Dynamics and mechanisms of arsenite oxidation by freshwater lake sediments

There has been increasing concern over As in freshwater environments from sources such as arsenical pesticides, smelters, coal-fired power plants, and erosion caused by intensive land use. Arsenic in the reduced state, As (III) (arsenite), is much more toxic, more soluble and mobile, than when in the oxidized state, As (V) (arsenate). This paper summarizes the dynamics and mechanisms involved in the oxidation of As (III) to As (V) by freshwater lake sediments. Sediments from selected freshwater lakes in southern Saskatchewan oxidize As (III) to As (V) predominantly through an abiotic process. Solution analysis of As (III) and As (V) by colorimetry, and examination of the oxidation state of surface-sorbed As species by X-ray photoelectron spectroscopy, indicate that Mn present in the sediment is the primary electron acceptor in the oxidation of As (III). The transformation of As (III) to As (V) by carbonate and silicate minerals, common in sediments, is not evident. The heat of activation, ΔH_a, for the depletion (oxidation plus sorption) of As (III) by the sediments, varies from 3.3 to 8.5 kcal mole⁻¹, indicating that the process is predominantly diffusion-controlled. The Mn present in a series of particle size fractions ( < 2– > 20 μm) of the sediments may potentially detoxify As (III) in aquatic systems, by converting it to As (V).     

Formation of spicules by sclerocytes from the freshwater spongeEphydatia muelleri in short-term cultures in vitro

Summary Cells from the freshwater spongeEphydatia muelleri were isolated by dissociating hatching gemmules. During the first 24 h the cells reaggregated, but the aggregates progressively disintegrated again to single cells, among which the spicule-forming sclerocytes were recognized. Such cultures were used to study spicule (megascleres) formation in vitro. The isolated sclerocytes formed the organic central axial filament onto which they deposited inorganic silicon. The size of the spicules (200 to 350μm in length) as well as the rate of spicule formation (1 to 10μm/h) under in vitro conditions were similar to the values measured in vivo. Immediately after completion of spicule formation, or even before, the sclerocyte could start formation of a new spicule; 5% of the cells were in the process of forming two spicules simultaneously. Cultivation of sclerocytes in the absence of silicon resulted in the formation of the axial filament only. We succeeded in maintaining the sclerocytes in a proliferating and spicule-forming state for up to 3 mo. These results demonstrate that the establishment of short-term cell cultures fromE. muelleri is possible; however, future studies must be undertaken to identify the growth factors required for a permanent culture of sponge cells.     

Elicitation of anthocyanin production in callus cultures of <Emphasis Type="Italic">Daucus carota</Emphasis> and the involvement of methyl jasmonate and salicylic acid

The effect of methyl jasmonate (MeJA) and salicylic acid (SA) on the anthocyanin accumulation, endogenous titres of polyamines and ethylene production in callus cultures of Daucus carota were studied. The interaction of these signaling molecules with elicitors from Aspergillus niger was investigated and the involvement of MeJA was elucidated through the use of the jasmonic acid (JA) biosynthetic inhibitor ibuprofen. MeJA and SA were both found to stimulate the anthocyanin production in the callus cultures. The highest levels of anthocyanin was observed in the cultures treated with 200 μM SA 0.36 % and 0.01 μM MeJA 0.37 %. The MeJA and SA treatments were also found to result in higher activity of Ca²⁺ ATPase suggesting that the enhancement of anthocyanin by SA and MeJA could be mediated through the involvement of the calcium channel. The treatment of the callus cultures with SA was found to result in marginally higher titres of endogenous polyamines (PAs) whereas MeJA resulted in lower levels of PAs as compared to the control. The SA treatment was found to result in lower ethylene production and the treatment with MeJA stimulated the ethylene production. These results suggest that the stimulation of anthocyanin production by MeJA and SA in callus cultures of D. carota is not related to the ethylene production.     

Physical processes and their role on the spatial and temporal variability of the spring phytoplankton bloom in the central Yellow Sea

The spatial and temporal variability of the spring phytoplankton bloom (SPB) in the central Yellow Sea is studied, using SeaWiFS surface chlorophyll remote-sensing data, AVHRR sea surface temperatures (SST), QuikSCAT sea surface wind speed (SSW) from 1998 to 2009 and the cruise survey data in 2007 and 2009. The influences of the hydrological conditions on the SPB are significant. (1) The rising SST and low SSW in spring play an important role in the development of the SPB. The SPB in the central Yellow Sea occurs primarily in April (from April 3 to April 24) and at this period the mean SST is generally greater than 10 °C, and 24 h averaged SSW is less than 5.4 m/s. The 99% of the SPB occurs when the SST is 9–14 °C and SSW is 0–7.9 m/s. (2) Specifically, the development of the SPB is from April 4 to April 7 and from April 4 to April 22 in 2007 and 2009 respectively. The longer duration of the SPB in 2009 than that in 2007 is related to the high SST in 2009, which is approximately 2 °C greater than that in 2007, and the weak SSW in 2009, which is much lower than that in 2007, which further indicate that these two factors are critical to the duration of the SPB. (3) The horizontal distribution of surface chlorophyll a in 2007 is found to be greater and located more northward than that in 2009. Comparing the spatial coverage of the SPB, the path of the Yellow Sea warm current, which is warmer and salty, and the location of maximum SST reveals that the spatial coverage of the SPB locates in the warmer temperature (>9 °C) and higher salinity (>33) waters in March and this warm and salty water was much more evident in 2007 than that in 2009 because a stronger warm current of the Yellow Sea in winter. (4) The vertical depths of the maximum chlorophyll layer (MCL) appear at three levels: surface, 10 m and 30 m in 2007, whereas the MCL occurs only at a sub-surface level in 2009 which is related to vertical stability of the water column, i.e., the water is vertically mixed in 2007 while vertically stratified in 2009.     

Physical processes and their role on the spatial and temporal variability of the spring phytoplankton bloom in the central Yellow Sea

The spatial and temporal variability of the spring phytoplankton bloom (SPB) in the central Yellow Sea is studied, using SeaWiFS surface chlorophyll remote-sensing data, AVHRR sea surface temperatures (SST), QuikSCAT sea surface wind speed (SSW) from 1998 to 2009 and the cruise survey data in 2007 and 2009. The influences of the hydrological conditions on the SPB are significant. (1) The rising SST and low SSW in spring play an important role in the development of the SPB. The SPB in the central Yellow Sea occurs primarily in April (from April 3 to April 24) and at this period the mean SST is generally greater than 10 °C, and 24 h averaged SSW is less than 5.4 m/s. The 99% of the SPB occurs when the SST is 9–14 °C and SSW is 0–7.9 m/s. (2) Specifically, the development of the SPB is from April 4 to April 7 and from April 4 to April 22 in 2007 and 2009 respectively. The longer duration of the SPB in 2009 than that in 2007 is related to the high SST in 2009, which is approximately 2 °C greater than that in 2007, and the weak SSW in 2009, which is much lower than that in 2007, which further indicate that these two factors are critical to the duration of the SPB. (3) The horizontal distribution of surface chlorophyll a in 2007 is found to be greater and located more northward than that in 2009. Comparing the spatial coverage of the SPB, the path of the Yellow Sea warm current, which is warmer and salty, and the location of maximum SST reveals that the spatial coverage of the SPB locates in the warmer temperature (>9 °C) and higher salinity (>33) waters in March and this warm and salty water was much more evident in 2007 than that in 2009 because a stronger warm current of the Yellow Sea in winter. (4) The vertical depths of the maximum chlorophyll layer (MCL) appear at three levels: surface, 10 m and 30 m in 2007, whereas the MCL occurs only at a sub-surface level in 2009 which is related to vertical stability of the water column, i.e., the water is vertically mixed in 2007 while vertically stratified in 2009.     

Effects of simulated elevated concentration of atmospheric CO2 and temperature on soil enzyme activity in the subalpine fir forest

Little is known about the responses of the activities of soil enzymes that are related to mass cycle to simulated climate change. Therefore, 72 intact soil columns from the primary fir (Abies faxoniana Rehder & E. H. Wilson) forest were parked in environment-controlled chambers with the CK (outside ambient CO₂ concentration and temperature), EC (elevated concentration CO₂ with (347.1 ± 22.1) μmol·mol^?1), ET (elevated temperature with (2.4 ± 0.4)°C), and ECT (elevated CO₂ concentration with (352.8 ± 27.6) μmol·mol^?1 and temperature with (2.2 ± 0.5)°C) treatments, and the activities of invertase, urease, nitrate reductase and acid phosphatase, which are related to the cycles of carbon, nitrogen and phosphorus in mineral soil (MS) and organic layer (OL) were measured simultaneously to understand the responses of these enzymes to climate change. Significant monthly variations on the activities of the studied enzymes were found in both OL and MS with the highest enzyme activities in summer, which were of ecological significance for soil nutrient availability and tree nutrition in the subalpine forest ecosystem. Different monthly patterns of enzyme activities were attributed to enzyme sources and soil layer. EC treatment had influenced slightly on the activities of the studied enzymes resulting from the higher CO₂ concentration in soil atmosphere and no indirect effect from the EC owing to a lack of trees planted on soils. ET treatment increased enzyme activities in comparison with the CK treatment because ET was beneficial to microbial growth and propagation. The increments of the enzyme activities in OL were higher than those in MS, implying that OL is more sensitive to climate change. ECT treatment sharply increased enzyme activities in comparison with the EC and CK, but there was no significant difference between ET and ECT, which was also attributed to no indirect effect by EC treatment owing to trees not planted on soils, implying that the increment of enzyme activities resulted from the temperature effect. However, further studies on indirect effect and complex effect on soil enzyme activity caused by EC, ET and ECT are needed to understand the soil enzyme responses to the climate change.     

Pattern analysis in landscape ecology: progress, challenges and outlook

Landscape pattern indices or landscape metrics, an important means in landscape pattern analysis, has resulted in the prosperity of landscape ecology. However, landscape pattern analysis was criticized recently for its poor correlation with ecological processes. In this paper, the current situation and challenges in landscape pattern analysis was elaborated, and the future of landscape pattern analysis was discussed. We believe that the landscape metrics is still the main method in spatial pattern analysis, and is important for landscape ecology. However, there are 3 challenges in landscape pattern analysis: (1) how to develop new methods by integrating explicit ecological sense in landscape pattern analysis? (2) How to link landscape pattern and ecological processes? (3) How to apply the theory of “matrix-patch-corridor” to practice? In future, 5 issues are to be addressed: (1) to develop a methodology to describe landscape pattern in a dynamic manner; (2) to explore the ecological sense of landscape pattern using a series of landscape metrics; (3) to develop new methods for landscape pattern analysis related to ecological processes; (4) to conduct landscape pattern analysis at multi-dimensions; (5) to explain the relationship between landscape pattern and ecological processes by multi-scale pattern analysis.     

Stratigraphic record of U37K in Sanmen Bay: the effect of SST and EI Niño on life activity in macrobenthos communities

Sea surface temperature (SST) from 1916–2003 was estimated by using the index of U₃₇^K of organic compounds in Sanmen Bay (SMB) sediment. It fluctuated between 15.97°C and 18.00°C with an average of 17.03°C. The estimated SST was 3.52°C lower than the annual average temperature measured in the same year but was close to the temperature measured in fall. The research suggested that the climate events (EI Ni?o) on large scale in Sanmen Bay were affected by the climate, similar to that in the East Pacific Ocean (EPC). The change scale was also affected by geographical location and local climate such as monsoon. According to the chronological basis, the events in SMB corresponded to those in EPC, but the scale of variation is not so strong as that in EPC. By comparing the community, biomass, individual density and biodiversity of macrobenthos during EI Ni?o (between 2002 and 2003) and non-EI Ni?o (between 2005 and 2006) periods, it was indicated that certain macrobenthos communities in SMB responded to EI Ni?o events. During the EI Ni?o period, Taiwan warm current (TWC) is much stronger than that in normal years. The diversity of macrobenthos during 2002 and 2003 was relatively low owing to invasion of the warm current that caused salinity change. The macrobenthos and zooplankton in Sanmen Bay responded to EI Ni?o events significantly. The diversity of macrobenthos decreased significantly because TWC invaded into the shallow bay from the floor and thus changed the temperature and salinity in the bay. On the other hand, zooplankton species, biomass and abundance increased in the period of EI Ni?o since the invaded warm current brought abundant species of zooplankton.     

Alteration of epithelial cell lipid synthesis by n-nitrosonornicotine

Summary Changes in the lipid composition of a cell membrane due to the binding of one cell modulator may affect binding of a second modulator, whether that binding is receptor-mediated (specific) or non-receptor-mediated (nonspecific). Such altered binding interactions have been demonstrated in oral epithelial cells, wherein N-nitrosonornicotine (NNN), a nonspecific ligand, enhances phorbol ester binding. To characterize membrane changes that may be responsible for such an effect, the current study examined lipid changes in hamster oral epithelial (HCP) cells associated with NNN binding. HCP cultures at two cell densities, 5 × 10⁶ cells/100 mm plate (subconfluent cultures) or 10 × 10⁶ cells/100 mm plate (confluent cultures) were incubated in Keratinocyte-Serum-Free Medium and exposed to 10μM NNN or DMSO (solvent control) for 48 h. Lipids were labeled with¹⁴C-acetate, then extracted, separated by thin layer chromatography, and the¹⁴C-lipids located by autoradiography and counted. Exposure of subconfluent cultures to NNN for 48 h, with¹⁴C-acetate present during the final 24 h, resulted in altered phospholipid and fatty acid labeling. Phospholipid labeling increased slightly in the presence of NNN compared to controls, while fatty acid labeling showed a modest but significant decrease in the presence of NNN. Similar changes occurred in the confluent cultures. Prelabeling of lipids in subconfluent cultures, followed by exposure to NNN in the absence of radiolabel, resulted in significantly (P<0.05) greater phospholipid labeling in the presence of NNN compared to control cultures. At the same time, fatty acid labeling decreased significantly. The NNN caused the cells to have decreased levels of several long chain polyunsaturated fatty acids and an increased amount of one long chain saturated (24:0) fatty acid. Significant differences were detected in the synthesis of various lipid classes between subconfluent and confluent cultures, but the presence of the NNN did not affect these differences. These results suggest that there is a shift of fatty acid type in the cells’ phospholipids in the presence of NNN, a finding that may reflect the membrane’s adaptation to the modulator’s presence.     

Neural correlates of behavioral gap detection in the inferior colliculus of the young CBA mouse

The gap detection paradigm is frequently used in psychoacoustics to characterize the temporal acuity of the auditory system. Neural responses to silent gaps embedded in white-noise carriers, were obtained from mouse inferior colliculus (IC) neurons and the results compared to behavioral estimates of gap detection. Neural correlates of gap detection were obtained from 78 single neurons located in the central nucleus of the IC. Minimal gap thresholds (MGTs) were computed from single-unit gap functions and were found to be comparable, 1–2 ms, to the behavioral gap threshold (2 ms). There was no difference in MGTs for units in which both carrier intensities were collected. Single unit responses were classified based on temporal discharge patterns to steady-state noise bursts. Onset and primary-like units had the shortest mean MGTs (2.0 ms), followed by sustained units (4.0 ms) and phasic-off units (4.2 ms). The longest MGTs were obtained for inhibitory neurons (xˉ = 14 ms). Finally, the time-course of behavioral and neurophysiological gap functions were found to be in good agreement. The results of the present study indicate the neural code necessary for behavioral gap detection is present in the temporal discharge patterns of the majority of IC neurons. Accepted: 6 February 1997     

An unexpected effect of capsaicin on spontaneous GABA-ergic IPSCS in hippocampal cell cultures

Vanilloid receptors 1 (VRs1) expressed in a subpopulation of sensory neurons and responsible for processing of chemical and thermal noxious stimuli were also shown to be expressed in several cerebral structures and to be involved in the regulation of glutamatergic synaptic transmission. In this study, we started to investigate the possibility that VRs1 are also involved in the regulation of GABA-ergic synaptic transmission. For this purpose, the effect of a VR1 agonist, capsaicin, on spontaneous GABA-ergic inhibitory postsynaptic currents (IPSCs) was studied in hippocampal cell cultures using a patch-clamp technique. It was found that capsaicin (10 μM) decreased both the frequency and amplitude of spontaneous IPSCs. This finding suggests the involvement of VRs1 in the regulation of neuronal firing in some GABA-ergic interneurons and in the modulation of the efficacy of GABA-ergic synaptic transmission. However, considering the direction of the effect (a decrease in the IPSC frequency) and lack of its desensitization, the involvement of other receptor(s) also cannot currently be ruled out. Neirofiziologiya/Neurophysiology, Vol. 38, No. 4, pp. 364–367, July–August, 2006.     

Growth and proliferation in vitro of Vaccinium corymbosum under different irradiance and radiation spectral composition

Plantlets of highbush blueberry (Vaccinium corymbosum) cvs. Atlantic, Berkeley and Elizabeth, were exposed in vitro to radiation of different spectral compositions obtained by filtering the cool-white light with either 2 types of polymethylmethacrylate (PMMA) layers or glass and different photosynthetic photon flux density (PPFD, ranging from 10 to 180 μmol m^-2 s^-1). Red colour of leaves was the first response to the light treatments: after 14 d under unfiltered light, the shoots exposed to higher PPFD showed dramatic reddening of leaves and sprouts, especially in cv. Atlantic; cutting wavelengths shorter than 520 nm (no-B-PMMA filter) prevented those effects. On average, cv. Atlantic yielded the highest number of shoots per explant (10.4), followed by cv. Elizabeth (9.1) and cv. Berkeley (6.5). No-B-PMMA increased the proliferation rate in all the 3 genotypes, especially in cv. Atlantic. On the other hand, cutting wavelengths between 650 and 760 nm (no-R-PMMA filter) generally depressed the proliferation rate. No-B-PMMA induced remarkable changes in the morphology of the shoots - more elongate leaves and longer internodes - especially in cv. Atlantic. This revised version was published online in July 2006 with corrections to the Cover Date.     

Antioxidative responses and proline level in leaves and roots of pea plants subjected to nickel stress

The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), glutathione S-transferase (GST) as well as proline content were studied in leaves and roots of 14 day-old pea plants treated with NiSO₄ (10, 100, 200 μm) for 1, 3, 6 and 9 days. Exposure of pea plants to nickel (Ni) resulted in the decrease in CuZnSOD as well as total SOD activities in both leaves and roots. The activity of APX in leaves of plants treated with 100 and 200 μm Ni increased following the 3rd day after metal application, while in roots at the end of the experiment the activity of this enzyme was significantly reduced. In both organs CAT activity generally did not change in response to Ni treatment. The activity of GST in plants exposed to high concentrations of Ni increased, more markedly in roots. In both leaves and roots after Ni application accumulation of free proline was observed, but in the case of leaves concentration of this amino acid increased earlier and to a greater extent than in roots. The results indicate that stimulation of GST activity and accumulation of proline in the tissues rather than antioxidative enzymes are involved in response of pea plants to Ni stress.     

Clonal differences in the response of dark and light reactions of photosynthesis to elevated atmospheric CO2 in poplar

Two hybrid poplar (Populus) clones (i.e., fast growing clone Beauprè and slow growing clone Robusta) were grown for two years from cuttings at close spacings in open top chambers (OTCs) under ambient (AC) and elevated [EC = AC + 350 μmol(CO2) mol-1] CO2 treatments. For clone Beauprè no down-regulation of photosynthesis was observed. Two years of growing under EC resulted in an increase in quantum yield of photosystem 2 (PS2), steady state irradiance saturated rate of net photosynthesis (P _Nmax), chlorophyll (Chl) content, and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPC) activity for this clone. We suppose that under non-limiting conditions of nitrogen and phosphorus content the response to EC was by building up light-harvesting complexes of PS2 and increasing photochemical efficiency of PS2. Due to a high rate of the primary reactions of photosynthesis and a high RuBPCO activity the end product of the response to EC was an increase in PNmax and a larger saccharides content. The Robusta clone showed a depression in the primary reactions of photosynthesis under EC. We found a decrease in quantum yield of PS2, Chl and phosphorus contents, and in RuBPCO activity. However, an increase in PNmax, saccharides content and Chl a/b ratio was observed. We speculate (1) that the phosphorus deficiency in combination with an increase in CO2 concentrations may lead to a potential damage of the assimilation apparatus of the primary reactions of photosynthesis and to a decrease in photochemical efficiency of PS2; (2) that the primary target of "down-regulation" takes place at PS2 for irradiances above 150 μmol m-2 s-1. This revised version was published online in September 2006 with corrections to the Cover Date.     

Influence of the Qinghai-Tibetan railway and highway on the activities of wild animals

The effect of traffic and railway construction on the activities of wild animals during the daytime along the Qinghai-Tibetan highway between Budongquan (35°17′ N; 93°16′ E) and Wudaliang (35°13′ N; 93°04′ E) was studied in August 2003 and August 2004. Furthermore, passageways cross the Qinghai-Tibetan railway were monitored to determine the relationship between the usage frequency of the passageways and the distance to the Qinghai-Tibetan highway and the dimension of the passageways. The results showed that the traffic during the daytime had some effects on the Tibetan antelope (Pantholops hodgsoni), Tibetan gazelle (Procapra picticaudata) and Kiang (Equus kiang) when they were crossing the road, and especially it is significant on the Tibetan antelope. At the same time, they could adapt themselves to the changes in the surroundings by learning and by adjusting their behavior. Most of their activities took place in the morning in order to avoid the effects of traffic, and they could also find and use the passageways cross the Qinghai-Tibetan railway. The dimensions of the passageways, the distance to the Qinghai-Tibetan highway, the surrounding habitat, and human activities could influence the efficiency of the passageways. Most passageways cross the Qinghai-Tibetan railway could not be effectively used by the wildlife because of the short length and low height or because of human activities in the contiguous areas of the passageways. However, the wildlife could adapt themselves to the changes in the surroundings caused by the construction of the Qinghai-Tibetan railway by learning and by adjusting their behavior.     

Influence of the Qinghai-Tibetan railway and highway on the activities of wild animals

The effect of traffic and railway construction on the activities of wild animals during the daytime along the Qinghai-Tibetan highway between Budongquan (35°17′ N; 93°16′ E) and Wudaliang (35°13′ N; 93°04′ E) was studied in August 2003 and August 2004. Furthermore, passageways cross the Qinghai-Tibetan railway were monitored to determine the relationship between the usage frequency of the passageways and the distance to the Qinghai-Tibetan highway and the dimension of the passageways. The results showed that the traffic during the daytime had some effects on the Tibetan antelope (Pantholops hodgsoni), Tibetan gazelle (Procapra picticaudata) and Kiang (Equus kiang) when they were crossing the road, and especially it is significant on the Tibetan antelope. At the same time, they could adapt themselves to the changes in the surroundings by learning and by adjusting their behavior. Most of their activities took place in the morning in order to avoid the effects of traffic, and they could also find and use the passageways cross the Qinghai-Tibetan railway. The dimensions of the passageways, the distance to the Qinghai-Tibetan highway, the surrounding habitat, and human activities could influence the efficiency of the passageways. Most passageways cross the Qinghai-Tibetan railway could not be effectively used by the wildlife because of the short length and low height or because of human activities in the contiguous areas of the passageways. However, the wildlife could adapt themselves to the changes in the surroundings caused by the construction of the Qinghai-Tibetan railway by learning and by adjusting their behavior.     

Elevated CO<Subscript>2</Subscript> and temperature differentially affect photosynthesis and resource allocation in flag and penultimate leaves of wheat

Differences in acclimation to elevated growth CO₂ (700 μmol mol⁻¹, EC) and elevated temperature (ambient +4 °C, ET) in successive leaves of wheat were investigated in field chambers. At a common measurement CO₂, EC increased photosynthesis and the quantum yield of electron transport (Φ) early on in the growth of penultimate leaves, and later decreased them. In contrast, EC did not change photosynthesis, and increased Φ at later growth stages in the flag leaf. Contents of chlorophyll (Chl), ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO), and total soluble protein were initially higher and subsequently lower in penultimate than flag leaves. EC decreased RuBPCO protein content relative to soluble protein and Chl contents throughout the development of penultimate leaves. On the other hand, EC initially increased the RuBPCO:Chl and Chl a/b ratios, but later decreased them in flag leaves. In the flag leaves but not in the penultimate leaves, ET initially decreased initial and specific RuBPCO activities at ambient CO₂ (AC) and increased them at EC. Late in leaf growth, ET decreased Chl contents under AC in both kinds of leaves, and had no effect or a positive one under EC. Thus the differences between the two kinds of leaves were due to resource availability, and to EC-increased allocation of resources to photon harvesting in the penultimate leaves, but to increased allocation to carboxylation early on in growth, and to light harvesting subsequently, in the flag leaves.     

Epidermal growth factor and insulin-like growth factor-1 protect MDA-231 cells from death induced by actinomycin D: The involvement of growth factors in drug resistance

Summary In the present study, we investigated the ability of epidermal growth factor (EGF), insulin-like growth factor-1 (IGF-1), and insulin to protect the human breast cancer cell line MDA-231 from death induced by the antitumor drug actinomycin D (ACT-D). ACT-D is an inhibitor of RNA and protein synthesis, and its cytotoxicity may result due to continuous depletion in some vital protein molecules. Cell death was induced in the MDA-231 cells by either continuous exposure to a low dose of ACT-D (0.2μg/ml), or by a short-time exposure to a high dose of ACT-D (2μg/ml) and further culturing in the absence of the drug. Cell death was evaluated by the trypan blue dye exclusion test, the release of lactic dehydrogenase into the culture medium, and the depletion in the cellular ATP content. EGF and IGF-1, each at an optimal concentration of 20 ng/ml, enhanced substantially survival of cells exposed either to a low or a high dose of ACT-D. The combination of EGF (10 ng/ml) and IGF-1 (10 ng/ml) had an additive survival effect, which proposes that each of the growth factors enhanced survival by a distinct pathway. Insulin up to 40 ng/ml had no effect on cell survival. Pretreatment of the cells for 1 to 5 h with EGF and IGF-1 protected cells from the cytotoxic effect of ACT-D. Exposure of the cells to 2μg/ml of ACT-D for 1 h resulted in a drastic inhibition in uridine incorporation and only in a slight inhibition in leucine incorporation. Further incubation in the absence of ACT-D resulted in a continuous decrease in uridine and in leucine incorporation, either in the absence or presence of the growth factors. However, EGF and IGF-1, but not insulin, attenuated significantly this continuous decrease. We assume that EGF and IGF-1 protect cell viability by a mechanism that maintains a critical level of some vital protein molecule above the critical level at which cells die. Our finding that EGF and IGF-1 induced resistance to ACT-D suggests that growth factors may be involved in the mechanism of drug resistance.     

Land use effects on terrestrial carbon sources and sinks

Current and past land use practices are critical in determining the distribution and sizeof global terrestrial carbon (C) sources and sinks. Although fossil fuel emissions dominate the an-thropogenic perturbation of the global C cycle, land use still drives the largest portion of anthropo-genic emissions in a number of tropical regions of Asia. The size of the emission flux owing to landuse change is still the biggest uncertainty in the global C budget. The Intergovernmental Panel on Climate Change (IPCC) reported a flux term of 1.7 PgC·a~(-1) for 1990-1995 but more recent es-timates suggest the magnitude of this source may be only of 0.96 PgC·a~(-1) for the 1990s. In add-ition, current and past land use practices are now thought to contribute to a large degree to the northern hemisphere terrestrial sink, and are the dominant driver for some regional sinks. However,mechanisms other than land use change need to be invoked in order to explain the inferred C sink in the tropics. Potential candidates are the carbon dioxide (CO_2) fertilization and climate change;fertilization due to nitrogen (N) deposition is believed to be small or nil. Although the potential formanaging C sinks is limited, improved land use management and new land uses such as refores-tation and biomass fuel cropping, can further enhance current terrestrial C sinks. Best manage-ment practices in agriculture alone could sequester 0.4-0.8 PgC per year in soils if implemented globally. New methodologies to ensure verification and permanency of C sequestration need to be developed.     

Regulation of photochemical efficiency of photosystem 2 in Norway spruce at the beginning of winter and in the following spring

Based on the analysis of fluorescence quenching, the nonphotochemical dissipative processes were investigated in Norway spruce needles during acclimation to winter and spring conditions. The maximum nonphotochemical fluorescence quenching (q_Nmax) was reached at lower irradiances in winter (up to 310 μmol m-2 s-1) than in spring (about 1130 μmol m-2 s-1), but its values were nearly the same (q_Nmax = 0.91±0.01) during both winter and spring measurements. In early winter the pronounced initial fluorescence quenching (q0) suggested that nonradiative energy dissipation in the antennae complexes dominated. Significantly lower q0 (by 40-60 % compared to winter needles) during acclimation of needles to spring conditions supported a significant contribution of quenching in the reaction centres. These findings support the hypothesis that the antennae systems and reaction centres cooperate in the protective dissipation of excess excitation energy. This revised version was published online in September 2006 with corrections to the Cover Date.