D. Vaughan

Microbial biomass and activity in soils amended with glucose

Abstract Four contrasting soils were amended with glucose at concentrations up to 10 mg g−1 soil. The soils were incubated at 22°C for 14 days and the biomass determined at various times by chloroform fumigation or substrate-induced respiration. The adenosine triphosphate (ATP) content or the amylase and dehydrogenase activities were also determined. The size of the increases in biomass, ATP content and the enzyme activities was generally related to the amount of glucose added. The initially higher ATP levels quickly declined, and apparent substrate conversion figures up to 84% indicated that substrate-induced respiration overestimated the biomass. There were generally no significant correlations between ATP, biomass or enzyme activities.

Changes in microbial biomass and activity in soils amended with phenolic acids

Abstract The phenolic acids p -hydroxybenzoic, ferulic, caffeic and vanillic acid, were added to soil of the Countesswells series that had been fallow or carried crops of potatoes, peas or barley for two consecutive years. Changes in phenolic acid concentration, the soil biomass, the respiration rate, and soil amylase activity were measured over 28 days. All the phenolic acids were sorbed by the soils which was generally in the order caffeic > ferulic = vanillic > hydroxybenzoic acid. The phenolic acids stimulated soil respiration and increased the biomass as determined by the substrate-induced respiration method. but the fumigation method of biomass assessment gave anomalous results. The soil amylase activity was initially increased by phenolic acid amendments but soon decreased, and after 7 days was less than in non-amended soil although activity had increased again after 28 days. The rates of respiration and the total phenolic acid concentrations were similar to unamended controls after 28 days. The immediate respiration response, measured 1–6 h after amendment, indicated that caffeic acid gave the largest initial response of the phenolic tested, this being 55–72% of that given by glucose. Soil from the potato plot showed the highest immediate response to the phenolic acid amendments measured as a proportion of the respiration response to glucose. The findings suggest that some crops stimulate the growth of phenolic-acid degrading organisms.

Effects of hydroxyproline on the growth of excised root segments of Pisum sativum under aseptic conditions

SummaryThe cis and trans isomers of 4-hydroxy-l-proline stimulated the extension growth of excised 2–4 mm pea root segments during culture. Increase in the uptake and subsequent incorporation of [14c]leucine into proteins was inhibited by both l-isomers, and so also were changes in chloride uptake capacity and in protein metabolism measured in terms of invertase and peroxidase activities. Changes in [14C]proline uptake and incorporation, and in respiration, were unaffected. Proline had no effect on changes in extension growth or protein metabolism but did prevent the effects of both hydroxyproline isomers. Azetidine-2-carboxylic acid inhibited extension growth and all the aspects of protein metabolism studied, the effects again being all prevented by proline. It is suggested that hydroxyproline enhances growth by interfering with protein synthesis in the cell walls.

Effects of Hydroxyproline on the Growth and Cell-Wall Protein Metabolism of Excised Root Segments of Pisum sativum

SummaryHydroxyproline, in the presence of sucrose, enhanced the extension growth of excised 2–4 mm pea root segments in aseptic media. About 90% of protein-bound hydroxyproline in the pea root segments was confined to the cell-wall fraction where it occurred as trans-4-hydroxy-l-proline. The amounts of wall-bound hydroxyproline increased dramatically towards the cessation of extension growth, but when the segments were cultured in trans-hydroxyproline, this increase was considerably less.Externally supplied cis and trans-hydroxyproline inhibited the formation of protein-bound [14C]hydroxyproline from [14C]proline without affecting the total amount of [14C]proline incorporated into proteins. Studies with αα′-dipyridyl showed that, although some of the externally supplied trans-[14C]hydroxyproline was incorporated directly into cell-wall proteins, most of it was first converted into proline which was then incorporated into proteins and subsequently reconverted, in part, into hydroxyproline. The effect of externally supplied hydroxyproline is discussed in relation to protein-bound proline hydroxylation.

Exudation of peroxidase from roots of Festuca rubra and its effects on exuded phenolic acids

Peroxidase is exuded from roots of Festuca rubra under axenic conditions. No phenolase was detected. Peroxidase can use phenolic acids. probably differentially, as hydrogen donors for the H2O2 substrate and could thus have an effect on the qualitative and quantitative determinations of phenolic acids also exuded by plants.

Effects of some chelating and phenolic substances on the growth of excised pea root segments

SummarySeveral chelating substances, such as 2,2′-dipyridyl, 8-hydroxyquinoline and desferal enhanced the growth of elongating segments of excised pea root tips when cultured in the presence of 2% sucrose, but their non-chelating analogues such as 4,4′-dipyridyl and 2-hydroxyquinoline were without effect. Some phenolic substances, such as cinnamic, ferulic, chlorogenic and caffeic acids, also enhanced the growth of excised segments. In general the substances which enhanced cell elongation also enhanced the development of invertase, but generally they did not enhance the increase in peroxidase activity or have any effect on the decrease in RNA content.[14C]cinnamic acid was continuously incorporated into the cell walls of elongating segments from which it could only be partially removed with NaOH, pronase, or HClO4. There was some evidence that the radioactivity was transferred from the cytoplasm and not incorporated directly into the cell walls. The implications of these results are discussed.

Amelioration by Volutella ciliata of the phytotoxicity of vanillic acid towards the growth of Pisum sativum L

Abstract An apparatus is described for studying the interaction between soil fungi and the growth of higher plants in the presence of specific phytotoxins. At concentrations above 1 mm, caffeic and vanillic acids inhibited the growth of Pisum sativum cultured in nutrient solutions under axenic conditions. Soil fungi capable of using phenolic acids as energy sources were isolated from soil on kaolin aggregates into which a phenolic acid had been incorporated. Some of the fungi ( Volutella ciliata, Gliocladium roseum and a Penicillium sp.) were isolated on to agar plates and grown in nutrient solutions containing a specific phenolic acid. One of the fungal isolates, V. ciliata , was compared with an XAD-4 resin, for effectiveness in reducing a phytotoxic concentration of vanillic acid towards the growth of pea seedlings. Reducing the concentration of vanillic acid from 1 to 0.2 mm enhanced the growth of the main root and increased the number of laterals so that the root system resembled that of control plants without the phenolic acid. The precise effect depended on the age of the plant when the phytotoxic concentration of the vanillic acid was reduced. At a 1 mM concentration of NO 3 -N (10% of concentration in the usual nutrient solution), concentrations as low as 10 μm vanillic acid were phytotoxic towards the growth of pea seedlings, and this effect was also ameliorated by V. ciliata . The V. ciliata produced no phytotoxins per se . Reducing phytotoxic concentrations of vanillic acid during the first 3 days of culture was more effective than subsequent reduction, and after 8 days the plants did not recover subsequently.

Scanning electron microscopy of calcium oxalate on mantle hyphae of hybrid larch roots from a farm forestry experimental site

Abstract An examination of roots of hybrid larch from a farm forestry site by scanning electron microscopy has revealed crystalline deposits encrusting mantle hyphae of the associated ectomycorrhizal fungus. Electron probe micro-analysis identified calcium in the crystals and X-ray diffraction showed them to be whewellite, the monohydrate form of calcium oxalate. The significance of the finding is discussed.

Distribution of soil invertase in relation to the root systems of Picea sitchensis (Bong.) carr. and Acer pseudoplatanus L. during development of young plants

A method is described for sampling rhizosphere soil under newly establishedPicea sitchensis andAcer pseudoplatanus. The technique involves taking soil samples to a depth of 150 mm at 100 mm intervals along transects, each 45° from its neighbour, radiating from the base of the stem. Invertase activities were measured in the soil samples and compared to their activities in fallow and rhizosphere soils. When the field soil was dry, the tree root systems were carefully excavated to retain as many fine roots as possible. The distribution of the soil invertase was matched to the spatial distribution of the roots showing the precise position of the rhizosphere relative to the initial ‘blind’ soil sampling. Statistics were applied to derive equations for calculating the percentage enzyme activity relative to that found in rhizosphere soil at various locations radiating from the base of the stem. This information was subsequently applied to soil sampled under trees of the same age as those excavated to give a non-destructive method for sampling rhizosphere soil routinely from under a large number of trees.

A critical examination of SEM ultrastructural features in two Penicillium thomii isolates from soil

A SEM ultrastructural study of two isolates of a soil fungus, Penicillium thomii, is presented, which compares the morphology of critical point-dried tissues with cryofixed material. The paper also reports features of the isolates which sometimes are different from the usual diagnostic morphological data for this fungus. Thus, branched penicilli have been seen in one of the isolates on MEA, yet monoverticillate penicilli are regarded as a major feature of P. thomii. In the same isolate the stipes appear non-vesiculate on both agars unlike the vesiculate stipes normally associated with this species from light microscope observations. Some wrinkling is seen in the stipes and phialides from critical point-dried specimens and this phenomenon is generally absent in cryofixed samples, although in one isolate, collapse of some of the phialides occurred. Critical point-drying results in shrinkage of conidia. Penicillium thomii is an important species in soil ecosystems and thus an accurate description of its morphological features is desirable for proper classification although it is a widely held belief that no character in Penicillium taxonomy is totally invariant.