Nitrification inhibitors from the roots of Leucaena leucocephala.

The nitrification inhibition (NI) bioassay guided fractionation of the methanol extract of lyophilized and milled roots of Leuceana leucocephala resulted in the isolation of four compounds, 1-4, as confirmed from their 1H and 13C NMR spectral data. Compound 1, gallocatechin, was the most active NI inhibitor at 12 microg/mL. Epigallocatechin, 2, and epicatechin, 4, isolated as mixtures, were not assayed individually for their NI inhibitory activities against the nitrification bacterium Nitrosomonas europaea.

Root system regulation of whole plant growth.

New evidence confirms earlier postulates that root signals to shoots, including abscisic acid, nitrate flux, and cytokinins, modify whole plant growth processes including leaf expansion, stomatal behavior, and biosynthesis of photosynthetic enzymes. Root signals are thought to reflect soil water, nutrient, and mechanical attributes, as sensed by roots. Meristematic activities in root tips initiate changes in root architecture, modifying the soil volume subject to root uptake, and may provide multiple sensory and signaling capabilities. Knowledge of root signals regulating whole plant growth processes suggests new analytical and experimental tools for integrated analysis of plant phasic development, optimal growth, and ecological fitness.

Comparative effectiveness of metal ions in inducing curvature of primary roots of Zea mays.

We used five cultivars of Zea mays (Bear Hybrid WF9 * 38MS, B73 * Missouri 17, Yellow Dent, Merit, and Great Lakes Hybrid 422) to reinvestigate the specificity of metal ions for inducing root curvature. Of 17 cations tested, 6 (Al3+, Ba2+, Ca2+, Cd2+, Cu2+, Zn2+) induced curvature. Roots curved away from Al3+, Ba2+, and Cd2+. Roots curved away from low (0.1 millimolar) concentrations of Cu2+ but toward higher (1-5 millimolar) concentrations. Roots initially curved away from Zn2+ but the direction of the subsequent curvature was unpredictable. In most cases, roots of all cultivars curved towards calcium. However, in some tests there was no response to calcium or even (especially in the cultivars Merit and B73 * Missouri 17) substantial curvature away from calcium. The results indicate that the induction of root curvature is not specific for calcium. The results are discussed relative to the possible role of calmodulin as a mediator of ion-induced root curvature.

Carbon Transport and Root Respiration of Split Root Systems of Phaseolus vulgaris Subjected to Short Term Localized Anoxia.

The influence of anoxia on carbon transport and root respiration was evaluated by applying [U-(14)C]sucrose to the foliage. Translocation patterns to the root systems of two dry edible bean genotypes (Phaseolus vulgaris L.) were examined after a 3-day exposure to aerated and nonaerated environments. Localized anoxia of root systems was simulated by growing roots in split configurations and exposing half of the system to anoxic conditions. Anoxia of the root system for 72 hours reduced the movement of (14)C label into the roots with concurrent accumulations in the hypocotyl region. The translocation of (14)C label to anoxic roots was less than 50% of the aerated controls of both genotypes. Most of the (14)C label translocated to anoxic root systems was excluded from respiratory metabolism during the 3-hour pulse/chase period and was an order of magnitude less than the aerated controls. These observations suggest that the bulk of (14)C label which entered the root during the anoxic period was unavailable for metabolism by the enzymes of glycolysis and/or was diluted by a relatively large metabolite pool. A higher percentage of (14)C label was translocated to the aerated half of the localized anoxia treatment relative to the half of the aerated controls. The proportion of (14)C label translocated to the root system in the aerated control was 20 and 16% compared to 28 and 25% in the aerated localized anoxia treatment for the genotypes Seafarer and line 31908, respectively. Line 31908 partitioned a greater percentage of (14)C-labeled compounds to the actively growing fraction of the root system in the localized anoxia treatment than did Seafarer. This suggests a greater reliance on previously stored carbohydrate for immediate root growth in Seafarer than in line 31908.

Measurement of CO(2) Dissolved in Aqueous Solutions Using a Modified Infrared Gas Analyzer System.

Total dissolved inorganic carbon (SigmaCO(2)) and aqueous carbon dioxide (H(2)CO(3) (*)) in nutrient solutions may be measured by the injection of small gas or liquid samples (1 microliter to 8 milliliters) into a gas stripping column connected in-line with an infrared gas analyzer. The measurement of SigmaCO(2) in solution requires sample acidification, while H(2)CO(3) (*) and gaseous CO(2) are measured without the addition of lactic acid. The standard curve for SigmaCO(2) was linear up to 300 nanomoles CO(2). Maximum sensitivity was approximately 300 picomoles. Measurements of H(2)CO(3) (*) were independent of pH. Consequently, SigmaCO(2) and H(2)CO(3) (*) could be used to calculate the pH, HCO(3) (-), and CO(3) (2-) values of nutrient solutions. Injection and complete analyses required from 0.8 to 2 minutes.