Search Results - (Author, Cooperation:T. A. Day)

2013-03-15

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Adaptation, Physiological/*genetics ; Animals ; Biological Evolution ; Cestoda/drug effects/*genetics/physiology ; Cestode Infections/drug therapy/metabolism ; Conserved Sequence/genetics ; Echinococcus granulosus/genetics ; Echinococcus multilocularis/drug effects/genetics/metabolism ; Genes, Helminth/genetics ; Genes, Homeobox/genetics ; Genome, Helminth/*genetics ; HSP70 Heat-Shock Proteins/genetics ; Humans ; Hymenolepis/genetics ; Metabolic Networks and Pathways/genetics ; Molecular Targeted Therapy ; Parasites/drug effects/*genetics/physiology ; Proteome/genetics ; Stem Cells/cytology/metabolism ; Taenia solium/genetics

1365-3040

Blackwell Publishing Journal Backfiles 1879-2005

Biology

We assessed whether growth of garden pea (Pisum sativum mutant Argenteum) was reduced under ecologically relevant enhancements of ultraviolet-B radiation (UV-B, 280–320 nm) by employing modulated field lampbanks which simulated 0, 16 or 24% ozone depiction. In addition, we determined whether enhanced UV-B altered the concentration and distribution of chlorophyll and UV-B-absorbing compounds in leaves, and whether this was dependent on leaf age. There were no significant UV-B effects on the four whole-plant parameters we examined (height, above-ground biomass, total leaflet area or average leaflet area). Of the 12 leaf-level parameters we examined, UV-B had a significant effect (P 〈 0.05) on only one parameter: the ratio of UV-B-absorbing compounds to chlorophyll, which was greatest at the highest UV-B level. Total chlorophyll concentrations tended to be lower under enhanced UV-B (P= 0.11), while the proportion of UV-B-absorbing compounds in the adaxial epidermis tended to be higher (P= 0.11). Total leaf concentrations of UV-B-absorbing compounds were unaffected by UV-B level. Cooler, suboptimal growing conditions during this late summer/early autumn experiment may have masked some potential UV-B effects. In contrast to the UV-B effects, we found strong leaf-age effects on nearly all parameters that we assessed. On an area basis, concentrations of total chlorophyll and UV-B-absorbing compounds increased with leaf age, while Chlorophyll a/b) ratios decreased. One of the few parameters unaffected by leaf age was the ratio of UV-B-absorbing compounds to total chlorophyll, which remained constant within a given UV-B treatment. Pea was much less sensitive to enhanced UV-B than in previous growth-chamber and greenhouse studies, and in nearly all cases UV-B treatment effects were overshadowed by leaf-age effects. In view of the large effect leaf age had on concentrations of UV-B-absorbing compounds, as well as their distribution within leaves, researchers may need to consider leaf age in UV-B experimental designs.

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1365-3040

Blackwell Publishing Journal Backfiles 1879-2005

Biology

The depth of penetration of Ultraviolet-B (UV-B, 300 and 320 nm) and visible (680 nm) light was measured in foliage of Abies lasiocarpa and Picea engelmannii using a fibre-optic microprobe. Measurements were made on foliage at four times during development: needles were sampled from within expanding buds (in bud); within 72 h of emergence from the bud scales (emergent); from elongating branches (elongating); and from foliage that emerged the previous summer (mature). Light attenuation in pre-emergent needles of both species was steep and showed strong wavelength dependence. Short wavelength 300-nm light was attenuated strongly in the developing epidermal layer, but a significant proportion of this potentially damaging UV-B radiation penetrated into the mesophyll. For A. lasiocarpa and P. engelmannii, 99% attenuation of 300-nm light occurred at 51 and 96 μm, respectively, well within the mesophyll. At this stage, however, the bud scales were opaque to light below 400nm. As the epidermal cell walls and cuticle continued to develop and chlorophyll accumulated following emergence from the bud scales, light attenuation, particularly of UV-B radiation, increased. Although no UV-B is transmitted through the epidermis-hypodermis of mature needles, small but measurable quantities of 300- and 320-nm light were measured in the photosynthetic mesophyll of post-emergent and elongating needles. Thus, shortly after emergence from the bud scales in mid-June to mid-July, when incident UV doses are highest, absorption of UV-B radiation by potentially sensitive chromophores in the mesophyll may disrupt physiological and developmental processes in these species. Soluble UV-absorbing pigments accumulated during needle maturation for P. engelmannii but not A. lasiocarpa, suggesting that, for A. lasiocarpa at least, the development of effective UV screening properties in the epidermis may not be related to the induction of soluble flavonoids.

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1365-3040

Blackwell Publishing Journal Backfiles 1879-2005

Biology

We examined how ultraviolet-B radiation (UV-B; 300 nm) screening effectiveness changes with leaf age in Rhododendron maximum growing in a shaded understory by measuring depth of penetration and epidermal transmittance with a fibre-optic microprobe. Depth of penetration (and epidermal transmittance) of UV-B decreased with leaf age in 1- to 4-year-old leaves, averaging 62 (32), 52 (22), 45 (16) and 48 μm (13%), respectively. Epidermal thickness increased with age in 1- to 4-year-old leaves due to a thickening of the cuticle from an average of 20 to 29μm. Ultraviolet-B-absorbing compound concentrations increased with age from 1–3 to 1–5 A300 cm−2 leaf area. Concentrations of UV-B-absorbing compounds (area basis) were a strong predictor of depth of penetration (r2= 0.82) and epidermal transmittance (r2= 0.95) of UV-B in mature (1–4 year-old) foliage. Chlorophyll concentrations (area basis) increased in leaves up to 3 years of age. Current-year leaves (30 d old) were exceptional in that while they were particularly effective at screening UV-B (depth of penetration and epidermal transmittance averaged 39μm and 5%, respectively) they had relatively low concentrations of UV-B-absorbing compounds (1.3 A300 cm−2). Our findings show that UV-B-screening effectiveness is not necessarily related to absorbing compound concentrations on a whole-leaf basis, possibly due to anatomical changes within the epidermis that occur with leaf age.

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1365-3040

Blackwell Publishing Journal Backfiles 1879-2005

Biology

In some plants, particularly herbaceous species, a considerable proportion of incident ultraviolet-B radiation (UV-B, 280-320 nm) penetrates into the leaf mesophyll where it is potentially damaging to nucleic acids and the photosyn-thetic machinery. We used optical techniques to look at the spatial variation in UV-B penetration through the epidermis of foliage of two herbaceous species (Chenopodium album and Smilacina stellata)and a conifer (Picea pun-gens). Measurements of UV-B penetration in intact foliage with a fibre-optic microprobe revealed that 300 nm radiation reached 161±36μm (mean±SD) into leaves of C. album, 154±40μm in S. stellata and 17±2μm in P. pungens, with epidermal transmittance being 39±14%, 55±19% and 0%, respectively. A thin polymer film was developed which fluoresced blue when irradiated by UV-B. Fresh epidermal leaf peels were placed over the film and irradiated with UV-B, and microscopic examination of the film from below allowed us to determine the spatial pattern of UV-B penetration through the epidermis. In herbaceous species, film fluorescence below cell walls, but not epidermal and guard cell protoplasts indicated that UV-B transmittance was much greater through anticlinal cell wall regions than protoplasts. Ultraviolet-B transmittance through large areas of epidermal cells could be induced by plasmolysis. Epidermal transmittance was also relatively high through stomal pores (and what appear to be nuclei in Smilacina), but relatively low through stomatal guard cells. Results from the fluorescing film technique were substantiated by direct measurements of UV-B transmittance through epidermal peels with a fibre-optic microprobe run paradermally along the bottom or inner side of irradiated peels. In Smilacina, we estimate that UV-B epidermal transmittance was up to 90% through anticlinal cell wall regions, but 〈10% through protoplast areas. In contrast to herbaceous species, we did not detect any UV-B transmittance through the epidermis of P. pungens with either the fluorescing film or the fibre-optic microprobe technique. The epidermis appears to be a much more spatially uniform UV-B filter in conifers than in these herbaceous species.

Electronic Resource

1365-2826

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Oestrogen replacement therapy reportedly suppresses hypothalamic-pituitary-adrenal (HPA) axis responses to an emotional stressor in postmenopausal women. However, most studies in the rat suggest a facilitatory role for oestrogen in the control of HPA axis function. One explanation for this difference may be the regimen of oestrogen replacement: during oestrogen replacement therapy, oestrogen levels are low and constant whereas most animal studies examined the HPA axis response when oestrogen levels are rising. In the present study, we assessed HPA axis stress responses in mature ovariectomized rats after plasma oestrogen levels had been maintained at physiological levels for a prolonged period (25 or 100 pg/ml for 7 days). In the case of both an emotional stressor (noise) and a physical stressor (immune challenge by systemic interleukin-1β administration), oestrogen replacement suppressed stress-related Fos-like immunolabelling, in hypothalamic neuroendocrine cells and plasma adrenocorticotropin hormone responses. From the present data, and past reports, it appears unlikely that these effects of oestrogen are due to a direct action on corticotropin-releasing factor or oxytocin cells. Therefore, to obtain some indication of oestrogen's possible site(s) of action, Fos-like immunolabelling was mapped in the amygdala and in brainstem catecholamine groups, which are neuronal populations demonstrating substantial evidence of involvement in the generation of HPA axis stress responses. In the amygdala, oestrogen replacement suppressed central nucleus responses to immune challenge, but not to noise. Amongst catecholamine cells, oestrogen replacement was more effective against responses to noise than immune challenge, suppressing A1 and A2 (noradrenergic) and C2 (adrenergic) responses to noise, but only A1 responses to immune challenge. These data suggest that, as in postmenopausal women on oestrogen replacement therapy, chronic low-level oestrogen replacement can suppress HPA axis stress responses in the rat. Moreover, oestrogen appears to exert effects at multiple sites within putative HPA axis control pathways, even though most of the relevant neuronal populations do not contain genomic receptors for this gonadal steroid and the pattern of oestrogen action differs for an emotional vs a physical stressor.

Electronic Resource

1460-9568

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Previous studies have shown that the medial prefrontal cortex can suppress the hypothalamic–pituitary–adrenal axis response to stress. However, this effect appears to vary with the type of stressor. Furthermore, the absence of direct projections between the medial prefrontal cortex and corticotropin-releasing factor cells at the apex of the hypothalamic–pituitary–adrenal axis suggest that other brain regions must act as a relay when this inhibitory mechanism is activated. In the present study, we first established that electrolytic lesions involving the prelimbic and infralimbic medial prefrontal cortex increased plasma adrenocorticotropic hormone levels seen in response to a physical stressor, the systemic delivery of interleukin-1β. However, medial prefrontal cortex lesions did not alter plasma adrenocorticotropic hormone levels seen in response to a psychological stressor, noise. To identify brain regions that might mediate the effect of medial prefrontal cortex lesions on hypothalamic–pituitary–adrenal axis responses to systemic interleukin-1β, we next mapped the effects of similar lesions on interleukin-1β-induced Fos expression in regions previously shown to regulate the hypothalamic–pituitary–adrenal axis response to this stressor. It was found that medial prefrontal cortex lesions reduced the number of Fos-positive cells in the ventral aspect of the bed nucleus of the stria terminalis. However, the final experiment, which involved combining retrograde tracing with Fos immunolabelling, revealed that bed nucleus of the stria terminalis-projecting medial prefrontal cortex neurons were largely separate from medial prefrontal cortex neurons recruited by systemic interleukin-1β, an outcome that is difficult to reconcile with a simple medial prefrontal cortex–bed nucleus of the stria terminalis–corticotropin-releasing factor cell control circuit.

Electronic Resource

1460-9568

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

The amygdala plays a pivotal role in the generation of appropriate responses to emotional stimuli. In the case of emotional stressors, these responses include activation of the hypothalamic–pituitary–adrenal (HPA) axis. This effect is generally held to depend upon the central nucleus of the amygdala, but recent evidence suggests a role for the medial nucleus. In the present study, c-fos expression, amygdala lesion and retrograde tracing experiments were performed on adult rats in order to re-evaluate the role of the central as opposed to the medial amygdala in generating neuroendocrine responses to an emotional stressor. Brief restraint (15 min) was used as a representative emotional stressor and was found to elicit c-fos expression much more strongly in the medial than central nucleus of the amygdala; relatively few Fos-positive cells were seen in other amygdala nuclei. Subsequent experiments showed that ibotenic acid lesions of the medial amygdala, but not the central amygdala, greatly reduced restraint-induced activation of cells of the medial paraventricular nucleus, the site of the tuberoinfundibular corticotropin-releasing factor cells that constitute the apex of the HPA axis. Medial amygdala lesions also reduced the activation of supraoptic and paraventricular nucleus oxytocinergic neurosecretory cells that commonly accompanies stress-induced HPA axis activation in rodents. To assess whether the role of the medial amygdala in the control of neuroendocrine cell responses to emotional stress might involve a direct projection to such cells, retrograde tracing of amygdala projections to the paraventricular nucleus was performed in combination with Fos immunolabelling. This showed that although some medial amygdala cells activated by exposure to an emotional stressor project directly to the paraventricular nucleus, the number is very small. These findings provide the first direct evidence that it is the medial rather than the central amygdala that is critical to hypothalamic neuroendocrine cell responses during an emotional response, and also provide the first evidence that the amygdala governs oxytocin as well as HPA axis responses to an emotional stressor.

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1460-9568

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Psychological stressors trigger the activation of medullary noradrenergic cells, an effect that has been shown to depend upon yet-to-be-identified structures located higher in the brain. To test whether the amygdala is important in this regard, we examined the effects of amygdala lesions on noradrenergic cell responses to restraint, and also looked at whether any amygdala cells that respond to restraint project directly to the medulla. Ibotenic acid lesions of the medial amygdala completely abolished restraint-induced Fos expression in A1 and A2 noradrenergic cells. In contrast, lesions of the central amygdala actually facilitated noradrenergic cell responses to restraint. Tracer deposits in the dorsomedial (but not ventrolateral) medulla retrogradely labelled many cells in the central nucleus of the amygdala, but none of these cells expressed Fos in response to restraint. These data suggest for the first time that the medial amygdala is critical to the activation of medullary noradrenergic cells by a psychological stressor whereas the central nucleus exerts an opposing, inhibitory influence upon noradrenergic cell recruitment. The initiation of noradrenergic cell responses by the medial amygdala does not involve a direct projection to the medulla. Accordingly, a relay through some other structure, such as the hypothalamic paraventricular nucleus, warrants careful consideration.

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1460-9568

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Recent investigations have implicated the medial prefrontal cortex (mPFC) in modulation of subcortical pathways that contribute to the generation of behavioural, autonomic and endocrine responses to stress. However, little is known of the mechanisms involved. One of the key neurotransmitters involved in mPFC function is dopamine, and we therefore aimed, in this investigation, to examine the role of mPFC dopamine in response to stress in Wistar rats. In this regard, we infused dopamine antagonists SCH23390 or sulpiride into the mPFC via retrodialysis. We then examined changes in numbers of cells expressing the c-fos immediate-early gene protein product, Fos, in subcortical neuronal populations associated with regulation of hypothalamic-pituitary-adrenal (HPA) axis stress responses in response to either of two stressors; systemic injection of interleukin-1β, or air puff. The D1 antagonist, SCH23390, and the D2 antagonist, sulpiride, both attenuated expression of Fos in the medial parvocellular hypothalamic paraventricular nucleus (mpPVN) corticotropin-releasing factor cells at the apex of the HPA axis, as well as in most extra-hypothalamic brain regions examined in response to interleukin-1β. By contrast, SCH23390 failed to affect Fos expression in response to air puff in any brain region examined, while sulpiride resulted in an attenuation of the air puff-induced response in only the mpPVN and the bed nucleus of the stria terminalis. These results indicate that the mPFC differentially processes the response to different stressors and that the two types of dopamine receptor may have different roles.

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1399-3054

Blackwell Publishing Journal Backfiles 1879-2005

Biology

We compared photosynthetic and UV-B-absorbing pigment concentrations, gas-exchange rates and photosystem II (PSII) electron transport rates in leaves of pea (Pisum sativum mutant Argenteum) grown without UV-B or under an enhanced UV-B treatment (18 kJ m−2 biologically effective daily dose) in a greenhouse. We also compared the distribution of chlorophyll by depth within leaves of each treatment by using image analysis of chlorophyll autofluorescence. Ultraviolet-B treatment elicited putative protective responses such as an 80% increase in UV-B-absorbing compound concentrations (leaf-area basis), and a slight increase in mesophyll thickness (178 in controls compared to 191 μm in UV-B-treated leaves). However, photosynthetic rates of UV-B-treated leaves were only 80% of those of controls. This was paralleled by reductions in leaf conductance to water vapor (50% of controls) and intercellular CO2 concentrations, suggesting that stomatal limitations were at least partly responsible for lower photosynthetic rates under the UV-B treatment. Total chlorophyll concentrations (leaf-area basis) in UV-B-treated leaves were only 70% of controls, and there was a shift in the relative distribution of chlorophyll with depth in UV-B-treated leaves. In control leaves chlorophyll concentrations were highest near the adaxial surface of the upper palisade, dropped with depth and then increased slightly in the bottom of the spongy mesophyll nearest the abaxial surface. In contrast, in UV-B-treated leaves chlorophyll concentrations were lowest at the adaxial surface of the upper palisade and increased with depth through the leaf. The most notable treatment difference in chlorophyll concentrations was in the upper palisade near the adaxial surface of leaves, where we estimate that chlorophyll concentrations in each 1-μm-thick paradermal layer were about 50% lower in UV-B-treated leaves than in controls. We found reduced electron transport capacity in UV-B-treated leaves, based on lower maximum fluorescence (Fm), variable to maximum fluorescence ratios (F,/Fm) and quantum yield of PSII electron transport (Y). However, the above were assessed from fluorometer measurements on the adaxial leaf surface and may reflect the markedly lower chlorophyll concentrations in the upper palisade of UV-B-treated leaves.

Electronic Resource

1399-3054

Blackwell Publishing Journal Backfiles 1879-2005

Biology

We examined the UV absorption spectra and the epidermal-transmittance spectra (280–350 nm) of foliage from 42 plant species. Sun foliage was sampled from naturally growing individuals of seven species in each of six life forms comprising two evergreen groups (gymnosperms and angiosperms) and four deciduous angiosperm groups (trees, shrubs and vines, herbaceous dicotyledons and grasses). There were large differences in absorption spectra of whole-leaf extracts among species. While absorbance declined with increasing wavelength in most woody species, there was a trough in absorbance around 300 nm in many herbaceous species. Absorption spectra were negatively correlated with epidermal-transmittance spectra in 31 of the 42 species. Relationships between absorbance and transmittance did not follow the theoretical exponential function. Species rankings of UV-screening effectiveness were similar when we assessed it by using epidermal transmittance at single wavelengths (300 or 320 nm) or different UV-action spectra to weight epidermal-transmittance spectra and estimate the levels of biologically effective UV reaching the mesophyll. Thus, differences in absolute epidermal transmittance among species appeared to overshadow spectral differences. Nevertheless, the differences we found in the internal UV spectral regime in foliage suggest that whole-plant action spectra will differ among species. While species rankings of UV-screening effectiveness were similar when different action spectra were used, the absolute amounts of biologically effective UV reaching the mesophyll of species varied considerably when different action spectra were used.

Electronic Resource

1432-1939

Key words Antarctica ; Climate change ; Colobanthus quitensis ; Deschampsia antarctica ; Ozone depletion

Springer Online Journal Archives 1860-2000

Biology

Abstract Along the west coast of the Antarctic Peninsula springtime ozone depletion events can lead to a two-fold increase in biologically effective UV-B radiation (UV-BBE) and summer air temperatures have risen ≈1.5°C during the past 50 years. We manipulated levels of UV radiation and temperature around Colobanthus quitensis (a cushion-forming plant, Caryophyllaceae) and Deschampsia antarctica (a tussock grass) along the Peninsula near Palmer Station for two field seasons. Ambient levels of UV were manipulated by placing filters that either transmitted UV (filter control), absorbed UV-B (reducing diurnal levels of UV-BBE by about 82%), or absorbed both UV-B and UV-A (reducing UV-BBE and UV-ABE by about 88 and 78%, respectively) on frames over naturally growing plants from November to March. Half the filters of each material completely surrounded the frames and raised diurnal and diel air temperatures around plants by an average of 2.3°C and 1.3°C, respectively. Reducing UV or warming had no effect on leaf concentrations of soluble UV-B absorbing compounds, UV-B absorbing surface waxes or chlorophylls. Warming had few effects on growth of either species over the first season. However, over the second field season warming improved growth of C. quitensis, leading to a 50% increase in leaf production (P 〈 0.10), a 26% increase in shoot production, and a 6% increase in foliar cover. In contrast, warming reduced growth of D. antarctica, leading to a 20% decline in leaf length, a 17% decline in leaf production (P 〈 0.10), and a 5% decline in foliar cover. Warming improved sexual reproduction in both species, primarily through faster development of reproductive structures and greater production of heavier seeds. Over the second field season, the percentage of reproductive structures that had reached the most developed (seed) stage in C. quitensis and D. antarctica was 20% and 15% higher, respectively, under warming. Capsules of C. quitensis produced 45% more seeds under warming and these seeds were 11% heavier. Growth of D. antarctica was improved when UV was reduced and these effects appeared to be cumulative over field seasons. Over the second season, tillers produced 55% more leaves and these leaves were 32% longer when UV-B was reduced. Tillers produced 137% more leaves that were 67% longer when both UV-B and UV-A were reduced. The effects of UV reduction were not as pronounced on C. quitensis, although over the second season cushions tended to be 17% larger and produce 21% more branches when UV-B was reduced, and tended to be 27% larger and produce 38% more branches when both UV-B and UV-A were reduced (P 〈 0.10). Few interactions were found between UV reduction and warming, although in the absence of warming, reducing UV led to slower development of reproductive structures in both species. The effects of warming and UV reduction were species specific and were often cumulative over the two field seasons, emphasizing the importance of long-term field manipulations in predicting the impacts of climate change.

Electronic Resource

1432-1939

Soil temperature ; Photosynthesis ; Picea engelmannii ; Pinus contorta ; Roots ; Snow

Springer Online Journal Archives 1860-2000

Biology

Summary The influence of cold soil and snowcover on photosynthesis and conductance of Picea engelmannii and Pinus contorta was investigated early in the growing season in the Medicine Bow Mountains, Wyoming, USA. Trees of both species growing in cold soil (〈1°C) associated with snowpack had 25–40% lower leaf photosynthesis than trees in warm soils (〉10°C). In cold soils leaf conductance of both species was lower, but more so in Pinus, leading to lower intercellular CO2 concentrations and greater stomatal limitation of photosynthesis. Soil temperature had no effect on predawn and midday shoot water potentials of Pinus and Picea and lower photosynthesis and conductance did not appear to be a result of lower bulk shoot water potential. Predawn, as well as midday, water potentials of Pinus were consistently higher than Picea suggesting that Pinus may have deeper roots, although trenching experiments indicated young Picea trees have more extensive lateral root systems than similar sized Pinus trees. Young Picea trees (〈2 m in height) in snowbanks were capable of utilizing warmer soil 4 m from their base. Under similar conditions Pinus in snowbanks had lower photosynthesis and conductance than controls and Pinus did not appear capable of utilizing warmer soils nearby. Under full sunlight, PPFD reflected from the snow surface was 400–1400 μmol m-2 s-1 higher than from snow-free surfaces. This reflected light resulted in a 10%–20% increase in photosynthesis of Picea. The beneficial effect of reflected light was apparent whether or not photosynthesis was reduced by low soil temperatures.

Electronic Resource

1432-1939

Deciduous ; Epidermal thickness ; Epidermal transmittance ; Evergreen ; Flavonoids

Springer Online Journal Archives 1860-2000

Biology

Abstract The ultraviolet-B radiation (UV-B, 300 nm) screening effectiveness of foliage of a diverse group of plants was examined by measuring epidermal transmittance and depth of penetration of UV-B with a fiberoptic microprobe. In addition, the concentration of UV-B-absorbing compounds and various anatomical characteristics were measured to assess whether they were useful predictors of UV-B screening. Sun foliage of naturally growing individuals of seven species were sampled in each of six life forms comprising two evergreen groups (gymnosperms and angiosperms) and four deciduous angiosperm groups (trees, shrubs and vines, herbaceous dicotyledons, and grasses). There was significant life-form variation in epidermal transmittance and depth of penetration of UV-B, concentration of UV-B-absorbing compounds (leaf-area basis), epidermal (including cuticle and hypodermis) thickness, and specific leaf area. Values of these parameters tended to be related to leaf longevity, with the most notable differences apparent between evergreen and deciduous species. The mean epidermal transmittance and depth of penetration of UV-B in foliage averaged 4% and 32 μm in evergreens, compared to 28% and 75 μm in deciduous species. These values are conservative estimates since the microprobe was oriented in foliage such that much of the side- and backscattered UV-B was ignored. The strongest predictors of epidermal transmittance and depth of penetration were epidermal thickness and the concentration of absorbing compounds, which averaged 32 μm and 1.50 A cm−2 in evergreens, but only 19 μm and 0.99 A cm−2 in deciduous foliage. However, the variation found in these relationships implies that additional factors warrant consideration in assessing UV-B-screening effectiveness. The relatively ineffective screening of UV-B by foliage of many deciduous plants suggests they may be more responsive to enhanced UV-B than evergreen species.

Electronic Resource

1432-1939

Conifer ; Epidermis ; Fiber-optic ; Optical properties ; Ozone depletion

Springer Online Journal Archives 1860-2000

Biology

Summary The unprecedented rate of depletion of the stratospheric ozone layer will likely lead to appreciable increases in the amount of ultraviolet-B radiation (UV-B, 280–320 nm) reaching the earth's surface. In plants, photosynthetic reactions and nucleic acids in the mesophyll of leaves are deleteriously affected by UV-B. We used a fiber-optic microprobe to make direct measurements of the amount of UV-B reaching these potential targets in the mesophyll of intact foliage. A comparison of foliage from a diverse group of Rocky Mountain plants enabled us to assess whether the foliage of some plant life forms appeared more effective at screening UV-B radiation. The leaf epidermis of herbaceous dicots was particularly ineffective at attenuating UV-B; epidermal transmittance ranged from 18–41% and UV-B reached 40–145 μm into the mesophyll or photosynthetic tissue. In contrast to herbaceous dicots, the epidermis of 1-year old conifer needles attenuated essentially all incident UV-B and virtually none of this radiation reached the mesophyll. Although the epidermal layer was appreciably thinner in older needles (7 y) at high elevations (Krumholtz), essentially all incident UV-B was attenuated by the epidermis in these needles. The same epidermal screening effectiveness was observed after removal of epicuticular waxes with chloroform. Leaves of woody dicots and grasses appeared intermediate between herbaceous dicots and conifers in their UV-B screening abilities with 3–12% of the incident UV-B reaching the mesophyll. These large differences in UV-B screening effectiveness suggest that certain plant life forms may be more predisposed than others to meet the challenge of higher UV-B levels resulting from stratospheric ozone depletion.

Electronic Resource

1432-1939

Diurnal ; Shoot conductance ; Photosynthesis ; Root ; Stem capacitance

Springer Online Journal Archives 1860-2000

Biology

Summary The effect of cold soils on stem sap flow, shoot gas exchange and water potential of Picea engelmannii (Parry) was investigated during the snowmelt period in the Medicine Bow Mountains, Wyoming, USA. Shoot net photosynthetic rates were higher in young trees (1.5–1.8 m in height) growing in cold soils (〈3.5° C) associated with snowpack, than trees in warm soils until about 1500 h. Higher shoot photosynthetic rates of trees in cold soils continued after snow was removed and could not be completely explained by higher visible irradiance over highly reflective snow. Following soil warming higher photosynthetic rates were evident in these trees for five days. High nutrient availability associated with snowmelt may improve shoot nutrient status leading to higher gas-exchange rates during snowmelt. Shoot conductance to water vapor was higher in trees in cold soil until midday, when declining shoot conductance led to lower intercellular CO2 concentrations. Midday through afternoon shoot water potentials of trees in cold soils were similar or higher than those of trees in warm soils and the lower afternoon shoot conductances in cold soils were not the result of lower bulk shoot water potentials. Decline in net photosynthesis of trees in cold soils at 1500 h paralleled increases in intercellular CO2 concentrations, implying a nonstomatal limitation of photosynthesis. This scenario occurred consistently in mid-afternoon following higher morning and midday photosynthesis in cold soils, suggesting a carbohydrate feedback inhibition of photosynthesis. Diurnal patterns in stem sap flow of all trees (cold and warm soils) reflected patterns of shoot conductance, although changes in stem sap flow lagged 1–3 h behind shoot conductance apparently due to stem water storage. Total daily stem sap flow was similar in trees in cold and warm soils, although diel patterns differed. The morning surge and night-time drop in sap flow commenced 1–2 h earlier in trees in cold soils. Overnight stem sap flow was lower in trees in cold soils, possibly due to higher resistance to root water uptake in cold soils, which may explain lower predawn shoot water potentials. However, midday shoot water potentials of trees in cold soils equalled or exceeded those of trees in warm soils. Higher resistance to root water uptake in P. engelmannii in cold soils was apparently overshadowed by transpirational forces and significant shoot water deficits did not develop.

Electronic Resource

1573-5052

Idaho ; Primary succession ; Sagebrush-steppe ; Seed density ; Soil nitrogen ; Soil phosphorus ; Spatial pattern

Springer Online Journal Archives 1860-2000

Biology

Abstract Cinder cones in Craters of the Moon National Monument in southcentral Idaho, USA were formed over 2200 yr B.P., but are still covered by large, relatively barren areas containing a sparse assemblage of plants. The spatial associations among 6 plant species on these sparsely vegetated areas were examined. All species were positively associated with the canopy region of Eriogonum ovalifolium var. depressum, an initial colonizer. All species were negatively associated with Pinus flexilis, a later-successional species. We examined soil seed densities and N and P levels under canopies of the 6 species to develop testable explanations for positive plant associations with E. ovalifolium. Soil seed densities of Phacelia hastata and Lewisia rediviva were higher under canopies of E. ovalifolium than under 4 of the 5 other species and bare areas. Soil total N under E. ovalifolium canopies was also higher than under 4 of the 5 other species and bare areas. Soil seed densities and N levels were similar under E. ovalifolium and Eriogonum umbellatum, both of which had dense, prostrate canopies. Soil available P levels under E. ovalifolium were not significantly different than under other species or bare ground. The positive associations of all species with E. ovalifolium is likely the result of seed-trapping by its prostrate canopy and more favorable establishment conditions under its canopy. The relative importance of these potential mechanisms can be tested with field experiments.

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