Interspecific differences in aluminium tolerance in relation to root cation-exchange capacity

Genotypic differences in aluminium (Al) tolerance hold considerable promise in overcoming an important limitation to plant growth in acid soils. Little is known, however, about the biochemical basis of such differences. Extracellular properties, particularly low root cation-exchange capacity (CEC), have been associated with Al tolerance, since roots of low CEC adsorb less Al than do those of high CEC. A solution culture study was conducted in which 12 plant species (monocots and dicots) were grown in solution culture of low ionic strength (ca 2 mM) for 8 d at four Al concentrations (0, 16, 28 and 55 M). The species differed significantly in Al tolerance as shown by differences in root length. Root length relative to that of the same species grown in the absence of Al varied from 6 to 117% at 16 M Al, and from 6 to 75% at 28 M Al. Species tolerance of Al was not closely associated with differences in root CEC. Although in some species Al sensitivity was associated with high adsorption of Al during a 10- or 40-min exposure to Al (expressed on a fresh mass or root length basis), this was not a good predictor of Al tolerance across all species studied.     

Plant-induced changes in the redox potentials of rice rhizospheres

Redox potentials in microsites of the rhizosphere of flooded rice were continuously measured for several days. Close to the root tips redox potential markedly increased. The highest increase was measured in the rhizosphere of the tips of short lateral roots. Aerobic redox conditions were reached there, except in a very strongly reduced soil. Both the extension of the oxidation zone around the root tips and the maximum redox potential reached were influenced by the reducing capacity of the soil. The radius of the redox rhizosphere varied from less than 1 mm in a strongly reduced soil up to 4 mm in a weakly reduced one. The root-induced oxidation processes in the rhizosphere depended on the atmospheric oxygen supply to the roots.     

Chloroplast movements in leaves: Influence on chlorophyll fluorescence and measurements of light-induced absorbance changes related to ΔpH and zeaxanthin formation

Light-induced chloroplast movements were found to cause changes in chlorophyll fluorescence emission, closely matching those in leaf absorptance, both in terms of the kinetics and the maximum extent of the changes observed in different species. The results demonstrate that chloroplast movements can have a significant effect on the efficiency of light utilization in photosynthesis. They further show that chloroplast movements need to be taken into account in measurements of fluorescence quenching and especially in measurements of light-induced optical changes used to monitor zeaxanthin formation and pH associated light scattering in leaves. Means of minimizing and of adjusting for the influences of chloroplast movements in such measurements are discussed.Abbreviations F fluorescence emission - PFD photon flux density - R reflectance - T transmittance - absorptance C.I.W.-D.P.B. Publication No. 1116.     

In vitro testing and the carcinogenic potential of several nitrosated indole compounds

4-chloro-methoxyindole is a naturally occurring compound in Vicia faba which can easily react with nitrite to form a N-nitroso compound. In this in vitro study, the potential genotoxic effects of nitrosated 4-chloro-6-methoxyindole and its structural analogue 4-chloroindole were evaluated for the first time by using both Salmonella and Chinese hamster V79 cells. Additionally, the inhibition of gap junctional intercellular communication in V79 cells by these compounds was determined; this is a validated parameter for tumor-promoting activity. Most assays were also performed with nitrosated indole-3-acetonitrile, a naturally occurring compound in brassicas. Both nitrosated chloroindoles were highly mutagenic to Salmonella typhimurium TA100 without the need of exogenous metabolic activation and were potent inducers of Sister Chromatid Exchanges. Nitrosated indole-3-acetonitrile generated the same effects, although at much higher concentrations. Equivocal results were obtained for the nitrosated chloroindoles in a forward mutation assay using the hypoxanthine guaninephosphoribosyltransferase locus. All nitrosated indole compounds significantly inhibited gap junctional intercellular communication. These results indicate that nitrosated chloroindoles and nitrosated indole-3-acetonitrile should be considered as mutagens and agents with potential tumor-promoting capacity.Abbreviations BrdU 5-bromo-2-deoxyuridine - 4Cl 4-chloroindole - 4C6MI 4-chloro-6-methoxy-indole - DMSO dimethyl sulfoxide - EBSS Earle's balanced salt solution - EMS ethyl methanesulfonate - GJIC gap junctional intercellular communication - HBSS Hanks balanced salt solution - HGPRT hypoxanthine guaninephosphoribosyl transferase - I₃A indole-3-acetonitrile - MNNG 1-methyl-1-nitroso-3-nitroguanidine - NOC N-nitroso compounds - NQO 4-nitroquinolone-N-oxide - SCE sister chromatid exchange - 6TG 6-thioguanine - TPA 12-O-tetradecanoylphorbol-13-acetate     

Theoretical basis of single breath gas absorption tests

Absorption of gas from alveoli is examined in a simplified model of the respiratory system during a stylized single breath consisting of constant inspiratory flow, constant expiratory flow, and breathholding. The equations describing gas behavior are general since they are based upon conservation of mass. The equations simplify considerably when gases that are not soluble in pulmonary tissue and/or blood are utilized. In a three-compartment model, diffusing capacity of the lung for carbon monoxide (D _CO ) will be underestimated except when both uneven distribution of lung volume andD _CO are present; under most circumstances, the standard clinical 10-s method [9] is at least as accurate as any other. When pulmonary capillary blood flow is calculated by the one point method [2] in a one-compartment lung, it is underestimated; in the three-compartment model, it is underestimated except when both uneven distribution of . and lung volume are present. The multiple single breath method [2] accurately measuresD _CO and . Measurement of pulmonary tissue volume is improved by correcting the value of the intercept of acetylene absorption to the time when carbon monoxide apparently began rather than utilizing the beginning of inspiration.Nomenclature D _CO diffusing capacity of the lung for CO (ml CO, STPD/min/mm Hg) - pulmonary capillary blood flow rate (L/min) - V _t pulmonary tissue volume (L) - V _A alveolar compartment volume (L) - V _Ao alveolar compartment volume at conclusion of inspiratory flow (L) - inspiratory flow rate (L/sec) - expiratory flow rate (L/sec) - Bunsen coefficient of pulmonary tissue for test gas (ml test gas/ml tissue/atm) - Bunsen coefficient of pulmonary tissue for test gas (ml test gas/ml blood/atm) - F _A fractional pressure of test gas in the alveolar compartment (atm)     

Acidified lakes: sediment treatment with sodium carbonate — a remedy?

Until now, additions of lime have been used to restore the buffering capacity of acidified lakes, but an alternative method which is more effective in the treatment of lakes with organogenic sediments has recently been applied in a full-scale experiment. The method, called CONTRACID, is based on the cation exchange properties of lake sediment. A sodium carbonate (soda ash) solution is injected into the sediment (by a harrow), so that the sediment becomes sodium stocked. A reverse exchange occurs during subsequent acidification. Liming has a limited effect on humic lakes, since Ca-humates have a reduced reverse exchange ability and also the lime, which remains undissolved, is rendered inactive. Ionic exchange processes and nutrient transport were studied in water/sediment cores andin situ enclosures after additions of soda ash-, lye- and lime solutions with subsequent re-acidification. Sodium carbonate additions in laboratory systems resulted in a sorption to the sediment of 42–62% of the added sodium ions (5 eq m⁻²) and a release of 14–78 mg Pm⁻² sediment. Similar results were obtained in the enclosures where phosphorus release stimulated algal growth. Sediment pH, elevated by the sodium base addition, was lowered by re-acidification. Limed systems released no phosphorus and only about 25% of the added lime remained active for future neutralization. With the injection of the sodium carbonate solution into the sediment, only about 12% of the added sodium was recovered in lake water by spring circulation. Lake water alkalinity was then 0.12 meq l⁻¹ and pH 6.7. Total phosphorus had been raised by 0.007 mg P l⁻¹ causing an increase in phytoplankton biomass. Observations indicate that manipulations of acidic lake sediment according to the CONTRACID method create a long-lasting neutralizing capacity and a biological stimulation (through phosphorus release), which makes the method an attractive alternative to frequent liming.     

Criteria for the identification of potential colonizers*

Man's interference with the environment encourages colonization by species that are often undesirable, hence a technique by which potential colonizers can be identified is urgently required. It can be developed when general prerequisites for successful colonization are identified. These prerequisites can then serve as criteria to distinguish potential colonizers from non-colonizers. The proposed relevant prerequisites are associated with two problems encountered by all colonists: small founding populations and a difference in the environmental conditions between the source area and the target, making the target rather unpredictable. Both these features increase the risk of random extinction, which can be overcome by possessing a potential for rapid population growth (high r) and for rapid adaptation to environmental conditions (high genetic variability). The parameters associated with meeting these prerequisites can serve for the identification of potential colonizers and for ranking species as to their colonization ability. The proposed technique may best be tested by comparing the intrinsic growth rate and the electrophoretic variability of species that have recently colonized with closely related species that have not done so under similar circumstances. The colonization of the eastern Mediterranean by Red Sea species immigrating via the Suez Canal created an appropriate system for such a test.     

On the role of ß-carotene in the reaction center chlorophyll a antennae of photosystem I

Absorption and low temperature fluorescence emission spectra were measured on chloroplast thylakoids and on purified reaction center chlorophyll a-protein complexes of photosystem I, CP-a₁. A clear association between the presence of ß-carotene and the occurrence of far red absorbing and emitting chlorophyll a components of the reaction center antennae of photosystem I was demonstrated. For this study chloroplasts and CP-a₁ were obtained from normal and carotenoid deficient plant material of various sources. The experimental material included 1) lyophilized pea chloroplasts extracted with petroleum ether, 2) the carotenoid deficient mutant C-6E of Scenedesmus obliquus and 3) wheat chloroplasts derived from normal and SAN-9789 treated plants. Removal of carotenoids, most likely principally ß-carotene, caused a loss of long wavelength absorbing chlorophylls in chloroplasts and purified CP-a₁, and the loss or diminution of the long wavelength peak seen in the low temperature fluorescence emission spectrum. This association between ß-carotene and special chlorophyll a forms may explain both the photoprotective and antenna functions ascribed to ß-carotene. In the absence of carotenoids in wheat and in the Scenedesmus mutant, the chlorophyll a antenna of photosystem I was extremely photosensitive. A triplet-triplet resonance energy transfer from chlorophyll a to ß-carotene and a singlet-singlet energy transfer from excited ß-carotene to chlorophyll would explain the photoprotective and antenna functions, respectively. The role of this association in determining some of the fluorescence properties of photosystem I is also discussed.     

Late pleistocene population dynamics: An alternative view

An attempt is made to argue for a more dynamic view of huntergatherer population behavior in place of the largely static one that has been widely accepted. Following a review of how the concept of carrying capacity has been used in both huntergatherer and ecological studies, attention is drawn to the role of stochastic factors in producing fluctuations over time among populations that are small in size. Some of the implications of this alternative view are briefly discussed.Research supported in part by NIH Grant GM 20467-03.This is a revised version of a paper presented at the symposium, Systems and Their Environments, at the Annual Meeting of the American Anthropological Association, 1973, New Orleans.