Chilling Injury in Cucumber Leaves in Relation to Temperature

An Arrhenius plot of the respiration rate of cucumber leavesshows a break at 12°C; below this temperature Q₁₀ is 5.7.Leaves can survive exposure to 10°C for a week, but if chilledat 8°C for 3 d they show some loss of fresh weight and leakelectrolytes when immersed in water. At 5°C there is a markedloss of water leakage of electrolytes within a few hours.     

A generalized approach to detection of organophosphate resistance in mosquitoes

Insecticide bioassays and biochemical microtitre assays were compared for detection of resistance to the organophosphate insecticides malathion and fenitrothion, using inbred laboratory strains of malaria vectors Anopheles albimanus Wiedemann, An.arabiensis Patton and An.stephensi Liston. With susceptible mosquitoes, the LT100 values determined from bioassays corresponded closely with times taken to abolish the activity of acetylcholinesterase activity in biochemical assays: approximately 2 h for malathion and 3 h for fenitrothion. Resistant strains of all three anophelines showed longer survival correlated with prolonged acetylcholinesterase activity. An.albimanus strains with insensitive acetylcholinesterase survived bioassays with discriminating doses of 1 h exposure to 5% malathion or 1% fenitrothion and were judged as resistant. It is concluded that enzyme-specific microassays provide a reliable means of detecting resistant individuals, with practical advantages over bioassays which do not reveal the resistance mechanism and require large numbers of healthy mosquitoes.     

Factors Affecting Absorption and Translocation of Simazine by Barley

The factors affecting the absorption and translocation of simazineby young barley plants in short-term experiments in water culturehave been investigated. Chromatographic examination of the xylemsap indicated no extensive breakdown of the herbicide in thetranspiration stream. Under varying conditions of humidity,light intensity, temperature, and in the presence of metabolicinhibitors, the concentration of simazine in the transpirationstream relative to that in the uptake medium was always lessthan unity. This could, in part, be attributed to retentionof simazine at a higher concentration on a fresh weight basisin the root tissues than in the ambient medium. There was littleevidence that the absorption and translocation of simazine wasinfluenced by metabolism except in so far as this affected movementof water, and micro-organisms present on the plant roots atambient laboratory levels had no effect on the uptake and transportof the herbicide. Simazine brings about a decrease in the rate of transpirationand a reduction in the total uptake of rubidium and phosphateat relatively high concentrations. However, when the phosphateconcentration in the ambient medium was below the level at whichtranslocation of this ion is affected by the rate of transpiration,the herbicide did not reduce uptake of phosphate. There is thereforeno evidence that in short-term experiments simazine has an effecton active transport processes.     

Studies on Uptake and Loss of Water by Barley Roots in Relation to Changes in Root Resistance

The uptake and loss of water by roots of young barley plantshave been measured using tracer techniques in sand culture undercontrasting conditions of transpiration and water potentialdifference. The results are compared with direct potometricmeasurements of water uptake. The apparent resistance to flowof water changed in response to differences in water potentialbetween the leaves and the root medium and in transpirationrate. We examine the significance of this in relation to netloss of water and possible mobilization of nutrients from drysoil. With the aid of a mathematical model, some considerationis given to the role of the endodermis as a barrier to diffusivemovement of water in the older parts of the root system.     

Feeding response of the stable fly, Stomoxys calcitrant L., to blood fractions and adenine nucleotides

Abstract Feeding responses of the stable fly ( Stomoxys calcitrans L., Diptera: Muscidae) to blood fractions and saline-based diets were studied in an artificial feeding device. Flies fed equally on whole blood, plasma and erythrocyte fractions while resuspended platelets or the buffy layer did not stimulate feeding. Evidence from filtration studies indicates that plasma contains both less-than-5000D and greater-than-100,000D phagostimulatory components. ATP, ADP and AMP in saline stimulate feeding in this insect in a dose-dependent manner. cAMP also stimulates feeding in the range of concentrations tested. It is argued that the less-than-5000D phagostimulant may be one or more of these adenine nucleotides.     

Rates of Cell Division in the Vegetative Shoot Apex of Rice (Oryza sativa L.)

The cell-doubling times in the shoot apical regions of 4-dayold rice plants have been measured using colchicine-inducedmetaphase accumulation. Plants were grown submerged at a constantillumination of 10 000 lx and constant temperature of 30°C.Colchicine was applied by adding the drug to the surroundingwater which therefore involved no other disturbance of the apexor the plant. The cells of the summit region were found to bemultiplying eight times slower than those of the flanks.     

The Sterility Testing of Aminoglycosides: A New Approach Using Enzymic Inactivation

The inactivation of various aminoglycosides prior to sterility testing has been studied. The preparation of the enzyme used in the inactivation, a 3-N-acetyl transferase of wide substrate specificity from Escherichia coli JR 225, is described. The enzyme is partially purified and some of its kinetic parameters described. The extent of the inactivation of the individual aminoglycosides can be related to the physiological efficiency of the enzyme. The lyophilization of the components of the inactivating system is successful when undertaken individually, but not together.