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PubMed1989

Transfer of radioactive caesium from soil to vegetation and comparison with potassium in upland grasslands.

The distribution and transfer of caesium and potassium between soils and vegetation has been investigated by field sampling and experimental studies on soils and vegetation typical of upland grassland in north west England. Total (137)Cs content to a depth of 0.05 m below root matt ranged from 13 000 to 18 000 Bq m(-2). This caesium content derives from three sources: the Windscale accident of 1957, weapons-testing fallout which peaked in the early 1960s, and the Chernobyl accident in May 1986. From 2200 to 6200 Bq m(-2) is attributed to the first two sources, and the remainder to Chernobyl. In December 1986, 23-78% of pre-Chernobyl (137)Cs was associated with soil underlying root matt and 0.5-5.5% was associated with vegetation. Plant/soil concentration ratios for pre-Chernobyl (137)Cs were in the range 0.5-6.5, the lowest values being associated with patches of Festuca/Agrostis turf. At the same time, 4-19% of (137)Cs deposited from Chernobyl was associated with vegetation, although higher values appeared in conjunction with the moss, Polytrichum commune. Corresponding total potassium contents were in the range 9.6-22 mg m(-2) to 0.05 m soil depth. Lower values were found at the wetter sites where, on average, 5.7% of the total potassium was present in vegetation. At drier sites the potassium content was higher and, on average, 8.9% was present in vegetation. Plant/soil concentration ratios ranged from 2.2 to 9.2. During accelerated growth of vegetation, on monoliths in glasshouse conditions over the winter of 1986/87, (137)Cs was transferred from soil and root matt to new growth, such that concentrations in fresh growth were similar to or higher than those observed in the field during December 1986. Removal of caesium by successive cuts resulted in up to 25% of the original estimated total being removed over a 240 day period. Increased concentrations coincided with the emergence of Carex sp. and Trichophorum caespitosum, as well as the development of Agrostis sp. and Festuca ovina. Observed Cs/K discrimination ratios, particularly for (137)Cs deposited from Chernobyl, were higher than previously reported in the literature. The experimental results were confirmed by field observations during spring 1987 and it is concluded that caesium deposited as a result of the Chernobyl accident will continue to be recycled in organic and low potassium soils.

Journal Article↗

PubMed2006

Thermal inactivation of Bacillus cereus and Clostridium perfringens vegetative cells and spores in pork luncheon roll.

The aim of this study was to design a thermal treatment(s) for pork luncheon roll, which would destroy Bacillus cereus and Clostridium perfringens vegetative cells and spores. B. cereus and C. perfringens vegetative and spore cocktails were used to inoculate luncheon meat. Samples were subjected to different temperatures and removal times. The decimal-reduction times (D-values) were calculated by linear regression analysis (D = -1/slope of a plot of log surviving cells versus time). The log(10) of the resulting D-values were plotted against their corresponding temperatures to calculate (-1/slope of the curve) the thermal resistance (z-values) of each cocktail. The D-values for vegetative cells ranged from 1 min (60 degrees C) to 33.2 min (50 degrees C) for B. cereus and from 0.9 min (65 degrees C) to 16.3 min (55 degrees C) for C. perfringens. The D-values for B. cereus spores ranged from 2.0 min (95 degrees C) to 32.1 min (85 degrees C) and from 2.2 min (100 degrees C) to 34.2 min (90 degrees C) for C. perfringens. The z-values were calculated to be 6.6 and 8.5 degrees C for B. cereus vegetative and spores, respectively, and 7.8 and 8.4 degrees C for C. perfringens vegetative cells and spores, respectively. The D-values of B. cereus and C. perfringens suggest that a mild cook of 70 degrees C for 12s and 1.3 min would achieve a 6 log reduction of B. cereus and C. perfringens vegetative cells, respectively. The equivalent reduction of B. cereus and C. perfringens spores would require the pork luncheon meat to be heated for 36 s at 105 and 110 degrees C, respectively. The results of this study provide the thermal inactivation data necessary to design a cooking protocol for pork luncheon roll that would inactivate B. cereus and C. perfringens vegetative cells and spores. The data may also be used in future risk assessment studies.

Animals↗

PubMed2006

Vegetation and carbon sequestration and their relation to water resources in an inland river basin of Northwest China.

In the Heihe River Basin in the arid inland area of northwest China, the distribution of water resources in vegetation landscape zones controls the ecosystems. The carbon sequestration capacity of vegetation is analyzed in relation to water resources and vegetation growing conditions. During the last 20 years, the vegetation ecosystems have degenerated in the Heihe River Basin. Simulation using the C-FIX model indicates that, at present, the total amount of NPP of vegetation accounts for about 18.16 TgC, and the average value is 106 gC/m(2)/yr over the whole basin. NPP has generally the highest value in the upperstream mountain area, middlestream artificial oases area, downstream river bank area, alluvial fan and the terminal lake depression where vegetation grows relatively well. The lowest value is found in the vast downstream desert and Gobi area. Protection of vegetation ecosystems and enhancement of carbon sequestration require such inland river basins as the Heihe River Basin to be brought under management in a comprehensive way, taking water as a key, to carry out a rational and efficient allocation and utilization of water resources.

Altitude↗

PubMed2006

Activated carbon adsorption of PAHs from vegetable oil used in soil remediation.

Vegetable oil has been proven to be advantageous as a non-toxic, cost-effective and biodegradable solvent to extract polycyclic aromatic hydrocarbons (PAHs) from contaminated soils for remediation purposes. The resulting vegetable oil contained PAHs and therefore required a method for subsequent removal of extracted PAHs and reuse of the oil in remediation processes. In this paper, activated carbon adsorption of PAHs from vegetable oil used in soil remediation was assessed to ascertain PAH contaminated oil regeneration. Vegetable oils, originating from lab scale remediation, with different PAH concentrations were examined to study the adsorption of PAHs on activated carbon. Batch adsorption tests were performed by shaking oil-activated carbon mixtures in flasks. Equilibrium data were fitted with the Langmuir and Freundlich isothermal models. Studies were also carried out using columns packed with activated carbon. In addition, the effects of initial PAH concentration and activated carbon dosage on sorption capacities were investigated. Results clearly revealed the effectiveness of using activated carbon as an adsorbent to remove PAHs from the vegetable oil. Adsorption equilibrium of PAHs on activated carbon from the vegetable oil was successfully evaluated by the Langmuir and Freundlich isotherms. The initial PAH concentrations and carbon dosage affected adsorption significantly. The results indicate that the reuse of vegetable oil was feasible.

Adsorption↗

PubMed2006

Electric and structural studies of hormone interaction with chloroplast envelope membranes isolated from vegetative and generative rape.

The electric and structural properties of envelope membranes of chloroplasts obtained from vegetative and generative plants of rape and the effect of hormone (IAA, GA(3) and zearalenone) treatment were determined by zeta potential and small-angle X-ray scattering (SAXS) methods. Chloroplasts were isolated from leaves cut off from the vegetative (before cooling) and generative apical parts of plants. The lipid composition of chloroplast envelope membranes were analyzed by chromatographic techniques. Envelopes from generative plants contained higher levels of digalactosyldiacylglycerol (DGDG) and smaller amounts of phospholipids (PLs) in comparison to those obtained from vegetative ones. Moreover, envelopes of generative plants were characterized by higher fractions of unsaturated fatty acids. The zeta potential changes caused by hormone treatment were higher for chloroplasts isolated from vegetative plants in comparison to chloroplasts isolated from generative ones. An especially strong effect was observed for chloroplasts treated with IAA. The thickness of bilayers of untreated chloroplasts from vegetative plants were larger by 0.4 nm when comparing to the thickness of layers obtained from generative ones. The effect of hormones (GA(3) and zearalenone) was detected only for vegetative chloroplasts. Both applied methods indicated differences in the properties of untreated and hormone-treated chloroplasts obtained from vegetative and generative plants.

Brassica napus↗

PubMed2000

Pollen fall-out from a tropical vegetation mosaic.

Pollen fall-out into 60 Oldfield traps set in 11 localities and a variety of vegetational contexts on an upland in tropical northeast Australia, range from 0.5k to 20k (mean 3.5k)grcm(-2)a(-1). The ranges attributable to the four major vegetation types in which the traps were situated overlap to such an extent as would make it virtually impossible to allocate an 'unknown' pollen count to a vegetation type on the basis of total pollen influx alone. Nevertheless, the composition of the pollen clearly differs according to the vegetation in which it is trapped and the amounts of other vegetation types within at least 100m. Substantial variations in catches from closely placed traps suggest the influence of very local site, including meteorological, conditions on the results. Pollen is carried between vegetation types, much less far from rainforest than from sclerophyll forest and woodland, regrowth scrub or herbaceous vegetation, but there is no numerically significant ubiquitous 'background' fall-out in the region. The data impose some constraints on the interpretation of fossil pollen spectra but also potentially permit a greater precision in some aspects of such applications.

Journal Article↗

PubMed2004

Exploring field vegetation reflectance as an indicator of soil contamination in river floodplains.

This study investigated the relation between vegetation reflectance and elevated concentrations of the metals Ni, Cd, Cu, Zn and Pb in river floodplain soils. High-resolution vegetation reflectance spectra in the visible to near-infrared (400-1350 nm) were obtained using a field radiometer. The relations were evaluated using simple linear regression in combination with two spectral vegetation indices: the Difference Vegetation Index (DVI) and the Red-Edge Position (REP). In addition, a multivariate regression approach using partial least squares (PLS) regression was adopted. The three methods achieved comparable results. The best R(2) values for the relation between metals concentrations and vegetation reflectance were obtained for grass vegetation and ranged from 0.50 to 0.73. Herbaceous species displayed a larger deviation from the established relationships, resulting in lower R(2) values and larger cross-validation errors. The results corroborate the potential of hyperspectral remote sensing to contribute to the survey of elevated metal concentrations in floodplain soils under grassland using the spectral response of the vegetation as an indicator. Additional constraints will, however, have to be taken into account, as results are resolution- and location-dependent.

Environmental Monitoring↗

PubMed2001

Why vegetable recipes are not very spicy.

Spices are aromatic plant materials that are used in cooking. Recently it was hypothesized that spice use yields a health benefit: cleansing food of parasites and pathogens before it is eaten, thereby reducing food poisoning and foodborne illnesses. In support, most spices have antimicrobial properties and use of spices in meat-based recipes is greatest in hot climates, where the diversity and growth rates of microorganisms are highest. A critical prediction of the antimicrobial hypothesis is that spices should be used less in preparing vegetables than meat dishes. This is because cells of dead plants are better protected physically and chemically against bacteria and fungi than cells of dead animals (whose immune system ceased functioning at death), so fewer spices would be necessary to make vegetables safe for consumption. We tested this corollary by compiling information on 2129 vegetable-only recipes from 107 traditional cookbooks of 36 countries. Analyses revealed that spice use increased with increasing ambient temperature, but less dramatically than in meat-based recipes. In all 36 countries, vegetable dishes called for fewer spices per recipe than meat dishes; 27 of these differences were significant. Of 41 individual spices, 38 were used less frequently in vegetable recipes; 30 of these differences were significant. Proportions of recipes that called for >1 spice and >1 extremely potent antimicrobial spice also were significantly lower for vegetable dishes. By every measure, vegetable-based recipes were significantly less spicy than meat-based recipes. Within-country analyses control for possible differences in spice plant availability and degrees of cultural independence. Results thus strongly support the antimicrobial hypothesis.

Journal Article↗

PubMed2001

Hepatocyte fatty acid desaturation and polyunsaturated fatty acid composition of liver in salmonids: effects of dietary vegetable oil.

The desaturation and elongation of [1-(14)C]18:3n-3 was investigated in hepatocytes from different populations and three different species of salmonids indigenous to Scotland, brown trout, Atlantic salmon and Arctic charr. Two groups of fish were sampled, before and after they were fed two experimental diets, a control diet containing fish oil and a diet containing vegetable oil (a 1:1 blend of linseed and rapeseed oils) for 12 weeks. At each sampling time, fatty acyl desaturation and elongation activity was determined in isolated hepatocytes, and samples of liver were also collected for lipid compositional analysis. At the initiation of the dietary trial, the liver polar-lipid fatty acid compositions of salmon and brown trout were very similar to each other, and the two charr populations were similar to each other, having lower total n-3 polyunsaturated fatty acids (PUFA) and 22:6n-3, but higher 20:5n-3 than the other salmonids. Initially, hepatocyte desaturation activity varied, with the highest activity in brown trout, followed by salmon and then charr. Production of 20:5n-3 was particularly high in brown trout. Desaturation of [1-(14)C]18:3n-3 was significantly greater in all fish fed the diet containing vegetable oil compared to fish fed the diet containing fish oil. The increase in activity was less in brown trout compared to the other groups of fish. Feeding the vegetable oil diet increased the levels of 18:2n-6, 20:3n-6, total n-6 PUFA, 18:3n-3, 18:4n-3, 20:3n-3 and 20:4n-3, and decreased 22:6n-3 and the n-3/n-6 ratio in salmon and brown trout. By contrast, in charr fed the vegetable oil diet, there was no increase in 18:3n-3, 18:4n-3, 20:3n-3 or 20:4n-3 in liver polar lipids and the level of 22:6n-3 was not decreased. In addition, there was only a modest increase in the levels of 18:2n-6 and total n-6 PUFA, and so the n-3/n-6 ratio was only slightly decreased. The percentage of 20:4n-6, which was not increased in salmon and brown trout fed vegetable oil, was increased in charr fed the vegetable oil diet. Overall, the results indicated that there were significant differences in liver PUFA metabolism between Arctic charr and the other salmonids, which could have important consequences, both physiologically and in their ability to be successfully cultured on diets containing vegetable oils.

Animal Feed↗

PubMed2005

Early increase in vegetative symptoms predicts IFN-alpha-induced cognitive-depressive changes.

BACKGROUND: The vegetative symptoms of depression resemble the symptoms of malaise associated with activation of the inflammatory response system (IRS), and can be regarded as an expression of a central motivational state that resets the organism's priorities to promote recovery from infection. Early vegetative symptoms, however, may also contribute to the high rates of depression seen later in the course of immune activation. We hypothesized that the onset of vegetative-depressive symptoms early in the treatment with the pro-inflammatory cytokine IFN-alpha in chronic hepatitis C patients would increase the risk for subsequent depressive cognitions. METHOD: Sixteen patients eligible for IFN-alpha treatment and free of psychiatric disorders were recruited. The DSM-IV, the Multidimensional Fatigue Inventory, and the Montgomery-Asberg Depression Rating Scale (MADRS) were administered at baseline and 1, 2, 4, 8, 12 and 24 weeks after treatment was initiated. Cognitive-depressive and vegetative-depressive symptom clusters were constructed. RESULTS: Fatigue and depression scores increased significantly during IFN-alpha treatment. Depression scores were highest at week 8 of treatment. First week increase in vegetative-depressive symptom score predicted cognitive-depressive symptom score at week 8 and at week 24. CONCLUSIONS: During IFN-alpha treatment, vegetative symptoms of depression appear earlier than, and are predictive of, their cognitive counterparts. This finding suggests that low mood state may in part be driven by the increase in early vegetative-depressive symptoms in the course of IFN-alpha-induced immune activation.

Adult↗

PubMed2002

Anti- and pro-oxidant water soluble activity of Cichorium genus vegetables and effect of thermal treatment.

Both the pro- and antiradical water soluble activity, toward DPPH(*), ROO(*), OH(*) radicals found in seven diet vegetables belonging to the Cichorium genus, and the effects of boiling, freezing, and freeze-drying on such activities were investigated. The vegetables were three red cultivars of Cichorium intybus var. silvestre from three different areas of production, that is, chicory from Chioggia, Treviso, and Verona, C. intybus var. foliosum (Belgian chicory), C. endivia var. latifolium (escarole), C. endiviavar. crispum ("crispa"), and a hybrid vegetable obtained by the cross between C. intybus var. silvestre and C. endivia var. latifolium (chicory from Castelfranco). The juices obtained by simple centrifugation of vegetables operating at 2 or 25 degrees C and submitted to the thermal technological treatments were assessed for antiradical activity using the DPPH(*) assay, the linoleic acid-beta-carotene system, and the deoxyribose assay. In all three assays used, each vegetable juice was shown to possess antiradical activity; there was a significant level in the C. endivia and the Belgian chicories and higher levels in the red C. intybus vegetables and the hybrid vegetable. All juice behaviors in the linoleic acid-beta-carotene system indicate that they also contain a thermally unstable component, which in a cold medium promptly promoted and accelerated linoleic acid peroxidation, therefore masking the presence of any thermally stable antiperoxyl radical components. The presence of these components, which efficiently protect linoleic acid from peroxidation, can be singled out only after inactivation by heating, or separation by dialysis, of the pro-oxidant components. Dialysis fractions showed that the pro-oxidant component has MW > 50000 Da and that the juices contain a number of antioxidant components which contribute to their antiradical activity.

Antioxidants↗

PubMed2000

Integrating remote sensing and local vegetation information for a high-resolution biogenic emissions inventory--application to an urbanized, semiarid region.

This paper presents a methodology for the development of a high-resolution (30-m), standardized biogenic volatile organic compound (BVOC) emissions inventory and a subsequent application of the methodology to Tucson, AZ. The region's heterogeneous vegetation cover cannot be modeled accurately with low-resolution (e.g., 1-km) land cover and vegetation information. Instead, local vegetation data are used in conjunction with multispectral satellite data to generate a detailed vegetation-based land-cover database of the region. A high-resolution emissions inventory is assembled by associating the vegetation data with appropriate emissions factors. The inventory reveals a substantial variation in BVOC emissions across the region, resulting from the region's diversity of both native and exotic vegetation. The importance of BVOC emissions from forest lands, desert lands, and the urban forest changes according to regional, metropolitan, and urban scales. Within the entire Tucson region, the average isoprene, monoterpene, and OVOC fluxes observed were 454, 248, and 91 micrograms/m2/hr, respectively, with forest and desert lands emitting nearly all of the BVOCs. Within the metropolitan area, which does not include the forest lands, the average fluxes were 323, 181, and 70 micrograms/m2/hr, respectively. Within the urban area, the average fluxes were 801, 100, and 100 micrograms/m2/hr, respectively, with exotic trees such as eucalyptus, pine, and palm emitting most of the urban BVOCs. The methods presented in this paper can be modified to create detailed, standardized BVOC emissions inventories for other regions, especially those with spatially complex vegetation patterns.

Air Pollution↗

PubMed1987

Topography of cell wall lytic enzyme in Chlamydomonas reinhardtii: form and location of the stored enzyme in vegetative cell and gamete.

Chlamydomonas lytic enzyme of the cell wall (gamete wall-autolysin) is responsible for shedding of cell walls during mating of opposite mating-type gametes. This paper reports some topographic aspects of lytic enzyme in cells. Both vegetative and gametic cells contain the same wall lytic enzyme. The purified enzyme is a glycoprotein with an apparent molecular mass of 67 kD by gel filtration and 62 kD by SDS PAGE, and is sensitive to metal ion chelators and SH-blocking agents. These properties are the same as those of the gamete wall-autolysin released into the medium by mating gametes. However, the storage form of the enzyme proves to be quite different between the two cell types. In vegetative cells, the lytic enzyme is found in an insoluble form in cell homogenates and activity is released into the soluble fraction only by sonicating the homogenates or freeze-thawing the cells, whereas gametes always yield lytic activity in the soluble fractions of cell homogenates. When vegetative cells are starved for nitrogen, the storage form of enzyme shifts from its vegetative state to gametic state in parallel with the acquisition of mating ability. Adding nitrogen to gametes converts it to the vegetative state concurrently with the loss of mating ability. We also show that protoplasts obtained by treatment of vegetative cells or gametes with exogenously added enzyme have little activity of enzyme in the cell homogenates, suggesting that lytic enzyme is stored outside the plasmalemma. When the de-walled gametes or gametes of the wall-deficient mutant, cw-15, of opposite mating types are mixed together, they mate normally but the release of lytic enzyme into the medium is practically negligible. When the de-walled vegetative cells are incubated, the lytic enzyme is again accumulated in the cells after the wall regeneration is almost complete.

Acid Phosphatase↗

PubMed2005

Vegetation's red edge: a possible spectroscopic biosignature of extraterrestrial plants.

Earth's deciduous plants have a sharp order-of-magnitude increase in leaf reflectance between approximately 700 and 750 nm wavelength. This strong reflectance of Earth's vegetation suggests that surface biosignatures with sharp spectral features might be detectable in the spectrum of scattered light from a spatially unresolved extrasolar terrestrial planet. We assess the potential of Earth's step-function-like spectroscopic feature, referred to as the "red edge," as a tool for astrobiology. We review the basic characteristics and physical origin of the red edge and summarize its use in astronomy: early spectroscopic efforts to search for vegetation on Mars and recent reports of detection of the red edge in the spectrum of Earthshine (i.e., the spatially integrated scattered light spectrum of Earth). We present Earthshine observations from Apache Point Observatory (New Mexico) to emphasize that time variability is key to detecting weak surface biosignatures such as the vegetation red edge. We briefly discuss the evolutionary advantages of vegetation's red edge reflectance, and speculate that while extraterrestrial "light-harvesting organisms" have no compelling reason to display the exact same red edge feature as terrestrial vegetation, they might have similar spectroscopic features at different wavelengths than terrestrial vegetation. This implies that future terrestrial-planet-characterizing space missions should obtain data that allow time-varying, sharp spectral features at unknown wavelengths to be identified. We caution that some mineral reflectance edges are similar in slope and strength to vegetation's red edge (albeit at different wavelengths); if an extrasolar planet reflectance edge is detected care must be taken with its interpretation.

Chlorophyll↗

PubMed1985

Penetration of beta-lactam antibiotics into cardiac vegetations, aorta and heart muscle in experimental Staphylococcus aureus endocarditis: comparison of ceftazidime, cefuroxime and methicillin.

The penetration of ceftazidime, cefuroxime and methicillin into cardiac vegetations, normal aorta wall tissue, heart muscle and heart muscle tissue fluid was measured in rabbits with Staphylococcus aureus (853E) endocarditis. After a 100 mg/kg intramuscular injection, ceftazidime attained significantly higher peak concentrations than cefuroxime and methicillin in all compartments with the exception of aorta where no difference was observed between ceftazidime and methicillin. The half life of ceftazidime in each compartment (50-65 min) was approximately twice that of cefuroxime and methicillin. The area under the concentration/time curve for ceftazidime in vegetations over a post dosing 6 h period was approximately five times greater than that for cefuroxime and three times that for methicillin. Ceftazidime remained for a longer time period in all compartments, however cefuroxime persisted the longest at supra-MIC concentrations in all compartments except serum. Compared to cefuroxime and methicillin where vegetation and aorta tissue levels were similar, ceftazidime attained peak levels in vegetations which were more than double those found in aorta tissue. Analysis of the percentage penetration from serum into vegetation, suggested that the higher concentrations of ceftazidime in vegetation tissue were probably not a function of increased fluid content relative to undamaged aorta but were more likely caused by an intrinsically better penetrating capacity for vegetation tissue.

Animals↗

PubMed2002

Brassica, biotransformation and cancer risk: genetic polymorphisms alter the preventive effects of cruciferous vegetables.

The chemoprotective effect of cruciferous vegetables is due to their high glucosinolate content and the capacity of glucosinolate metabolites, such as isothiocyanates (ITC) and indoles, to modulate biotransformation enzyme systems (e.g., cytochromes P450 and conjugating enzymes). Data from molecular epidemiologic studies suggest that genetic and associated functional variations in biotransformation enzymes, particularly glutathione S-transferase (GST)M1 and GSTT1, which metabolize ITC, alter cancer risk in response to cruciferous vegetable exposure. Moreover, genetic polymorphisms in receptors and transcription factors that interact with these compounds may further contribute to variation in response to cruciferous vegetable intake. This review outlines the metabolism and mechanisms of action of cruciferous vegetable constituents, discusses the recent human studies testing effects of cruciferous vegetables on biotransformation systems and summarizes the epidemiologic and experimental evidence for an effect of genetic polymorphisms in these enzymes on response to cruciferous vegetable intake. Taken together, genetic differences in biotransformation enzymes and the factors that regulate them, as well as variation in glucosinolate content of cruciferous vegetables and the methods used to prepare these foods underscore the multiple layers of complexity that affect the study of gene-diet interactions and cancer risk in humans.

Biotransformation↗

PubMed1983

An examination of the environmental half-time for radionuclides deposited on vegetation.

After radionuclides are deposited on vegetation, environmental removal processes combine with radioactive decay to reduce the quantity of initial contamination. The time in which one-half of the radioactivity is removed from vegetation by environmental processes alone is referred to as the environmental half-time, Tw. For long-lived radionuclides, the dose to man via ingestion of contaminated terrestrial foods may be directly influenced by values of Tw, provided that environmental removal processes dominate root uptake and time is sufficiently long between initial exposure of vegetation and harvest. Values of Tw reported in the literature for various radionuclides and methods of deposition are examined. Factors affecting the variability of Tw are related in part to the physicochemical form of the depositing substance, vegetation type and growth form, climate, season, and experimental procedure. For growing vegetation, values of Tw are generally lower than those reported for dormant vegetation. Values of Tw for iodine vapor and iodine particulate are less than values of Tw reported for particulates of other elements. Values of Tw determined on a per unit vegetation mass basis are also less than values of Tw determined on a per unit ground area basis, the differences being attributable to the effects of growth dilution. Although an assessor has a range from which to select a value of Tw for the purpose of estimating contamination by long-lived radionuclides, the variability in Tw is small in comparison to many other parameters used in environmental radiological assessments.

Half-Life↗

PubMed1995

Gibberellins promote vegetative phase change and reproductive maturity in maize.

Postembryonic shoot development in maize (Zea mays L.) is divided into a juvenile vegetative phase, an adult vegetative phase, and a reproductive phase that differ in the expression of many morphological traits. A reduction in the endogenous levels of bioactive gibberellins (GAs) conditioned by any one of the dwarf1, dwarf3, dwarf5, or anther ear1 mutations in maize delays the transition from juvenile vegetative to adult vegetative development and from adult vegetative to reproductive development. Mutant plants cease producing juvenile traits (e.g. epicuticular wax) and begin producing adult traits (e.g. epidermal hairs) later than wild-type plants. They also cease producing leaves and begin producing reproductive structures later than wild-type plants. These mutations greatly enhance most aspects of the phenotype of Teopod1 and Teopod2, suggesting that GAs suppress part but not all of the Teopod phenotype. Application of GA 3 to Teopod2 mutants and Teopod1, dwarf3 double mutants confirms this result. We conclude that GAs act in conjunction with several other factors to promote both vegetative and reproductive maturation but affect different developmental phases unequally. Furthermore, the GAs that regulate vegetative and reproductive maturation, like those responsible for stem elongation, are downstream of GA 20 in the GA biosynthetic pathway.

Gibberellins↗