莰烯醛O-取代肟的合成及其抗肿瘤活性

以莰烯醛肟与卤代物为原料经亲核取代反应合成了9个未见报道的莰烯醛O-取代肟类化合物,分别为2-(3,3-二甲基双环[2.2.1]庚-2-亚基)乙醛O-苄基肟(2a)、2-(3,3-二甲基双环[2.2.1]庚-2-亚基)乙醛O-丁基肟(2b)、2-(3,3-二甲基双环[2.2.1]庚-2-亚基)乙醛O-(4-氯丁基)肟(2c)、2-(3,3-二甲基双环[2.2.1]庚-2-亚基)乙醛O-(3-溴苄基)肟(2d)、2-(3,3-二甲基双环[2.2.1]庚-2-亚基)乙醛O-(4-叔丁基苄基)肟(2e)、2-(3,3-二甲基双环[2.2.1]庚-2-亚基)乙醛O-(4-氯苄基)肟(2f)、2-(3,3-二甲基双环[2.2.1]庚-2-亚基)乙醛O-(4-氰基苄基)肟(2g)、2-(3,3-二甲基双环[2.2.1]庚-2-亚基)乙醛O-(2,6-二氯苄基)肟(2h)、2-(3,3-二甲基双环[2.2.1]庚-2-亚基)乙醛O-(邻氟苄基)肟(2i)。利用FT-IR、GC-MS、1H NMR以及13C NMR对产物结构进行了表征。以化合物2a为例,探索了不同工艺条件对产物得率的影响,在甲苯为溶剂,n(莰烯醛肟)∶n(氯化苄)∶n(四丁基溴化铵)为1.0∶1.8∶0.08,反应温度为60℃,反应时间为20 h的最佳工艺条件下,产物的得率为84.1%。通过体外抗肿瘤活性测试,探讨了化合物2a^2i对肝癌细胞HepG2和人乳腺癌细胞MCF7的抑制作用,结果表明:化合物2b对HepG2细胞的抑制作用较好,其半数抑制浓度(IC 50)值为36.3μmol/L;化合物2d、2h、2i对MCF7有一定的抑制作用,其中化合物2h对MCF7的抑制作用较好,其IC50值为19.2μmol/L。     

A simple method for measuring acetylene reduction of intact, nodulated black locust seedlings

A simple method is described for measuring acetylene (C(2)H(2)) reduction of nodulated black locust (Robinia pseudoacacia L.) seedlings. The C(2)H(2) reduction chamber consists of a standard plant pot sealed at one end with a stopper having holes for the seedling and a gas inlet port, and sealed at the other end with a stoppered collar with a gas port. The chamber temperature is regulated by circulating water at a controlled temperature through a copper coil surrounding the plant pot. A pump recirculates an approximately ten percent C(2)H(2) atmosphere through the system. Nine-week-old black locust seedlings, grown in sand culture and inoculated with Rhizobium, were used to obtain ethylene (C(2)H(4)) production curves. Ethylene production was linear for up to 60 minutes indicating that, for this particular symbiosis, (1) a simple closed system is adequate and (2) a short duration assay (10 minutes) will reliably estimate C(2)H(2) reduction over a longer period (up to at least 60 minutes). The water content of the soil medium had no influence on the C(2)H(2)/(C(2)H(2) + C(2)H(4)) ratio, which supports the suitability of C(2)H(2) as an internal standard for calculating C(2)H(2) reduction. This system has several desirable features. First, plant disturbance is minimized. Second, plants can be grown in inexpensive pots and no transplanting is necessary. Third, gas exchange and mixing are facilitated by a recirculating pump. Finally, root and nodule temperature can be controlled.     

Responses of foliar gas exchange to long-term elevated CO(2) concentrations in mature loblolly pine trees

Branches of field-grown mature loblolly pine (Pinus taeda L.) trees were exposed for 2 years (1992 and 1993) to ambient or elevated CO(2) concentrations (ambient + 165 micro mol mol(-1) or ambient + 330 micro mol mol(-1) CO(2)). Exposure to elevated CO(2) concentrations enhanced rates of net photosynthesis (P(n)) by 53-111% compared to P(n) of foliage exposed to ambient CO(2). At the same CO(2) measurement concentration, the ratio of intercellular to atmospheric CO(2) concentration (C(i)/C(a)) and stomatal conductance to water vapor did not differ among foliage grown in an ambient or enriched CO(2) concentration. Analysis of the relationship between P(n) and C(i) indicated no significant change in carboxylation efficiency of ribulose-1,5-bisphosphate carboxylase/oxygenase during growth in elevated CO(2) concentrations. Based on estimates derived from P(n)/C(i) curves, there were no apparent treatment differences in dark respiration, CO(2) compensation point or P(n) at the mean C(i). In 1992, foliage in the three CO(2) treatments yielded similar estimates of CO(2)-saturated P(n) (P(max)), whereas in 1993, estimates of P(max) were higher for branches grown in elevated CO(2) than in ambient CO(2). We conclude that field-grown loblolly pine trees do not exhibit downward acclimation of leaf-level photosynthesis in their long-term response to elevated CO(2) concentrations.     

红松播种苗施肥效应研究

本文采用正交设计对红松播种苗进行了施肥效应研究,测定了不同施肥组合条件下苗木的形态指标。结果表明:影响苗木生长的各肥料因子的顺序依次为C(追施尿素)、A(施基肥)、B(追施二铵),促进苗木生长的较佳施肥组合为A3(4)B1C3,即基肥用量为有机肥7 500 g/m2 二铵7g/m2或有机肥7 500 g/m2 二铵7 g/m2 硫酸钾12 g/m2;追肥二铵用量为0;追肥尿素的用量为30 g/m2。     

Gas exchange and dry matter allocation responses to elevation of atmospheric CO(2) concentration in seedlings of three tree species

Photosynthetic rates of 13-month-old Pinus radiata D. Don, Nothofagus fusca (Hook f.) ?rst. and Pseudotsuga menziesii (Mirb.) Franco seedlings grown and measured at elevated atmospheric concentrations of CO(2) (~620 microl l(-1)) were 32 to 55% greater than those of seedlings grown and measured at ambient (~310 microl l(-1)) concentrations of CO(2). Seedlings grown in ambient and elevated concentrations of CO(2) had similar rates of photosynthesis when measured at ~620 microl l(-1) CO(2), but when measured at ~310 microl l(-1) CO(2), the P. radiata and N. fusca seedlings which were grown at elevated CO(2) had lower rates of photosynthesis than the seedlings grown at an ambient concentration of CO(2). Stomatal conductances in general were lower when measured at ~620 microl l(-1) CO(2) than at ~310 microl l(-1) CO(2). Stomatal conductances declined in all species grown at both CO(2) concentrations when the leaf-air water vapor concentration gradient (DeltaW) was increased from 10 to 20 mmol H(2)O mol(-1) air. The percent enhancement in photosynthesis for P. radiata and P. menziesii at elevated CO(2) was greater at 20 mmol than at 10 mmol DeltaW, suggesting that elevated CO(2) may moderate the effects of atmospheric water stress. Dry matter allocation patterns were not significantly different for plants grown in ambient or high CO(2) air.     

Physiological adjustment of two full-sib families of ponderosa pine to elevated CO(2)

Seeds from two full-sib families of ponderosa pine (Pinus ponderosa) with known differences in growth rates were germinated and grown in an ambient (350 micro l l(-1)) or elevated (700 micro l l(-1)) CO(2) concentration. Gas exchange at both ambient and elevated CO(2) concentrations was measured 1, 6, 39, and 112 days after the seed coat was shed. Initial stimulation of CO(2) exchange rate (CER) by elevated CO(2) was large (> 100%). On Day 1, CER of seedlings grown in elevated CO(2) and measured at ambient CO(2) was significantly lower than the CER of seedlings grown and measured at ambient CO(2), indicating physiological adjustment of the seedlings exposed to elevated CO(2). Physiological acclimation to elevated CO(2) was complete by Day 39 when there was no significant difference in CER between seedlings grown and measured at ambient CO(2) and seedlings grown and measured at elevated CO(2). After 4 months, the light response of seedlings in the two treatments was determined at both ambient and elevated CO(2). Light compensation point, CER at light saturation, and apparent quantum efficiency of seedlings grown and measured at ambient CO(2) were not significantly different from those of seedlings grown and measured at elevated CO(2). With a short-term increase in CO(2), CER at light saturation (5.16 +/- 0.52 versus 3.13 +/- 0.30 micro mol CO(2) m(-2) s(-1)) and apparent quantum efficiency (0.082 +/- 0.011 versus 0.045 +/- 0.003 micro mol CO(2) micro mol(-1) quanta) were significantly increased. Leaf C/N ratio was significantly increased in the elevated CO(2) treatment. There were few significant differences between families for any response to elevated CO(2). Under the experimental conditions, high growth rate was not correlated with a greater response to elevated CO(2).     

Drought and the diurnal patterns of stem CO2 efflux and xylem CO2 concentration in young oak (Quercus robur)

A young potted oak (Quercus robur L.) tree was subjected to drought by interrupting the water supply for 9 days. The tree was placed in a growth chamber in which daily patterns of temperature and radiation were constant. The effects of drought on the water and carbon status of the stem were examined by measuring stem sap flow rate, stem water potential, stem diameter variations, stem CO(2) efflux rate (F(CO2)) and xylem CO(2) concentration ([CO(2)*]). Before and after the drought treatment, diurnal fluctuations in F(CO2) and [CO(2)*] corresponded well with variations in stem temperature (T(st)). Daytime depressions in F(CO2) did not occur. During the drought treatment, F(CO2) still responded to stepwise changes in temperature, but diurnal fluctuations in F(CO2) were no longer correlated with diurnal fluctuations in T(st). From the moment daily growth rate of the stem became zero, diurnal fluctuations in F(CO2) became closely correlated with diameter variations, exhibiting clear daytime depressions. The depressions in F(CO2) were likely the result of a reduction in metabolic activity caused by the lowered daytime stem water status. Xylem [CO(2)*] showed clear daytime depressions in response to drought. When the tree was re-watered, F(CO2) and [CO(2)*] exhibited sharp increases, coinciding with an increase in stem diameter. After resumption of the water supply, daytime depressions in F(CO2) and [CO(2)*] disappeared and diurnal fluctuations in F(CO2) and [CO(2)*] corresponded again with variations in T(st).     

用二次正交旋转组合设计优化马占相思增殖培养基

在马占相思组织培养初步取得成功的基础上，采用二次正交旋转组合设计对马占相思增殖培养基进行优化，建立增殖率(Y)对Ca^2 浓度(X1)、6-BA浓度(X2)及NAA浓度(X3)3个试验因子的正交回归模型：Y=2．280-0．168X1-0．259X2 0．185X1^2-0．210X2^2 0．167X3^2 0．326X1X2。从模型推知，当Ca^2 浓度为0．58倍常规MS培养基浓度(255g／L)，6BA为0．76mg／L，NAA为0．16mg／L时，增殖率达最大值为4．32，实验结果与预测值相符。     

脱氢枞酸基ATRP引发剂的合成与表征

以脱氢枞酸为原料,通过酰氯化得到脱氢枞酸酰氯(DA-Cl)后与乙二醇(EG)反应合成脱氢枞酸羟乙酯(DA-EH),然后再与2-溴代异丁酰溴(2-BiBr)进行酯化反应,合成了脱氢枞酸基原子转移自由基聚合(ATRP)引发剂——脱氢枞酸(2-溴代异丁酸乙基)酯(DA-2-iBBrEH)。通过单因素试验考察了不同条件对合成DA-EH和DA-2-iBBrEH的影响规律。结果表明,DA-EH合成的优化条件为:催化剂为4-二甲氨基吡啶(DMAP),n(DA-Cl)∶n(EG)∶n(DMAP)为1∶5∶5,反应时间5h,反应温度50℃;DA-2-iBBrEH合成的适宜条件为:催化剂为DMAP,n(DA-EH)∶n(2-BiBr)∶n(DMAP)为1∶2∶2。利用傅里叶红外光谱(FT-IR)、核磁共振氢谱(1HNMR)和核磁共振碳谱(13CNMR)对两者的结构进行了确证。以DA-2-iBBrEH为引发剂,采用ATRP法制备了聚甲基丙烯酸甲酯均聚物(PMMA)。GPC测试结果表明,DA-2-iBBrEH具有良好的ATRP反应引发活性,所制备的PMMA的数均相对分子质量(Mn)为8500,相对分子质量分布(PDI)为1.3。     

异长叶烯基噻唑类化合物的合成及其抑菌、抗肿瘤活性研究

以异长烯酮为原料,通过缩合、亲核取代和环化等手段合成了11种新型异长叶烯基噻唑类化合物,同时采用1H NMR、13C NMR、LC-MS和FT-IR对化合物进行了鉴定,从而确定了化合物的结构。对目标化合物进行了抑菌活性实验,结果表明:(E)-4-(4-甲氧基苯基)-2-(2-(1,1,5,5-四甲基-3,4,5,6-四氢-1H-2,4a-亚甲基-7(2H)-亚基)肼基)噻唑(2e)与(E)-4-(4-甲基苯基)-2-(2-(1,1,5,5-四甲基-3,4,5,6-四氢-1H-2,4a-亚甲基-7(2H)-亚基)肼基)噻唑(2g)对细菌(大肠杆菌与金黄色葡萄球菌)具有较好的抑制效果,最低抑菌质量浓度(MIC)为7.8 mg/L。(E)-4-氯苯基-2-(2-(1,1,5,5-四甲基-3,4,5,6-四氢-1H-2,4a-亚甲基-7(2H)-亚基)肼基)噻唑(2b)对真菌(白念球菌与热带假丝酵母)抑制效果优于其他化合物,其MIC值为15.6 mg/L。采用噻唑蓝(MTT)法对目标化合物进行了人体肝癌细胞(HepG 2)抗癌活性测试,化合物2g(IC50=43.9±0.9 mg/L)对HepG 2具有较好的抗癌活性。     

Elevated atmospheric CO2 concentration alters the effect of phosphate supply on growth of Japanese red pine (Pinus densiflora) seedlings

We demonstrated that the inorganic phosphate (P(i)) requirement for growth of Japanese red pine (Pinus densiflora Sieb. & Zucc.) seedlings is increased by elevated CO(2) concentration ([CO(2)]) and that responses of the ectomycorrhizal fungus Pisolithus tinctorius (Pers.) Coker & Couch to P(i) supply are also altered. To investigate the growth response of non-mycorrhizal seedlings to P(i) supply in elevated [CO(2)], non-mycorrhizal seedlings were grown for 73 days in ambient or elevated [CO(2)] (350 or 700 micromol mol(-1)) with nutrient solutions containing one of seven phosphate concentrations (0, 0.02, 0.04, 0.06, 0.08, 0.10 and 0.20 mM). In ambient [CO(2)], the growth response to P(i) was saturated at about 0.1 mM P(i), whereas in elevated [CO(2)], the growth response to P(i) supply did not saturate, even at the highest P(i) supply (0.2 mM), indicating that the P(i) requirement is higher in elevated [CO(2)] than in ambient [CO(2)]. The increased requirement was due mainly to an altered shoot growth response to P(i) supply. The enhanced P(i) requirement in elevated [CO(2)] was not associated with a change in photosynthetic response to P(i) or a change in leaf phosphorus (P) status. We investigated the effect of P(i) supply (0.04, 0.08 and 0.20 mM) on the ectomycorrhizal fungus P. tinctorius in mycorrhizal seedlings grown in ambient or elevated [CO(2)]. Root ergosterol concentration (an indicator of fungal biomass) decreased with increasing P(i) supply in ambient [CO(2)], but the decrease was far less in elevated [CO(2)]. In ambient [CO(2)] the ratio of extramatrical mycelium to root biomass decreased with increasing P(i) supply but did not change in elevated [CO(2)]. We conclude that, because elevated [CO(2)] increased the P(i) requirement for shoot growth, the significance of the ectomycorrhizal association was also increased in elevated [CO(2)].     

Celastrus paniculatus seed water soluble extracts protect cultured rat forebrain neuronal cells from hydrogen peroxide-induced oxidative injury

The effects of aqueous extracts of Celastrus paniculatus (CP) seeds were shown to have antioxidant properties in rats. In the study reported here, we have investigated the free radical scavenging capacity of three aqueous extracts (WSEs) obtained from CP seeds: a room temperature extract (WF); a hot water extract (HF); an acid extract (AF). All the WSEs exhibited a dose-dependent free radical scavenging capacity for 1,1-diphenyl-2-picryl-hydrazyl radical (DPPH) and also for superoxide-generated assays (in vitro assays). In addition, we used enriched forebrain primary neuronal cell (FBNC) cultures to evaluate the neuroprotective effects of the three CP-WSE extracts on H(2)O(2)-induced toxicity. FBNC were pre-treated with the CP-WSE and then with H(2)O(2) to evaluate the protection afforded against H(2)O(2)-induced toxicity. The criteria for neuroprotection by the WSEs were based on a mitochondrial function test following the H(2)O(2)-induced neurotoxicity. All the WSEs significantly attenuated H(2)O(2)-induced neuronal death, and AF was the most effective in protecting the neuronal cells against oxidative injury caused by H(2)O(2). In 10 day FBNC, cellular superoxide dismutase activity was not affected by the WSEs or H(2)O(2), but catalase activity was decreased and levels of malondialdehyde were increased by H(2)O(2) treatment. When the neuronal cells were treated with WSEs prior to H(2)O(2) exposure, catalase activity was increased and levels of malondialdehyde were decreased significantly. The data presented here suggest that CP seed WSEs protected neuronal cells in part by their free radical scavenging properties, by reducing lipid peroxidation, and also by their ability to induce the antioxidant enzyme catalase. Our results indicate that WSEs might exert neuroprotective effects against increased oxidative stress resulting from free radical damage that is associated with a number of neurodegenerative diseases.     

Effects of hypoxia and elevated carbon dioxide concentration on water flux through Populus roots

Restricted gas exchange between the rhizosphere and aerial environment reduces the concentration of oxygen (O(2)) and elevates the concentration of carbon dioxide (CO(2)) in the root zone, thereby leading to increased resistance to root water uptake. In this study, the effects of hypoxia and 20% CO(2) on water flux (J(v)) through roots of hybrid poplar (Populus trichocarpa Torr. & A. Gray x P. deltoides Bartr. ex Marsh) were measured in detached root systems under pressure in solution culture. Because stomata closed and there was no change in foliar water potential in hypoxic plants, root resistance was measured in detached systems as opposed to using whole plant measurements. However, under aerated conditions root resistance values were similar in intact plants and excised roots. Water fluxes through pressurized root systems treated with nitrogen and low oxygen (< 2% O(2)), elevated CO(2) (20% CO(2)), and low O(2) with elevated CO(2) concentrations were reduced to 40, 51 and 58%, respectively, of J(v) of plants aerated with ambient air. Reductions in J(v) occurred more rapidly in response to elevated CO(2) than to low O(2) concentrations. The effects of low O(2) and elevated CO(2) were not additive. Changes in pH that resulted from elevated CO(2) concentrations did not account for the reduction in J(v). When root systems of intact plants were pretreated for 24 or 48 h with low O(2) concentration, J(v) measured on pressurization was reduced by 33 and 48%, respectively, compared to aerated roots. Stomatal conductance was also reduced, however, so leaf water potential of plants with hypoxic roots were similar to those of aerated controls.     

Diurnal and seasonal changes in the impact of CO(2) enrichment on assimilation, stomatal conductance and growth in a long-term study of Mangifera indica in the wet-dry tropics of Australia

We studied assimilation, stomatal conductance and growth of Mangifera indica L. saplings during long-term exposure to a CO(2)-enriched atmosphere in the seasonally wet-dry tropics of northern Australia. Grafted saplings of M. indica were planted in the ground in four air-conditioned, sunlit, plastic-covered chambers and exposed to CO(2) at the ambient or an elevated (700 micro mol mol(-1)) concentration for 28 months. Light-saturating assimilation (A(max)), stomatal conductance (g(s)), apparent quantum yield (phi), biomass and leaf area were measured periodically. After 28 months, the CO(2) treatments were changed in all four chambers from ambient to the elevated concentration or vice versa, and A(max) and g(s) were remeasured during a two-week exposure to the new regime. Throughout the 28-month period of exposure, A(max) and apparent quantum yield of leaves in the elevated CO(2) treatment were enhanced, whereas stomatal conductance and stomatal density of leaves were reduced. The relative impacts of atmospheric CO(2) enrichment on assimilation and stomatal conductance were significantly larger in the dry season than in the wet season. Total tree biomass was substantially increased in response to atmospheric CO(2) enrichment throughout the experimental period, but total canopy area did not differ between CO(2) treatments at either the first or the last harvest. During the two-week period following the change in CO(2) concentration, A(max) of plants grown in ambient air but measured in CO(2)-enriched air was significantly larger than that of trees grown and measured in CO(2)-enriched air. There was no difference in A(max) between trees grown and measured in ambient air compared to trees grown in CO(2)-enriched air but measured in ambient air. No evidence of down-regulation of assimilation in response to atmospheric CO(2) enrichment was observed when rates of assimilation were compared at a common intercellular CO(2) concentration. Reduced stomatal conductance in response to atmospheric CO(2) enrichment was attributed to a decline in both stomatal aperture and stomatal density.     

Carbon dioxide exchange of developing avocado (Persea americana Mill.) fruit

Net efflux of CO(2) from attached avocado (Persea americana Mill.) fruit was measured periodically from three weeks after anthesis to fruit maturity. Net CO(2) exchange was determined in daylight (light respiration, R(l)) at a photosynthetic photon flux (PPF) greater than 600 micromol m(-1) s(-1), and in the dark (dark respiration, R(d)). Dark respiration and R(l) were highest during the early cell division stage of fruit growth (about 25 and 22 nmol CO(2) g(dw) (-1) s(-1), respectively) and decreased gradually until fruit maturity to about 1 and 0.5 nmol CO(2) nmol CO(2) g(dw) (-1) s(-1), respectively. Fruit photosynthesis, calculated from the difference between R(d) and R(l), ranged from 0.5 to 3.1 nmol CO(2) g(dw) (-1) s(-1). Net rate of CO(2) assimilation on a fruit dry weight basis was highest during the early stages of fruit growth and reached the lowest rate at fruit maturity. Net rate of CO(2) assimilation of fruit exposed to light was 0.4 to 2.5% of that for fully expanded leaves. Although the relative amount of carbon assimilated by the fruit was small compared with the total amount of carbon assimilated by the leaves, the data indicate that avocado fruit contribute to their own carbon requirement by means of CO(2) assimilated in the light.     

Effects of elevated CO(2) concentration and nutrition on net photosynthesis,stomatal conductance and needle respiration of field-grown Norway spruce trees

To study the effects of elevated CO(2) on gas exchange, nonstructural carbohydrate and nutrient concentrations in current-year foliage of 30-year-old Norway spruce (Picea abies (L.) Karst.) trees, branches were enclosed in ventilated, transparent plastic bags and flushed with ambient air (mean 370 &mgr;mol CO(2) mol(-1); control) or ambient air + 340 &mgr;mol CO(2) mol(-1) (elevated CO(2)) during two growing seasons. One branch bag was installed on each of 24 selected trees from control and fertilized plots. To reduce the effect of variation among trees, results from each treated branch were compared with those from a control branch on the same whorl of the same tree. Elevated CO(2) increased rates of light-saturated photosynthesis on average by 55% when measured at the treatment CO(2) concentration. The increase was larger in shoots with high needle nitrogen concentrations than in shoots with low needle nitrogen concentrations. However, shoots grown in elevated CO(2) showed a decrease in photosynthetic capacity compared with shoots grown in ambient CO(2). When measured at the internal CO(2) concentration of 200 &mgr;mol CO(2) mol(-1), photosynthetic rates of branches in the elevated CO(2) treatments were reduced by 8 to 32%. The elevated CO(2) treatment caused a 9 to 20% reduction in carboxylation efficiency and an 18% increase in respiration rates. In response to elevated CO(2), starch, fructose and glucose concentrations in the needles increased on average 33%, whereas concentrations of potassium, nitrogen, phosphorus, magnesium and boron decreased. Needle nitrogen concentrations explained 50-60% of the variation in photosynthesis and CO(2) acclimation was greater at low nitrogen concentrations than at high nitrogen concentrations. We conclude that the enhanced photosynthetic rates found in shoots exposed to elevated CO(2) increased carbohydrate concentrations, which may have a negative feedback on the photosynthetic apparatus and stimulate cyanide-resistant respiration. We also infer that the decrease in nutrient concentrations of needles exposed to elevated CO(2) was the result of retranslocation of nutrients to other parts of the branch or tree.     

Leaf physiology, production, water use, and nitrogen dynamics of the grassland invader Acacia smallii at elevated CO(2) concentrations

Invasion by woody legumes can alter hydrology, nutrient accumulation and cycling, and carbon sequestration on grasslands. The rate and magnitude of these changes are likely to be sensitive to the effects of atmospheric CO(2) enrichment on growth and water and nitrogen dynamics of leguminous shrubs. To assess potential effects of increased atmospheric CO(2) concentrations on plant growth and acquisition and utilization of water and nitrogen, seedlings of Acacia smallii Isely (huisache) were grown for 13 months at CO(2) concentrations of 385 (ambient), 690, and 980 micro mol mol(-1). Seedlings grown at elevated CO(2) concentrations exhibited parallel declines in leaf N concentration and photosynthetic capacity; however, at the highest CO(2) concentration, biomass production increased more than 2.5-fold as a result of increased leaf photosynthetic rates, leaf area, and N(2) fixation. Measurements of leaf gas exchange and aboveground biomass production and soil water balance indicated that water use efficiency increased in proportion to the increase in atmospheric CO(2) concentration. The effects on transpiration of an accompanying decline in leaf conductance were offset by an increase in leaf area, and total water loss was similar across CO(2) treatments. Plants grown at elevated CO(2) fixed three to four times as much N as plants grown at ambient CO(2) concentration. The increase in N(2) fixation resulted from an increase in fixation per unit of nodule mass in the 690 micro mol mol(-1) CO(2) treatment and from a large increase in the number and mass of nodules in plants in the 980 micro mol mol(-1) CO(2) treatment. Increased symbiotic N(2) fixation by woody invaders in response to CO(2) enrichment may result in increased N deposition in litterfall, and thus increased productivity on many grasslands.     

Flavonoids with DNA strand-scission activity from Rhus javanica var. roxburghiana

The flavonoids isolated from the stems of Rhus javanica var. roxburghiana, taxifolin (1), fisetin (2), fustin (3), 3,7,4'-trihydroxyflavanone (4) and 3,7,4'-trihydroxyflavone (5) caused breakage of supercoiled plasmid pBR322 DNA in the presence of Cu(II). Cu(I) was shown to be an essential intermediate by using the Cu(I)-specific sequestering reagent neocuproine. The Cu(II)-mediated DNA scissions induced by 1, 2, 3 and 5 were inhibited by the addition of catalase and exhibited DNA strand break by the addition of KI and superoxide dimutase (SOD), while in the Cu(II)-mediated DNA scissions induced by 4 was inhibited by the addition of KI, SOD, and catalase. It is concluded that 1, 2, 3, and 5 can induce H(2)O(2) and superoxide anion, while 4 can induce OH() and H(2)O(2) and subsequent oxidative damage of DNA in the presence of Cu(II).     

Vertical gradients in photosynthetic gas exchange characteristics and refixation of respired CO(2) within boreal forest canopies

We compared vertical gradients in leaf gas exchange, CO(2) concentrations, and refixation of respired CO(2) in stands of Populus tremuloides Michx., Pinus banksiana Lamb. and Picea mariana (Mill.) B.S.P. at the northern and southern boundaries of the central Canadian boreal forest. Midsummer gas exchange rates in Populus tremuloides were over twice those of the two conifer species, and Pinus banksiana rates were greater than Picea mariana rates. Gas exchange differences among the species were attributed to variation in leaf nitrogen concentration. Despite these differences, ratios of intercellular CO(2) to ambient CO(2) (c(i)/c(a)) were similar among species, indicating a common balance between photosynthesis and stomatal conductance in boreal trees. At night, CO(2) concentrations were high and vertically stratified within the canopy, with maximum concentrations near the soil surface. Daytime CO(2) gradients were reduced and concentrations throughout the canopy were similar to the CO(2) concentration in the well-mixed atmosphere above the canopy space. Photosynthesis had a diurnal pattern opposite to the CO(2) profile, with the highest rates of photosynthesis occurring when CO(2) concentrations and gradients were lowest. After accounting for this diurnal interaction, we determined that photosynthesizing leaves in the understory experienced greater daily CO(2) concentrations than leaves at the top of the canopy. These elevated CO(2) concentrations were the result of plant and soil respiration. We estimated that understory leaves in the Picea mariana and Pinus banksiana stands gained approximately 5 to 6% of their carbon from respired CO(2).