Elevated CO2 Reduces Vessel Diameter and Lignin Deposition in Some Legume Plants Grown in Mini-FACE Rings

Studies on stem (and leaf) structure and histology of a semi-natural grassland community, permanently growing in mini-FACE rings under elevated concentrations of atmospheric CO₂ (560 μmol mol⁻¹) are presented. Histochemical analysis of stem sections from legume plants grown under high CO₂ concentration revealed both a reduction of lignin deposition in spring vascular bundles of Trifolium repens L., and a decrease in size of the xylem vessels in Vicia hybrida L. and Vicia sativa L. Thus, the effects of elevated CO₂ on the stem histology of the species investigated are rather species-specific and/or organ-specific, and of major account especially in the early phases of vegetative growth, in particular as regards lignin deposition mechanisms. In leaves, neither differences as to lignification nor any other anatomical structure modification were found under CO₂ enrichment. This revised version was published online in July 2006 with corrections to the Cover Date.     

Elevated atmospheric CO2 decreases oxidative stress and increases essential oil yield in leaves of Thymus vulgaris grown in a mini-FACE system

Potted one-year-old plants of Thymus vulgaris L. (thyme, Lamiaceae, C3 metabolism), were grown for three months (10 June–10 September, 2004) in a “mini-free-air-CO₂-enrichment” (“mini-FACE”) system, under 500 μmol mol^?1 and ambient concentrations of atmospheric carbon dioxide (CO₂). Compared to ambient CO₂, elevated CO₂ stimulated leaf superoxide dismutase (SOD, EC 1.15.1.1) activity only at the first sampling-time (July), followed by no variation or even a trend of decreased activity on the other two sampling-times (August and September). Under high CO₂, guaiacol peroxidase (GPX, EC 1.11.1.7) and catalase (CAT, EC 1.11.1.6) leaf activities showed no variation or drop throughout the duration of the experiment. By contrast, under elevated CO₂, leaf glutathione reductase (GR, EC 1.6.4.2) activity increased on all the sampling-times, and also a duration-dependent upward trend of glutathione (GSH) content was recorded, with this increase becoming significant – compared with ambient CO₂ – at the third sampling-time (September). Simultaneously, leaves from plants grown under high CO₂ showed a marked increase in essential oil yield, with slight increments in phenolic component and decrements in mono- and sesquiterpene components. Also, a drop in thiobarbituric acid reactive substances (TBARS) content under elevated CO₂ was displayed. Thus, in general, the results reported here point to a downregulation of leaf antioxidant enzymes under elevated CO₂, supporting the notion of reduced reactive oxygen species (ROS) formation under these circumstances. Relying instead on antioxidant-regenerating enzymes, namely GR, fairly high GSH content and essential oils, might be a ‘low cost’ life strategy for growth under elevated CO₂, not requiring synthesis/activation of energy-intensive and expensive metabolic processes.     

Thermotolerance and Related Antioxidant Enzyme Activities Induced by Heat Acclimation and Salicylic Acid in Grape (Vitis vinifera L.) Leaves

Thermotolerance and related antioxidant enzyme activities induced by both heat acclimation and exogenous salicylic acid (SA) application were studied in grapevine (Vitis vinifera L. cv. Jingxiu). Heat acclimation and exogenous SA application induced comparable changes in thermotolerance, ascorbic acid (AsA), glutathione (GSH), and hydrogen peroxide (H₂O₂) concentrations, and in activities of the antioxidant enzymes superoxide dismutase (SOD), peroxidase (POD), glutathione reductase (GR), ascorbic peroxidase (APX) and catalase (CAT) in grape leaves. Within 1 h at 38 °C, free SA concentration in leaves rose from 3.1 μg g⁻¹ FW to 19.1 μg g⁻¹ FW, then sharply declined. SA application and heat acclimation induced thermotolerance were related to changes of antioxidant enzyme activities and antioxidant concentration, indicating a role for endogenous SA in heat acclimation in grape leaves.     

Photosynthetic responses to elevated CO2and O3 in field-grown potato(Solanum tuberosum)

Potato plants (Solanum tuberosum L. cv. Bintje) were grown to maturity in open-top chambers under three carbon dioxide (CO₂; ambient and 24 h d⁻¹ seasonal mean concentrations of 550 and 680 μmol mol⁻¹) and two ozone levels (O₃; ambient and an 8 h d⁻¹ seasonal mean of 50 nmol mol⁻¹). Chlorophyll content, photosynthetic characteristics, and stomatal responses were determined to test the hypothesis that elevated atmospheric CO₂ may alleviate the damaging influence of O₃ by reducing uptake by the leaves. Elevated O₃ had no detectable effect on photosynthetic characteristics, leaf conductance, or chlorophyll content, but did reduce SPAD values for leaf 15, the youngest leaf examined. Elevated CO₂ also reduced SPAD values for leaf 15, but not for older leaves; destructive analysis confirmed that chlorophyll content was decreased. Leaf conductance was generally reduced by elevated CO₂, and declined with time in the youngest leaves examined, as did assimilation rate (A). A generally increased under elevated CO₂, particularly in the older leaves during the latter stages of the season, thereby increasing instantaneous transpiration efficiency. Exposure to elevated CO₂ and/or O₃ had no detectable effect on dark-adapted fluorescence, although the values decreased with time. Analysis of the relationships between assimilation rate and intercellular CO₂ concentration and photosynthetically active photon flux density showed there was initially little treatment effect on CO₂-saturated assimilation rates for leaf 15. However, the values for plants grown under 550 μmol mol⁻¹ CO₂ were subsequently greater than in the ambient and 680 μmol mol⁻¹ treatments, although the beneficial influence of the former treatment declined sharply towards the end of the season. Light-saturated assimilation was consistently greater under elevated CO₂, but decreased with time in all treatments. The values decreased sharply when leaves grown under elevated CO₂ were measured under ambient CO₂, but increased when leaves grown under ambient CO₂ were examined under elevated CO₂. The results obtained indicate that, although elevated CO₂ initially increased assimilation and growth, these beneficial effects were not necessarily sustained to maturity as a result of photosynthetic acclimation and the induction of earlier senescence.     

Response of aboveground grassland biomass and soil moisture to moderate long-term CO2 enrichment

Rising atmospheric CO₂ concentrations may alter C cycling and community composition, however, long-term studies in (semi-)natural ecosystems are still rare. In May 1998, the Giessen FACE (Free Air Carbon dioxide Enrichment) experiment started in a grassland ecosystem near Giessen, Germany, consisting of three enrichment (E plots) and three ambient control rings (A plots). Carbon dioxide concentrations were raised to +20% above ambient all-year-round during daylight hours. The wet grassland (Arrhenatheretum elatioris Br.-Bl.; not ploughed for >100 years) has been fertilized with 40 kg ha⁻¹ yr⁻¹ N, and mown two times each year for decades. Since 1993, the biomass has been monitored and since 1997 it was divided into grasses, legumes and non-leguminous forbs.During the 5 years prior to CO₂ enrichment, the annual biomass yield from the A plots was non-significantly higher (3%) than the later E plots yield. Under CO₂ enrichment, the biomass increased significantly from the third enrichment year on by 9.8%, 7.7% and 11.2% in the years 2000–2002, respectively. The increase was surprisingly high considering the moderate CO₂ enrichment regime of only +20% and sub-optimal N supply, possibly suggesting a non-linear response of temperate grassland ecosystems to rising atmospheric CO₂ levels.The leaf area index did not change significantly under elevated CO₂, nor did the soil moisture in the top 15 cm increase. No correlation existed between the magnitude of the yield stimulation under elevated CO₂ and the precipitation sums preceding the respective harvests. The grass biomass increased significantly under FACE, while the forb biomass declined strongly in the fourth and fifth year. The legume fraction was mostly below 1% of the total yield, and did not respond to CO₂ enrichment. These findings are in contrast to other grassland results and possible reasons are discussed.     

Antioxidative responses to different altitudes in leaves of alpine plant Polygonum viviparum in summer

Mountain environmental stresses result in increased formation of hydrogen peroxide (H₂O₂) and accumulation of malondialdehyde (MDA) in leaves of Polygonum viviparum. The activities of several antioxidative system enzymes such as superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), peroxidase (POD, EC 1.11.1.7), glutathione reductase (GR, EC 1.6.4.2), dehydroascorbate reductase (DHAR, EC 1.8.5.1) and the contents of several non-enzymatic antioxidants such as reduced form of ascorbate (ASC), dehydroascorbate (DHA), reduced glutathione (GSH), and oxidized glutathione (GSSG) were investigated in leaves of P. viviparum, which were collected from three altitudes (2,200, 3,200, and 3,900 m) of Tianshan Mountain in China. The activities of these four antioxidative enzymes were accompanied by increases of H₂O₂ levels from 2,200 to 3,200 m. However, the activities of CAT and POD were decreased, whereas the activities of SOD and GR continually increased at 3,900 m. Analyses of isoforms of SOD, CAT, POD, and GR showed that the leaves of P. viviparum exposed different altitude conditions are capable of differentially altering the intensity. Additionally, two new isoforms of SOD were detected at 3900 m. A continual increase in the ASC, ASC to DHA ratio, GSH and GSH/[GSH + GSSG] ratio, and the activity of DHAR were observed in leaves of P. viviparum with the elevation of altitude. These results suggest that the higher contents of ASC, GSH as well as an increase in reduced redox state may be essential to antioxidation processes in the leaves of P. viviparum, whereas antioxidant enzymes system is a cofactor in the processes.     

Antioxidant defences of the apoplast

Summary The apoplast of barley and oat leaves contained superoxide dismutase (SOD), catalase, ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, and glutathione reductase activities. The activities of these enzymes in the apoplastic extracts were greatly modified 24 h after inoculation with the biotrophic fungal pathogenBlumeria graminis. The quantum efficiency of photosystem II, which is related to photosynthetic electron transport flux, was comparable in inoculated and healthy leaves during this period. Apoplastic soluble acid invertase activity was also modified in inoculated leaves. Inoculation-dependent increases in apoplastic SOD activity were observed in all lines. Major bands of SOD activity, observed in apoplastic protein extracts by activity staining of gels following isoelectric focusing, were similar to those observed in whole leaves but two additional minor bands were found in the apoplastic fraction. The apoplastic extracts contained substantial amounts of dehydroascorbate (DHA) but little or no glutathione (GSH). Biotic stress decreased apoplastic ascorbate and DHA but increased apoplastic GSH in resistant lines. The antioxidant cycle enzymes may function to remove apoplastic H₂O₂ with ascorbate and GSH derived from the cytoplasm. DHA and oxidized glutathione may be reduced in the apoplast or returned to the cytosol for rereduction.Abbreviations AA reduced ascorbate - APX ascorbate peroxidase - DHA dehydroascorbate (oxidised ascorbate) - DHAR dehydroascorbate reductase - G6PDH glucose-6-phosphate dehydrogenase - GSH reduced glutathione - GSSG glutathione disulphide - GR glutathione reductase - MDHA monodehydroascorbate - MDHAR monodehydroascorbate reductase - SOD superoxide dismutase     

Cd~(2+)胁迫对小桐子幼苗叶片抗氧化系统的影响

以小桐子幼苗为材料,设置不同浓度CdCl_2处理,测定Cd~(2+)胁迫对小桐子幼苗叶片中可溶性蛋白、丙二醛(MDA)含量,以及5种抗氧化酶活性和2种抗氧化剂含量的变化,探讨镉胁迫对小桐子幼苗抗氧化系统的影响。结果表明:(1)Cd~(2+)胁迫导致小桐子幼苗叶片中可溶性蛋白含量降低、MDA含量增加;(2)随着镉胁迫时间的延长,幼苗叶片中愈创木酚过氧化物酶(POD)、过氧化氢酶(CAT)、超氧化物歧化酶(SOD)、抗坏血酸专一性过氧化酶(APX)、谷胱甘肽还原酶(GR)等抗氧化酶活性表现出先升高然后降低的变化趋势;(3)幼苗叶片中还原型抗坏血酸(ASA)和还原型谷胱甘肽(GSH)含量随着胁迫时间延长而降低,但其中氧化型抗坏血酸(DHA)和氧化型谷胱甘肽(GSSG)含量则升高。研究表明,镉胁迫初期能诱导小桐子幼苗抗氧化系统活性显著增强,提高其抗氧化能力,但随着胁迫时间的延长,致使其抗氧化酶的活性和抗氧物质含量下降,植株遭受明显氧化胁迫,幼苗生长受到镉的严重毒害。     

Decomposition of leaf and root tissue of three perennial grass species grown at two levels of atmospheric CO2 and N supply

Leaf and root tissue of Lolium perenne L., Agrostis capillaris L. and Festuca ovina L. grown under ambient (350 μl l^-1 CO₂) and elevated (700 μl l^-1) CO₂ in a continuously ¹⁴C-labelled atmosphere and at two soil N levels, were incubated at 14°C for 222 days. Decomposition of leaf and root tissue grown in the low N treatment was not affected by elevated [CO₂], whereas decomposition in the high N treatment was significantly reduced by 7% after 222 days. Despite the increased C/N ratio (g g^-1) of tissue cultivated at elevated [CO₂] when compared with the corresponding ambient tissue, there was no significant correlation between initial C/N ratio and ¹⁴C respired. This finding suggests that the CO₂-induced changes in decomposition rates do not occur via CO₂-induced changes in C/N ratios of plant materials. We combined the decomposition data with data on ¹⁴C uptake and allocation for the same plants, and give evidence that elevated [CO₂] has the potential to increase soil C stores in grassland via increasing C uptake and shifting C allocation towards the roots, with an inherent slower decomposition rate than the leaves. An overall increase of 15% in ¹⁴C remaining after 222 days was estimated for the combined tissues, i.e., the whole plants; the leaves made a much smaller contribution to the C remaining (+6%) than the roots (+26%). This shows the importance of clarifying the contribution of roots and leaves with respect to the question whether grassland soils act as a sink or source for atmospheric CO₂. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of NaCl stress on H2O2 metabolism in rice leaves

The effect of NaCl stress on H₂O₂ metabolismin detached rice leaves was studied. NaCl (200 mM)treatment did not cause the accumulation ofH₂O₂ and resulted in no increase in lipidperoxidation and membrane leakage of leaf tissues. The activities of peroxidase, ascorbate peroxidase,superoxide dismutase, and glutathione reductase wereobserved to be greater in NaCl-stressed rice leavesthan in control leaves. However, glycolate oxidasewas lower in NaCl-treated rice leaves than in thecontrol leaves. There was no difference in catalaseactivity between NaCl and control treatments. Theseresults suggest that some antioxidant enzymes can beactivated in response to oxidative stress induced byNaCl.     

Changes in antioxidant enzyme activities in detached leaves of cucumber exposed to chilling

We studied changes in biochemical and physiological status, level of oxidative damage, and antioxidant enzyme activities in detached leaves of cucumber plants (Cucumis sativus L. cv. Pyunggangnaebyungsamchuk) that were exposed to a low temperature (4°C). Chlorophyll fluorescence (F_v/F_m) declined during the chilling treatment, but was slowly restored after the tissues were returned to 25°C. Likewise, the fluorescence quenching coefficient and relative water content decreased during the stress period, but then increased during recovery. In contrast, we detected a significant rise in protein and hydrogen peroxide contents in the chilled leaves, as well as higher activities for superoxide dismutase, ascorbate peroxidase, peroxidase, and glutathione reductase. However, the level of catalase decreased not only during chilling but also after 24 h of recovery. These results indicate that exposure to low temperatures acts as an oxidative stress. Moreover, we propose that a regulating mechanism exists in the detached cucumber leaves and contains an antioxidant defense system that induces active oxygen species, thereby alleviating the effects of chilling stress within 12 h.     

Effect of elevated CO2, temperature and limited water supply on antioxidant status during regrowth of nodulated alfalfa

Atmospheric CO₂ is a major contributor to the greenhouse effect and is one of the main inducers of climate change. Previous studies with nodulated alfalfa plants have shown that elevated CO₂ increased the growth of plants grown under well‐watered or limited water supply conditions. The beneficial effects of atmospheric CO₂ enrichment included higher photosynthetic rates, growth and water‐use efficiency and an increase in the root/shoot ratio. However, at the moment, we do not have information on the possible implications of the beneficial effect of elevated CO₂ as it may relate to a higher capacity of the violaxanthin–antheraxanthin–zeaxanthin (VAZ) cycle, the dissipation of excess radiation as heat and the effect on photooxidation, and to an improved leaf antioxidant system (Halliwell–Asada cycle). The aim of the present study was to determine the effects of the interaction between CO₂ (ambient, around 350 vs 700 μmol mol⁻¹), temperature (ambient vs ambient + 4°C) and water availability (well irrigated vs partially irrigated) on the leaf antioxidant status of nodulated alfalfa during regrowth. Parameters measured in this study included relative growth rate (RGR), H₂O₂ content, oxidative damage [measured as thiobarbituric acid‐reacting substances (TBARS)], leaf pigment composition (chlorophylls and xanthophylls), ascorbate (ASA) and glutathione pool levels and antioxidant enzymes. Our results revealed that during alfalfa regrowth, the effects of elevated CO₂, limited water supply, temperature and their interactions on growth were not related to significant or general changes in leaf antioxidant capacity, H₂O₂ accumulation or oxidative stress (TBARS concentrations). The beneficial effects of CO₂ enrichment in well‐watered and limited water‐subjected plants were not associated with an increase in the capacity of alfalfa leaves to dissipate excess radiation as heat through the VAZ cycle or with an increase in the antioxidant capacity, measured in terms of Halliwell–Asada cycle enzymes and antioxidant compounds. Furthermore, elevated CO₂ did not affect RGRs during the last 15 days of regrowth and reduced the activity of several antioxidant enzymes (catalase, superoxide dismutase and glutathione reductase and ASA peroxidase in limited water‐subjected plants), suggesting a lower basal rate of oxygen activation and H₂O₂ formation, leading to a relaxation of the antioxidant system.     

Plant shading increases lipid peroxidation and intensifies senescence-induced changes in photosynthesis and activities of ascorbate peroxidase and glutathione reductase in wheat

Plants of spring wheat (Triticum aestivum L. cv. Saxana) were grown during the autumn. Over the growth phase of three leaves (37 d after sowing), some of the plants were shaded and the plants were grown at 100 (control without shading), 70, and 40 % photosynthetically active radiation. Over 12 d, chlorophyll (Chl) and total protein (TP) contents, rate of CO₂ assimilation (P _N), maximal efficiency of photosystem 2 photochemistry (F_V/F_P), level of lipid peroxidation, and activities of antioxidative enzymes ascorbate peroxidase (APX) and glutathione reductase (GR) were followed in the 1_st, 2_nd, and 3_rd leaves (counted according to their emergence). In un-shaded plants, the Chl and TP contents, P _N, and F_V/F_P decreased during plant ageing. Further, lipid peroxidation increased, while the APX and GR activities related to the fresh mass (FM) decreased. The APX activity related to the TP content increased in the 3_rd leaves. The plant shading accelerated senescence including the increase in lipid peroxidation especially in the 1^st leaves and intensified the changes in APX and GR activities. We suggest that in the 2_nd and 3_rd leaves a degradation of APX was slowed down, which could reflect a tendency to maintain the antioxidant protection in chloroplasts of these leaves.     

Cadmium toxicity is reduced by nitric oxide in rice leaves

We evaluate the protective effect of nitric oxide (NO) against Cadmium (Cd) toxicity in rice leaves. Cd toxicity of rice leaves was determined by the decrease of chlorophyll and protein contents. CdCl₂ treatment resulted in (1) increase in Cd content, (2) induction of Cd toxicity, (3) increase in H₂O₂ and malondialdehyde (MDA) contents, (4) decrease in reduced form glutathione (GSH) and ascorbic acid (ASC) contents, and (5) increase in the specific activities of antioxidant enzymes (superoxide dismutase, glutathione reductase, ascorbate peroxidase, catalase, and peroxidase). NO donors [N-tert-butyl-α-phenylnitrone, 3-morpholinosydonimine, sodium nitroprusside (SNP), and ASC + NaNO₂] were effective in reducing CdCl₂-induced toxicity and CdCl₂-increased MDA content. SNP prevented CdCl₂-induced increase in the contents of H₂O₂ and MDA, decrease in the contents of GSH and ASC, and increase in the specific activities of antioxidant enzymes. SNP also prevented CdCl₂-induced accumulation of NH₄ ⁺, decrease in the activity of glutamine synthetase (GS), and increase in the specific activity of phenylalanine ammonia-lyase (PAL). The protective effect of SNP on CdCl₂-induced toxicity, CdCl₂-increased H₂O₂, NH₄ ⁺, and MDA contents, CdCl₂-decreased GSH and ASC, CdCl₂-increased specific activities of antioxidant enzymes and PAL, and CdCl₂-decreased activity of GS were reversed by 2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide, a NO scavenger, suggesting that protective effect by SNP is attributable to NO released. Reduction of CdCl₂-induced toxicity by NO in rice leaves is most likely mediated through its ability to scavenge active oxygen species including H₂O₂.     

Ribulose-1,5-bisphosphate regeneration limitation in rice leaf photosynthetic acclimation to elevated CO2

Our previous study has demonstrated that both RuBP carboxylation limitation and RuBP regeneration limitation exist simultaneously in rice grown under free-air CO₂ enrichment (FACE, about 200 μmol mol⁻¹ above the ambient air CO₂ concentration) conditions [G.-Y. Chen, Z.-H. Yong, Y. Liao, D.-Y. Zhang, Y. Chen, H.-B. Zhang, J. Chen, J.-G. Zhu, D.-Q. Xu, Photosynthetic acclimation in rice leaves to free-air CO₂ enrichment related to both ribulose-1,5-bisphosphate carboxylase limitation and ribulose-1,5-bisphosphate regeneration limitation. Plant Cell Physiol. 46 (2005) 1036–1045]. To explore the mechanism for forming of RuBP regeneration limitation, we conducted the gas exchange measurements and some biochemical analyses in FACE-treated and ambient rice plants. Net CO₂ assimilation rate (A_net) in FACE leaves was remarkably lower than that in ambient leaves when measured at the same CO₂ concentration, indicating that photosynthetic acclimation to elevated CO₂ occurred. In the meantime the maximum electron transport rate (ETR) (J_max), maximum carboxylation rate (V_cmax) in vivo, and RuBP contents decreased significantly in FACE leaves. The whole chain electron transport rate and photophosphorylation rate reduced significantly while ETR of photosystem II (PSII) did not significantly decrease and ETR of photosystem I (PSI) was significantly increased in the chloroplasts from FACE leaves. Further, the amount of cytochrome (Cyt) f protein, a key component localized between PSII and PSI, was remarkably declined in FACE leaves. It appears that during photosynthetic acclimation the decline in the Cyt f amount is an important cause for the decreased RuBP regeneration capacity by decreasing the whole chain electron transport in FACE leaves.     

Localization of antioxidant enzymes in the cellular compartments of sorghum leaves

The localization of antioxidant enzymes between the mesophyll and bundle sheath cells were determined in sorghum (Sorghum vulgare L.) leaves. The activity of antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD), ascorbate peroxidase (APX) and glutathione reductase (GR) were assayed in whole leaf, mesophyll and bundle sheath fractions of sorghum leaves subjected to water-limited conditions. Drought was imposed by withholding water and the plants were maintained at different water potentials ranging from 0.5–2.0 MPa. The purity of the isolates was tested using the marker enzymes like RuBPcase and PEPcase. GR was mostly localized in mesophyll fraction, while SOD, APX and peroxidase were located in bundle sheath cells. Catalase was found to be equally distributed between the two cell types. Under water stress conditions, most of the SOD activity was found in the bundle sheath tissues. Little or no activity of the enzymes CAT, APX or POD was found in the mesophyll extracts when exposed to water stress. GR activity increased when exposed to low water regimes. From this study, it is clear that antioxidants are differentially distributed between the mesophyll and bundle sheath cells in sorghum leaves. Under water stress conditions, the mesophyll cells showed less damage from oxidative stress when compared to the bundle sheath cells. This is critical for determining the sensitivity of sorghum to extreme climatic conditions.     

Effect of salicylic acid potentiates cadmium-induced oxidative damage in <Emphasis Type="Italic">Oryza sativa</Emphasis> L. leaves

In the present investigation, we studied the possible potentiating effect of salicylic acid (SA) under Cd toxicity in Oryza sativa L. leaves. Cd treatments for 24 h reduced the shoot length, dry biomass and total chlorophyll content followed by high Cd accumulation in shoots. About 16 h presoaking with SA resulted in partial protection against Cd, as observed by minor changes in length, biomass and total chlorophyll. SA priming resulted in low Cd accumulation. Enhanced thiobarbituric acid reactive substances (TBARS), hydrogen peroxide (H₂O₂) and superoxide anion (O₂ ⁻) content were seen when Cd was applied alone, while under SA priming the extent of TBARS, H₂O₂ and O₂ ⁻ were significantly low, suggesting SA-regulated protection against oxidative stress. The antioxidant enzymes like Catalase (CAT), guaiacol peroxidase (GPx), glutathione reductase (GR) and superoxide dismutase (SOD) showed varied activities under Cd alone. CAT activity increased after Cd treatment, followed by a decline in GPX and GR activity. SOD also declined at the highest concentrations with an initial increase. Under SA-priming conditions, the efficiency of the antioxidant enzymes was significantly elevated. GPx and SOD activity showed significant increase in activity. The ascorbate activity increased after Cd treatment, followed by a decline in glutathione under SA-free condition. SA priming showed gradual increase in these non-enzymic antioxidants. Our results indicate that Cd-induced oxidative stress can be regulated by SA.     

The effect of cadmium on CO<Subscript>2</Subscript> exchange,variable fluorescence of chlorophyll,and the level of antioxidant enzymes in pea leaves

CO₂ exchange, variable chlorophyll fluorescence, the intensity of lipid peroxidation (POL), and the activity of antioxidant enzymes in leaves of two-week-old pea seedlings (Pisum sativum L.) exposed to 0.01, 0.1, and 1 mM aqueous solutions of Cd(NO₃)₂ for 2 h were studied. Incubation with Cd²⁺ ions resulted in a reduction of the maximum quantum efficiency of photosynthesis, CO₂ uptake rate, and photosystem II (PSII) activity, as assessed by F _v/F ₀ ratio. The intensity of POL in leaves of all treated seedlings was below or close to the control level. The activity of superoxide dismutase (SOD) and glutathione reductase (GR) increased in all treatments; the activity of ascorbate peroxidase (AP) exceeded the control level only in seedlings exposed to the high Cd²⁺ concentration (1 mM), and the activity of peroxidase increased at the low concentration (0.01 mM). We found that the reduction in the activity of the photosynthetic apparatus under conditions of 2-h-long Cd²⁺-induced stress was not related to an intensification of POL processes. It was concluded that stimulation of the activity of antioxidant enzymes—SOD, GR, AP, and peroxidase—is a pathway for pea plant adaptation to toxic effect of cadmium.Translated from Fiziologiya Rastenii, Vol. 52, No. 1, 2005, pp. 21–26.Original Russian Text Copyright © 2005 by Balakhnina, Kosobryukhov, Ivanov, Kreslavskii.     

Expression of arabidopsis cytosolic ascorbate peroxidase gene in response to ozone or sulfur dioxide

The effects of ozone or sulfur dioxide on antioxidant enzymes were investigated in Arabidopsis thaliana. Plants were fumigated with 0.1–0.15 ppm ozone or sulfur dioxide up to about 1 week in an environment-controlled chamber. Both pollutants increased the activities of ascorbate peroxidase and guaiacol per-oxidase in leaves, but had little effect on the activities of superoxide dismutase, catalase, monodehydroascorbate reductase, dehydroascorbate reductase or glutathione reductase. Ozone was more effective than sulfur dioxide in increasing the activities of the peroxidases. Ascorbate peroxidase activity increased 1.8-fold without a lag period during fumigation with 0.1 ppm ozone, while guaiacol peroxidase activity increased 4.4-fold with a 1-day lag. Expression of the APX1 gene encoding cytosolic ascorbate peroxidase was further investigated. Its protein levels in leaves exposed to 0.1 ppm ozone for 4 or 8 days were 1.5-fold higher than in controls. Both ozone and sulfur dioxide elevated APX1 mRNA levels in leaves at 4 and 7 days, whereas at 1 day only ozone was effective. The induction of APX1 mRNA levels by ozone (3.4- to 4.1-fold) was more prominent than that by sulfur dioxide (1.6-to 2.6-fold). The APX1 mRNA level increased by day and decreased by night. Exposure of plants to 0.1 ppm ozone enhanced the APX1 mRNA level within 3 h, which showed a diurnal rhythm similar to that of the control. These results demonstrate that near-ambient concentrations of ozone as well as similar concentrations of sulfur dioxide can induce APX1 gene expression in A. thaliana.Environmental Biology Division