VARIATION IN ALCOHOL DEHYDROGENASE ACTIVITY AND FLOOD TOLERANCE IN WHITE CLOVER,TRIFOLIUM REPENS

Flooding results in induction of anaerobic metabolism in many higher plants. As an important component of anaerobic energy production, alcohol dehydrogenase (ADH) activity increases markedly in response to flooding in white clover, Trifolium repens. Significant inter-individual variation in flood-induced ADH activity exists in natural populations of T. repens. The genetic basis of this variation was analyzed by offspring-midparent regression of data from 75 greenhouse reared families; the estimated heritability of flood-induced ADH activity was 0.55 (±0.13). Genetic variation in flood-induced ADH activity has pronounced effects on physiological response and flood tolerance in this species. ADH activity is positively correlated with the rate of ethanol production, indicating that observed in vitro activity differences are manifested in in vivo physiological function. T. repens plants with higher ADH activities during flooding have greater flood tolerance (measured as growth rate when flooded/unflooded growth rate). Variation in ADH activity during flooding accounts for more than 79% of the variance in flood tolerance. On the basis of a limited field survey of populations occupying three sites differing in exposure to flooding conditions, individuals from site C, the most frequently flooded site, expressed significantly higher average ADH activity when flooded than individuals from site A, a site with no history of flooding. Since ADH activity levels are not correlated with electrophoretic mobility variation in T. repens, this work supports previous suggestions that regulatory variation in enzyme activity may play a central role in biochemical adaptations to environmental stress.     

Are Sulfurous Soil Amendments (S0, Fe(II)SO4, Fe(III)SO4) an Effective Tool in the Restoration of Heathland and Acidic Grassland after Four Decades of Rock Phosphate Fertilization?

This paper deals with the complex issue of reversing long‐term improvements of fertility in soils derived from heathlands and acidic grasslands using sulfur‐based amendments. The experiment was conducted on a former heathland and acid grassland in the U.K. that was heavily fertilized and limed with rock phosphate, chalk, and marl. The experimental work had three aims. First, to determine whether sulfurous soil amendments are able to lower pH to a level suitable for heathland and acidic grassland re‐creation (approximately 3 pH units). Second, to determine what effect the soil amendments have on the available pool of some basic cations and some potentially toxic acidic cations that may affect the plant community. Third, to determine whether the addition of Fe to the soil system would sequester PO₄^? ions that might be liberated from rock phosphate by the experimental treatments. The application of S⁰ and Fe^(II)SO₄^? to the soil was able to reduce pH. However, only the highest S⁰ treatment (2,000 kg/ha S) lowered pH sufficiently for heathland restoration purposes but effectively so. Where pH was lowered, basic cations were lost from the exchangeable pool and replaced by acidic cations. Where Fe was added to the soil, there was no evidence of PO₄^? sequestration from soil test data (Olsen P), but sequestration was apparent because of lower foliar P in the grass sward. The ability of the forb Rumex acetosella to apparently detoxify Al³⁺, prevalent in acidified soils, appeared to give it a competitive advantage over other less tolerant species. We would anticipate further changes in plant community structure through time, driven by Al³⁺ toxicity, leading to the competitive exclusion of less tolerant species. This, we suggest, is a key abiotic driver in the restoration of biotic (acidic plant) communities.     

33P translocation in the thallus of the mat-forming lichen Cladonia portentosa

The extent of vertical migration of ³³P in thalli of the heathland lichen Cladonia portentosa was investigated under field conditions. ³³P-labelled orthophosphate was introduced into the bottom 25 mm of podetia cut to a length of 50 mm from the apices. The distribution of label was scanned using a molecular imager immediately after incubation, and after growing for 8 wk and 6 months. Differences in the relative distribution of label between podetia harvested at the beginning and the end of the experiment showed that there had been a significant migration of ³³P upwards out of the labelled 25 mm stratum towards the apex. This was confirmed by statistically significant changes in the median (md) and the 90 percentile of total relative distribution of ³³P label. In a control treatment in which label was introduced into the apical 25 mm of podetia, which were then grown inverted (top down), no upward movement of label was detected. By contrast, a statistically significant reduction in the md of the distribution indicated migration downwards towards the thallus apex. The results are consistent with the hypothesis that P is recycled within podetia of mat-forming lichens, migrating from degrading basal regions upwards to the growing apices following a source–sink relationship.     

Pheophytin-mediated energy storage of photosystem II particles detected by photoacoustic spectroscopy

The photoacoustic (PA) characteristics (energy storage and heat dissipation) of photosystem II (PSII) core-enriched particles from barley were studied (i) in conditions where there was electron flow, i.e., in the presence of a combination of the electron acceptor K₃ Fe (CN)₆, referred to as FeCN, and the electron donor diphenylcarbazide (DPC), and (ii) in conditions where electron flow was suppressed, i.e., in the absence of FeCN and DPC. The experimental data show that a decrease of heat dissipation with a minimum at 540 nm can be interpreted as energy storage resulting from the presence of pheophytin (Pheo) in the PSII particles. On account of the capability of the PA method to measure the energy absorbed by the chromophores which is converted to heat, it is suggested that the PA detection of Pheo present in the PSII complex will permit to clarify the function of processes involving non-radiative relaxation of excited states in P680-Pheo-Q_A interactions.Abbreviations -Car -Carotene - Chl Chlorophyll - DPC Diphenylcarbazide - EPR Electron Paramagnetic Resonance - FeCN potassium ferricyanide - HEPES N-2-hydroxyethylenepiperazine-N-2-ethanesulfonate - P680 reaction center of PSII - PA Photoacoustic - Pheo pheophytin - PSI photosystem I - PSII photosystem II - Q_A primary electron acceptor of PSII     

Determination of “active” cytochrome P-450 from relaxation kinetics of product formation

We estimate the active part of cytochrome P-450, which is involved in a special substrate transformation, by measuring the initial change of the production rate as a function of the relaxation transitions between two different steady states of the reaction cycle of cytochrome P-450 using the light-reversibility of the carbon monoxide inhibition. The kinetic data of such relaxations are interpreted within a model cycle, which reduces the reaction cycle to three steps. The estimation of the rate constant of the first reduction step, derived from model simulation of the production rate, is confirmed by independent experimental study of the reduction kinetics.An application of our model to the O-deethylation of 7-ethoxycoumarin reveals that — in a time average — 10%–15% of the spectroscopically detectable cytochrome P-450 is involved in that transformation.Abbreviations Cyt. P-450 microsomal cytochrome P-450 - 7-EC 7-ethoxycoumarin     

Participation of capsaicin-sensitive neurons in the cardiovascular effects of neurotensin in guinea pigs

Intravenous (IV) infusions of neurotensin (NT) in anesthetized guinea pigs elicited dose-dependent pressor effects and tachycardia. Both effects were significantly reduced or abolished in guinea pigs given a chronic treatment with the neurotoxin capsaicin. In guinea pig isolated atria NT evoked a positive inotropic and chronotropic effect. Both effects were completely abolished in atria derived from capsaicin-treated guinea pigs. The positive inotropic and chronotropic effects of NT in guinea pig atria were mimicked by capsaicin and calcitonin gene-related peptide (CGRP). These results were interpreted as an indication that NT produces its cardiovascular effects in guinea pigs by activating capsaicin-sensitive sensory neurons.     

Conversion of Neuropeptide K to Neurokinin A and Vesicular Colocalization of Neurokinin A and Substance P in Neurons of the Guinea Pig Small Intestine

The highest concentration of neurokinin A-like immunoreactivity and substance P-like immunoreactivity in the guinea pig small intestine was associated with the myenteric plexus-containing longitudinal muscle layer. Chromatographic analysis of extracts of this tissue demonstrated the presence of neurokinin A and neuropeptide K but the probable absence of neurokinin B. A fraction of synaptic vesicles of density 1.133 +/- 0.003 g/ml was prepared from the myenteric plexus-containing tissue by density gradient centrifugation in a zonal rotor and was enriched 29 +/- 12-fold in the concentration of neurokinin A-like immunoreactivity and 43 +/- 13-fold in the concentration of substance P-like immunoreactivity. This fraction was separated from the fraction of vasoactive intestinal peptide-containing vesicles (density, 1.154 +/- 0.009 g/ml). Chromatographic analysis of lysates of the vesicles indicated the presence of neurokinin A but not neuropeptide K. It is postulated that beta-pre-protachykinin is processed to substance P, neurokinin A, and neuropeptide K in the cell bodies of myenteric plexus neurons but that conversion of neuropeptide K to neurokinin A takes place during packaging into storage vesicles for axonal transport. The data are consistent with the proposal that neurokinin A and substance P are stored in the same synaptic vesicle, but the possibility of cosedimentation of different vesicles of very similar density cannot be excluded.     

Transductional analysis of chromosome replication time

Summary Following transduction of exponentially growing cultures of Escherichia coli with phage P1, cells with recombinant phenotype begin to increase in number after an initial lag of about one generation time. We show that transductants for markers located at different positions on the chromosome begin to increse at different times, in reverse order to that in which they are replicated. The period over which this happens is equal in duration to the time taken to replicate the chromosome and we have used this relationship to calculate the C-period of E. coli K12 growing at 30°C. We exclude transduction-induced filamentation as the cause of the initial lag and suggest that the lag may result from the way in which donor DNA is inherited.     

Induced tolerance of neonate Heliothis zea to host plant allelochemicals and carbaryl following incubation of eggs on foliage of Lycopersicon hirsutum f. glabratum

Summary Incubation of Heliothis zea (Boddie) eggs on foliage of Lycopersicon hirsutum f. glabratum C.H. Mull (accession PI 134417) results in neonates with elevated levels of tolerance to the toxic effects of PI 134417 foliage attributable to 2-tridecanone found in the glandular trichomes which abound on that foliage. The neonates from such eggs are also shown to have elevated levels of tolerance to the carbamate insecticide carbaryl. Incubation of eggs in an atmosphere containing 2-tridecanone similarly produced elevated levels of tolerance to 2-tridecanone among resulting neonates, indicating that 2-tridecanone is the likely inducing agent and that exposure to 2-tridecanone vapor, which is known to emanate from PI 134417 foliage, is sufficient for induction. Analysis of the cytochrome P-450 content in gut microsomes of fifth instar larvae indicated that exposure of larvae to 2-tridecanone in artificial diet or to PI 134417 foliage resulted in significantly elevated levels of cytochrome P-450 relative to larvae fed diet without 2-tridecanone or foliage of L. esculentum which contains no 2-tridecanone. In addition, removal of the glandular trichomes from PI 134417 foliage eliminated the ability of that foliage to induce elevated levels of cytochrome P-450. These results provide circumstantial evidence that cytochrome P-450 may be involved in the induced tolerance to xenobiotics among neonates from eggs exposed to 2-tridecanone or PI 134417 foliage.Support for this research was provided by the USDA Competitive Research Grants Program in Biological Stress under Grant No. 83-CRCR-1-1241 and Grant No. 85-CRCR-1-1615, and the North Carolina Agricultural Research Service. Paper No. 10856 of Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC, USA 27650. Use of trade names does not imply endorsement of products named nor criticisms of similar ones not mentioned     

Phytochrome-mediated regulation of β-amylase mRNA level in mustard (Sinapis alba L.) cotyledons

Phytochrome, activated by continuous red light, increases the amount of total polyadenylated RNA during photomorphogenesis of mustard (Sinapis alba L.) cotyledons. In-vitro translation of total polyadenylated RNA in a reticulocyte translation system has shown that the activity of translatable -amylase mRNA is increased by phytochrome about threefold in the 3-d-old cotyledons, based on equal amounts of polyadenylated RNA, and about eightfold on a per-cotyledon basis. Cordycepin prevents the accumulation of translatable -amylase mRNA. It is concluded that the phytochrome-mediated control of -amylase synthesis is exerted on the level of mRNA synthesis. During seedling development in continuous red light, a phytochrome-dependent increase of -amylase mRNA can be observed at least 6 h before the onset of -amylase synthesis. If, after a period of enzyme synthesis, phytochrome action is interrupted by long-wavelength far-red light followed by darkness, -amylase mRNA as well as -amylase synthesis remain at a high level for 8–10 h and then decline sharply. It is concluded that -amylase mRNA, having an apparent lifetime of the order of 8–10 h, can be formed under the influence of phytochrome during early seedling development but it activates -amylase synthesis only after a lag-phase of about 8 h, when the cotyledons acquire competence to synthesize the enzyme. The consequences of these findings for the signal-transduction chain of phytochrome are discussed.Abbreviations EDTA Na₂-ethylenediaminotetraacetic acid - PAGE polyacrylamide gel electrophoresis - poly(A)⁺RNA polyadenylated mRNA - P_r, P_fr red- and far-red-absorbing forms of phytochrome - SDS sodium dodecyl sulfate - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol