Photosynthesis of two Arctic macroalgae under different ambient radiation levels and their sensitivity to enhanced UV radiation

The change in optimal quantum efficiency (F _v/F _m) of the Arctic species Laminaria saccharina and Palmaria palmata was investigated in a long-term experiment in situ under different radiation levels during the summer of 1997 in the Kongsfjord (Ny-Ålesund, Spitsbergen, Norway, 78°55.5′N, 11°56.0′E). Whole plants were incubated in an open box system made of UV-transparent Perspex and exposed to solar radiation (λ>295?nm), solar radiation excluding UVB (λ?>?320?nm) and solar radiation excluding UVA?+ UVB (λ?>?400?nm). Increasing radiation levels were simulated by transplantation of the pre-adapted algae from their growth depth at 2?m to a water depth of 1?m. Sensitivity to artificially increased UV radiation was determined by exposure of algae from the three treatments to 6?h of strong UV radiation. P. palmata was relatively insensitive to increasing UV radiation and recovered very fast and almost completely in 2?h. Even plants pre-cultured in ambient radiation levels excluding UVA?+?UVB or UVB only showed no photoinhibition after exposure to extra UV radiation in the laboratory. L. saccharina was, in comparison to P. palmata, more sensitive and showed photoinhibition under solar radiation and solar minus UVB radiation after transplantation from 2 to 1?m water depth. However, after 3?weeks at 1?m depth, F _v/F _m of L. saccharina was equal in all treatments and restored to the original values at the start of the experiment. Sensitivity to extra UV radiation in the laboratory increased in time, although recovery was also fast and occurred within 20?h.     

Egg size and clutch size in two Daphnia species grown at different food levels

The effect of three different Scenedesmus food concentrations(0.04, 0.2 and 1 mg C l^–1) on maternal investment wasstudied in two cladoceran species of similar size, Daphnia pulicariaand D.hyalina. It was observed that as food concentration decreased(between 1 and 0.2 mg C l^–1), there was an increase insize, protein content, lipid content, carbon and mass of theegg, while, at the same time, the clutch size of the femalesbecame smaller. Such an increase in ‘per offspring investment’was reflected in an increase in body length, body carbon andbody mass of neonates as the food available for females decreased.However, in D.pulicaria this tendency was not maintained downat 0.04 mg C l^–1 in which there was a decrease of theegg characteristics mentioned above. Although, there are notavailable all the egg and neonate parameters of D.hyalina at0.04 mg C l^–1, the body length of the neonates was largerthan at 0.2 and 1 mg C l^–1. These results show that, asfood diminishes, these two cladoceran species are able to respondby decreasing clutch size, but increasing the size of egg, therebyincreasing the probability of neonate survival. This tendencyis probably maintained until the food concentration is too lowand the females have to reduce the energy allocated for reproduction.     

Modification of leaf cytology and anatomy in Brassica napus grown under above ambient levels of supplemental UV-B radiation.

Plants exposed to natural solar radiation usually show acclimation responses on a daily and seasonal basis. Many of these responses are complex and modified by interactions with acclimation responses to other climatic factors. While changes in photosynthetically active radiation (PAR, 400-700 nm) are the driving force for many acclimation responses in plants, radiation outside the PAR range is also important. Recently, interest has increased in the potential role of UV-A (320-400 nm) and UV-B (280-320 nm) components of sunlight in plant developmental, physiological and daily acclimation processes. In order to explore the role of UV-B further, Brassica napus L. cv Paroll plants were grown to maturity under 13 kJ d(-1) of biologically effective ultraviolet-B radiation (UV-B(BE), 280-320 nm) plus 800 micromol photons m(-2) s(-1) photosynthetically active radiation (PAR, 400-700 nm) or PAR alone. Leaf anatomy and palisade cell structure were quantified using stereological techniques. The leaves of plants grown under UV-B radiation exhibited an increase in overall leaf width, although no change in leaf anatomy was discerned. Palisade cells in UV-B exposed leaves showed a significant decrease in chloroplast, mitochondrial, starch, and microbody volume density (Vv), while the vacuolar Vv increased compared to cells exposed to PAR only. In UV-B exposed leaves, there was an increase in the appressed and non-appressed thylakoid surface area density (Sv) within the chloroplasts. Since the relative proportion of appressed to non-appressed thylakoid surface area did not change, both thylakoid systems changed in concert with each other. Thylakoid stacks were broader and shorter in leaves subjected to UV-B. In general these responses were similar to those which occurred in plants moved from a high to low PAR environment and similar to mature plants exposed to 13 kJ d(-1) UV-B(BE) for only a short period of time. Although UV absorbing pigments increased by 21% in UV-B exposed leaves, there was no significant difference in chlorophyll a,b or carotenoid content compared to plants exposed to only PAR.     

The effects of altered levels of UV-B radiation on an Antarctic grass and lichen

We report a long-term experiment on the photosynthetic response of natural vegetation of Deschampsia antarctica (Poaceae) and Turgidosculum complicatulum (Lichenes) to altered UV-B levels on Léonie Island, Antarctica.UV-B above the vegetation was reduced by filter screens during two seasons. Half of the screens were transparent to UV-A and UV-B (ambient treatment) or absorbing UV-B and part of the UV-A (below-ambient treatment). Half of the wedge- shaped filters had side walls leading to an enhancement of the daily mean temperature in summer by 2–4 °C, simulating rising mean air temperature on the Antarctic Peninsula. The other half of the filters were without side walls resulting in close-to-ambient temperature underneath. Plots without filters served as controls.UV-B supplementation of an extra 1.3 kJ UV-B_BE was achieved using UV-mini-lamp systems during 15 days in the second season.We found no evidence that altered incident UV-B levels and temperature had an effect on maximum photosystem II efficiency (F _v/F _m) and effective photosystem II efficiency (F/F _m) in both species. UV-B reduction did not influence contents of chlorophyll, carotenoids and methanol-soluble UV absorbing compounds in D. antarctica.Flowering shoot length of D. antarctica was not affected by UV-B reduction. Temperature enhancement tended to result in longer inflorescence axes. Results of two austral summer seasons of UV- reduction in natural stands of D. antarctica and T. complicatulum suggest that current ambient levels of UV-B do not have a direct effect on the photosynthetic performance and pigment contents of these species. Cumulative effects on growth have not been recorded after two years but can not be excluded on a longer term.     

Relationships between photosystem II efficiency and photochemical reflectance index under different levels of illumination: comparison among species grown at high- and low elevations through different seasons

Previously, we found a significant association between photosystem II efficiency (ΦPSII) and photochemical reflectance index (PRI) measured at predawn among different species at different elevations and throughout several seasons. However, this relationship has not been evaluated under varied levels of illumination. Here, we used the Taiwan species Pinus taiwanensis (a conifer distributed at 750–3,000 m a.s.l.), Stranvaesia niitakayamensis (an evergreen tree, 1,700–3,100 m) and two Miscanthus spp. (perennial C₄ Gramineae, coastline–3,200 m) to elucidate the ΦPSII–PRI relationship. We studied six levels of photosynthetic photon flux density (PPFD) (0, 200, 400, 800, 1,200 and 2,000 μmol m⁻² s⁻¹) over several growth seasons at high (2,600 m a.s.l.) and low (800 m a.s.l.) elevation sites. In comparing the same species or genus, ΦPSII and PRI were closely correlated in darkness or under the same level of PPFD, with data obtained from different seasons and elevations pooled for regression analysis. Because both the intercept and slope of the ΦPSII–PRI equation showed a negative curvilinear correlation with PPFD, we could fit an empirical regression model, ΦPSII = c + d·ln(PPFD) + e·[ln(PPFD)]² + f·PRI + g·PRI·ln(PPFD) + h·PRI·[ln(PPFD)]², for multiple regression analysis. Using this model, we found a close correlation between the estimated and measured ΦPSII (r ² = 0.842−0.937, P < 0.001) for all four species examined and for mango (Mangifera indica) measured under both artificial illumination and sunlight (data from Weng et al. 2010). This empirical regression model could simulate both seasonal and diurnal variations of leaf-scale photosynthetic efficiency at high and low elevations.     

Aquatic plant diversity in four river floodplains: a comparison at two hierarchical levels

The present study focuses on the role ofenvironmental factors in plant diversity and community organization at both water-body and river floodplain levels. The cover of each plant species was measured at 841 sampling plots along 63 cut-off channels located in four river floodplains. Environmental variables were documented either at river level (suspended matter, water physico-chemistry, river slope) or at cut-off channel level (channel capacity, slope, substrate grain-size). At both river and cut-off channel levels, increasing slope (i.e. increasing erosion during floods) and decreasing nutrient-content of the water raise species richness and uniqueness (number of species found only in one river), according to hypotheses on the combined role of disturbances and productivity in biodiversity. Rivers that are not eroded during floods are nutrient-rich and present the lowest richness and uniqueness at the river level, but dewatering combined with high connectivity increase richness at the cut-off channel level.     

Growth and NPK uptake of high-yielding cotton grown at different nitrogen levels in a permanent-plot experiment

Growth and N, P, K uptake of Acala SJ-2 cotton (Gossypium hirsutum) were investigated in an irrigated permanent-plot field (Typic chromoxerert) at Bet Dagan, Israel, under semi-arid conditions using different nitrogen levels: 0, 60, 120, 180 and 240 kg N ha⁻¹. The total dry matter accumulation at these levels was 9.0, 10.7, 15.1, 17.1 and 15.6 ton ha⁻¹, respectively. The uptake of N, P and K was 110, 144, 267, 322 and 301 kg N ha⁻¹∶31, 34, 46, 44 and 38 kg P ha⁻¹; and 120, 151, 208, 251 and 230 kg K ha⁻¹, respectively. Dry matter production, as well as N, P, K uptake by the cotton plants were greatly increased by raising the N application levels to 120 or 180 kg N ha⁻¹, but the pattern of accumulation and relative distribution of dry matter and NPK among plant organs were not considerably affected. Joint contribution from the Dept. of Soil Chemistry and Plant Nutrition, ARO, the Volcani Center, Bet Dagan, Israel (No. 1413-E, 1985 series)     

Family planning inDaphnia: resistance to starvation in offspring born to mothers grown at different food levels

Summary We observed a shift in maternal investment per offspring in clonal cultures of twoDaphnia species. Mothers grown at high food levels produced large clutches of smaller eggs but their offspring could not survive long under starvation conditions. Genetically identical mothers grown at low food levels produced small cultches of larger eggs, and their offspring, albeit low in numbers, were able to survive long periods of starvation. Our data show thatDaphnia mothers are capable of assessing food level and use this information in adjusting their fractional peroffspring allocation of reproductive resources.     

Mycorrhizal influence on protein and lipid of durum wheat grown at different soil phosphorus levels

 Root colonization by arbuscular mycorrhizal fungi (AMF) may affect protein and lipid composition of plants by altering P nutrition or by eliciting other metabolic responses in the host plant. This study was conducted to determine the effects of an AMF and soil P on seed protein and lipid contents and yield of two genotypes of durum wheat (Triticum durum L.). Plants were grown in a greenhouse using soil: sand mixes with different levels of P, and with or without the AMF Glomus mosseae [(Nicol. and Gerd.) Gerd. and Trappe]. Percentage AMF root colonization decreased as P added to soil increased. The wheat genotype CR057 had higher AMF root colonization but lower seed P and protein concentrations than CR006. Without added soil P, protein concentration was significantly lower and lipid concentration and seed dry weight higher in arbuscular mycorrhizal (AM) than in nonAM plants. Seed lipid and protein contents were highly correlated with P content of plants. In nonAM plants, seed lipid and protein contents were low with no added soil P and did not differ with added soil P. Seed protein/lipid (Pro/L) concentration ratios of AM plants were higher than those of nonAM plants only when no P was added to the soil. The data indicate different patterns of seed P accumulation and different relationships between seed P and protein and lipid in AM and nonAM plants. Thus, both the presence and degree of AMF root colonization affected seed lipid metabolism in these durum wheat genotypes. Accepted: 18 May 1999     

The combined effects of CO2 concentration and solar UV-B radiation on faba bean grown in open-top chambers

The response of faba bean seedlings to the combined effects of increased atmospheric CO2 concentrations ([CO2]) and solar UV-B irradiance was studied using open-top chambers transparent to UV-B radiation. The purpose of the study was to determine whether effects of increased [CO2] on growth and physiology are modified by the present solar UV-B fluence rate in the Netherlands. Seedlings were exposed to 350 or 700 micromoles mol-1 CO2. At both [CO2], solar UV-B irradiance was either present or reduced using polyester foil opaque to UV-B radiation. To obtain information on the time dependence of increased [CO2] and UV-B radiation effects, three harvests were performed during the experiment. CO2 enrichment resulted in increased biomass production at all harvests. At the final harvest, UV-B radiation did not affect biomass production but a significant decrease was observed after 14 d of treatment. A reduction of the UV-B fluence increased shoot length at both [CO2] throughout the experiment. UV-B radiation slightly altered biomass allocation. Plants grown at reduced levels of UV-B radiation invested less biomass in flowers and more in stem material compared to plants grown at ambient UV-B levels. CO2 enrichment resulted in a stimulation of net photosynthesis after 26 and 38 d of treatment. UV-B reduction did not alter this response. After 26 d of treatment, photosynthetic acclimation to CO2 enrichment was observed, which was probably the result of accumulation of carbohydrates in the leaves. After 38 d, photosynthetic acclimation was no longer present. The UV absorbance of methanolic leaf extracts was increased by CO2 enrichment only. Both CO2 enrichment and solar UV-B reduced the transmittance of radiation through intact attached leaves. Interaction between [CO2] and UV-B radiation was limited to UV-A transmittance of leaves. Under prevalent experimental conditions, UV-B radiation did not affect the measured physiological parameters. Most open-top chambers used for climate change research are constructed of materials which do not transmit UV-B radiation. Our results indicate that part of the 'chamber effects' on plant height often described in the literature might be explained by the absence of solar UV-B radiation in these chambers.     

Influence of temperature on root development and phosphate influx in winter wheat grown at different P levels

Root development was studied in winter wheat ( Triticum aestivum L. cv Starke II) grown at 5,10, 15 and 20°C in nutrient solutions with phosphate concentrations of 10, 100 or 1000 μM . The plants were grown for 38 days (5 and 10°C), 19 days (15°C) or 14 days (20°C). At the end of the cultivation period the phosphate influx in the roots was determined with ³²P-phosphate. Root development (lateral and seminal roof length and number) was monitored throughout the cultivation period on the same individuals by repeated (approximately every second day) photocopying of the roots for measurements with digitizer and appropriate software. The 5°C treatment yielded no laterals, and the seminals were only slightly affected by the different phosphate treatments. The 10 μM phosphate treatment gave high root:shoot dry weight ratio, high average lateral root length and high specific root length [m root (g root fresh weight)^-1]. The 1000 μM phosphate treatment yielded the highest number of laterals per m seminal root, and usually also the highest absolute numbers. Phosphate influx decreased with increased P status of the roots. It is argued that phosphate influx is dependent on factors such as P status, root geometry and relative root extension rate.     

Yield responses of two ryegrass and two white clover varieties grown in contrasting mixtures with applications of phosphate at different depths and on different soils

To validate earlier findings using ³²P in upland soil and at different depths in lowland soil, ryegrass varieties S.23 or Titania were grown in mixtures with white clover varieties S.184 or Olwen. Unlabelled phosphate (0 or 43 kg P/ha) was applied to the surface or at 30 cm depth in lowland soil, and dry matter yields of grass and clover were measured. In June, on lowland soil, the greatest yield of clover was obtained by surface application. The most productive mixture was S.23/Olwen, although in August Titania outyielded S.23. By October S.23 again outyielded Titania. These results validated the isotopically discovered interactions between phosphate depth and grass/clover mixtures. On upland peat and mineral soil, 0 or 43 kg P/ha was surface applied to the same varietal mixtures. In May, phosphate application to mineral soil slightly decreased clover presence, while clover was increased by mixture with Titania rather than S.23. In July, no significant phosphate effects were found, but in October phosphate increased clover yield and, at least on mineral soil, S.23/Olwen responded most.     

Epidermal transmittance and phenolic composition in leaves of atrazine-tolerant and atrazine-sensitive cultivars of Brassica napus grown under enhanced UV-B radiation

Experiments were conducted on the atrazine-tolerant mutant Stallion and the atrazine-sensitive cv. Paroll of Brassica napus L., which were grown under either visible light or with the addition of UV-B radiation (280–320 nm) for 15 days. The mutant has been shown to be sensitive to high levels of visible light as compared to the atrazine-sensitive cultivar and therefore we wished to determine plant response to UV-B radiation with respect to potential pigment changes, certain anatomical features, radiation penetration and partial photosynthesis. With regard to pigment changes, we were particularly interested in whether the compositional shift in flavonol pigments under enhanced UV-B radiation, previously suggested to favour increased antioxidant activity, is confined to the adaxial epidermis, which generally receives most UV-B radiation or whether the pigment shift is also inducible in the abaxial epidermis.As was to be expected, the penetration of UV-B radiation (310 nm) was lower in the UV-B-exposed plants, which was correlated with an increased amount of UV-screening pigments in the adaxial and abaxial epidermal layers. The main flavonoid glycosides showed the largest shift from kaempferol to quercetin as aglycone moiety in the adaxial epidermal layer. However, in the abaxial epidermal layer the hydroxycinnamic acid (HCA) derivatives and kaempferol glycosides were predominant. Penetration of 430 nm light was higher after UV-B exposure, and probably contributed to the fact that photosynthetic efficiency of photosystem II was unchanged or higher after UV-B exposure. UV-B radiation decreased leaf area in the atrazine-tolerant mutant only. Both cultivars showed an increased leaf thickness after UV-B exposure due to cell elongation mainly of the palisade tissue. This was especially evident in the mutant.     

Effects of retinoids on regenerating limbs: comparison of retinoic acid and arotinoid at different amputation levels

Summary Retinoic acid and the synthetic retinoid, arotinoid, were compared for their efficacy in inducing proximodistal (PD) pattern duplication in regenerating axolotl limbs, after amputation through either the distal zeugopodium (lower arm or leg) or distal stylopodium (upper arm or leg). At each level of amputation, the morphology of the duplications produced was the same for both retinoids, and the mean level of proximalization was dose-dependent. Blastema formation was delayed by both retinoids and the delay was associated with regression of the limb stump. Blastemas which produced PD duplication to the stylopodial or girdle level grew out from the stump in a posterior direction. In several zeugopodial regenerates, a partially duplicated, PD-reversed zeugopodium regenerated between the stump cartilages and a completely duplicated zeugopodium distally. Arotinoid was 50 times more effective than retinoic acid in evoking duplication. The dose of arotinoid required to duplicate a stylopodium in a stylopodial regenerate was several times higher than the dose required to duplicate a zeugopodium in a zeugopodial regenerate, suggesting differences either in the sensitivity of zeugopodial and stylopodial cells to retinoid, or in the numbers of positional value specifying these segments.     

Determination of laccase activity in mixed solvents: comparison between two chromogens in a spectrophotometric assay

Spectrophotometric determination of laccase activity with ABTS acting as chromogen yields exceedingly low values whenever conducted in a water-organic mixed solvent. Nevertheless, there is firm evidence that laccase is able to oxidize substrates such as phenols and amines quantitatively in these mixed solvents. We show that the apparently small rate of ABTS oxidation by laccase in a mixed solvent, such as buffered water-dioxane 1:1, is not amenable to the denaturation of laccase but rather to the decreased stability of ABTS(.+). We propose HAA as a more reliable chromogen for the determination of laccase activity in mixed solvents.     

Determination of aflatoxin levels in peanut butter using HPLC and ELISA procedures: Inter-laboratory comparison

Mycotoxin Research - Six laboratories analyzed portions of the same aqueous acetonitrile extracts of three peanut butters for aflatoxin concentrations by an HPLC procedure (using immunoaffinity...