Drought Induces Oxidative Stress and Enhances the Activities of Antioxidant Enzymes in Growing Rice Seedlings

When rice seedlings grown for 10 and 20 days were subjected to in vitro drought stress of −0.5 and −2.0 MPa for 24 h, an increase in the concentration of superoxide anion (O₂^.−), increased level of lipid peroxidation and a decrease in the concentration of total soluble protein and thiols was observed in stressed seedlings compared to controls. The concentration of H₂O₂ as well as ascorbic acid declined with imposition of drought stress, however glutathione (GSH) concentration declined only under severe drought stress. The activities of total superoxide dismutases (SODs) as well as ascorbate peroxidase (APX) showed consistent increases with increasing levels of drought stress, however catalase activity declined. Mild drought stressed plants had higher guaiacol peroxidase (GPX) and chloroplastic ascorbate peroxidase (c-APX) activity than control grown plants but the activity declined at the higher level of drought stress. The activities of enzymes involved in regeneration of ascorbate i.e. monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) were higher in drought stressed plants compared to controls. Results suggest that drought stress induces oxidative stress in rice plants and that besides SOD, the enzymes of ascorbate-glutathione cycle, which have not been studied in detail earlier under stressful conditions, appear to function as important component of antioxidative defense system under drought stress.     

Effects of ambient oxygen and of fixed nitrogen on concentrations of glutathione, ascrobate, and associated enzymes in soybean root nodules

Soybean (Glycine max [L.] Merr.) root nodules contain the enzymes of the ascorbate-glutathione cycle for defense against activated forms of oxygen. Nodulated roots of hydroponically grown soybean plants were exposed to atmospheres containing 2, 21, 50, or alternating 21 and 50 kilopascals of O₂. The activities of ascorbate (ASC) peroxidase, monodehydroascorbate (MDHA) reductase, dehydroascorbate (DHA) reductase, and glutathione (GSSG) reductase were higher in nodules exposed to high pO₂. Nodule contents of ascorbate and reduced glutathione were also greater in the high pO₂ treatments. Treatment of nodulated plants with fixed nitrogen (urea) led to concomitant decreases in acetylene reduction activity, in leghemoglobin content, and in activities of ASC peroxidase, DHA reductase, and GSSG reductase. Activity of MDHA reductase and glutathione concentrations in nodules were not affected by treatment with urea. The enzymes of the ascorbate-glutathione cycle were also detected in uninfected soybean roots, although at levels substantially below those in nodules. These observations indicate that the ascorbate-glutathione cycle can adjust to varying physiological conditions in nodules and that there is a key link between N₂ fixation and defenses against activated forms of oxygen.     

Nickel-induced oxidative stress and the role of antioxidant defence in rice seedlings

Seedlings of rice (Oryza sativa L.) cv. Pant-12 grown in sand cultures containing 200 and 400 μM NiSO₄, showed a decrease in length and fresh weight of roots and shoots. Nickel was readily taken up by rice seedlings and the concentration was higher in roots than shoots. Nickel-treated seedlings showed increased rates of superoxide anion (O₂ ^•− ) production, elevated levels of H₂O₂ and thiobarbituric acid reactive substances (TBARS) demonstrating enhanced lipid peroxidation, and a decline in protein thiol levels indicative of increased protein oxidation compared to controls. With progressively higher Ni concentrations, non-protein thiol and ascorbate (AsA) increased, whereas the level of low-molecular-weight thiols (such as glutathione and hydroxyl-methyl glutathione), the ratio of these thiols to their corresponding disulphides, and the ratio of AsA to dehydroascorbic acid declined in the seedlings. Among the antioxidant enzymes studied, the activities of all isoforms of superoxide dismutase (Cu-Zn SOD, Mn SOD and Fe SOD), guaiacol peroxidases (GPX) and ascorbate peroxidase (APX) increased in Ni-treated seedlings, while no clear alteration in catalase activity was evident. Activity of the ascorbate-glutathione cycle enzymes monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR)—significantly increased in Ni-treated seedlings. However such increase was apparently insufficient to maintain the intracellular redox balance. Results suggest that Ni induces oxidative stress in rice plants, resulting in enhanced lipid peroxidation and decline in protein thiol levels, and that (hydroxyl-methyl) glutathione and AsA in conjunction with Cu-Zn SOD, GPX and APX are involved in stress response.     

The responses of the enzymes related with ascorbate–glutathione cycle during drought stress in apple leaves

To explore the significance of the ascorbate–glutathione cycle under drought stress, the leaves of 2-year-old potted apple (Malus domestica Borkh.) plants were used to investigate the changes of each component of the ascorbate–glutathione cycle as well as the gene expression of dehydroascorbate reductase (DHAR, EC 1.8.5.1), ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) under drought stress. The results showed that the malondialdehyde (MDA) and H₂O₂ concentrations in apple leaves increased during drought stress and began to decrease after re-watering. The contents of total ascorbate, reduced ascorbic acid (AsA), total glutathione and glutathione (GSH) were obviously upregulated in apple leaves when the soil water content was 40–45%. With further increase of the drought level, the contents of the antioxidants and especially redox state of AsA and GSH declined. However, levels of them increased again after re-watering. Moreover, drought stress induced significant increase of the activities of enzymes such as APX, scavenging H₂O₂, and also of monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), DHAR and GR used to regenerate AsA and GSH, especially when the soil water content was above 40–45%. During severe drought stress, activities of the enzymes were decreased and after re-watering increased again. Gene expression of cytoplasmic DHAR, cytoplasmic APX and cytoplasmic GR showed similar changes as the enzyme activities, respectively. The results suggest that the ascorbate–glutathione cycle is up-regulated in response to drought stress, but cannot be regulated at severe drought stress conditions.     

Arsenite treatment induces oxidative stress,upregulates antioxidant system,and causes phytochelatin synthesis in rice seedlings

The effects of arsenite treatment on generation of reactive oxygen species, induction of oxidative stress, response of antioxidative system, and synthesis of phytochelatins were investigated in two indica rice (Oryza sativa L.) cvs. Malviya-36 and Pant-12 grown in sand cultures for a period of 5–20 days. Arsenite (As₂O₃; 25 and 50 μM) treatment resulted in increased formation of superoxide anion (O₂^.−), elevated levels of H₂O₂ and thiobarbituric acid reactive substances, showing enhanced lipid peroxidation. An enhanced level of ascorbate (AA) and glutathione (GSH) was observed irrespective of the variation in the level of dehydroascorbate (DHA) and oxidized glutathione (GSSG) which in turn influenced redox ratios AA/DHA and GSH/GSSG. With progressive arsenite treatment, synthesis of total acid soluble thiols and phytochelatins (PC) increased in the seedlings. Among antioxidative enzymes, the activities of superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6), total ascorbate peroxidase (APX, EC 1.11.1.11), chloroplastic ascorbate peroxidase, guaiacol peroxidase (EC 1.11.1.7), monodehydroascorbate reductase (EC 1.6.5.4), and glutathione reductase (EC 1.6.4.2) increased in arsenite treated seedlings, while dehyroascorbate reductase (EC 1.8.5.1) activity declined initially during 5–10 days and increased thereafter. Results suggest that arsenite treatment causes oxidative stress in rice seedlings, increases the levels of many enzymatic and non-enzymatic antioxidants, and induces synthesis of thiols and PCs, which may serve as important components in mitigating arsenite-induced oxidative damage.     

Ascorbate-glutathione metabolism during PEG-induced water deficit in <Emphasis Type="Italic">Trifolium repens</Emphasis>

In order to elucidate the response of the ascorbate-glutathione (ASC-GSH) cycle to drought stress, the activities of antioxidant enzymes and the levels of molecules involved in the ASC-GSH metabolism were studied in Trifolium repens L. seedlings subjected to PEG-induced water deficit. Compared to the control, the contents of H₂O₂, thiobarbituric acid reactive substances (TBARS), ascorbate (ASC), dehydroascorbate (DHA), and glutathione disulfide (GSSG) increased in PEG-treated seedlings, whereas the glutathione (GSH) content kept constant during the drought period. Further more, the ASC/DHA and GSH/GSSG ratios decreased in the presence of PEG. Except for that of monodehydroascorbate reductase (MDHAR), the activities of ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) were up-regulated during water deficit, and the increases in APX and DHAR activities were much higher than those in GR activity. These data indicate that fluctuations in the ASC-GSH metabolism resulted from PEG treatment may have a positive effect on drought stress mitigation in T. repens.     

Nitric oxide alleviates manganese toxicity by preventing oxidative stress in excised rice leaves

In the present study, we have investigated the effects of nitric oxide (NO) on alleviating manganese (Mn)-induced oxidative stress in rice leaves. Exogenous MnCl₂ treatment to excised rice leaves for 24 and 48 h resulted in increased production of H₂O₂ and lipid peroxides, decline in the levels of antioxidants, glutathione and ascorbic acid, and increased activities of antioxidative enzymes, superoxide dismutase, guaiacol peroxidase, catalase, ascorbate peroxidase, dehydroascorbate reductase, and glutathione reductase. Treatment of rice leaves with 100 μM sodium nitroprusside (SNP), a NO donor, was effective in reducing Mn-induced increased levels of H₂O₂, lipid peroxides and increased activities of antioxidative enzymes. The levels of reduced ascorbate and glutathione were considerably recovered due to SNP treatment. The effect of SNP was reversed by the addition of NO scavenger, 2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (c-PTIO) suggesting that ameliorating effect of SNP is due to release of NO. The results indicate that MnCl₂ induces oxidative stress in excised rice leaves, lowers the levels of reduced ascorbate and glutathione, and elevates activities of the key antioxidative enzymes. NO appears to provide a protection to the rice leaves against Mn-induced oxidative stress and that exogenous NO application could be advantageous in combating the deleterious effects of Mn-toxicity in rice plants.     

Antioxidant capacity of sage grown on heavy metal-polluted soil

Oxidative stress response and essential oil composition of sage (Salvia officinalis L.), grown on industrially polluted soil were studied. Sage plants were grown on the soil polluted with Cd, Cu, Pb, Zn, and non-polluted control soil. One-year-old sage possessed a high potential for heavy metal accumulation mainly in the roots. Heavy metal pollution resulted in root and shoot dry biomass inhibition. The increased levels of hydrogen peroxide and MDA showed that the heavy metal uptake caused oxidative stress. The increase towards the control was observed in the levels of glutathione, ascorbate, dehydroascorbate, catalase, dehydroascorbate reductase, and glutathione peroxidase. Weak activities of the most enzymes of the ascorbate-glutathione cycle allowed to suppose that H₂O₂ neutralization is rather non-enzymatic than enzymatic process. Observed decline in α- and β-thujones and elevated camphor content in the sage leaves did not indicate a deterioration of the essential oil quality. Sage grown on heavy metal-polluted soil successfully accumulated cadmium, lead, and zinc, which is resulted in plant biomass inhibition, but essential oil yield and quality was not declined.     

Regulation of the ascorbate-glutathione cycle in wild almond during drought stress

In wild species of almond (Prunus spp.), the activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR), as well as the levels of ascorbate/glutathione pools and H₂O₂ were subjected to water deficit and shade conditions. After 60 days of water shortage, the species were subjected to a rewatering treatment. During water recovery, leaves exposed to sunlight and leaves under shade conditions of about 20–35% of environmental irradiance were sampled. After 70 days without irrigation, mean predawn leaf water potential of all the species fell from −0.32 to −2.30 MPa and marked decreases in CO₂ uptake and transpiration occurred. The activities of APX, MDHAR, DHAR, and GR increased in relation to the severity of drought stress in all the wild species studied. Generally, APX, MDHAR, DHAR, and GR were down-regulated during the rewatering phase and their activities decreased faster in shaded leaves than in sun-exposed leaves. The levels in total ascorbate, glutathione, and H₂O₂ were directly related to the increase in drought stress and subsequently decreased during rewatering. The antioxidant response of wild almond species to drought stress limits cellular damage caused by reactive oxygen species during periods of water deficit and may be of key importance for the selection of drought-resistant rootstocks for cultivated almond.     

Senescence of leaf sheaths of ryegrass stubble: changes in enzyme activities related to H2O2 metabolism

Changes in the levels of reactive oxygen species (O2^.-, H₂O₂), and of activities of enzymes involved in their detoxification were investigated during senescence of leaf sheaths of ryegrass stubble. The accumulation of H₂O₂ in the medium leaf sheaths coincided with a drop in the levels of total glutathione, of pyridine nucleotides and of activities of monodehydroascorbate reductase and dehydroascorbate reductase. Conversely, a paradoxical increase in the ascorbate/ascorbate plus dehydroascorbate ratio was observed, which appears to be inconsistent with H₂O₂ accumulation. Our results suggest that oxalate might be an essential source of H₂O₂ in senescent leaf sheaths, and that oxalate oxidase might be involved in the defence of foliar tissue against pathogens during the progress of senescence. Moreover, it is assumed that glucid catabolism of the ryegrass stubble might be a starting point of a metabolic drain leading to ascorbate, then to oxalate during the late phase of leaf sheath senescence.     

Iron deficiency enhances the levels of ascorbate,glutathione, and related enzymes in sugar beet roots

Summary.  The effects of Fe deficiency stress on the levels of ascorbate and glutathione, and on the activities of the enzymes ferric chelate reductase, glutathione reductase (EC 1.6.4.2), ascorbate free-radical reductase (EC 1.6.5.4) and ascorbate peroxidase (EC 1.11.1.11), have been investigated in sugar beet (Beta vulgaris L.) roots. Plasma membrane vesicles and cytosolic fractions were isolated from the roots of the plants grown in nutrient solutions in the absence or presence of Fe for two weeks. Plants responded to Fe deficiency not only with a 20-fold increase in root ferric chelate reductase activity, but also with moderately increased levels of the general reductants ascorbate (2-fold) and glutathione (1.6-fold). The enzymes of the ascorbate-glutathione cycle in roots were also affected by Fe deficiency. Glutathione reductase activity was enhanced 1.4-fold with Fe deficiency, associated to an increased ratio of reduced to oxidized glutathione, from 3.1 to 5.2. The plasma membrane fraction from iron-deficient roots showed 1.7-fold higher ascorbate free-radical reductase activity, whereas in the cytosolic fraction the enzyme activity was not affected by Fe deficiency. The activity of the cytosolic hemoprotein ascorbate peroxidase decreased approximately by 50% with Fe deprivation. These results show that sugar beet responds to Fe deficiency with metabolic changes affecting components of the ascorbate-glutathione cycle in root cells. This suggests that the ascorbate-glutathione cycle would play certain roles in the general Fe deficiency stress responses in strategy I plants. Received November 19, 2001; accepted September 30, 2002; published online April 2, 2003 RID="*" ID="*" Correspondence and reprints: Departamento de Nutrición Vegetal, Estación Experimental de Aula Dei, CSIC, Apartado 202, 50080 Zaragoza, Spain.     

Cadmium-induced oxidative damage and antioxidant responses in Brassica juncea plants

Indian mustard (Brassica juncea L. cv. Vitasso) plants exposed to 10, 30, 50 and 100 μM of Cd for 5 d in hydroponic culture were analysed with reference to the distribution of Cd²⁺, the accumulation of biomass and antioxidants and antioxidative enzymes in leaves. Cd induced a decrease in plant biomass. The maximum accumulation of Cd occurred in roots followed by stems and leaves. Cd induced a decrease in catalase (CAT) and guiacol peroxidase (GPX) activities but an increase in ascorbate peroxidase (APX) and monodehydroascorbate reductase (MDHAR) activities. Enhancement in dehydroascorbate reductase (DHAR) activity was also at 10 μM Cd. Glutathione reductase (GR) activity showed pronounced stimulation after all treatments, but glutathione S-transferase (GST) and glutathione peroxidase (GPOX) activities decreased. The effectiveness of ascorbate-glutathione cycle (AGC) was determined by the ratio of ascorbate to H₂O₂. This ratio decreased in the Cd-treated leaves which indicated that the cycle was disordered.     

Effects of salt-tolerant rootstock grafting on ultrastructure,photosynthetic capacity,and H<Subscript>2</Subscript>O<Subscript>2</Subscript>-scavenging system in chloroplasts of cucumber seedlings under NaCl stress

Plant growth, photosynthetic parameters, chloroplast ultrastructure, and the ascorbate-glutathione cycle system in chloroplasts of self-grafted and rootstock-grafted cucumber leaves were investigated. Grafted plants were grown hydroponically and were exposed to 0, 50, and 100 mM NaCl concentrations for 10 days. Under NaCl stress, the hydrogen peroxide (H₂O₂) content in cucumber chloroplasts increased, the chloroplast ultrastructure was damaged, and the gas stomatal conductance, intercellular CO₂ concentration, as well as shoot dry weight, plant height, stem diameter, leaf area, and leaf relative water content were inhibited, whereas these changes were less severe in rootstock-grafted plants. The activities of ascorbate peroxidase (APX; EC 1.11.1.11), glutathione reductase (GR; EC 1.6.4.2), and dehydroascorbate reductase (DHAR EC 1.8.5.1) were higher in the chloroplasts of rootstock-grafted plants compared with those of self-grafted plants under 50 and 100 mM NaCl. Similar trends were shown in leaf net CO₂ assimilation rate and transpiration rate, as well as reduced glutathione content under 100 mM NaCl. Results suggest that rootstock grafting enhances the H₂O₂-scavenging capacity of the ascorbate–glutathione cycle in cucumber chloroplasts under NaCl stress, thereby protecting the chloroplast structure and improving the photosynthetic performance of cucumber leaves. As a result, cucumber growth is promoted.     

Activation of ascorbate-glutathione cycle inArabidopsis leaves in response to aminotriazole

Aminotriazole(AT)-induced changes in growth, hydrogen peroxide content and activities of H₂O₂-scavenging antioxidant enzymes were investigated in the growing leaves ofArabidopsis plants (Arabidopsis thaliana cv Columbia). Catalase activity of rosette leaves was reduced by 65% with an application of 0.1 mM AT (a herbicide known as a catalase inhibitor), whereas the leaf growth and H₂O₂ content were almost unaffected. However, an approximate 1.6 to 2-fold increase in cytosolic ascorbate peroxidase (APX) activity concomitant with a substantial activation of glutathione reductase (GR) (approx. 22% increase) was observed during leaf growth in the presence of 0.1 mM AT. The activity of cytosolic APX in leaves was also increased by 1.8-fold with an application of exogenous 2 mM paraquat (an inducer of H₂O₂ production in plant cells) in the absence of AT. These results collectively suggest that (a) cytosolic APX and GR operate to activate an ascorbate-glutathione cycle for the removal of H₂O₂ under severe catalase deactivation, and (b) the expression of APX seems to be regulated by a change of the endogenous H₂O₂ level in leaf cells.     

Dehydroascorbate reductase and glutathione reductase play an important role in scavenging hydrogen peroxide during natural and artificial dehydration of Jatropha curcas seeds

Changes in H₂O₂ and the main antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR) and glutathione reductase (GR), in endospermic and embryonic tissues were studied in developing and artificially dried Jatropha curcas seeds. Immature seeds were desiccation-tolerant at 80 days after flowering, as they were able to germinate fully after artificial drying on silica gel had reduced their water content to 10–12% of fresh weight. In both endospermic and embryonic tissues, H₂O₂ level and, consequently, lipid peroxide content, decreased during seed development as well as after artificial dehydration of developing seeds. All examined antioxidant enzymes except DHAR showed a decrease in total activity in mature stages as compared with early stages. Expression analysis of SOD genes revealed that the decrease in total SOD activities was related to the decrease in Cu/Zn-SOD expression, while the continuous activity of SOD during maturation was related to an increase in Mn-SOD expression. Artificial drying resulted in increased SOD and DHAR activity, irrespective of the developmental stage. Our results revealed weak participation of CAT and APX in H₂O₂ scavenging, as well as no significant alterations in GR activities either during maturation or after artificial drying. Changes in SOD and GR isoenzyme patterns occurred during maturation-related drying, but not after artificial drying. These results highlight the role of ascorbate-glutathione cycle enzymes (DHAR and GR) in H₂O₂ scavenging during maturation or after artificial drying of developing J. curcas seeds.     

Polyamines as antioxidant protectors against paraquat damage in radish (Raphanus sativus L.) cotyledons

Pretreatment of radish cotyledons with polyamines (PAs; especially 1 mM spermidine) significantly improved their tolerance to subsequent 50 μM paraquat (PQ)-induced oxidative damage. Symptoms in the cotyledons, e.g., large accumulations of H₂O₂, and losses of fresh weight, chlorophyll, and proteins, were remarkably alleviated. Likewise, analysis of several enzymes belonging to the Superoxide dismutase (SOD)/ascorbate-glutathione cycle showed that pretreatment with PAs prevented typical PQ-induced declines in the total activities of SOD, ascorbate peroxidase (APX), and glutathione reductase (GR). Dehydroascorbate reductase (DHAR) activity, which normally decreases sharply under prolonged PQ exposure, was also highly maintained by PA treatment. In a native gel assay, two SOD isozymes (FeSOD and Cu/ZnSODI), two APX isozymes (APX1 and APX2), and two GSSG-specific isozymes (GR1 and GR2) proved to be more responsible for PQ tolerance, as manifested by the strong increases in their activities by spermidine (Spd) pretreatment. In addition, experiments with protein synthesis inhibitors (actinomycin D and cycloheximide) indicated that Spd could stimulatede novo synthesis of SOD and APX at the translational level. We can conclude that PAs may function as antioxidant protectors by invoking an efficient SOD/ascorbate-glutathione cycle in radish cotyledons exposed to PQ.     

Calcium and L-histidine effects on ascorbate-glutathione cycle components under nickel-induced oxidative stress in tomato plants

The effects of NiSO₄, calcium, and L-histidine (His) on the components of ascorbate-glutathione cycle, antioxidant enzymes and lipid peroxidation in a tomato cultivar Early Urbana Y was investigated. The activities of enzymes including catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX), superoxide dismutase (SOD), glutathione reductase (GR), lipoxygenase (LOX), and phenylalanine ammonia lyase (PAL) were measured. In addition, the content of H₂O₂, ascorbate (ASC), dehydroascorbate (DHA), reduced glutathione (GSH), chlorophyll (Chl) a+b, carotenoids, proteins, malondialdehyde (MDA), membrane aldehydes, and electrolyte leakage (EL) were determined. Results suggest that the excess of Ni increased the content of H₂O₂, MDA, membrane aldehydes and proteins in roots as well as GPX, LOX, APX activities, and EL in leaves, whereas Ca and His ameliorated these effects. Moreover, decreasing leaf GSH and DHA content and GR activity were observed under the Ni stress, but these parameters were raised by Ca plus His treatment. However, no improvement in leaf protein, ASC, root GSH content, and activities of PAL and CAT were observed by using Ca or His under Ni stress.     

EFFECTS OF CALCIUM NITRATE STRESS ON ASCORBATE-GLUTATHIONE CYCLE METABOLISM IN LEAVES OF HYDROPONICALLY-GROWN GRAFTED EGGPLANT SEEDLINGS

 以日本引进的设施专用耐盐茄(Solanum melongena)品种‘Torvum Vigor’为砧木, 栽培茄(S. torvum)品种‘苏崎茄’为接穗, 用营养液栽培, 对80 mmol&;#8226;L^–1 Ca(NO₃)₂胁迫下茄子嫁接苗和自根苗叶片抗坏血酸-谷胱甘肽循环系统中抗氧化酶活性和抗氧化物及H₂O₂含量进行比较。结果表明, Ca(NO₃)₂胁迫下茄子幼苗叶片H₂O₂含量有所增加, 但嫁接苗叶片H₂O₂含量显著低于自根苗。Ca(NO₃)₂胁迫下嫁接苗叶片抗氧化酶(APX、DHAR和GR)活性、AsA和GSH再生率、氧化还原力(AsA/DHA值和GSH/GSSG值)均显著高于自根苗。综上所述, Ca(NO₃)₂胁迫下嫁接苗保持良好的AsA-GSH循环效率, 清除H₂O₂效率较高, 细胞受氧化损伤程度较轻, 表现出较强的耐盐性。