Dependency of growth yield,maintenance and K s-values on the dissolved oxygen concentration in continuous cultures of Azotobacter vinelandii

Azotobacter vinelandii was grown diazotrophically in sucrose-limited chemostat cultures at either 12, 48, 108, 144 or 192 M dissolved oxygen. Steady state protein levels and growth yield coefficients (Y) on sucrose increased with increasing dilution rate (D). Specific rate of sucrose consumption (q) increased in direct proportion to D. Maintenance coefficients (m) extrapolated from plots of q versus D, as well as from plots of 1/Y versus 1/D exhibited a nonlinear relationship to the dissolved oxygen concentration. Constant maximal theoretical growth yield coefficients (Y ^G) of 77.7 g cells per mol of sucrose consumed were extrapolated irrespective of differences in ambient oxygen concentration. For comparison, glucose-, as well as acetate-limited cultures were grown at 108 M oxygen. Fairly identical m- and Y ^G-values, when based on mol of substrate-carbon with glucose and sucrose grown cells, indicated that both substrates were used with the same efficiency. However, acetate-limited cultures showed significantly lower m- and, at comparable, D, higher Y-values than cultures limited by either sucrose or glucose. Substrate concentrations (K _s) required for half-maximal growth rates on sucrose were not constant, they increased when the ambient oxygen concentration was raised and, at a given oxygen concentration, when D was decreased. Since biomass levels varied in linear proportion to K _s these results are interpreted in terms of variable substrate uptake activity of the culture.Abbreviations D dilution rate - K _s substrate concentration required for half maximal growth rate - m maintenance coefficient - q specific rate of substrate consumption - Y growth yield coefficient - Y ^G maximum theoretical growth yield coefficient     

Stimulation of Inositol Incorporation into Lipids of PC 12 Cells by Nerve Growth Factor and Bradykinin

The effects of bradykinin (BK) and lithium on the phosphatidylinositol cycle were examined in PC12 cells cultured for 20 h in the presence [PC12(+)] or in the absence [PC12(-)] of nerve growth factor (NGF). BK (1 microM) induced a small stimulation of the incorporation of myo-[2-3H]inositol into the lipids of PC12(-) cells and a three- to fourfold stimulation of such incorporation into the lipids of PC12 (+) cells. About 15 h of incubation with NGF and greater than 10 min of incubation with BK were needed for maximal stimulation of inositol incorporation by BK. In the presence of 25 mM LiCl, BK stimulated the inositol monophosphate levels nine-fold in PC12 (-) and 30-fold in PC12 (+) cells. After incubation for 20 h with NGF, an increased binding of [3H]BK to the PC12 (+) cells was observed at 4 degrees C. Exposure of the cells for 30 min to 25 mM LiCl enhanced the effect of BK on the inositol incorporation into total inositol lipids, especially in PC12(+) cells. In these cells, LiCl in the presence of BK also increased several-fold the intracellular levels of inositol bisphosphate and inositol trisphosphate.     

The effectiveness of some Indonesian strains of Rhizobium on four tropical legumes

Nodules were collected from 14 legume species from the Indonesian Islands of South Sulawesi, Java and Sumatra. Their rhizobia were isolated and growth characteristics, nodulation ability and nitrogen fixing effectiveness were assessed against recommended commercially available Australian strains. The test legumes wereMacroptilium atropurpureum Urb. cv. Siratro,Vigna unguiculata (L.) Walp. cv Eureka,Centrosema pubescens Benth cv. Belalto andDesmodium heterocarpon (L) DC. A significant portion of the native rhizobial isolates were of the fast growing type. Dry matter and total nitrogen production forM. atropurpureum andV. unguiculata was highest when inoculated with native strains while the commerical strains produced superior dry matter production forC. pubescens andD. heterocarpon. However the total nitrogen production of native and commercial strains was not significantly different for the latter two legumes. The study indicated that a potential exists for developing inocula from local Rhizobium strains.     

Human recombinant insulin-like growth factor I. I. Development of a serum-free medium for clonal density assay of growth factors using balb/c 3T3 mouse embryo fibroblasts

Summary A serum-free clonal density growth assay was developed for the quantification of the biological activity of human recombinant insulin-like growth factor I (IGF-I). The assay measures IGF-I stimulated growth of Balb/c 3T3 cells cultured over 4 d on poly-d-lysine-coated plastic surfaces in a serum-free medium formulation composed of a 1∶1 (vol/vol) mixture of Ham's F12 and Dulbecco's modified Eagle's media, supplemented with 3.0 ng/ml bovine basic fibroblast growth factor (bFGF), 10 μg/ml human transferrin, 100 μg/ml ovalbumin, and 1.0 μM dexamethanose. Low-temperature trypsinization of serum-supplemented stock cultures combined with the use of poly-d-lysine-coated plates made it unnecessary to use serum or fibronectin to promote cell attachment and survival. Serum-free growth conditions were optimized with respect to the concentrations of the supplements. Addition of IGF-I resulted in 3.5-fold more cells than control cultures without IGF-I after 4 d. Deletion of bFGF resulted in no IGF-I stimulation of growth. The concentrations of various preparations of IGF-I required to achieve one-half maximal stimulation of cell number (ED₅₀), ranged between 1.25 and 4.7 ng/ml. In parallel assays, IGF-I was 6.6 times more potent than human recombinant insulin-like growth factor II and 32 times more potent than insulin. When cells were seeded into medium containing IGF-I, transferrin, ovalbumin, and dexamethasone but no bFGF, growth was minimal. Dose-response addition of bFGF showed an ED₅₀, of 0.9 ng/ml. The methods reported are useful to monitor the biological potency of recombinant and natural-source growth factors as well as providing a new means of studying the multiple growth factor requirements of Balb/c 3T3 cells in cultures. This work was supported by a contract from IMCERA Bioproducts, Inc.     

Reorientation of Microfibrils and Microtubules at the Outer Epidermal Wall of Maize Coleoptiles During Auxin-Mediated Growth

Auxin-mediated elongation growth of isolated subapical coleoptile segments of maize (Zea mays L.) is controlled by the extensibility of the outer cell wall of the outer epidermis (Kutschera et al., 1987). Here we investigate the hypothesis that auxin controls the extensibility of this wall by changing the orientation of newly deposited microfibrils through a corresponding change in the orientation of cortical microtubules. On the basis of electron micrographs it is shown that cessation of growth after removal of the endogenous source of auxin is correlated with a relative increase of longitudinally orientated microfibrils and microtubules at the inner wall surface. Conversely, reinduction of growth by exogenous auxin is correlated with a relative increase of transversely orientated microfibrils and microtubules at the inner wall surface. These changes can be detected 30–60 min after the removal and addition of auxin, respectively. The functional significance of directional changes of newly desposited wall microfibrils for the control of elongation growth is discussed.     

Effect of TSH in human thyroid cells: evidence for both mitogenic and antimitogenic effects.

The well-known mitogenic effects of TSH observed in vivo on the thyroid are not always reproducible of human thyroid cells in vitro where conflicting results have been obtained. In order to clarify this issue, we have used primary cultures of human thyroid cells obtained from normal tissue and maintained in serum-free medium for several days. In this in vitro model we have studied the effect of TSH on growth by measuring three different parameters: [3H]-thymidine incorporation, cell counts, and DNA measurement. Monolayer cultures were plated at both low and high cell density (2 x 10(4) and 8 x 10(4) cells/25 mm well, respectively). Although at either cell density cultures were equally able to functionally respond to TSH in terms of cAMP accumulation a significant growth response to TSH was observed only in low density cultures. In high density cultures TSH had an antimitogenic effect. Moreover, TSH potentiated the mitogenic effect of insulin only in low density cultures. In contrast to TSH, FCS induced a similar proliferative response at both high and low cell density. Following TSH stimulation, cAMP content was always increased, paralleling the effect of growth in low density but not in high density cultures. The cAMP analogues dibutyryl-cAMP and 8-bromo-cAMP, as well as cholera toxin and forskolin, did not mimic the mitogenic effect of TSH but had an antiproliferative effect. In addition, these agents blunted the proliferative effect of insulin. These data suggest that in thyroid cells TSH is able to elicit both a mitogenic and an antimitogenic effect depending on the environmental conditions such as cell density.(ABSTRACT TRUNCATED AT 250 WORDS)     

Stochastic simulation of clonal growth in the tall goldenrod,Solidago altissima

Summary As clonal plants grow they move through space. The movement patterns that result can be complex and difficult to interpret without the aid of models. We developed a stochastic simulation model of clonal growth in the tall goldenrod, Solidago altissima. Our model was calibrated with field data on the clonal expansion of both seedlings and established clones, and model assumptions were verified by statistical analyses.When simulations were based on empirical distributions with long rhizome lengths, there was greater dispersal, less leaf overlap, and less spatial aggregation than when simulations were based on distributions with comparatively short rhizome lengths. For the field data that we utilized, variation in rhizome lengths had a greater effect than variation for either branching angles or rhizome initiation points (see text). We also found that observed patterns of clonal growth in S. altissima did not cause the formation of fairy rings. However, simulations with an artificial distribution of branching angles demonstrate that fairy rings can result solely from a plant's clonal morphology.Stochastic simulation models that incorporated variation in rhizome lengths, branching angles, and rhizome initiation points produced greater dispersal and less leaf overlap than deterministic models. Thus, variation for clonal growth parameters may increase the efficiency of substrate exploration by increasing the area covered and by decreasing the potential for intraclonal competition. We also demonstrated that ramet displacements were slightly, but consistently lower in stochastic simulation models than in random-walk models. This difference was due to the incorporation of details on rhizome bud initiation into stochastic simulation models, but not random-walk models. We discuss the advantages and disadvantages of deterministic, stochastic simulation, and random-walk models of clonal growth.     

Continuous shoot growth monitoring in hydroponics

A weighing apparatus for automatic recording of fresh weight of shoots of spinach plants ( Spinacia oleracea L., cv. Subito) growing in nutrient solution is described. The system was tested for 17 days in a controlled environment and enabled the determination of the relative growth rate (RGR) of the shoot fresh weight. Results from three consecutive growth experiments demonstrated diurnal fluctuations in the relative growth rate of the shoot fresh weight. In general, relative growth rates were between 0.32 and 0.36 day⁻¹ 16 days after sowing and decreased to between 0.11 and 0.18 day⁻¹ during the 12 following days. The variance between three replicate growth curves was compared with the variance of a growth function fitted through destructively obtained spinach shoot weight data.     

Inhibition of auxin-induced elongation and xyloglucan breakdown in azuki bean epicotyl segments by fucose-binding lectins

Auxin-induced elongation of epicotyl segments of azuki bean ( Vigna angularis Ohwi and Ohashi cv. Takara) was suppressed by fucose-binding lectins from Tetragonolobus purpureus Moench and Ulex europaeus L. These lectins also inhibited auxin-induced cell wall loosening (decrease in the minimum stress-relaxation time of the cell walls) of segments. Auxin caused a decrease in molecular mass of xyloglucans extracted with 24% KOH from the cell walls. The lectins inhibited auxin-induced changes in molecular mass of the xyloglucans. The autolytic release of xylose-containing products from the pectinase-treated cell walls was also suppressed by the lectins. Fucose-binding lectins pretreated with fucose exhibited little or no inhibitory effect on auxin-induced elongation, cell wall loosning, or breakdown of xyloglucans. These results support the view that the breakdown of xyloglucans is involved in the cell wall loosening responsible for auxin-induced elongation in dicotyledons.     

Influence of mefluidide on growth,development, and cell wall digestibility of sorghum

Application of mefluidide (N-[2,4-dimethyl-5-([(trifluoromethyl)sulfonyl]amino) phenyl]acetamide) inhibits plant development in perennial grasses. This study examined the effect of mefluidide on the morphological development and digestibility of sorghum. In the greenhouse, 5.9 × 10^–5 g active ingredient (a.i.) plant^–1 applied at the seedling, eight-leaf and boot stages reduced mean plant height 70%, 59%, and 2%, respectively. Heights were also reduced 14%, 15% and 35% by 5.9 × 10^–8, 5.9 × 10^–7 and 5.9 × 10^–6 gram a.i. plant^–1 applied at the eight-leaf stage. Field application of 0.26 or 0.52 kg ha^–1 mefluidide at either the eight-leaf or flagleaf stage reduced mean plant height of all cultivars. Basal tiller numbers increased 319% 28 d, and dry matter production was reduced 65% 42 d following mefluidide application at the eight-leaf stage. Treated stems were 34% higher and treated leaves were 7% higher in cellulase dry matter digestibility than control plants following mefluidide application at the eight-leaf stage. These results indicate that mefluidide application to vegetative stages in sorghum may enhance the forage value of the plants while it inhibits normal plant growth.