铜胁迫对紫花苜蓿幼苗叶片抗氧化系统的影响

采用1/4强度Hoagland营养液培养法研究了不同浓度Cu处理(O、10、30、50、100μmol·L-1 CuSO4)对紫花苜蓿幼苗叶片生理生化特性的影响.结果表明:30、50、100μmol·L-1 Cu处理使叶片中过氧化氢(H2O2)、羟基自由基(OH·)和丙二醛(MDA)含量升高;随Cu浓度的增加,愈创木酚过氧化物酶(POD)、谷胱甘肽还原酶(GR)和抗坏血酸过氧化物酶(APX)的活性逐渐上升,过氧化氢酶(CAT)和葡萄糖-6-磷酸脱氢酶(G6PDH)的活性先上升后下降;30、50、100 μmol·L-1Cu处理增强Fe-SOD和酯酶(EST)的活性,使叶片中谷胱甘肽(GSH)和抗坏血酸(AsA)含量显著升高.＞10 μmol·L-1的Cu处理下,叶片中抗氧化系统清除活性氧的能力上升,以防止叶片在Cu诱导的氧化胁迫下受到伤害.     

Discrete analysis of plasma oxalate with alkylamine glass bound sorghum oxalate oxidase and horseradish peroxidase

We have reported a simple method of determination of plasma oxalate using a Cl(-) and NO(3)(-) insensitive oxalate oxidase purified from grain sorghum leaf and commercially available peroxidase from horseradish [Pundir et al., Ind. J. Biochem. Biophys., 35 (1998) 120-122]. The present report describes the immobilization of both the enzymes onto alkylamine glass, their kinetic properties and application for discrete analysis of plasma oxalate. In the analytic method, H(2)O(2) generated from plasma oxalate by immobilized oxalate oxidase is measured colorimetrically at 520 nm by oxidative coupling with 4-aminophenazone, and phenol catalyzed by immobilized peroxidase. The minimum detection limit of the method is 2.5 micromol/l. Analytic recovery of added oxalate in plasma was 89. 5+/-4.1% (mean+/-S.D.). The within and between day CV for plasma oxalate measurement were <9.37 and <11.0%, respectively. The normal range of plasma oxalate as measured by the present method was 3.6 to 5.7 micromol/l. The method is not only free from interference by plasma Cl(-) and NO(3)(-) but also provides the reuse of glass beads and thus reduces the cost of analysis for routine.     

光果甘草生殖生物学特性的初步研究

对光果甘草的花部特征、花粉活力、柱头可授性和花粉-胚珠比(P/O)进行了初步研究.结果表明:(1)光果甘草雄蕊异型,雌雄蕊异位,有利于避免自花授粉;(2)开花当天花粉活力在上午12:00最高,为91.8%,14:00迅速下降,16:00到达最低,16:00以后逐渐上升;(3)柱头可授性可持续4 d,以开花当天可授性最强;(4)花粉-胚珠比(P/O)为1 751.1±217.002,表明其繁育系统类型为兼性异交.     

Different hydroxyl radical scavenging activity of water-soluble beta-alanine C60 adducts

Three C(60) derivatives [C(60) (NHCH(2)CH(2)COONa)(n)(H)(n)], n=1, 5, 9] (A, B, C) with different additional number of beta-alanine were synthesized by the control of relative amount of C(60) and beta-alanine added. Hydroxyl radical scavenging activity of the adducts was evaluated in a copper-catalyzed Haber-Weiss reaction by chemiluminescence technology. The 50% inhibition concentrations (IC(50)'s) of A, B, and C were 147.2 micromol/L, 76.3 micromol/L, and 96.2 micromol/L, respectively. The difference should be closely related to the numbers of residual C=C bonds in C(60), steric effect and electron-withstanding effect of amino group especially.     

Regulation of Antioxidant Enzymes by Salicylic Acid in Cucumber Leaves

Activities of the antioxidant enzymes involved in superoxide anion (O2-) and hydrogen peroxide (H2O2) metabolism were determined and the contents of O2 and 14202 were also measured. All concentrations of sahcylic acid (SA) tested (0.5, 1.0, 2.5 and 5.0 mmoL/L) significantly enhanced superoxide dismutase (SOD) and peroxidase (POD) activities not only in the first treated true leaf (leaf 1 ) but also in the second untreated true leaf (leaf 2) of Cucumis sativus L. When the leaves were treated with 1 mmol/L SA within 6 to 72 h, the activity of POD increased by 22 % to 67% in the treated leaf 1 and by 14% to 86% in the untreated leaf 2. However, no changes were observed during 3 h after treatment and at 96 h following treatment. Measurement of O2- and H202 showed that there was a significant decrease in 02' content and an increase in H202 content after SA treatment, but catalase (CAT) activity was only slighfiy inhibited and this suggested that the reason of the increase in H2O2 by SA treatment is not due to the inhibition of CAT but rather the increase in SOD activity. It was also found that SA at all concentrations tested could not induce new SOD isozyme but it induced 1 to 2 bands of new POD isozyme within one day after treatment. The results indicate that SA might involve in the regulation of antioxidant enzymes.     

外源甜菜碱对水分胁迫下桃树生理响应的影响

以4年生盆栽“庆丰”桃树为试材,研究了水分胁迫下桃树叶片中甜菜碱含量的变化规律及叶面喷施甜菜碱对水分胁迫下桃树生理响应的影响.结果表明：正常供水情况下,桃树叶片中甜菜碱含量为75.9～80.5 μg·g^-1FM , 随着水分胁迫程度的加深,甜菜碱含量逐渐增加,停水第16 天时达278.9 μg·g^-1FM ;正常供水时桃叶片细胞质膜透性为8.06%～8.61%,水分胁迫下增至28.62%,叶面喷施100和500 mg·L^-1甜菜碱16d后分别为26.25%和21.79%;过氧化氢(H₂O₂)含量由正常情况下的27.2～32.5 μmol·g^-1FM 增至胁迫后的76.4 μmol·g^-1FM,叶面喷施100和500 mg·L^-1甜菜碱后分别为73.2和68.5 μmol·g^-1 FM;水分胁迫下,抗坏血酸过氧化物酶(AsA-POD)活性峰值为0.435 mg·g^-1 FM,甜菜碱处理后峰值达到0.490 mg·g^-1 FM;游离脯氨酸与可溶性糖在干旱胁迫下逐渐累积, 500 mg·L^-1甜菜碱处理分别为2.878 mg·g^-1 FM和37.6 mg·g^-1 FM,均低于单纯胁迫及100 mg·L^-1甜菜碱处理;可溶性蛋白质含量在水分胁迫下呈下降趋势,甜菜碱处理后最小值为4.03 mg·g^-1 FM,较单纯胁迫下的最低值（3.14 mg·g^-1 FM）高20.3%.表明叶面喷施甜菜碱能在一定程度上减轻桃树的受害程度,提高其抗旱性.     

Hydrogen peroxide causes cardiac dysfunction independent from its effects on matrix metalloproteinase-2 activation

Hydrogen peroxide (H2O2) causes cardiac dysfunction through multiple mechanisms. As oxidative stress can activate matrix metalloproteinases (MMPs) and, in particular, MMP-2 activity is associated with oxidative stress injury in the heart, we hypothesized that MMP-2 activation by H2O2 in isolated rat hearts contributes to cardiac dysfunction in this model. Isolated working rat hearts were perfused at 37 degrees C with a recirculating Krebs-Henseleit buffer+/-5 mmol/L pyruvate, known to protect hearts from oxidative stress. H2O2 (300 micromol/L) was added as a single bolus after 20 min of equilibration, and cardiac function was monitored for 60 min. MMPs activities in both the heart and perfusate samples were assessed by gelatin zymography. Tissue high energy phosphates were analysed by HPLC. The actions of 2 MMP inhibitors, doxycycline (75 micromol/L) or Ro 31-9790 (3 micromol/L), were also assessed. H2O2 at 300 micromol/L produced a rapid decline in cardiac mechanical function, which was maximal at 5 min. A peak in perfusate MMP-2 activity was also observed at 5 min. The deleterious effect of H2O2 on cardiac function was abolished by pyruvate but not by the MMPs inhibitors. This study suggests that in intact hearts, H2O2 induces contractile dysfunction independent of MMPs activation.     

The quantitatively important relationship between homocysteine metabolism and glutathione synthesis by the transsulfuration pathway and its regulation by redox changes

Homocysteine is a key junction metabolite in methionine metabolism. It suffers two major metabolic fates: transmethylation catalyzed by methionine synthase or betaine homocysteine methyl transferase and transsulfuration catalyzed by cystathionine beta-synthase leading to cystathionine. The latter is subsequently converted to cysteine, a precursor of glutathione. Studies with purified mammalian methionine synthase and cystathionine beta-synthase have revealed the oxidative sensitivity of both junction enzymes, suggesting the hypothesis that redox regulation of this pathway may be physiologically significant. This hypothesis has been tested in a human hepatoma cell line in culture in which the flux of homocysteine through transsulfuration under normoxic and oxidative conditions has been examined. Addition of 100 microM H(2)O(2) or tertiary butyl hydroperoxide increased cystathionine production 1.6- and 2.1-fold from 82 +/- 7 micromol h(-)(1) (L of cells)(-)(1) to 136 +/- 15 and 172 +/- 23 micromol h(-)(1) (L of cells)(-)(1), respectively. The increase in homocysteine flux through the transsulfuration pathway exhibited a linear dose dependence on the concentrations of both oxidants (50-200 microM H(2)O(2) and 10-200 microM tertiary butyl hydroperoxide). Furthermore, our results reveal that approximately half of the intracellular glutathione pool in human liver cells is derived from homocysteine via the transsulfuration pathway. The redox sensitivity of the transsulfuration pathway can be rationalized as an autocorrective response that leads to an increased level of glutathione synthesis in cells challenged by oxidative stress. In summary, this study demonstrates the importance of the homocysteine-dependent transsulfuration pathway in the maintenance of the intracellular glutathione pool, and the regulation of this pathway under oxidative stress conditions. Aberrations in this pathway could compromise the redox buffering capacity of cells, which may in turn be related to the pathophysiology of the different homocysteine-related diseases.     

Influence of Photoperiod and Leaf Age on Crassulacean Acid Metabolism in Portulacaria afra (L.) Jacq

The possibility that Crassulacean acid metabolism (CAM) is subject to long day photoperiodic control in Portulacaria afra (L.) Jacq., a facultative CAM plant, was studied. Periodic measurements of ¹⁴CO₂ uptake, stomatal resistance, and titratable acidity were made on plants exposed to long and short day photoperiods. Results indicates that waterstressed P. afra had primarily nocturnal CO₂ uptake, daytime stomatal closure, and a large diurnal acid fluctuation in either photoperiod. Mature leaf tissue from nonstressed plants under long days exhibited a moderate diurnal acid fluctuation and midday stomatal closure. Under short days, there was a reduced diurnal acid fluctuation in mature leaf tissue. Young leaf tissue taken from nonstressed plants did not utilize the CAM pathway under either photoperiod as indicated by daytime CO₂ uptake, lack of diurnal acid fluctuation, and incomplete daytime stomatal closure.

The induction of CAM in P. afra appears to be related to the water status of the plant and the age of the leaf tissue. The photosynthetic metabolism of mature leaves may be partly under the control of water stress and of photoperiod, where CAM is favored under long days.

     

过氧化氢参与烟草叶片衰老调节的研究（简报）

叶片衰老是一个复杂的过程．多年来人们对叶片衰老的机制开展了大量的研究。许多研究证明叶片中H2O2的迅速积累与叶片的衰老密切相关^[1-3],然而,H2O2的积累是衰老的结果还是作为信号启动衰老？H2O2作为植物细胞的信号分子,调控一系列重要的生理生化过程,如系统获得抗性（SAR）、细胞衰老与程序化死亡（PCD）、气孔关闭、根的生长、细胞壁的发育等^[4]。H2O2参与脱落酸（A—BA）、甲基茉莉酸（MJ）诱导的水稻叶片衰老,且H2O2产生早于叶片衰老^[2,5]。     

Bis(6-ethylpicolinato)oxovanadium(IV) complex with normoglycemic activity in KK-A(y) mice.

A novel bis(6-ethylpicolinato)(H(2)O)oxovanadium(IV) complex (VO(6epa)(2) x (H(2)O)) was prepared and its structure was revealed by X-ray analysis (space group Pc(#7), a=10.838(2), b=11.148(5), c=16.642(3) A, and Z=2). Because VO(6epa)(2) x (H(2)O) exhibited higher in vitro insulinomimetic activity compared to that of vanadyl sulfate in terms of inhibition of free fatty acid (FFA) release from isolated rat adipocytes in the presence of epinephrine, its in vivo effect on whether the complex has a blood glucose normalizing effect was examined in KK-A(y) mice, a model animal of type 2 diabetes mellitus. VO(6epa)(2) x (H(2)O) was found to normalize the high blood glucose levels of KK-A(y) mice when given intraperitoneally at doses of 49 micromol/kg body weight for the first 4 days and then 39 micromol/kg body weight for 10 days. In addition, VO(6epa)(2) x (H(2)O) improved glucose tolerance ability as examined by the oral glucose test and seemed to have little toxicity in terms of serum parameters. VO(6epa)(2) x (H(2)O) showed higher normoglycemic activity than bis(6-methylpicolinato)oxovanadium(IV) (VO(6mpa)(2)) at the same dose. These results indicated that greater enhancement of the blood glucose normalizing effect in KK-A(y) mice by ethyl substitution compared to methyl substitution may be due to its being more strongly lipophilic.     

Redox control bioreactor: a unique biological water processor

The redox control bioreactor (RCB) is a new hollow fiber membrane bioreactor (HFMBR) design in which oxygen and hydrogen gases are provided simultaneously through separate arrays of juxtaposed hollow fiber (HF) membranes. This study applied the RCB for completely autotrophic conversion of ammonia to N(2) through nitrification with O(2) and denitrification using hydrogen as an electron donor (i.e., autohydrogentrophic denitrification). The hypothesis of this research was that efficient biofilm utilization of O(2) and H(2) at respective HFs would limit transport of these gases to bulk fluid, thereby enabling completely autotrophic ammonia conversion to N(2) through the co-occurrence of ammonia oxidation (O(2)-HF biofilms) and autohydrogenotrophic denitrification (H(2)-HF biofilms). A prototype RCB was fabricated and operated for 215 days on a synthetic, organic-free feedstream containing 217 mg L(-1) NH(4)(+)-N. When O(2) and H(2) were simultaneously supplied, the RCB achieved a steady NH(4)(+)-N removal flux of 5.8 g m(-2) day(-1) normalized to O(2)-HF surface area with a concomitant removal flux of 4.4 g m(-2) day(-1) (NO(3)(-))+NO(2)(-))-N based on H(2)-HF surface area. The significance of H(2) supply was confirmed by an increase in effluent NO(3)(-)-N when H(2) supply was discontinued and a decline in NO(3)(-)-N when H(2) supply was restarted. Increases in H(2) pressure caused decreased ammonia utilization, suggesting that excess H(2) interfered with nitrification. Microprobe profiling across radial transects revealed significant gradients in dissolved O(2) on spatial scales of 1 mm or less. Physiological and molecular analysis of biofilms confirmed that structurally and functionally distinct biofilms developed on adjacent, juxtaposed fibers.     

Pyruvate prevents cardiac dysfunction and AMP-activated protein kinase activation by hydrogen peroxide in isolated rat hearts

Ischemia-reperfusion injury in the heart results in enhanced production of H2O2 and activation of AMP-activated protein kinase (AMPK). Since mutations in AMPK result in cardiovascular dysfunction, we investigated whether the activation of AMPK mediates the H2O2-induced reduction in cardiac mechanical function. Isolated working rat hearts were perfused at 37 degrees C with Krebs-Henseleit solution. Following a 20-minute equilibration period, a single bolus of H2O2 (300 micromol/L) was added and the hearts were perfused for an additional 5 min. H2O2 induced a dramatic and progressive reduction in cardiac function. This was accompanied by rapid and significant activation of AMPK, an increase in Thr-172 phosphorylation of AMPK, and an increase in the creatine to phosphocreatine (Cr/PCr) ratio. Addition of pyruvate (5 mmol/L) to the perfusate prevented the H2O2-mediated reduction in cardiac mechanical dysfunction, activation of myocardial AMPK activity, increase in AMPK phosphorylation and the increase in the Cr/PCr ratio. Hearts challenged with H2O2 (300 micromol/L) in presence of either AMPK inhibitor Compound C (10 micromol/L) or its vehicle (dimethyl sulfoxide (DMSO), 0.1%) showed reduced impairment in cardiac mechanical function. Compound C but not its vehicle significantly inhibited myocardial AMPK activity. Thus, H2O2 induces cardiac dysfunction via both AMPK-dependent and independent mechanisms.     

一氧化氮对小麦叶片老化过程的调节

用不同浓度(0．05、0．10、0．20、0．50mmol／L)的外源一氧化氮(nitric oxide,NO)供体硝普钠(sodium nitroprusside,SNP)处理正常生长小麦(Triticum aestivum L．)叶片(二叶一心期时全展第一叶)。结果显示低浓度SNP(0．05、0．10、0．20mmol／L)可以明显降低叶片H2O2和MDA的水平,其中0．10mmol／L SNP的作用最为明显;而较高浓度SNP(0．50mmol／L)则作用相反。进一步采用0．10mmol／L SNP处理不同叶位的小麦叶片(四叶一心期),结果表明低浓度NO对不同老化阶段中叶片的H2O2、O2^7和MDA累积都有缓解作用,并明显减缓叶绿素、可溶性叶蛋白尤其是Rubisco的降解,有效延缓了叶片的老化进程。在完整叶绿体体外老化实验中也发现,不同浓度SNP(0．05、0．10、0．20、0．50、1．00、5．00mmol／L)的作用同样表现双重性,其中0．20mmol／L SNP对膜结构及Rubisco保护作用最明显。上述结果证实,低浓度外源NO可延缓小麦叶片的老化过程,并可能与其降低叶片活性氧(ROS)水平及缓解氧化损伤有关。     

Dose-dependent effect of hydrogen peroxide on calcium mobilization in mouse pancreatic acinar cells.

We have employed confocal laser scanning microscopy to investigate how intracellular free calcium concentration ([Ca2+]i) is influenced by hydrogen peroxide (H2O2) in collagenase-dispersed mouse pancreatic acinar cells. In the absence of extracellular calcium, treatment of cells with increasing concentrations of H2O2 resulted in an increase in [Ca2+]i, indicating the release of calcium from intracellular stores. Micromolar concentrations of H2O2 induced an oscillatory pattern, whereas 1 mmol H2O2/L caused a slow and sustained increase in [Ca2+]i. H2O2 abolished the typical calcium release stimulated by thapsigargin or by the physiological agonist cholecystokinin octapeptide (CCK-8). Depletion of either agonist-sensitive or mitochondrial calcium pools was unable to prevent calcium release induced by 1 mmol H2O2/L, but depletion of both stores abolished it. Additionally, lower H2O2 concentrations were able to release calcium only after depletion of mitochondrial calcium stores. Treatment with either the phospholipase C inhibitor U-73122 or the inhibitor of the inositol 1,4,5-trisphosphate (IP3) receptor xestospongin C did not modify calcium release from the agonist-sensitive pool induced by 100 micromol H2O2/L, suggesting the involvement of a mechanism independent of IP3 generation. In addition, H2O2 reduced amylase release stimulated by CCK-8. Finally, either the H2O2-induced calcium mobilization or the inhibitory effect of H2O2 on CCK-8-induced amylase secretion was abolished by dithiothreitol, a sulphydryl reducing agent. We conclude that H2O2 at micromolar concentrations induces calcium release from agonist-sensitive stores, and at millimolar concentrations H2O2 can also evoke calcium release from the mitochondria. The action of H2O2 is mediated by oxidation of sulphydryl groups of calcium ATPases independently of IP3 generation.     

Heterogeneity of local myocardial flow and oxidative metabolism

In mammalian hearts, local myocardial flow (LMF) varies between 20 and 200% of the mean. It is not clear whether oxidative metabolism has a similar degree of heterogeneity. Therefore, we investigated the relation between LMF and local oxidative metabolism in isolated rabbit hearts. Buffer oxygenation with (18)O(2) resulted in labeled myocardial oxidation water (H(2)(18)O). In four hearts, myocardial oxygen consumption (MVO(2)) was calculated from the H(2)(18)O production and compared with that calculated according to Fick. In eight additional hearts, LMF was measured using microspheres. Coronary venous H(2)(18)O kinetics and local H(2)(18)O residues were determined and analyzed by mathematical modeling. MVO(2) recovery from H(2)(18)O was >93% compared with that according to Fick. LMF ranged from 1.91 to 11.24 ml. min(-1). g(-1), and local H(2)(18)O residue ranged from 0.41 to 1.04 micromol/g. Both variables correlated (r = 0.62, n = 64, P < 0.001). Measurements in nine hearts were fitted by modeling using capillary permeability-surface area products (PS(c)) from 2 to 10 ml. min(-1). g(-1). With flow-proportional PS(c), a 3.33-fold difference in LMF was associated with a 6.45-fold difference in local MVO(2). Both LMF and local oxidative metabolism are spatially heterogeneous, and they correlate to one another.     

一氧化氮对小麦叶片老化过程的调节

用不同浓度(0.05、0.10、0.20、0.50 mmol/L)的外源一氧化氮(nitric oxide,NO)供体硝普钠(sodiumnitroprusside,SNP)处理正常生长小麦(Triticum aestivum L.)叶片(二叶一心期时全展第一叶).结果显示低浓度SNP(0.05、0.10、0.20 mmol/L)可以明显降低叶片H2O2和MDA的水平,其中0.10 mmol/LSNP的作用最为明显;而较高浓度SNP(0.50 mmol/L)则作用相反.进一步采用0.10 mmol/L SNP处理不同叶位的小麦叶片(四叶一心期),结果表明低浓度NO对不同老化阶段中叶片的H2O2、O-2和MDA累积都有缓解作用,并明显减缓叶绿素、可溶性叶蛋白尤其是Rubisco的降解,有效延缓了叶片的老化进程.在完整叶绿体体外老化实验中也发现,不同浓度SNP(0.05、0.10、0.20、0.50、1.00、5.00 mmol/L)的作用同样表现双重性,其中0.20 mmol/L SNP对膜结构及Rubisco保护作用最明显.上述结果证实,低浓度外源NO可延缓小麦叶片的老化过程,并可能与其降低叶片活性氧(ROS)水平及缓解氧化损伤有关.     

Novel peroxidase mimics: mu-Aqua manganese-Schiff base dimers

The interaction of manganese(II) carboxylate salts [Mn(O(2)CR)(2), where R=ethane, pentane] with H(2)L(1) [N,N'-bis(3-methoxy-2-hydroxybenzaldehyde)-1,2-phenylenediamine] and H(2)L(2) [N,N'-bis(3-ethoxy-2-hydroxybenzaldehyde)-1,2-phenylenediamine] was studied. MnL(1)(O(2)CEt)(H(2)O) (1), MnL(1)(O(2)CPe(n))(H(2)O) (2), MnL(2)(O(2)CEt)(H(2)O)(2) (3) and MnL(2)(O(2)CPe(n))(H(2)O)(2) (4) were isolated and thoroughly characterised by elemental analysis, FAB mass spectrometry, infrared and (1)H NMR spectroscopy, magnetic susceptibility measurements, molar conductivities, and cyclic and normal pulse voltammetry. Compounds 1 and 2 were crystallographically characterised revealing a tetragonally elongated octahedral geometry for the manganese coordination sphere and also a dimeric nature through mu-aqua bridges. Complexes 1-4 behave as efficient peroxidase mimics in the presence of the water-soluble trap ABTS, probably due to their ease to coordinate the substrate molecule. A correlation between rhombicity of the complexes and peroxidase activity has also been established.     

Reactive oxygen species in the elongation zone of maize leaves are necessary for leaf extension

The production and role of reactive oxygen species (ROS) in the expanding zone of maize (Zea mays) leaf blades were investigated. ROS release along the leaf blade was evaluated by embedding intact seedlings in 2',7'-dichlorofluorescein-containing agar and examining the distribution of 2',7'-dichlorofluorescein fluorescence along leaf 4, which was exposed by removing the outer leaves before embedding the seedling. Fluorescence was high in the expanding region, becoming practically non-detectable beyond 65 mm from the ligule, indicating high ROS production in the expansion zone. Segments obtained from the elongation zone of leaf 4 were used to assess the role of ROS in leaf elongation. The distribution of cerium perhydroxide deposits in electron micrographs indicated hydrogen peroxide (H(2)O(2)) presence in the apoplast. 2',7'-Dichlorofluorescein fluorescence and apoplastic H(2)O(2) accumulation were inhibited with diphenyleneiodonium (DPI), which also inhibited O*(2)(-) generation, suggesting a flavin-containing enzyme activity such as NADPH oxidase was involved in ROS production. Segments from the elongation zone incubated in water grew 8% in 2 h. KI treatments, which scavenged H(2)O(2) but did not inhibit O*(2)(-) production, did not modify growth. DPI significantly inhibited segment elongation, and the addition of H(2)O(2) (50 or 500 microM) to the incubation medium partially reverted the inhibition caused by DPI. These results indicate that a certain concentration of H(2)O(2) is necessary for leaf elongation, but it could not be distinguished whether H(2)O(2), or other ROS, are the actual active agents.     

The high oxygen atmosphere toward the end-Cretaceous; a possible contributing factor to the K/T boundary extinctions and to the emergence of C(4) species.

Angiosperm plants were grown under either the present day 21 kPa O(2) atmosphere or 28 kPa, as estimated for the end-Cretaceous (100-65 MyBP). CO(2) was held at different levels, within the 24-60 Pa range, as also estimated for the same period. In C(3) Xanthium strumarium and Atriplex prostrata, leaf area and net photosynthesis per unit leaf area, were reduced by the high O(2), while the whole-plant respiration/photosynthesis ratio increased. The high O(2) effects were strongest under 24 Pa, but still significant under 60 Pa CO(2). Growth was reduced by high O(2) in these C(3) species, but not in Flaveria sp., whether C(3), C(4), or intermediary grown under light intensities <350 micromol m(-2) s(-1) PPF. Photosynthesis of C(3) Flaveria sp. was reduced by high O(2), but only at light intensities >350 micromol m(-2) s(-1) PPF. It is concluded that the high O(2) atmosphere at the end-Cretaceous would have reduced growth of at least some of the vegetation, thus adversely affecting dependent fauna. The weakened biota would have been predisposed to the consequences of volcanism and the K/T boundary bolide impact. Conversely, photosynthesis and growth of C(4) Zea mays and Atriplex halimus were little affected by high, 28 kPa, O(2). This suggests an environmental driver for the evolution of C(4) physiology.