The effect of chromium and aluminum on growth,root morphology,photosynthetic parameters and transpiration of the two barley cultivars

The effect of aluminum and chromium on two barley genotypes differing in Al tolerance was studied in a hydroponic experiment. Al stress decreased plant growth, biomass production, chlorophyll content and photosynthetic efficiency determined as variable to maximum chlorophyll fluorescence ratio (F_v/F_m), net photosynthetic rate (P_N), intercellular CO₂ concentration (c_i), stomatal conductance (g_s) and transpiration rate (E) less in an Al-tolerant genotype Gebeina than in an Al-sensitive genotype Shang 70–119. Cr stress also caused marked reduction in growth and photosynthetic traits in barley plants. Higher reduction was observed at pH 4.0 as compared to pH 6.5. Combined stress of Cr and Al, caused further reduction in growth and photosynthetic parameters.     

Genotype-Dependent Effect of Exogenous Nitric Oxide on Cd-induced Changes in Antioxidative Metabolism, Ultrastructure, and Photosynthetic Performance in Barley Seedlings (Hordeum vulgare)

A greenhouse hydroponic experiment was performed using Cd-sensitive (cv. Dong 17) and Cd-tolerant (Weisuobuzhi) barley seedlings to evaluate how different genotypes responded to cadmium (Cd) toxicity in the presence of sodium nitroprusside (SNP), a nitric oxide (NO) donor. Results showed that 5 μM Cd increased the accumulation of O₂^•−, H₂O₂, and malondialdehyde (MDA) but reduced plant height, chlorophyll content, net photosynthetic rate (P _n), and biomass, with a much more severe response in the Cd-sensitive genotype. Antioxidant enzyme activities increased significantly under Cd stress in the roots of the tolerant genotype, whereas in leaves of the sensitive genotype, superoxide dismutase (SOD) and ascorbate peroxide (APX), especially cytosol ascorbate peroxidase (cAPX), decreased after 5–15 days Cd exposure. Moreover, Cd induces NO synthesis by stimulating nitrate reductase and nitric oxide synthetase-like enzymes in roots/leaves. A Cd-induced NO transient increase in roots of the Cd-tolerant genotype might partly contribute to its Cd tolerance. Exogenous NO dramatically alleviated Cd toxicity, markedly diminished Cd-induced reactive oxygen species (ROS) and MDA accumulation, ameliorated Cd-induced damage to leaf/root ultrastructure, and increased chlorophyll content and P _n. External NO counteracted the pattern of alterations in certain antioxidant enzymes induced by Cd; for example, it significantly elevated the depressed SOD, APX, and catalase (CAT) activities in the Cd-sensitive genotype after 10- and 15-day treatments. Furthermore, NO significantly increased stromal APX and Mn-SOD activities in both genotypes and upregulated Cd-induced decrease in cAPX activity and gene expression of root/leaf cAPX and leaf CAT1 in the Cd-sensitive genotype. These data suggest that under Cd stress, NO, as a potent antioxidant, protects barley seedlings against oxidative damage by directly and indirectly scavenging ROS and helps to maintain stability and integrity of the subcellular structure.     

Effect of Aluminium on Oxidative Stress Related Enzymes Activities in Barley Roots

The impact of aluminium stress on activities of enzymes of the oxidative metabolism: superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POD), NADH peroxidase (NADH-POD) and oxalate oxidase (OXO) was studied in barley (Hordeum vulgare L. cv. Alfor) root tips. SOD appeared to be involved in detoxification mechanisms at highly toxic Al doses and after long Al exposure. POD and APX, H₂O₂ consuming enzymes, were activated following similar patterns of expression and exhibiting significant correlation between their elevated activities and root growth inhibition. The signalling role of NADH-POD in oxidative stress seems to be more probable than that of OXO, which might be involved in Al toxicity mechanism. This revised version was published online in July 2006 with corrections to the Cover Date.     

Salicylic Acid Application Mitigates Oxidative Damage and Improves the Growth Performance of Barley under Drought Stress

Drought is a severe environmental constraint, causing a significant reduction in crop productivity across the world. Salicylic acid (SA) is an important plant growth regulator that helps plants cope with the adverse effects induced by various abiotic stresses. The current study investigated the potential effects of SA on drought tolerance efficacy in two barley (Hordeum vulgare) genotypes, namely BARI barley 5 and BARI barley 7. Ten-day-old barley seedlings were exposed to drought stress by maintaining 7.5% soil moisture content in the absence or presence of 0.5, 1.0 and 1.5 mM SA. Drought exposure led to severe damage to both genotypes, as indicated by phenotypic aberrations and reduction of dry biomass. On the other hand, the application of SA to drought-stressed plants protected both barley genotypes from the adverse effects of drought, which was reflected in the improvement of phenotypes and biomass production. SA supplementation improved relative water content and proline levels in drought-stressed barley genotypes, indicating the osmotic adjustment functions of SA under water-deficit conditions. Drought stress induced the accumulation of reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂) and superoxide (O₂ ^•− ), and the lipid peroxidation product malondialdehyde (MDA) in the leaves of barley plants. Exogenous supply of SA reduced oxidative damage by restricting the accumulation of ROS through the stimulation of the activities of key antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) and glutathione peroxidase (GPX). Among the three-applied concentrations of SA, 0.5 mM SA exhibited better mitigating effects against drought stress considering the phenotypic performance and biochemical data. Furthermore, BARI barley 5 showed better performance under drought stress than BARI barley 7 in the presence of SA application. Collectively, our results suggest that SA played a crucial role in improving water status and antioxidant defense strategy to protect barley plants from the deleterious effects of water deficiency.     

Analysis of acid-soil stress in sorghum genotypes with emphasis on aluminium and magnesium interactions

Acid-soil stress in 12 sorghum (Sorghum bicolor (L.) Moench) genotypes was attributed mainly to aluminium (Al) toxicity. Root damage and magnesium (Mg) deficiency are two independent aspects of plant sensitivity to Al, either in acid soil or in nutrient solution. At moderate soil acidity, Mg deficiency dominantly limited growth whilst at high acidity root damage overruled the effect of Mg deficiency on the growth response. In nutrient solutions containing Al, increased Mg supply improved both root development and Mg nutrition of plants, whereas increased calcium (Ca) supply, or nutrition with ammonium (NH₄) instead of nitrate (NO₃), alleviated root damage but amplified Mg deficiency. At lowered pH the syndrome of Al toxicity was more profound. The implications of Mg-Al interactions, root damage, Mg supply and genotype selection are elucidated.     

根际低氧胁迫对网纹甜瓜生长、根呼吸代谢及抗氧化酶活性的影响

采用气雾法栽培系统,研究了根际低氧（10% O₂和5% O₂）胁迫对网纹甜瓜果实发育期间植株生长、根呼吸代谢及抗氧化酶活性的影响.结果表明：与对照相比,低氧胁迫下,网纹甜瓜株高、根长降低,植株鲜、干物质量显著下降;根呼吸速率极显著低于对照（21% O₂）,且5% O₂处理下降幅度大于10% O₂处理;乳酸脱氢酶（LDH）、乙醇脱氢酶（ADH）和丙酮酸脱羧酶（PDC）活性较对照显著升高,而苹果酸脱氢酶（MDH）活性显著降低;根系中超氧化物歧化酶（SOD）、过氧化物酶（POD）、过氧化氢酶（CAT）活性和丙二醛（MDA）含量显著高于对照,其中10% O₂处理抗氧化酶活性升高幅度显著大于5% O₂处理,而MDA含量5% O₂处理高于10% O₂处理.说明网纹甜瓜果实发育期间根际氧浓度降到10%及其以下时,根系有氧呼吸明显受阻,无氧呼吸代谢被促进,同时根系抗氧化酶发生应激反应,但随低氧胁迫时间的延长,根细胞质膜过氧化程度加剧,根系受到伤害,植株生长受到抑制,最终导致果实产量和品质下降.     

Aluminium-induced drought and oxidative stress in barley roots

The aim of the present study was to examine the relation between Al accumulation in root tissues, root growth inhibition, root water content, cell viability and expression of oxidative and drought stress-related genes in barley roots growing on the filter paper. Al-induced root growth inhibition correlated with Al uptake and cell death. Water content of Al-treated root represented only half of the control one. The expression of the dehydrin gene dhn4, which is a marker for drought stress in plant tissues, was strongly induced during Al stress. Al treatment also induced expression of oxidative stress-related genes such as glutathione peroxidase (gpx), pathogen-related peroxidase (prx8), glutathione reductase (gr) and dehydroascorbate reductase (dhar). The present results suggest correlation between Al uptake, Al-induced drought stress, oxidative stress, cell death and root growth inhibition.     

Aluminum stress in the roots of naked barley

Phytotoxicity of aluminum (Al) is the major limiting factor for the crops grown in acid soils rapidly inhibiting root elongation. In this study, changes in root growth, total activity and isozyme patterns of antioxidant enzymes such as peroxidase, ascorbate peroxidase, catalase and glutathione reductase by Al stress were investigated in the roots of naked barley (Hordeum vulgare L. cv. Kwangwhalssalbori). As Al concentration increased up to 500 M, the rooting rate and root elongation substantially decreased. Growth results suggested that this cultivar is an Al-sensitive species. Total activities of antioxidant enzymes generally increased at lower Al concentrations and then gradually decreased at higher Al concentrations. They also increased when the exposure time to Al was extended up to 48 hr. Changes in the isozyme patterns of antioxidant enzymes were investigated byin situ enzyme activity staining on a non-denaturing PAGE gel. They generally coincided with the changes in the total activity in parallel. Changes in the total activity of antioxidant enzymes also coincided with the changes of the root growth. Since growth reduction in the roots by Al stress could be related with the changes in the activities of antioxidant enzymes, these results suggested that Al might cause the oxidative stress in the roots of this cultivar of naked barley.     

Chromium (VI)-induced hormesis and genotoxicity are mediated through oxidative stress in root cells of Allium cepa L.

Chromium (VI) genotoxicity was evaluated in Allium bioassay by using different treatment protocols. Treatment of bulbs of Allium cepa L. with Cr(VI) at a range of concentrations for 5 days (120 h) exhibited low dose (12.5 μM) stimulation and high dose (25–200 μM) inhibition of root growth apparently indicating hormesis. Inhibition of root growth was correlated with the dose-dependent increase in generation of reactive oxygen species (ROS), cell death, lipid peroxidation, repression of antioxidative enzymes (catalase, superoxide dismutase, ascorbate peroxidase), induction of DNA damage, chromosome aberrations or micronuclei in root cells. The above effects were, however, reversed when the duration of Cr(VI) treatment was limited to 3–24 h followed by recovery in tap water for 4 days that resulted in the dose-dependent stimulation of root growth, mitosis and increased activity of the antioxidative enzymes that obliterated oxidative stress and genotoxicity. The above Cr(VI)-induced stimulation of root growth was effectively countered by pre- or post-treatments of dimethylthiourea, a ROS-scavenger. These findings underscored that Cr(VI), depending on the magnitude of the dose (concentration × time), could either be stimulatory or inhibitory for root growth that underlined the crucial role of ROS having obvious implications in agriculture, post harvest technology and human health.     

Comparative response of two wucai (<Emphasis Type="Italic">Brassica campestris</Emphasis> L.) genotypes to heat stress on antioxidative system and cell ultrastructure in root

The effects on root growth, root antioxidant capacity, and cellular ultrastructure were investigated using two wucai genotypes (heat-tolerant WS-1 and heat-sensitive WS-6) under heat stress (40/30 °C) for 5 days. Heat stress caused decreases in root biomass, relative water content (RWC), root vigor, and root traits of two wucai genotypes. In addition, it resulted in reactive oxygen species (ROS) accumulation and increased hydrogen peroxide (H₂O₂) content, superoxide anion (O₂ ^?) formation rate, and malondialdehyde (MDA) content, but the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were inhibited to different extents in two genotype wucai roots. However, these data indicated that the decline extent of WS-1 (heat tolerant) in root growth and antioxidant capacity was significantly lower than that of WS-6 (Heat sensitive). Microscopic analyses revealed that WS-1 (heat tolerant) showed a better cellular shape than WS-6 under heat stress and slightly oxidative damage; nuclear and mitochondria in WS-1 were of a better intact shape and clear bilayer membrane. Most importantly, the thicker root cell wall in heat-tolerant wucai genotype responding to heat stress was first reported. These results suggested that the ability of heat-tolerant wucai genotype to minimize the heat stress depended upon the higher self-regulation capacity and effectiveness of the antioxidant metabolism.     

N-acetyl-cysteine alleviates Cd toxicity and reduces Cd uptake in the two barley genotypes differing in Cd tolerance

A hydroponic experiment was carried out to study the physiological mechanisms of N-acetyl cysteine (NAC) in mitigating cadmium (Cd) toxicity in two barley (Hordeum vulgare L.) genotypes, Dong 17 (Cd-sensitive) and Weisuobuzhi (Cd-tolerant). Addition of 200 μM NAC to a culture medium containing 5 μM Cd (Cd + NAC) markedly alleviated Cd-induced growth inhibition and toxicity, maintained root cell viability, and dramatically depressed O ₂ ^·? and ·OH, and malondialdehyde accumulation, significantly reduced Cd concentration in leaves and roots, especially in the sensitive genotype Dong 17. External NAC counteracted Cd-induced alterations of certain antioxidant enzymes, e.g., brought root superoxide dismutase and glutathione reductase, leaf/root peroxidase and glutathione peroxidase activities of the both genotypes down towards the control level, but elevated Cd-stress-depressed leaf catalase in Dong 17 and root ascorbate peroxidase activities in both genotypes. NAC counteracted Cd-induced alterations in amino acids and microelement contents. Furthermore, NAC significantly reduced Cd-induced damage to leaf/root ultrastructure, e.g. the shape of chloroplasts in plants treated with Cd + NAC was relatively normal with well-structured thylakoid membranes and parallel pattern of lamellae but less osmiophilic plastoglobuli compared with Cd alone treatment; nuclei of root cells were better formed and chromatin distributed more uniformly in both genotypes. These results suggested that under Cd stress, NAC may protects barley seedlings against Cd-induced damage by directly and indirectly scavenging reactive oxygen species and by maintaining stability and integrity of the subcellular structure.     

Salt-Induced Changes in Physio-Biochemical and Antioxidant Defense System in Mustard Genotypes

Salinity stress is a major factor limiting plant growth and productivity of many crops including oilseed. The present study investigated the identification of salt tolerant mustard genotypes and better understanding the mechanism of salinity tolerance. Salt stresses significantly reduced relative water content (RWC), chlorophyll (Chl) content, K⁺ and K⁺ /Na⁺ ratio, photosynthetic rate (P_N), transpiration rate (Tr), stomatal conductance (gs), intercellular CO₂ concentration (Ci) and increased the levels of proline (Pro) and lipid peroxidation (MDA) contents, Na⁺ , superoxide (O₂^•− ) and hydrogen peroxide (H₂O₂) in both tolerant and sensitive mustard genotypes. The tolerant genotypes maintained higher Pro and lower MDA content than the salt sensitive genotypes under stress condition. The activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), glutathione peroxidase (GPX), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) were increased with increasing salinity in salt tolerant genotypes, BJ-1603, BARI Sarisha-11 and BARI Sarisha-16, but the activities were unchanged in salt sensitive genotype, BARI Sarisha-14. Besides, the increment of ascorbate peroxidase (APX) activity was higher in salt sensitive genotype as compared to tolerant ones. However, the activities of glutathione reductase (GR) and glutathione S-transferase (GST) were increased sharply at stress conditions in tolerant genotypes as compared to sensitive genotype. Higher accumulation of Pro along with improved physiological and biochemical parameters as well as reduced oxidative damage by up-regulation of antioxidant defense system are the mechanisms of salt tolerance in selected mustard genotypes, BJ-1603 and BARI Sarisha-16.     

Mercury-induced changes in growth variables and antioxidative enzyme activities in Indian mustard

Abstract

In a hydroponic system, experiments were conducted to study the effect of different levels of mercury treatments (0, 5, 10, 25 and 50 µM Hg) on Indian mustard (Brassica juncea L. Czern & Coss.) cv. Pusa Jai Kisan. Concentration-dependent inhibitory effects were observed on growth characteristics (plant dry mass, leaf area, shoot and root length). These were accompanied by an increase in shoot Hg content and in oxidative stress characteristics such as the MDA and H₂O₂ levels. The plant growth decreased maximally at 50 µM of Hg. Despite a reduction in growth, activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) were enhanced with increase in Hg-treatments. The Hg-induced alterations in growth are linked with increase in lipid peroxidation (MDA and H₂O₂), whereas the enhancement in activities of antioxidant enzymes protects plants from Hg-induced oxidative stress.     

Caffeic acid inhibits in vitro rooting in mung bean [Vigna radiata (L.) Wilczek] hypocotyls by inducing oxidative stress

Caffeic acid (CA), which is ubiquitously present in plants, is a potent phytotoxin affecting plant growth and physiology. The aim of our study was to investigate whether CA-induced inhibition of adventitious root formation (ARF) in mung bean {Vigna radiata (L.) Wilczek [Phaseolus aureus Roxb.]} involves the induction of conventional stress responses. The effect of CA (0–1000 μM) on ARF in mung bean was determined by measuring the generation of reactive oxygen species (ROS) in terms of malondialdehyde and hydrogen peroxide (H₂O₂) content, root oxidizability and changes in levels of antioxidant enzymes. Our results show that CA significantly enhanced MDA content, indicating severe lipid peroxidation, and increased H₂O₂ accumulation and root oxidizability in the lower rooted hypocotylar region (LRHR) of mung bean, thereby inducing oxidative stress and cellular damage. In response to CA, there was a significant upregulation in the activities of scavenging enzymes, such as superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase, catalase and glutathione reductase, in LRHRs of mung bean. Based on these results, we conclude that CA inhibits ARF in mung bean hypocotyls by inducing ROS-generated oxidative stress and upregulating the activities of antioxidant enzymes.     

Effects of low pH and aluminum stresses on common beans (Phaseolus vulgaris) differing in low-phosphorus and photoperiod responses

Using common beans differing greatly in the response to photoperiod and low-phosphorus (P) stress, we investigated their responses to acidity and aluminum (Al) toxicity and the relationship between Al tolerance and organic acid exudation under Al or low P stress. A genotype Ginshi was found to be sensitive to low pH treatment. When exposed to pH 4.5, serious curvature in the root tips of cv. Ginshi was observed; however, it was completely corrected by the application of 5 or 10 μmol/L AlCl₃; increasing calcium (Ca) could ameliorate Al toxicity, but it could not correct root curvature at pH 4.5. Common beans showed significant differences in both root growth and Al tolerance, and the varieties from the Andes were more tolerant to Al toxicity than those from the Mesoamerican origin. In the presence of 50 μmol/L AlCl₃, all the common bean genotypes exuded citrate, and a significant difference in the amounts of citrate was observed among genotypes. The genotypes originated in the Mesoamerica tended to release more citrate than other origins in the presence of Al. The P-inefficient genotype DOR364 exuded more citrate than the P-efficient genotype G19833 in the presence of 50 μmol/L AlCl₃, whereas no organic acids were detected in root exudates under low-P stress. A reduction of citrate exudation in the DOR364, but a slight increase of citrate exudation in the G19833, was observed under Al stress after they were exposed to 6-d P starvation. These results suggest that different low-P or Al tolerance in common beans might not be associated with organic acid exudation.     

The metal distribution and the change of physiological and biochemical process in soybean and mung bean plants under heavy metal stress

Soybean [Glycine max (Linn.) Merrill] and mung bean [Vigna radiate (Linn.) Wilczek] plants were challenged with 5 kinds of heavy metals [cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb) and mercury (Hg)] in a hydroponic system. We applied 4 different metal treatments to study the effects of heavy metals on several physiological and biochemical parameters in these species, including root length, heavy metal concentrations and allocation in different organs, superoxide dismutase, catalase, and peroxidase activities, the content of malondialdehyde (MDA), protein and chlorophyll. The data showed that the growth of the roots of soybean and mung bean was equally sensitive to external Hg concentrations. Soybean was more sensitive to external Cd concentrations, and mung bean was more sensitive to external Cr, Cu and Pb concentrations. Normal concentrations of heavy metal would not cause visible toxic symptoms, and a low level of heavy metal even slightly stimulated the growth of plants. With the rise of heavy metal concentration, heavy metal stress induces an oxidative stress response in soybean and mung bean plants, characterized by an accumulation of MDA and the alternation pattern of antioxidative enzymes. Meanwhile, the growth of plants was suppressed, the content of chlorophyll decreased and leaves showed chlorosis symptoms at high metal concentrations.     

Manganese-excess induces oxidative stress,lowers the pool of antioxidants and elevates activities of key antioxidative enzymes in rice seedlings

Manganese (Mn) is an essential element for plant growth but in excess, specially in acidic soils, it can become phytotoxic. In order to investigate whether oxidative stress is associated with the expression of Mn toxicity during early seedling establishment of rice plants, we examined the changes in the level of reactive oxygen species (ROS), oxidative stress induced an alteration in the level of non-enzymic antioxidants and activities of antioxidative enzymes in rice seedlings grown in sand cultures containing 3 and 6 mM MnCl₂. Mn treatment inhibited growth of rice seedlings, the metal increasingly accumulated in roots and shoots and caused damage to membranes. Mn treated plants showed increased generation of superoxide anion (O₂ ^.−), elevated levels of H₂O₂ and thiobarbituric acid reactive substances (TBARS) and decline in protein thiol. The level of nonprotein thiol, however, increased due to Mn treatment. A decline in contents of reduced ascorbate (AsA) and glutathione (GSH) as well as decline in ratios of their reduced to oxidize forms was observed in Mn-treated seedlings. The activities of antioxidative enzymes superoxide dismutase (SOD) and its isoforms Mn SOD, Cu/Zn SOD, Fe SOD as well as guaiacol peroxidase (GPX) increased in the seedlings due to Mn treatment however, catalase (CAT) activity increased in 10 days old seedlings but it declined by 20 days under Mn treatment. The enzymes of Halliwell-Asada cycle, ascorbate peroxidase (APX) monodehydoascorbate reductase (MDHAR), dehyroascorbate reductase (DHAR) and glutathione reductase (GR) increased significantly in Mn treated seedlings over controls. Results suggest that in rice seedlings excess Mn induces oxidative stress, imbalances the levels of antioxidants and the antioxidative enzymes SOD, GPX, APX and GR appear to play an important role in scavenging ROS and withstanding oxidative stress induced by Mn.     

Capacity to control oxidative stress-induced caspase-like activity determines the level of tolerance to salt stress in two contrasting maize genotypes

The response of two maize (Zea mays L.) genotypes, named GR (salt-tolerant) and SK (salt-sensitive), to salt stress (150 mM NaCl) was investigated under controlled environmental growth conditions. Genotype SK experienced more oxidative damage than the GR genotype when subjected to salt stress, which corresponded to higher O₂ ^? production rate and H₂O₂ content in the SK genotype than the GR genotype. Induction of caspase-like activity in response to salt stress was stronger in the SK genotype than in the GR genotype. On the other hand, induction of antioxidant enzyme activity to scavenge O₂ ^? and H₂O₂ in response to salt stress was weaker in the SK genotype than in the GR genotype. Consequently, the higher level of oxidative damage in the SK genotype in response to salt stress was manifested as more extensive cell death and biomass reduction in the SK genotype than it was in the GR genotype. Our results suggest that a direct relationship exists between salt stress-induced oxidative damage and cell death-inducing caspase-like activity, with tolerance to the salt stress being controlled by the efficiency of the plant antioxidant enzymes in limiting salt stress-induced oxidative damage and thus limiting cell death-inducing caspase-like activity.     

Aluminum-induced cell death of barley-root border cells is correlated with peroxidase- and oxalate oxidase-mediated hydrogen peroxide production

The function of root border cells (RBC) during aluminum (Al) stress and the involvement of oxalate oxidase, peroxidase and H₂O₂ generation in Al toxicity were studied in barley roots. Our results suggest that RBC effectively protect the barley root tip from Al relative to the situation in roots cultivated in hydroponics where RBC are not sustained in the area surrounding the root tip. The removal of RBC from Al-treated roots increased root growth inhibition, Al and Evans blue uptake, inhibition of RBC production, the level of dead RBC, peroxidase and oxalate oxidase activity and the production of H₂O₂. Our results suggest that even though RBC actively produce active oxygen species during Al stress, their role in the protection of root tips against Al toxicity is to chelate Al in their dead cell body.     

The Effect of Salinity Pretreatment on Cd Accumulation and Cd-Induced Stress in <Emphasis Type="Italic">BADH</Emphasis><Emphasis Type="Italic">-</Emphasis>Transgenic and Nontransgenic Rice Seedlings

The influence of betaine aldehyde dehydrogenase (BADH) and salinity pretreatment on oxidative stress under cadmium (Cd) toxicity was investigated in rice cv. Xiushui 11 and its BADH-transgenic line Bxiushui 11. The results showed that plants previously treated with 4.25 and 8.5 mM NaCl, respectively, for 5 days each had higher Cd concentrations in both roots and shoots of the two rice genotypes compared with the controls. Malondialdehyde (MDA) content in both leaves and roots was increased by salinity pretreatment and was significantly lower in the salinity-pretreatment plants than in the controls when the plants were consequently exposed to Cd stress. Salinity pretreatment also increased proline content and the activities of superoxide dismutase (SOD) and peroxidase (POD) in both leaves and roots. It can be assumed that salinity pretreatment enhances the defensive ability of plants against oxidative stress through increasing activities of antioxidative enzymes. The BADH-transgenic line (Bxiushui 11) had lower Cd and MDA content, higher SOD and POD activities, and higher proline content than its wild type (Xiushui 11). The current results suggest that betaine, a product of BADH expression, improves the tolerance of rice plants to Cd stress through increasing the activities of antioxidative enzymes and osmoprotectant content.