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Growth and morphological responses to different UV wavebands in cucumber (Cucumis sativum) and other dicotyledonous seedlings (2004)

Shinkle, James R. ; Atkins, Alaina K. ; Humphrey, Erin E. ; [et al.]

Oxford, UK; Malden , USA : Munksgaard International Publishers

Physiologia plantarum 120 (2004), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: We examined the influence of short-term exposure of different UV wavebands on the fine-scale kinetics of hypocotyl growth of dim red light-grown cucumbers (Cucumis sativus L.) and other selected dicotyledonous seedlings to evaluate: (1) whether responses induced by UV-B radiation (280–320 nm) are qualitatively different from those induced by UV-A (320–400 nm) radiation, and (2) whether different wavebands within the UV-B elicit different responses. Responses to brief (30 min) irradiations with 3 different UV wavebands all included transient inhibition of elongation during irradiation followed by wavelength specific responses. Irradiations with proportionally greater short wavelength UV-B (37% of UV-B between 280 and 300 nm) induced inhibition of hypocotyl elongation within 20 min of onset of irradiation, while UV-B including only wavelengths longer than 290 nm (and only 8% of UV-B between 290 and 300 nm) induced inhibition of hypocotyl elongation with a lag of 1–2 h. The response to short wavelength UV-B was persistent for at least 24 h, while the response to long wavelength UV-B lasted only 2–3 h. The UV-A treatment induced reductions in elongation rates of approximately 6–9 h following exposure followed by a continued decline in rates for the following 15–18 h. Short wavelength UV-B also induced positive phototropic curvature in both cucumber and Arabidopsis seedlings, and this response was present in nph-1 mutant Arabidopsis seedlings defective in normal blue light phototropism. Reciprocity was not found for the response to short wavelength UV-B. The short wavelength and long wavelength UV-B responses differed in dose–response relationships and both short wavelength responses (phototropic curvature and elongation inhibition) increased sharply at wavelengths below 300 nm. These results indicate that different photosensory processes are involved in mediating growth and morphological responses to short wavelength UV-B (280–300 nm), long wavelength UV-B (essentially 300–320 nm) and UV-A. The existence of two separate types of hypocotyl inhibition responses to UV-B, with one that depends on the intensity of the light source, provides alternate interpretations to findings in other studies of UV-B induced photomorphogenesis and may explain inconsistencies between action spectra for inhibition of stem growth.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.0031-9317.2004.0237.x

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Early-season effects of supplemented solar UV-B radiation on seedling emergence, canopy structure, simulated stand photosynthesis and competition for light (1995)

BARNES, PAUL W. ; FLINT, STEPHAN D. ; CALDWELL, MARTYN M.

Oxford, UK : Blackwell Publishing Ltd

Global change biology 1 (1995), S. 0

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ISSN: 1365-2486

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography

Notes: Mixtures and monocultures of wheat (Triticum aestivum) and wild oat (Avena fatua), a common weedy competitor of wheat, were exposed to enhanced solar UV-B radiation simulating a 20% reduction in stratospheric ozone to assess the timing and seasonal development of the UV-B effects on light competition in these species. Results from two years of field study revealed that UV-B enhancement had no detectable effect on the magnitude or timing of seedling emergence in either species. End-of-season measurements showed significant UV-B inhibition of leaf insertion height in wild oat in mixture and monoculture in the second year (irrigated year) but not in the first year (drought year). Leaf insertion height of wheat was not affected by UV-B in either year. The UV-B treatment had no detectable effect on monoculture or total (combined species) mixture LAI but did significantly increase (5–7%) the fractional contribution of wheat to the mixture LAI after four weeks of growth in both years. In addition, the UV-B treatment had subtle effects on LAI height profiles with early season mixtures showing significant reductions in wild oat LAI in lower canopy layers in both years while midseason Year 2 mixtures showed significant reductions in wild oat LAI in upper canopy layers. The changes in canopy structure were found to significantly increase (6–7%) the proportional simulated clear sky canopy photosynthesis and light interception of wheat in mixture. These findings, and others, indicate that the effects of UV-B enhancement on competition are realized very early in canopy development and provide additional support for the hypothesis that UV-B enhancement may shift the balance of competition between these species indirectly by altering competitive interactions for light.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-2486.1995.tb00005.x

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3

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Non-invasive measurements of leaf epidermal transmittance of UV radiation using chlorophyll fluorescence: field and laboratory studies (2000)

Barnes, Paul W. ; Searles, Peter S. ; Ballaré, Carlos L. ; [et al.]

Copenhagen : Munksgaard International Publishers

Physiologia plantarum 109 (2000), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: Ratios of chlorophyll fluorescence induced by ultraviolet (UV) and bluegreen (BG) radiation [F(UV)/F(BG)] were determined with a Xe-PAM fluorometer to test the utility of this technique as a means of non-intrusively assessing changes in the pigmentation and optical properties of leaves exposed to varying UV exposures under laboratory and field conditions. For plants of Vicia faba and Brassica campestris, grown under controlled-environmental conditions, F(UV-B)/F(BG) was negatively correlated with whole-leaf UV-B-absorbing pigment concentrations. Fluorescence ratios of V. faba were similar to, and positively correlated with (r2=0.77 [UV-B]; 0.85 [UV-A]), direct measurements of epidermal transmittance made with an integrating sphere. Leaves of 2 of 4 cultivars of field-grown Glycine max exposed to near-ambient solar UV-B at a mid-latitude site (Buenos Aires, Argentina, 34° S) showed significantly lower abaxial F(UV-B)/F(BG) values (i.e., lower UV-B epidermal transmittance) than those exposed to attenuated UV-B, but solar UV-B reduction had a minimal effect on F(UV-B)/F(BG) in plants growing at a high-latitude site (Tierra del Fuego, Argentina, 55° S). Similarly, the exotic Taraxacum officinale did not show significant changes in F(UV-B)/F(BG) when exposed to very high supplemental UV-B (biologically effective UV-B=14–15 kJ m−2 day−1) in the field in Tierra del Fuego, whereas a native species, Gunnera magellanica, showed significant increases in F(UV-B)/F(BG) relative to those receiving ambient UV-B. These anomalous fluorescence changes were associated with increases in BG-absorbing pigments (anthocyanins), but not UV-B-absorbing pigments. These results indicate that non-invasive estimates of epidermal transmittance of UV radiation using chlorophyll fluorescence can detect changes in pigmentation and leaf optical properties induced by UV-B radiation under both field and laboratory conditions. However, this technique may be of limited utility in cold environments where UV and low temperatures can stimulate the production of BG-absorbing pigments that interfere with these indirect measurements of UV-transmittance.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1034/j.1399-3054.2000.100308.x

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Inhibition of hypocotyl elongation by ultraviolet-B radiation in de-etiolating tomato seedlings. I. The photoreceptor (1995)

Ballaré, Carlos L. ; Barnes, Paul W. ; Flint, Stephan D.

Oxford, UK : Blackwell Publishing Ltd

Physiologia plantarum 93 (1995), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: Broad-band UV-B radiation inhibited hypocotyl elongation in etiolated tomato (Lycopersicon esculentum Mill. cv. Alisa Craig) seedlings. This inhibition could be elicited by 〈 3 μmol m−2 s−1 of UV-B radiation provided against a background of white light (〉 620 μmol m−2 s−1 between 320 and 800 nm), and was similar in wild-type and phytochrome-1-deficient aurea mutant seedlings. These observations suggest that the effect of UV-B radiation is not mediated by phytochrome. An activity spectrum obtained by delivering 1 μmol m−2 s−1 of monochromatic UV radiation against a while light background (63 μmol m−2 s−1 showed maximum effectiveness around 300 nm, which suggests that DNA or aromatic residues in proteins are not the chromophores mediating UV-B induced inhibition of elongation. Chemicals that affect the normal (photo)chemistry of flavins and possibly pterins (KI, NaN, and phenylacetic acid) largely abolished the inhibitor) effect of broad-hand UV-B radiation when applied to the root zone before irradiation. KI was effective at concentrations 〈 10−4M, which have been shown in vitro to be effective in quenching the triplet excited stales of flavins but not fluorescence from pterine or singlet states of flavins. Elimination of blue light or reduction of UV-A, two sources of flavin excitation, promoted hypocotyl elongation, but did not affect the inhibition of elongation evened by UV-B. Kl applied after UV-B irradiation had no effect on the inhibition response. Taken together these findings suggest that the chromophore of the photoreceptor system invoked in UV-B perception by tomato seedlings during de-etiolation may be a flavin.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1399-3054.1995.tb05104.x

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5

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Inhibition of hypocotyl elongation by ultraviolet-B radiation in de-etiolating tomato seedlings. II. Time-course, comparison with flavonoid responses and adaptive significance (1995)

Ballaré, Carlos L. ; Barnes, Paul W. ; Flint, Stephan D. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Physiologia plantarum 93 (1995), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: UV-B radiation inhibits hypocotyl elongation in etiolated tomato (Lycopersicon esculentum Mill. cv. Alisa Craig) seedlings acting through a photoreceptor system with peak apparent effectiveness around 300 nm. In order lo further characterize the response and gain insight into its potential ecological significance, the time-course of inhibition was measured and compared with the time-course of flavonoid accumulation in the same seedlings. When a background of strong (〉 620 μmol m−2 s−1) white light (WL) was supplemented with low irradiance UV-B (∼ 3 μmol m−2 s−1). substantial (∼ 50%) inhibition of elongation occurred within 3 h of the light treatment. The magnitude of UV-B-induced elongation inhibition was similar in wild type (WT) and au-mutant seedlings, in spite of the large differences between genotypes in rate and temporal pattern of elongation. In comparison to the effect of UV-B on elongation, induction of flavonoid accumulation in WT and au seedlings undergoing de-etiolation was a much slower response. Several UV-absorbing compounds appeared to be specifically induced by light, and some of them accumulated faster under the WL + UV-B treatment than under WL alone. However, there was little or no delectable effect of WL on flavonoid levels until up to 3 h of treatment, and the specific UV-B effect was measurable only after 6 h of continuous treatment. Indeed. UV-B-screening properties of crude alcoholic extracts were not different between WL and WL + UV-B treatments until after 9 or 24 h. When the light treatments were applied to seedlings that were just breaking through the soil surface. UV-B was found to consistently retard seedling emergence. These results suggest that the rapid inhibition of elongation in de-etiolating seedlings is an evolved response lo UV-B, which may serve to minimize seedling exposure to sunlight until protective pigmentation responses (triggered by WL and UV-B) have taken place in the seedlings epidermis.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1399-3054.1995.tb05105.x

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6

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Photomorphogenic effects of UV-B radiation on hypocotyl elongation in wild type and stable-phytochrome-deficient mutant seedlings of cucumber (1991)

Ballaré, Carlos L. ; Barnes, Paul W. ; Kendrick, Richard E.

Oxford, UK : Blackwell Publishing Ltd

Physiologia plantarum 83 (1991), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: Hypocotyl elongation responses to ultraviolet-B (UV-B) radiation were investigated in glasshouse studies of de-etiolated seedlings of a long-hypocotyl mutant (lh) of cucumber (Cucumis sativus L.) deficient in stable phytochrome, its near isogenic wild type (WT), and a commercial cucumber hybrid (cv. Burpless). A single 6- or 8-h exposure to UV-B applied against a background of white light inhibited hypocotyl elongation rate by ca 50% in lh and WT seedlings. This effect was not accompanied by a reduction in cotyledon area expansion or dry matter accumulation. Plants recovered rapidly from inhibition and it was possible to stimulate hypocotyl elongation in plants exposed to UV-B by application of gibberellic acid. In all genotypes inhibition of elongation was mainly a consequence of UV-B perceived by the cotyledons; covering the apex and hypocotyl with a filter that excluded UV-B failed to prevent inhibition. These results indicate that reduced elongation does not result from assimilate limitation or direct damage to the apical meristem or elongating cells, and strongly suggest that it is a true photomorphogenic response to UV-B. The fact that UV-B fluences used were very low in relation to total visible light, and the similarity in the responses of lh and wild-type plants, are consistent with the hypothesis that UV-B acts through a specific photoreceptor. It is argued that, given the weak correlation between UV-B and visible-light levels in most natural conditions, the UV-B receptor may play an important sensory function providing information to the plant that cannot be derived from light signals perceived by phytochrome or blue/UV-A sensors.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1399-3054.1991.tb02483.x

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7

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Species distribution and community organization in a Nebraska Sandhills mixed prairie as influenced by plant/soil-water relationships (1982)

Barnes, Paul W. ; Harrison, A. Tyrone

Springer

Oecologia 52 (1982), S. 192-201

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ISSN: 1432-1939

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary Plant and soil water relationships in a typical nebraska Sandhills prairie were examined to 1) explain the observed distribution patterns of several dominant grasses along a topographic gradient, and 2) show how spatial and temporal variations in soil moisture are critical to community organization on a sandy substrate. An experimental transect encompassing the major community and soil types along a steep, west-facing vegetated dune was established. Maximum available water was shown to be significantly higher in the fine textured surface soils of the lowland sites than the coarse textured sands of the dune sites. Seasonal (1979) patterns of available soil moisture of the sampling sites on the transect showed that in the upper elevation dune sands, moisture was available in the entire profile with surface depletions not occurring until mid to late summer. In contrast, moisture in the surface 60–80 cm in the fine textured lowland soils was exhausted by early to mid-summer with the entire profile nearly dry by late summer. Deep-rooted, C4 species, Andropogon hallii and Calamovilfa longifolia which are common on upper, coarser sandy soils showed significantly greater water stress on fine textured soils than on dune sands. C3, shallowrooted species, Agropyron smithii, Stipa comata, and Koeleria cristata always experienced lower mid-day and predawn leaf water potentials than the C4 species. The C3 species, with the exception of Koeleria are most abundant on finer textured soils that provide substantial moisture during their peak activity in the spring. It appears that the C4 species show more conservative water use patterns than the C3 species as significantly lower leaf conductances in the C4's were measured when soil water was abundant. The C3 species appear to be opportunistic with available water and rapidly deplete surface soil moisture as a result of high transpiration rates. These data suggest that the temporal and spatial distribution of available water along this gradient controls species distribution according to rooting morphology, photosynthetic physiology, and water deficits, incurred by transpirational losses. Competitive interactions between species that utilize soil moisture differently may be an important factor in community organization.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00363836

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Influence of an overstorey tree (Prosopis glandulosa) on associated shrubs in a savanna parkland: implications for patch dynamics (1996)

Barnes, Paul W. ; Archer, Steve

Springer

Oecologia 105 (1996), S. 493-500

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ISSN: 1432-1939

Keywords: Facilitation ; Nurse plant ; Photosynthesis ; Primary production ; Water relations

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The arborescent legume, honey mesquite (Prosopis glandulosa), appears to play a central role in patch dynamics of southern Texas savannas by modifying soils and microclimate and by facilitating the ingress, establishment and/or growth of shrubs in its understorey. As an indirect test for the occurrence and persistence of facilitation in mature shrub clusters (patches), we examined the gas exchange, water relations and production of associated shrubs growing in patches where a Prosopis overstorey was present and in patches where Prosopis had succumbed to natural mortality. Surface (0–10 cm) soils associated with shrub patches were enriched in total [N] and [C] compared to soils of neighboring herbaceous zones. However, there were no detectable differences in soil [N] or [C] in patches with and without Prosopis. Foliar [N] and biomass of various shrub species were also statistically comparable for patches with and without Prosopis. These results are in accordance with other studies that indicate the nutrient legacy associated with Prosopis occupation of a patch may persist for decades after its demise. In comparison to plants growing in the absence of Prosopis, leaf water potentials (predawn and midday), and net photosynthesis and water vapor conductance (morning and midday) of outer-canopy sunlit leaves over an annual growth cycle were comparable for two common evergreen shrubs, Zanthoxylum fagara and Berberis trifoliolata, growing in patches with a live Prosopis. These findings indicate that the presence of Prosopis was not enhancing the growth or activity of mature understorey shrubs; facilitation may, therefore, be important only during early stages of cluster development. In addition, we found no indication that the loss of Prosopis has initiated a downward phase in a cyclic succession of patch initiation, growth and death. Rather, the understorey shrubs appear to be able to maintain growth and productivity in the absence of a Prosopis overstorey, and may, therefore, represent persistent components of woody patches on these savanna landscapes.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00330012

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