Browsing by Author "Macur, Richard Eugene"

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Iron nutrition of plants and interactions with vascular wilt disease and light
(Montana State University - Bozeman, College of Agriculture, 1989) Macur, Richard Eugene
The relationship between iron nutritional status and Verticillium Wilt disease in tomato possessing single gene resistance to Race 1 of Verticillium dahliae was investigated using hydroponic culture media. Iron limiting conditions increased the sensitivity of resistant tomatoes to the pathogen as expressed by wilting and chlorosis. Distance of fungal vascular invasion was approximately the same in both iron replete and iron limited treatments. Comparison of near-isolines revealed that the magnitude of disease expressed in Fe deficient Pixie II (resistant) was considerably less than that expressed by the susceptible Pixie variety. Infection of tomato did not enhance iron stress severity as quantified by root peroxidase activity and chlorophyll content of young leaves. The release of iron from horse spleen ferritin through photochemical reduction of Fe(III) to Fe(II) was studied in vitro. Spectrophotometric measurement of the Fe(ferrozine)3^2+ complex (specific for Fe(II)) was used to quantify rates of Fe mobilization: Cool white fluorescent plus incandescent light effectively promoted the rate of Fe release. Compounds known to be present in plants may provide further regulation of photorelease. Reductive removal from ferritin was inhibited by phosphate, and hydroxide, whereas citrate, oxalate, tartrate, and caffeate enhanced the release. Of the organic acids studied, caffeate was the only compound which induced detectable Fe release in the absence of irradiation. Rate constants ranged from 2.7 x 10^-3 sec^-1 (pH = 4.6) to 2.1 x 10^-3 sec^-1 (pH = 7.1) at 26.5°C. Synthesis of the photosynthetic apparatus is dependent on both light and iron. Thus, the findings provide one possible mechanism coupling chloroplast iron demand with iron release from ferritin. Treatments known to alter either phenolic metabolism or overall enzyme activity were utilized to examine the Fe reductive mechanisms involved in iron stress response at the roots. Although specific compounds caused elevation of internal o-dihydroxyphenol content, the overall root reduction capacity of Fe stressed plants was significantly suppressed. However, plant roots retained significant capacity to reduce Fe after tissues were subjected to severe protein denaturizing treatments. Thus, indications for both secreted reductant and enzymatic reduction mechanisms were observed.
Linking microbial populations and geochemical processes in soils, mine tailings, and geothermal environments
(Montana State University - Bozeman, College of Agriculture, 2004) Macur, Richard Eugene; Chairperson, Graduate Committee: William P. Inskeep.
The primary goal of this work was to identify and characterize the microbial populations responsible for transformations of As and 2,4-D in soils and waters. Chemical, spectroscopic, and microscopic techniques were used to characterize the aqueous and solid phase geochemistry of soils, mine tailings, and a geothermal spring. The role of specific microbial populations in these systems was examined using cultivation-independent molecular methods [total DNA extraction, 16S rDNA amplification, denaturing gradient gel electrophoresis (DGGE), and sequence analysis] coupled with either characterization of microorganisms isolated from the same systems, or inference of physiological characteristics from (i) closely related (16S rDNA sequence) cultured microorganisms and (ii) the geochemical environments in which they were detected. The microbial reduction of As(V) to As(III) and the subsequent effects on As mobilization in contaminated mine tailings was examined under transport conditions. Enhanced elution of As from mine tailings apparently resulted from the enrichment of aerobic As(V)-reducing Caulobacter leidyi, Sphingomonas yanoikuyae, and Rhizobium loti -like populations after liming. Arsenite was rapidly oxidized to As(V) via microbial activity in unsaturated Madison River Valley soil columns. Eight aerobic heterotrophic bacteria with varying As redox phenotypes were isolated from these columns. Three isolates, identified as Agrobacterium tumefaciens, Pseudomonas fluorescens, and Variovorax paradoxus -like organisms, were As(III) oxidizers and all were apparently important members of the soil microbial community responsible for net As(III) oxidation. Successional changes in microbial communities colonizing an As-rich acid-sulfate-chloride geothermal spring stream channel in Norris Geyser Basin of Yellowstone National Park were examined. Enhanced As(III) oxidation correlated in time and space with the appearance of three Hydrogenobaculum -like populations. The formation of an As(V)-rich hydrous-ferric-oxide mat correlated with the detection of Thiomonas, Acidimicrobium, and Metallosphaera —like populations whose nearest cultivated relatives (based on 16S rDNA sequence) were Fe-oxidizers. Fingerprints of microbial communities (DGGE) established under increasing concentrations of 2,4-D (0 - 500 mg kg'1) in batch soil microcosms showed that at least 100 mg kg'1 2,4-D was required to obtain apparent shifts in community structure. The microbial community selected at high 2,4-D concentrations was predominantly composed of Burkholderia -like populations, which harbored homologs of tfdA genes.