Malate: A Possible Source of Error in the NAD Glutamate Dehydrogenase Assay

The effects of externally induced metabolic perturbations areoften studied through changes of the enzyme activity patternsin crude plant extracts. From glutamate dehydrogenase (GDH)it is reported that environmental changes not only influencethe amount of the enzymatic activity, but also the ratio ofthe aminating to the deaminating activities (NADH/NAD⁺ ratio).Using crude cell extracts of suspension cultures of wheat (Triticumaestivum L. cv. Heines Koga II) we find evidence that the pretreatmentof the homogenate directly influences this ratio. Dialysis ofthese crude cell extracts resulted in a 70% loss of the NAD⁺activity, while the NADH activity remained unchanged. The deaminatingactivity in the dialysed extract could be completely restoredupon addition of a dialysable factor which was identified tobe malate. The interference of malate with the glutamate dehydrogenasereaction is caused through the action of malate dehydrogenaseand glutamate oxaloacetate transaminase which are both presentin high activities in the extracts. Only in exhaustively dialysedcell extracts can the proper deaminating GDH activity be determined.The results are discussed in the light of the controversialreports on the variable ratio of the NADH/NAD⁺ activity of GDH. Key words: Glutamate dehydrogenase, malate, NADH/NAD⁺, activity, Triticum aestivum     

A Krypton Diffusion Porometer for the Direct Field Measurement of Stomatal Resistance

A stomatal diffusion porometer is described which measures directlythe diffusion of radioactive krypton through amphistomatousleaves. The porometer is relatively small and portable and iseasily used under field conditions. It consists of a miniaturediffusion chamber above an acrylic plastic reservoir which contains1200 cm³ of air enriched with ⁸⁵Kr. Geiger tubes in the diffusionchamber and in the reservoir monitor the relative concentrationsof 85Kr. Krypton is allowed to diffuse from the larger reservoirthrough the leaf into the diffusion chamber and the time forits concentration in relation to that in the reservoir to changebetween two fixed values is recorded. When this time lapse wascalibrated against known resistances a linear relationship,independent of temperature was found. Sources of error are analysedand some experiments are described in which the porometer wasused to measure diurnal changes in stomatal resistance. Resistancesof potted sunflower plants (Helianthus annuus L.) grown in agreenhouse were measured with both the krypton diffusion porometerand a condensation-type porometer and the results were usedto calculate both cuticular and stomatal resistances. Demonstrationof field measurements with the porometer include data from eucalyptustrees {Eucalyptus camaldulensis Dehn) and from an unirrigatedcotton crop {Gossypium hirsutum var. SJ 2) growing under semi-aridconditions. Stomatal conductance of the cotton crop during theopening phase was linearly related to solar radiation.     

Nucleus-Cytosol Interactions--A Source of Stoichiometric Error in Flow Cytometric Estimation of Nuclear DNA Content in Plants

Discrepancies of 2–20% were noted in nuclear DNA contentestimates using mixed and unmixed extracts of several plantspecies combinations (target/standard). This may be becausecytosolic components affect dye accessibility to DNA. Severaldilution experiments showed clearly how cytosol concentrationmodified dye accessibility. Heat treatment suggested that dyeaccessibility could be related to chromatin sensitivity to decondensation.Some methods (nucleus isolation, dilution) can decrease, butnot eliminate, stoichiometric error. The high sensitivity ofthe nucleus to the medium highlights the problem of reliabilitylimits in estimating genome size. The choice between internaland external standardization and the interpretation of intraspecificvariation in ‘nuclear DNA content’ are discussed.Copyright 2000 Annals of Botany Company Propidium iodide, dye accessibility, chromatin condensation, standardization, intraspecific variation     

Experimental Studies of the Relation between Carbon Assimilation and Stomatal Movement: II. The Use of the Resistance Porometer in estimating Stomatal Aperture and Diffusive Resistance

Two purely physical sources of error in the ‘resistanceporometer’ as ordinarily used are considered to be ofappreciable importance, viz. that due to the flow through theleaf being augmented with water vapour which is removed againby a drying agent before the air passes through the standardcapillary, and that due to the leaf temperature differing fromthe capillary temperature. In a bad case the total error mightamount to 10 or 15 per cent. of the ‘leaf resistance’. Modifications to deal with these sources of error and with themore important errors due to the responses of the enclosed stomatato variations in CO₂ supply are described.     

Nonsynchronized Oscillations in Stomatal Resistance among Sclerophylls of Eucalyptus umbra

Oscillations in stomatal resistance to viscous air flow have been recorded in the juvenile and adult sclerophylls of Eucalyptus umbra R. T. Baker, in both controlled and natural environments. Under constant illumination, temperature, and humidity, irregular oscillations in stomatal resistance with a periodicity of approximately 20 to 30 minutes occurred spontaneously, when the soil water potential was approximately −0.2 bar. In the natural summer environment, similar stomatal oscillations developed with periods ranging from 60 to 100 minutes only after imposition of soil moisture stress equivalent to −2 to −3 bars water potential. These cycles in stomatal resistance were not synchronized among the leaves of a given plant in any of the experiments.     

Split Nucleoli as A Source of Error in Nerve Cell Counts

The number of nerve cells in a given ganglion or nucleus is usually determined by counting the nucleoli in serial sections. The possibility that nucleoli may split and appear in more than one section is recognized as a source of error. A determination of the value of this error was made as follows; from nodose ganglia of four cats were cut serial transverse sections in which the sections varied in thickness. Thus from one ganglion, four sections were cut at 12 μ, then six at 9μ, and eight at 6μ. The process was repeated over and over until the entire ganglion was sectioned. The other ganglia were sectioned similarly. After mounting and staining, separate counts were made of the nucleoli of each given ganglion from the sections of different thicknesses. If nucleoli split according to theoretical expectations, the percentage of nucleoli split in thick sections should be less than the percentage split in thinner sections and the counts based on the sections of different thicknesses should vary accordingly. The results obtained indicate that the counts from thin sections do not differ appreciably from counts from much thicker sections, i. e., the thickness of the sections does not affect the count. It is, therefore, concluded that no correction should be made for split nucleoli if the sections are around 10 μ in thickness and none but distinct and definite nucleoli are counted.     

Evidence for Two Photoreactions and Possible Involvement of Phytochrome in Light-dependent Stomatal Opening

Leaves of the xantha mutant of Helianthus annuus have a higher rate of transpiration and a lower diffusive resistance in the light than in the dark. Stomates of this nonphotosynthetic mutant open in the light and close in the dark.     

A Comparison of Nonparametric Error Rate Estimation Methods in Classification Problems

Assessment of the misclassification error rate is of high practical relevance in many biomedical applications. As it is a complex problem, theoretical results on estimator performance are few. The origin of most findings are Monte Carlo simulations, which take place in the “normal setting”: The covariables of two groups have a multivariate normal distribution; The groups differ in location, but have the same covariance matrix and the linear discriminant function LDF is used for prediction. We perform a new simulation to compare existing nonparametric estimators in a more complex situation. The underlying distribution is based on a logistic model with six binary as well as continuous covariables. To study estimator performance for varying true error rates, three prediction rules including nonparametric classification trees and parametric logistic regression and sample sizes ranging from 100‐1,000 are considered. In contrast to most published papers we turn our attention to estimator performance based on simple, even inappropriate prediction rules and relatively large training sets. For the major part, results are in agreement with usual findings. The most strikingly behavior was seen in applying (simple) classification trees for prediction: Since the apparent error rate Êrr.app is biased, linear combinations incorporating Êrr.app underestimate the true error rate even for large sample sizes. The .632+ estimator, which was designed to correct for the overoptimism of Efron's .632 estimator for nonparametric prediction rules, performs best of all such linear combinations. The bootstrap estimator Êrr.B0 and the crossvalidation estimator Êrr.cv, which do not depend on Êrr.app, seem to track the true error rate. Although the disadvantages of both estimators – pessimism of Êrr.B0 and high variability of Êrr.cv – shrink with increased sample sizes, they are still visible. We conclude that for the choice of a particular estimator the asymptotic behavior of the apparent error rate is important. For the assessment of estimator performance the variance of the true error rate is crucial, where in general the stability of prediction procedures is essential for the application of estimators based on resampling methods. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Wind Power Error Estimation in Resource Assessments

Estimating the power output is one of the elements that determine the techno-economic feasibility of a renewable project. At present, there is a need to develop reliable methods that achieve this goal, thereby contributing to wind power penetration. In this study, we propose a method for wind power error estimation based on the wind speed measurement error, probability density function, and wind turbine power curves. This method uses the actual wind speed data without prior statistical treatment based on 28 wind turbine power curves, which were fitted by Lagrange''s method, to calculate the estimate wind power output and the corresponding error propagation. We found that wind speed percentage errors of 10% were propagated into the power output estimates, thereby yielding an error of 5%. The proposed error propagation complements the traditional power resource assessments. The wind power estimation error also allows us to estimate intervals for the power production leveled cost or the investment time return. The implementation of this method increases the reliability of techno-economic resource assessment studies.     

Using Stomatal Resistance Index of Plants to Evaluate the Quality of Atmospheric Environment in Fuzhou

This paper deals with studies on the stomatal resistance of plants in different polluted environment in the Fuzhou region and their use in evaluating the quality of atmospheric environment. The results show that among the seven function areas under investigation, the plants in Mawei, Guantou and Fuzhou have larger stomatal resistance, the average value is 6–7s cm. In Mawei function area, half of the plants have normal stomatal resistance of 2–4s/cm, only in a few industrial-mining and heavy-traffic areas, the stomatal resistance of plants is 6–12s/cm, which is of grade Ⅲ to Ⅱ and exceeds the normal level, indicating that these areas have been lightly polluted. In the other four function areas (Gushan, Tingjiang, Changle, Minhou), the average value of stomatal resistance is 3s/cm, which is of grade Ⅳ or normal. The average value of stomatal resistance in the sixty observation sites is 4.14s/cm, which is a little higher than the normal level. From the stomataJ resistance values we can infer that the stomatal openings of most plants in the Fnzhou region are normal, but the transpiration rate of plants is comparatively low, which is 5.19μgH20 cm-2·s-1 in average. This is due to the moist subtropics climate where the precipitation and vapourization is similar in amount. The stomatal resistance value not only correlates positively with the pollutant contents in leaves, but also conforms to the polluted states of SO2 and TSP. From what we have mentioned above we can conclude that the Fuzhon region is not polluted except for a few industrial-mining, heavy traffic and crowded sightseeing areas which are only lightly polluted. This conclusion is in agreement with that of the local environmental monitoring department, that is, "the present environmental quality of the Fuzhou Economic-Technological Development Region is fine". We believe that it is an ideal means to use stomatal resistance index of plants in evaluating the quality of atmospheric environment.     

Stomatal Diffusion Resistance of Snap Beans. II. Effect of Light

The effect of light on the stomatal resistance of abaxial and adaxial leaf surfaces of snap beans (Phaseolus vulgaris L.) was studied in the growth chamber and in the field. The adaxial stomata required more light to open than the abaxial stomata; the abaxial stomatal apertures were still about 50% open at 1% full sunlight and light-induced closure was never observed under daytime field conditions. A given value of abaxial stomatal resistance was obtained at a given illumination of the abaxial guard cells whether illumination was adaxial or abaxial.     

Histological Compartmentation of Phosphate in Vicia faba L. Leaflet : Possible Significance to Stomatal Functioning

Guard cells, epidermal cells, palisade parenchyma cells, and spongy parenchyma cells of Vicia faba L. leaflet were analyzed for inorganic phosphate and phosphorus. On a molar basis, cells in the epidermal layer contained about 15-fold more inorganic phosphate than mesophyll cells did. Although a metabolic role for this asymmetric distribution cannot be defined unequivocally, we note that high epidermal inorganic phosphate would buffer against pH changes in the epidermis during stomatal movements.     

The Relation between Photosynthesis and Stomatal Resistance of Each Leaf Surface in Cotton Leaves

The relation between photosynthesis and stomatal resistance of each leaf surface in cotton leaves (Gossypium hirsutum) was studied during ageing and with increase in light intensity. During ageing of leaves the stomatal resistance of the upper surface increases before that of the lower surface. This observation would suggest that the stomata of the upper leaf surface commence to age before those of the lower leaf surface. The earlier commencement of the increase in upper stomatal resistance results in the decline in photosynthesis at an early stage of ageing being negatively correlated with the upper stomatal resistance and not related to the lower stomatal resistance. The results indicate that in this initial phase of ageing the decrease in photosynthesis and increase in stomatal resistance of the upper surface are not causally related but occur simultaneously. At a more advanced stage of ageing the lower stomatal resistance also increases and then the decline in photosynthesis becomes related to the increase in stomatal resistance of both leaf surfaces. When illumination of leaves is increased stepwise, the resultant increase in photosynthesis is related to the reduction in stomatal resistance of each leaf surface. At low light intensities the stomatal resistance of the lower surface is low while that of the upper surface is relatively high. The difference between them decreases with increase in light intensity. This would indicate that the upper stomata require a higher light intensity to open than the lower stomata. The stormatal resistance of the two leaf surfaces is not related to the stomatal frequencey.     

Poria weirii as a Possible Commercial Source of Peroxidase

Poria weirii produced peroxidase in yields amounting to 35% of those obtained from the same weight of horseradish roots. The three isozymes detected were distinct from those of horseradish.