Relative growth rate, biomass allocation pattern and water use efficiency of three wheat cultivars during early ontogeny as dependent on water availability

We have investigated the water use efficiency of whole plants and selected leaves and allocation patterns of three wheat cultivars (Mexipak, Nesser and Katya) to explore how variation in these traits can contribute to the ability to grow in dry environments. The cultivars exhibited considerable differences in biomass allocation and water use efficiency. Cultivars with higher growth rates of roots and higher proportions of biomass in roots (Nesser and Katya) also had higher leaf growth rates, higher proportions of their biomass as leaves and higher leaf area ratios. These same cultivars had lower rates of transpiration per unit leaf area or unit root weight and higher biomass production per unit water use. They also had higher ratios of photosynthesis to transpiration, and lower ratios of intercellular to external CO₂ partial pressure. The latter resulted from large differences in stomatal conductance associated with relatively small differences in rates of photosynthesis. There was little variation between cultivars in response to drought, and differences in allocation pattern and plant water use efficiency between cultivars as found under well-watered conditions persisted under dry conditions. At the end of the non-watered treatment, relative growth rates and transpiration rates decreased to similar values for all cultivars. High ratios of photosynthesis to transpiration, and accordingly high biomass production per unit of transpiration, is regarded as a favourable trait for dry environments, since more efficient use of water postpones the decrease in plant water status.     

14-3-3 Protein homologues play a central role in the fusicoccin signal transduction pathway

The plasma membrane located fusicoccin binding protein (FCBP) is an essential element in the fusicoccin (FC) signal transduction pathway. We obtained primary sequence information for the 31 kD subunit of the FCBP. These sequences showed that the FCBP is homologous to members of the 14-3-3 protein family. Both the 31 and 30 kD subunits cross-react with 14-3-3 antibodies. In native form the FCBP occurs as a dimer, but it is also part of a complex with higher molecular mass. The monomeric forms of the FCBP (the 30 and 31 kD subunits) do not have ³H-FC binding activity. We discuss how the FCBP, as a member of the 14-3-3 protein family, may be able to bind FC and how the FC-signal is transduced to the effector protein, the H⁺-ATPase.     

Continuous monitoring of lactate during exercise in humans using subcutaneous and transcutaneous microdialysis

We have evaluated the possibility of monitoring the plasma lactate concentration in human volunteers during cycle ergometer exercise using subcutaneous and transcutaneous microdialysis. In transcutaneous microdialysis, the relative increase in dialysate lactate concentration exceeded that of plasma lactate concentration by a factor of 6 during exercise due to exercise-induced lactate secretion in sweat. During exercise the subcutaneous microdialysis dialysate lactate concentration underestimated the plasma lactate concentration possibly due to diffusion limitation or adipose tissue lactate production. While it was demonstrated that microdialysis can be used for on-line lactate monitoring, neither subcutaneous nor transcutaneous dialysate lactate concentration were linearly related to the plasma lactate concentration during exercise, and it was found therefore that it was not possible to monitor directly plasma lactate concentration during exercise.     

Properties of the K+ inward rectifier in the plasma membrane of xylem parenchyma cells from barley roots: Effects of TEA+, Ca2+, Ba2+ and La3+

Xylem parenchyma cells are situated around the (apoplastic) xylem vessels and are involved in the control of the composition of the xylem sap by exporting and resorbing solutes. We investigated properties of the K⁺ inward rectifier in the plasma membrane of these cells by performing patch clamp experiments on protoplasts in the whole-cell configuration. Inward currents were sensitive to the K⁺ channel blocker TEA⁺ at a high concentration (20 mm). Barium, another classical K⁺ channel blocker, inhibited K⁺ currents with a K _i of about 1.3 mm. In contrast to guard cells, the cytosolic Ca²⁺ level proved to be ineffective in regulating the K⁺ conductance at hyperpolarization. External Ca²⁺ blocked currents weakly in a voltage-dependent manner. From instantaneous current-voltage curves, we identified a binding site in the channel pore with an electrical distance of about 0.2 to 0.5. Lanthanum ions reduced the inward current in a voltage-dependent manner and simultaneously displaced the voltage at which half of the channels are in the open state to more positive values. This finding was interpreted as resulting from a sum of two molecular effects, an interaction with the mouth of the channel that causes a reduction of current, and a binding to the voltage sensor, leading to a shielding of surface charges and, subsequently, a modulation of channel gating.A comparison between the K⁺ inward rectifier in xylem parenchyma cells, guard cells and KAT1 from Arabidopsis leads to the conclusion that these rectifiers form subtypes within one class of ion channels. The ineffectiveness of Ca²⁺ to control K⁺ influx in xylem parenchyma cells is interpreted in physiological terms.     

Metabolic shift analysis at high cell densities

Abstract: In high cell density cultures it is virtually inevitable that the environment to which the cells are exposed is heterogeneous. Thus, with suspended cultures, individual cells are subject to temporal changes in their environment whereas with aggregated or immobilized cells, the culture can be considered as being formed by a number of subpopulations, each with its own environmental characteristics. In addition, in a high cell density environment, high concentrations of end products may negatively influence the growth rate. This may result in the selection of organisms with an altered metabolic behaviour or with a decreased sensitivity to the adverse effects of the product. We discuss the consequences of this heterogeneity with regard to carbon source metabolism in view of the ability of many bacterial species to adapt to environmental conditions. Selection of variant organisms was found to occur with Clostridium butyricum when grown for a prolonged time in a medium containing approx. I-50 mM glucose. In contrast to the original strain, these variants could sustain a high maximal growth rate in the presence of butyric acid. In addition, they had acquired the capacity to spontaneously form aggregates and were able to carry out a completely solventogenic fermentation. Heterogeneous metabolic activity in aggregated cells is demonstrated with cultures of Lactobacillus laevolacticus , an aggregateforming lactic acid bacterium that converts glucose completely to o-lactate. By using microelectrodes, we show that the fraction of metabolically active cells decreases with increasing aggregate size: in larger aggregates steep pH gradients occur with the effect that only the outer layer of the aggregate is metabolically active, i.e. contributes to lactic acid formation, whereas with smaller aggregates all cells remain active. As a result, the net specific lactic acid production rate of the population as a whole is not invariably increased with increased aggregate size.     

The effect of acetylene on N transformations in an acid oak-beech soil

The effectiveness of acetylene (C₂H₂) as inhibitor of nitrification was studied in relation to the decomposition of C₂H₂. This was done by examining the effects of single and multiple additions of different C₂H₂ concentrations (10, 100, 1000 Pa) on mineral N and NO₃ ^–-N production in samples of the organic (FH) and upper mineral (Ah) layer of an acid oak-beech forest soil. The decomposition of C₂H₂ was much faster in Ah samples than in FH samples. A single addition of 10 Pa C₂H₂ was not sufficient for complete inhibition of nitrification in the Ah samples. Nitrification was blocked completely by all other C₂H₂ treatments in both FH and Ah samples. Addition of C₂H₂ decreased net mineral N production in Ah samples but not in FH samples. Addition of carboxymethyl-cellulose and chitin to Ah soil had no affect on the rate of decomposition of C₂H₂. Chitin had a negative effect on net NO₃ ^–-N production.     

Immune network behavior—II. From oscillations to chaos and stationary states

Two types of behavior have been previously reported in models of immune networks. The typical behavior of simple models, which involve B cells only, is stationary behavior involving several steady states. Finite amplitude perturbations may cause the model to switch between different equilibria. The typical behavior of more realistic models, which involve both B cells and antibody, consists of autonomous oscillations and/or chaos. While stationary behavior leads to easy interpretations in terms of idiotypic memory, oscillatory behavior seems to be in better agreement with experimental data obtained in unimmunized animals. Here we study a series of models of the idiotypic interaction between two B cell clones. The models differ with respect to the incorporation of antibodies, B cell maturation and compartmentalization. The most complicated model in the series has two realistic parameter regimes in which the behavior is respectively stationary and chaotic. The stability of the equilibrium states and the structure and interactions of the stable and unstable manifolds of the saddle-type equilibria turn out to be factors influencing the model's behavior. Whether or not the model is able to attain any form of sustained oscillatory behavior, i.e. limit cycles or chaos, seems to be determined by (global) bifurcations involving the stable and unstable manifolds of the equilibrium states. We attempt to determine whether such behavior should be expected to be attained from reasonable initial conditions by incorporating an immune response to an antigen in the model. A comparison of the behavior of the model with experimental data from the literature provides suggestions for the parameter regime in which the immune system is operating.     

Quantitative Determination of the Spatial Distribution of Nitrosomonas europaea and Nitrobacter agilis Cells Immobilized in κ-Carrageenan Gel Beads by a Specific Fluorescent-Antibody Labelling Technique

A novel technique, combining labelling and stereological methods, for the determination of spatial distribution of two microorganisms in a biofilm is presented. Cells of Nitrosomonas europaea (ATCC 19718) and Nitrobacter agilis (ATCC 14123) were homogeneously distributed in a κ-carrageenan gel during immobilization and allowed to grow out to colonies. The gel beads were sliced in thin cross sections after fixation and embedding. A two-step labelling method resulted in green fluorescent colonies of either N. europaea or N. agilis in the respective cross sections. The positions and surface areas of the colonies of each species were determined, and from that a biomass volume distribution for N. europaea and N. agilis in κ-carrageenan gel beads was estimated. This technique will be useful for the validation of biofilm models, which predict such biomass distributions.