Cultivar differences in boron uptake and distribution in celery (Apium graveolens), tomato (Lycopersicon esculentum) and wheat (Triticum aestivum)

Species and cultivar differences in boron (B) uptake at low B availability and tolerance to high external B are known for many species but mechanisms explaining such differences remain obscure. Here we contrast B uptake and distribution between two cultivars of tomato and celery that differ significantly in their susceptibility to B deficiency. The celery cultivar S48-54-1 and tomato cultivar Brittle are known to be more susceptible to B deficiency (inefficient) than the closely related cultivars Emerson Pascal and Rutgers (efficient), respectively. B uptake and distribution was also compared in two wheat lines differing in tolerance to B excess (Chinese Spring, sensitive and Lophopyrum Amphiploid, tolerant). Results showed that there is no significant difference in either the specific uptake rate (I_M) of ¹⁰B or the relative growth rate (RGR) between the efficient cultivar (Emerson Pascal) and less efficient cultivar (S48-54-1) of celery. However, the distribution of ¹⁰B among plant organs (leaves, stems and roots) of Emerson Pascal was different from S48-54-1. In Emerson Pascal more than 63% of accumulated B was present in the shoots while in S48-54-1 only 45% of accumulated B was present in shoots. In tomato plants, in addition to differences in B distribution among plant organs between the efficient (Rutgers) and less efficient (Brittle) cultivars, the specific uptake rate of ¹⁰B was significantly higher in the efficient cultivar. In wheat, the tolerant line (Amphiploid) took up less B than the less tolerant cultivar (Chinese Spring), and the pattern of B distribution among plant organs was different with a greater percentage of B found in roots of Chinese Spring compared to Amphiploid. Differences in sensitivity to B deficiency and excess amongst cultivars and species were a consequence of either reduced B uptake as in wheat (Amphiploid), a restriction in B translocation from roots to shoot as in celery (S48-54-1) or a combination of both process as in tomato (Brittle).     

Sodium-dependent and -independent Choline Uptake by Type II Epithelial Cells from Rat Lung

The uptake of ³H-labeled choline by a suspension of isolated type II epithelial cells from rat lung has been studied in a Ringer medium. Uptake was linear for 4 min at both 0.1 μm and 5.0 μm medium choline; at 5 μm, only 10% of the label was recovered in a lipid fraction. Further experiments were conducted at the low concentration (0.1 μm), permitting characterization of the properties of high-affinity systems. Three fractions of choline uptake were detected: (i) a sodium-dependent system that was totally inhibited by hemicholinium-3 (HC-3); (ii) a sodium-independent uptake, when Na⁺ was replaced by Li⁺, K⁺ or Mg²⁺, inhibited by HC-3; (iii) a residual portion persisting in the absence of Na⁺ and unaffected by HC-3. Choline uptake was sigmoidally related to the medium Na⁺ concentration. Kinetic properties of the uptake of 0.1 μm ³H-choline in the presence and absence of medium Na⁺ were examined in two ways. (a) Inhibition by increasing concentrations of unlabeled choline (0.5–100 μm) was consistent with the presence of two Michaelis-Menten-type systems in the presence of Na⁺; a Na⁺-dependent portion (a mean of 0.52 of the total) had a K _m for choline of 1.5 μm while K _m in the absence of Na⁺ (Li⁺ substituting) was 18.6 μm. (b) Inhibition by HC-3 (0.3–300 μm) gave K_i values of 1.7 μm and 5.0 μm HC-3 for the Na⁺-dependent and -independent fractions. The apparent K _m of the Na⁺-dependent uptake is lower than that reported previously for lung-derived cells and is in the range of the K _m values reported for high-affinity, Na⁺-dependent choline uptake by neuronal cells. Received: 18 February 1997/Revised: 7 December 1997     

Effects of a localized supply of nitrate on NO3 - uptake rate and growth of roots in Lolium multiflorum Lam.

Roots of higher plants are usually exposed to varying spatial and temporal changes in concentrations of soil mineral nitrogen. A split root system was used to see how Lolium multiflorum Lam. roots adapt to such variations to cope with their N requirements. Plants were grown in hydroponic culture with their root system split in two spatially separated compartments allowing them to be fed with or without KNO₃. Net NO₃ ^- uptake, ¹⁵NO₃ ^- influx and root growth were studied in relation to time. Within less than 24 h following deprivation of KNO₃ to half the roots, the influx in NO₃ ^- fed roots was observed to increase (about 200% of the influx measured in plant uniformly NO₃ ^- supplied control plant) thereby compensating the whole plant for the lack of uptake by the N deprived roots. Due to the large NO₃ ^- concentrations in the roots, the NO₃ ^- efflux was also increased so that the net uptake rate increased only slightly (35% maximum) compared with the values obtained for control plants uniformly supplied with NO₃ ^-. This increase in net NO₃ ^- uptake rate was not sufficient to compensate the deficit in N uptake rate of the NO₃ ^- deprived split root in the short term. Over a longer period (>1 wk), root growth of the part of the root system locally supplied with NO₃ ^- was stimulated. An increase in root growth was mainly responsable for the greater uptake of nitrate in Lolium multiflorum so that it was able to fully compensate the deficit in N uptake rate of the NO₃ ^- deprived split root.     

Phytotoxicity of hydrogen fluoride and fluoroborate and their uptake from solution culture by Lycopersicon esculentum and Avena sativa

The aims of this paper were to determine the phytoavailability and phytotoxicity of hydrogen fluoride (HF) and fluoroborate (BF ₄ ^- ) in solution when exposed to the root of the plant. As fluoroborate undergoes a slow hydrolysis to F and borate ions, the stability of BF ₄ ^- under solution culture conditions was determined. Fluoroborate was found to have a zero order rate constant of 0.0136 and took approximately 72 days to hydrolyse completely.Tomato (Lycopersicon esculentum) and oat (Avena sativa) plants were grown in dilute nutrient solutions which contained a range of activities of HF and BF ₄ ^- . Dry matter production of both tomato and oat plants grown in nutrient solutions were found to be restricted by increased activity of HF and BF ₄ ^- in solution. Tomatoes were more sensitive to HF and BF ₄ ^- than oats. Limitations to dry matter production coincided with increased uptake of F for F concentrations in tissue of both tomatoes and oats. Fluoride uptake of both HF and BF by tomatoes and oats was orders of magnitude higher compared to similar activities of other ionic species of F reported in previous studies. Possible mechanisms of uptake are discussed.     

Characterization of tissue tolerance to iron by molecular markers in different lines of rice

Ferrous iron (Fe2+) toxicity is a major disorder in rice prod uction on acid, flooded soils. Rice ( Oryza sativa L.) genotypes differ widely in tolerance to Fe2+ toxicity, which makes it possible to bre ed more tolerant rice varieties. Tissue tolerance to higher iron concentrations in plants has been considered to be important to Fe2+ tolerance in ri ce. Segregation for leaf bronzing and growth reduction due to Fe2+ to xicity was observed in a doubled haploid (DH) population with 135 lines derived from a Fe2+ tolerant japonica variety, Azucena, and a sensitive indic a variety, IR64 in a solution culture with Fe2+ stress condition at a Fe2+concentration of 250 mg L-1 at pH 4.5. To better understand the mechanism of tissue tolerance, Leaf Bronzing Index (LBI), total iron concentration in shoot tissue and the enzymes of ascorbate peroxidase (AP), dehydroascorbate reductase (DR) and glutathione reductase (GR), and concentrations of ascorbate (AS) and dehydroascorbate (DHA), which are involved in the ascorbate-specific H2O2-scavenging system, were determined for the population under Fe2+ stress. A non-normal distribution of LBI was found. About 38 lines showed no bronzing, while the lines with non-zero LBI values ranged from 0.05 to 0.85 and showed a normal distribution. The other parameters measured showed normal distribution. The total iron concentrations in the 38 tolerant lines ranged from 1.76 mg Fe g-1 to 4.12 mg Fe g-1 and was in a similar range as in the non-tolerant genotype (2.04 – 4.55 mg Fe g-1). No significant differences in the activities of the enzymes were found between the parents under normal culture, but remarkably higher Fe2+ induced enzyme activities were observed in the tolerant parent. AS was similar between the parents under both normal and Fe2+ stress, but its concentration was sharply decreased under Fe2+ stress. DHA was much lower in the tolerant parent than in the sensitive parent under Fe2+ stress. Single locus analysis and interval mapping analysis based on 175 molecular markers revealed that the interval flanked by RG345 and RZ19 on chromosome one was an important location of gene(s) for Fe2+ tolerance. The ascorbate-specific system for scavenging Fe2+-mediated oxygen free radicals may be an important mechanism for tissue Fe2+ tolerance. A gene locus with relative small effect on root ability to exclude Fe2+ was also detected.     

Effect of phosphorus supply on the formation and function of proteoid roots of white lupin (Lupinus albus L.)

We investigated (1) the effect of constant and altered inorganic phosphate (P_i) supply (1–100 mmol m^–3) on proteoid root production by white lupin ( Lupinus albus L.); and (2) the variation in citrate efflux, enzyme activity and phosphate uptake along the proteoid root axis in solution culture. Proteoid root formation was greatest at P_i solution concentrations of 1–10 mmol m^–3 and was suppressed at 25 mmol m^–3 P_i and higher. Except at 1 mmol m^–3 P_i, the formation of proteoid roots did not affect plant dry matter yields or shoot to root dry matter ratios, indicating that proteoid roots can form under conditions of adequate P supply and not at the expense of dry matter production. Plants with over 50% of the root system as proteoid roots had tissue P concentrations considered adequate for maximum growth, providing additional evidence that proteoid roots can form on P-sufficient plants. There was an inverse relationship between the P_i concentration in the youngest mature leaf and proteoid root formation. Citrate efflux and the activities of enzymes associated with citric acid synthesis (phosphoenolpyruvate carboxylase and malate dehydrogenase) varied along the proteoid root axis, being greatest in young proteoid rootlets of the 1–3 cm region from the root tip. Citrate release from the 0–1 and 5–9 cm regions of the proteoid root was only 7% (per unit root length) of that from the 1–3 cm segment. Electrical potential and ³²P_i uptake measurements showed that P_i uptake was more uniform along the proteoid root than citrate efflux.     

Rate-limiting mass transfer in immunosorbents: characterisation of the adsorption of paraquat-protein conjugates to anti-paraquat Sepharose 4B

A series of paraquat-protein conjugates of different molecular size has been prepared by the coupling of paraquat hexanoate to the proteins lysozyme, ovalbumin, bovine serum albumin. The characteristics of the adsorption of these conjugates to an immunosorbent consisting of monoclonal anti-paraquat antibodies covalently immobilised to Sepharose 4B have been determined. Equilibrium adsorption isotherms were found to obey the Langmuir equation and indicated that 80% or more of the antibody binding sites were accessible to the conjugates. The rates of mass transfer of the conjugates to their adsorption sites on the immobilised antibodies was well described by a model in which mass transfer is controlled by transfer across the external film and diffusion within the porous adsorbent bead. The effective diffusivities of the conjugates within the immunosorbent were measured and has allowed the effect of the size of the adsorbing molecule on the rate of adsorption to be considered. The amount of paraquat that could be adsorbed and the rates of adsorption decreased as the size of the protein to which it is conjugated increased. The diffusivity of the conjugates within the pores of the adsorbent is reduced between two and five times compared to their diffusivities in free solution. The reduction is greater for the larger proteins and the variations of the effective diffusivities and the pore diffusivities with the molecular weight of the conjugate can be well described with simple correlations.     

Alginate beads as an affinity material for alpha amylases

Calcium-alginate beads were found to bind a variety of enzymes in a nonspecific fashion. However, alpha amylases from porcine pancreas, Bacillus subtilis (BAN 240L) and wheat germ bound at a significant level and B. subtilis and wheat germ amylases could be eluted with 1M maltose. The wheat germ alpha amylase could be purified 45 fold with 70% recovery. The SDS - PAGE pattern showed significant purification by this single step strategy.     

Pharmacological characterization of the effects of taurine on calcium uptake in the rat retina

Summary Taurine is known to increase ATP-dependent calcium ion (Ca²⁺) uptake in retinal membrane preparations and in isolated rod outer segments (ROS) under low calcium conditions (10M) (Pasantes-Morales and Ordóñez, 1982; Lombardini, 1991). In this report, ATP-dependent Ca²⁺ uptake in retinal membrane preparations was found to be inhibited by 5M cadmium (Cd²⁺), suggesting the involvement of cation channel activation. The activation of cGMP-gated cation channels, which are found in the ROS, is a crucial step in the phototransduction process. An inhibitor of cGMP-gated channels, LY83583, was found to inhibit taurine-stimulated ATP-dependent Ca²⁺ uptake but had no effect on ATP-dependent Ca²⁺ uptake in the absence of taurine, indicating that taurine may be increasing ATP-dependent Ca²⁺ uptake through a mechanism of action involving the opening of cGMP-gated channels. The activation of cGMP-gated channels with dibutyryl-cGMP and with phosphodiesterase inhibition using zaprinast caused an increase in ATP-dependent Ca²⁺ uptake in isolated ROS, but not in taurine-stimulated ATP-dependent Ca²⁺ uptake. LY83583 had the same effects in isolated ROS as in retinal membrane preparations. Another inhibitor of cGMP-gated channels, Rp-8-Br-PET-cGMPS, produced the same pattern of inhibition in isolated ROS as LY83583. Thus, there appears to be a causal link between taurine and the activation of the cGMP-gated channels in the ROS under conditions of low calcium concentration, a connection that suggests an important role for taurine in the visual signalling function of the retina.