0 to 7.5% efficiency. Under the same experimental conditions, none of the conjunctival fibroblast strains were able to grow. The results presented support the conclusion that pterygial fibroblasts have acquired many of the properties of the transformed phenotype.     

Endothelin-Mediated Calcium Response and Inositol 1,4,5-Trisphosphate Release in Neuroblastoma-Glioma Hybrid Cells (NG108-15): Cross Talk with ATP and Bradykinin

Abstract: Addition of endothelins (ETs) to neuroblastomaglioma hybrid cells (NG108-15) induced increases in cytosolic free Ca²⁺ ([Ca²⁺]_i) levels of labeled inositol monophosphates and inositol 1,4,5-trisphosphate [Ins(1,4,5)P₃]. The increases in [^Ca2+]_i elicited by the three ETs (ET-1, ET-2, and ET-3) were transient and did not show a sustained phase. Chelating extracellular Ca²⁺ in the medium by adding excess EGTA decreased the ET-mediated Ca²⁺ response by 40-50%. This result indicates that a substantial portion of the increase in [Ca²⁺]_i was due to influx from an extracellular source. However, the increase in [Ca²⁺]_i was not affected by verapamil or nifedipine (10^?5M). A rank order potency of ET-1 ET-2 ET-3 is shown for the stimulated increase in [Ca²⁺]_i, as well as labeled inositol phosphates, in these cells. ATP (10^?4M) and bradykinin (10^?7M) also induced the increases in [Ca²⁺]_i and Ins(1,4,5)P₃ in NG108-15 cells, albeit to a different extent. When compared at 10^?7M, bradykinin elicited a five- to sixfold higher increase in the level of Ins(1,4,5)P₃, but less than a twofold higher increase in [Ca²⁺]_i than those induced by ET-1. Additive increases in both Ins(1,4,5)P₃ and [Ca²⁺]_i were observed when ET-1, ATP, and bradykinin were added to the cells in different combinations, suggesting that each receptor agonist is responsible for the hydrolysis of a pool of polyphosphoinositide within the membrane. ET-1 exhibited homologous desensitization of the Ca²⁺ response, but partial heterologous desensitization to the Ca²⁺ response elicited by ATP. On the contrary, ET-1 did not desensitize the response elicited by bradykinin, although bradykinin exhibited complete heterologous desensitization to the response elicited by ET-1. Taken together, these results illustrate that, in NG108-15 cells, a considerable amount of receptor cross talk occurs between ET and other receptors that transmit signals through the polyphosphoinositide pathway.     

Relationships among non-Acremonium sp. fungal endophytes in five grass species.

Many cool-season grasses (subfamily Pooideae) possess maternally transmitted fungal symbionts which cause no known pathology and often enhance the ecological fitness and biochemical capabilities of the grass hosts. The most commonly described endophytes are the Acremonium section Albo-lanosa spp. (Acremonium endophytes), which are conidial anamorphs (strictly asexual forms) of Epichloë typhina. Other endophytes which have been noted are a Gliocladium-like fungus in perennial ryegrass (Lolium perenne L.) and a Phialophora-like fungus in tall fescue (Festuca arundinacea Schreb.). Here, we report the identification of additional non-Acremonium sp. endophytes (herein designated p-endophytes) in three more grass species: Festuca gigantea, Festuca arizonica, and Festuca pratensis. In each grass species, the p-endophyte was cosymbiotic with an Acremonium endophyte. Serological analysis and sequence determinations of variable portions of their rRNA genes indicated that the two previously identified non-Acremonium endophytes are closely related to each other and to the newly identified p-endophytes. Therefore, the p-endophytes represent a second group of widely distributed grass symbionts.     

Action of lipolytical enzymes in biphasic organic-aqueous systems: dynamics of the irreversible Michaelis-Menten reaction

Through simple model analysis, the mass action kinetic model for lipolytic enzymes in biphasic aqueous-organic systems can be simplified using the quasi-steady state assumption (or the quasi-equilibrium state assumption) for the adsorbed enzyme E* or the enzyme-substrate complex E*S. Some parameter combinations leading to the above assumptions are derived confirmed by full numerical integration of the whole enzymatic process. The results may be classified into three categories: (1) the quasi-equilibrium state assumption for E*, (2) the quasi-steady state assumption for E*, and (3) the quasi-steady state assumption for E*S. Further simplification for both E* and E*S is also discussed. (c) 1993 Wiley & Sons, Inc.     

Video microscopic analysis of ionophore induced acrosome reactions of lobster (Homarus americanus) sperm

Sperm from the American lobster (Homarus americanus) are normally nonmotile. However, during fertilization, the sperm undergo a calcium-dependent acrosome reaction that propels them forward about 18 μMm. The reaction occurs in two phases, eversion and ejection, which take place too quickly to permit analysis by direct observation. The purposes of this study were to examine the structural changes occurring in sperm during the normal acrosome reaction and to determine the rate of the reaction using video microscopy. The reaction was induced in vitro by ionophore A23187 and recorded using a video system attached to a Nikon Nomarski interference microscope. Videotapes were played back frame by frame (30 frames/sec), and images of reactions from 10 sperm were analyzed. The acrosome reaction, including the eversion of the acrosomal vesicle and ejection of the subacrosomal material and nucleus, can be divided into 4 steps: (1) expansion of the apical cap followed by expansion of the remainder of the acrosomal cylinder; expansion of the cylinder begins at its apical end and proceeds toward its base, (2) eversion of the apical half of the acrosomal vesicle and initial contraction of the apical cap, (3) eversion of the basal half of the acrosomal vesicle, continued contraction of the apical cap, and ejection of the subacrosomal material and nucleus, and (4) final contraction of the apical cap and ejection of the acrosomal filament. During steps 2, 3, and 4, the mean forward movement of sperm is 12.7, 3.9, and 1.1 μMm, respectively. Although the time required to complete the reaction ranged from 0.66 to 5.16 s, most sperm reacted in less than 3. s, and these sperm were considered to have typical rates. For sperm that reacted in less than 3 s, both step 1 and step 4 take about 0.2 s and show little variation among sperm. the time required to complete steps 2 and 3 averaged 0.63 and 0.37 s, respectively. Forward movement of the sperm during the acrosome reaction is caused by eversion of the inner and outer acrosomal material and contraction of the apical cap. The protein(s) responsible for this contraction is not yet known. © 1993 Wiley-Liss, Inc.     

Proper phosphorylation of septin 12 regulates septin 4 and soluble adenylyl cyclase expression to induce sperm capacitation

Septin-based ring complexes maintain the sperm annulus. Defective annular structures are observed in the sperm of Sept12- and Sept4-null mice. In addition, sperm capacitation, a process required for proper fertilization, is inhibited in Sept4-null mice, implying that the sperm annulus might play a role in controlling sperm capacitation. Hence, we analyzed sperm capacitation of sperm obtained from SEPT12 Ser196 phosphomimetic (S196E), phosphorylation-deficient (S196A), and SEPT4-depleted mutant mice. Capacitation was reduced in the sperm of both the Sept12 S196E- and Sept12 S196A-knock-in mice. The protein levels of septins, namely, SEPT4 and SEPT12, were upregulated, and these proteins were concentrated in the sperm annulus during capacitation. Importantly, the expression of soluble adenylyl cyclase (sAC), a key enzyme that initiates capacitation, was upregulated, and sAC was recruited to the sperm annulus following capacitation stimulation. We further found that SEPT12, SEPT4, and sAC formed a complex and colocalized to the sperm annulus. Additionally, sAC expression was reduced and disappeared in the annulus of the SEPT12 S196E- and S196A-mutant mouse sperm. In the sperm of the SEPT4-knockout mice, sAC did not localize to the annulus. Thus, our data demonstrate that SEPT12 phosphorylation status and SEPT4 activity jointly regulate sAC protein levels and annular localization to induce sperm capacitation.