Henri Laudelout

Effect of aluminium on the mineral nutrition of rice

A study of the effect of increasing aluminium concentration in a dilute nutrient solution on various aspects of the mineral nutrient uptake by the rice plant has shown that aluminium exerts a stimulation on dry matter production and nutrient uptake until a concentration threshold was reached. The value of this threshold was influenced by nutrient solution composition and cultivar. Its location could be calculated by adjusting to the experimental points a rate law from enzyme kinetics on substrate inhibition curve. On the other hand, total uptake of aluminium and its concentration in the tops was a monotonic function of aluminium concentration in the nutrient solution, the effect of which was greatly enhanced by increased phosphate concentration. A sensitive cultivar accumulated more aluminium than a resistant one.The effect of phosphate on the alleviation of aluminium toxicity was slight in the range of concentration studied.Nitrogen uptake either as ammonium or nitrate nitrogen was clearly influenced by aluminium concentration when its instantaneous value was measured by the technique of the continuously flowing culture solution. The ammonium uptake rate of two cultivars different in sensitivity to aluminium was such that the sensitive variety took up less ammonium and acidified less the culture solution flowing through the root sysstem with a residence time of a few hours.Minor elements concentration in the tops of the rice plants did not seem to be greatly influenced by aluminium with the notable exception of manganese, the uptake of which was clearly depressed by increasing aluminium concentration.Attempts were made at using the speciation of the nutrient solutions with or without aluminium complexation by fluoride in order to rank the various ionic forms of aluminium according to their toxicity. It seems that the well-known result of primary toxicity due to the free Al-ion is also true for rice but that some toxicity is associated with the AlSO4-ion.

Calorimetric measurement of free energy utilization by Nitrosomonas and Nitrobacter

SummaryCalorimetric estimates of the utilization efficiency of the free-energy derived from substrate oxidation by cell suspensions of two nitrifying bacteria, Nitrosomonas and Nitrobacter, provided two ranges of values: 11 to 27% and 15 to 51%, respectively. About 15 to 30% of the utilized free-energy is used for driving endergonic reactions other than CO2 fixation, probably the synthesis of polyphosphates.The molar heat of substrate oxidation does not seem to be influenced by the age of cells harvested during growth or by the length of the incubation period during which cells have been kept in a buffer suspension in a starved condition. The loss of respiratory activity measured either by oxygen uptake or heat evolution in the presence of the specific substrate, nitrite or ammonium, decreases according to kinetics which are influenced by the aerobiosis of the suspension. The viability of the starved cells decreases in a way which is similar to that of the respiratory activity. It seemed impossible to obtain cells which had lost their viability but kept the ability to oxidize their substrate.Two inhibitors of the respiratory chain, quinacrine and cyanide, are without effect on the molar heat of substrate oxidation and consequently on the free-energy utilization efficiency. 2.4 dinitrophenol did decrease the rate of heat evolution during substrate oxidation at concentrations at which the rate of oxygen uptake was not depressed, with the consequences that free-energy efficiency was apparently increased.

Movement of Nitrite Through a Loess Soil

Abstract Columns of an undisturbed loess soil were used for a study of the movement of tritiated water, chloride and nitrate, in order to investigate the properties of the upper one meter layer of the soil with respect to the transfer of nitrate towards the aquifer. Statistics of the values obtained regarding the Peclet number Pe and the mobile fraction β in the water filled porosity showed that spatial variation of the main transfer properties was within the limits of commonly measured soil properties. The agreement between the calculated and experimental solute profile was not as good as that which was observed for the effluent. The recovery of chloride was 99% and of nitrate 115%, a difference which could have been caused by some mineralization of the organic matter in the column. In all breakthrough curves, the chloride and nitrate came ahead of tritiated water. This well-known electrolyte exclusion phenomenon was used for checking the physical validity of the nonlinear adjustment of the theoretical curves to the experimental points. Two independent determinations of the salt exclusion volume were obtained either from the movement of tritiated water and chloride through the soil or from the BET specific surface of the soil at a given ionic strength. Taking the BET value for the specific surface, the exclusion volume, V excl was found to be 6.3 × 10 −2 cm 3 g −1 . The calculation of V excl from the comparison of elution curves for tritiated water and chloride was found to give 4.2 × 10 −2 cm 3 g −1 .

Minimal size of Nitrobacter membrane frangments retaining nitrite oxidizing activity

SummaryThe minimal size of active membrane fragments from sonic homogenates of a Nitrobacter cell suspension is about 22 mμ. Nitrite oxidizing activity is absent from particles smaller than that although the distribution of cytochrome a, a link in the respiratory chain responsible for nitrite oxidation, does not show any abnormality below the critical size indicated.Two independent estimates of the parameters of the cumulative distribution function for particle size in sonic homogenates have been made using either statistics from electron micrographs or sedimentation pattern observed after density gradient centrifugation. The distribution function was found to be of the log-normal type which was considered to be a consequence of the observed kinetics of sonic comminution. Another estimate of the parameters of the distribution function was made by fixed angle centrifugation, a method much less accurate with respect to size determination but which allowed a rapid estimate of nitrite oxidizing capacity remaining in particles smaller than the given size.Results from the first two determinations of the distribution function for particle size and of its parameters were then used for correcting the error in the estimate of the critical size from the activity found in supernatants from centrifugations in fixed angle rotors.

Self-diffusion of sodium on clay surfaces as influenced by two other alkali cations

Abstract The surface self-diffusion of sodium was studied in mixed NaLi and NaRb-clay suspensions. The Rb + ions were found to increase the surface mobility of sodium while the Li + ions produced a very light opposite effect. This was attributed to a modification of the relative distribution of the Na + ions between the Stern and Gouy layers when another cation was introduced on the clay surface.

Selfdiffusion of anions in clay gels

Abstract Selfdiffusion studies of iodide in clay gels have shown that the effect of decreasing the anion “exclusion volume” by increasing electrolyte concentration was more than offset by an ensuing tactoid formation which occurred in a way that increased the path of the diffusing anions. This effect is more pronounced when the solid content of the gel is higher.

Tactoids in hydrogen montmorillonite suspensions

Abstract The problem of the aggregation in hydrogen-clay suspensions is studied through a parallel determination of the catalytic properties and of the size distribution of hydrogen-clay particles. The presence of elementary platelets in the suspensions could not be demonstrated. It is suggested that the acidic montmorillonite is slightly but sufficiently aggregated to influence the physicochemical properties of the adsorbed hydrogen ions.