不同镉水平下大麦幼苗生长和镉及养分吸收的品种间差异

利用水培试验研究了不同Cd水平下大麦幼苗的Cd和几种矿质元素吸收、积累、生长和生物学产量的品种间差异 .结果表明 ,1μmol·L-1Cd处理显著降低麦苗株高、绿叶数、叶绿素计读数、地上部和根系干重 ,显著抑制植株对Zn、Mn、Cu的吸收和累积 ;品种之间存在着显著差异 ,无芒六棱受抑制最为严重 ,米麦 114和浙农 1号表现出相对较强的抗性 .麦苗Cd含量和累积量品种之间也有显著差异 ,浙农 1号的Cd含量最高 ,米麦 114最低 .相关分析表明 ,麦苗生物学产量与地上部Cd含量、累积量及根系Cd含量呈显著负相关 ,其中与地上部Cd含量的相关性最强 ,与根系Cd累积量无显著相关 .     

Allometric Effects of <Emphasis Type="Italic">Agriophyllum squarrosum</Emphasis> in Response to Soil Nutrients,Water, and Population Density in the Horqin Sandy Land of China

We monitored the allometric effects for greenhouse-grown Agriophyllum squarrosum plants in response to variations in population density and the availability of soil nutrients and water. Biomass allocations were size-dependent. The plasticity of roots, stems, leaves, and reproductive effort was “true” in response to changes in nutrient content. At a low level of soil minerals, plants allocated more resources to the development of roots and reproductive organs than to leaves, but data for stem allocations were consistent for tradeoffs between the effects of nutrients and plant size. The plasticities of leaf allocation and reproductive effort were “true” whereas those of root and stem allocations were “apparent” in response to fluctuations in soil water, being a function of plant size. Decreasing soil water content was associated with higher leaf allocation and lower reproductive effort. Except for this “apparent” plasticity of leaf allocation, none was detected with population density on biomass allocation. Architectural traits were determinants of the latter. For roots, the determining trait was the ratio of plant height to total biomass; for stems and reproduction, plant height; and for leaves, the ratio of branch numbers to plant height.     

Salicylic acid-mediated alleviation of cadmium toxicity in hemp plants in relation to cadmium uptake,photosynthesis, and antioxidant enzymes

To assess the role of salicylic acid (SA) in alleviating cadmium (Cd) toxicity in hemp (Cannabis sativa L.) plants, the growth parameters, Cd accumulation, photosynthetic performance and activities of major antioxidant enzymes were investigated in hemp seedlings treated with 500 μM SA, under 0, 25, 50, and 100 mg Cd kg⁻¹ sands (DW) conditions, respectively. Cd exposure resulted in a small reduction in biomass (12.0–26.9% for root, and 8.7–29.4% for shoot, respectively), indicating hemp plants have innate capacity to tolerant Cd stress. This was illustrated by little inhibition in photosynthetic performance, unchanged malondialdehyde content, and enhancement of superoxide dismutase (SOD) and peroxidases (POD) activities in hemp plants. Cd content in root is 25.0–29.5 times’ higher than that in shoot, suggesting the plant can be classified as a Cd excluder. It is concluded that SA pretreatment counteracted the Cd-induced inhibition in plant growth. The beneficial effects of SA in alleviating Cd toxicity can be attributed to the SA-induced reduction of Cd uptake, improvement of photosynthetic capacity, and enhancement of SOD and POD activities.     

Modulation of Exogenous Glutathione in Phytochelatins and Photosynthetic Performance Against Cd Stress in the Two Rice Genotypes Differing in Cd Tolerance

Greenhouse hydroponic experiments were conducted using Cd-sensitive (Xiushui63) and tolerant (Bing97252) rice genotypes to evaluate genotypic differences in response of photosynthesis and phytochelatins to Cd toxicity in the presence of exogenous glutathione (GSH). Plant height, chlorophyll content, net photosynthetic rate (Pn), and biomass decreased in 5 and 50 μM Cd treatments, and Cd-sensitive genotype showed more severe reduction than the tolerant one. Cadmium stress caused decrease in maximal photochemical efficiency of PSII (Fv/Fm) and effective PSII quantum yield [Y(II)] and increase in quantum yield of regulated energy dissipation [Y(NPQ)], with changes in Cd-sensitive genotype being more evident. Cadmium-induced phytochelatins (PCs), GSH, and cysteine accumulation was observed in roots of both genotypes, with markedly higher level in PCs and GSH on day 5 in Bing97252 compared with that measured in Xiushui63. Exogenous GSH significantly alleviated growth inhibition in Xiushui63 under 5 μM Cd and in both genotypes in 50 μM Cd. External GSH significantly increased chlorophyll content, Pn, Fv/Fm, and Y(II) of plants exposed to Cd, but decreased Y(NPQ) and the coefficient of non-photochemical quenching (qN). GSH addition significantly increased root GSH content in plants under Cd exposure (except day 5 of 50 μM Cd) and induced up-regulation in PCs of 5 μM-Cd-treated Bing97252 throughout the 15-day and Xiushui63 of 5-day exposure. The results suggest that genotypic difference in the tolerance to Cd stress was positively linked to the capacity in elevation of GSH and PCs, and that alleviation of Cd toxicity by GSH is related to significant improvement in chlorophyll content, photosynthetic performance, and root GSH levels.     

镉、铅及其相互作用对小白菜根系生理生态效应的研究

采用溶液培养方法,以镉,铅作为胁迫因子,研究了不同镉,铅浓度对小白菜根系生理生态的影响。实验结果表明;培养液中镉超过０．１ｍｇ／Ｌ,侧根数目减少,根的分枝程度降低,根系生物量和体积下降,根系生长发育受阻,根系不发达,根系对锰,锌的吸收受到抑制,根系活动降低,对硝酸盐吸收能力下降,蛋白质分解加快,游离氨基酸积累,氮代谢紊乱,失调。     

The effects of external potassium and magnesium concentrations on the magnesium and potassium inflow rates and growth of micropropagated cherry rootstocks, “F.12/1” (Prunus avium L.) and “Colt” (Prunus avium L.) × Prunus pseudocerasus L.)

The effects (and interaction) of two solution concentrations of Mg (50, 500, μM) and two of K (250, 4250 μM) on the growth of micropropagated plants of “F. 12/1” and “Colt” were investigated using a flowing solution culture system. Magnesium inflow and growth of “Colt” and “F. 12/1” were inhibited to a similar extent by an increased concentration of K in the nutrient solution. However, the consequences of this inhibition were different. Reduced inflow of Mg in “F. 12/1” caused Mg deficiency symptoms at high and low concentrations of K, whereas this only occurred with a combination of high K concentration and low Mg concentration in “Colt”. The distribution of dry matter within the plant was significant in determining susceptibility to Mg deficiency. Since “F. 12/1” has a smaller root:shoot ratio than Colt it is unable to sustain the same concentration of Mg in leaves as “Colt” irrespective of external K concentration. The molar ratio of K:Mg in soil solutions should remain <8.5:1 in order to ensure maximum growth of “F. 12/1” and “Colt”. This revised version was published online in June 2006 with corrections to the Cover Date.     

Influences of Arbuscular Mycorrhizal Fungus Glomus mosseae on Growth and Nutrition of Lentil Irrigated with Arsenic Contaminated Water

Arsenic (As) contamination of irrigation water represents a major constraint to Bangladesh agriculture. While arbuscular mycorrhizal (AM) fungi have their most significant effect on P uptake, they have also been shown to alleviate metal toxicity to the host plant. This study examined the effects of As and inoculation with an AM fungus, Glomus mosseae, on lentil (Lens culinaris L. cv. Titore). Plants were grown with and without AM inoculum for 9 weeks in a sand and terra green mixture 50:50 v/v and watered with five levels of As (0, 1, 2, 5, 10 mg As L⁻¹ arsenate). Inoculum of Rhizobium leguminosarum b.v. Viceae strain 3841 was applied to all plants. Plants were fed with modified Hoagland solution (1/10 N of a full-strength solution and without P). Plant height, leaf number, pod number, plant biomass and shoot and root P concentration/offtake increased significantly due to mycorrhizal infection. Plant height, leaf/ pod number, plant biomass, root length, shoot P concentration/offtake, root P offtake and mycorrhizal infection decreased significantly with increasing As concentration. However, mycorrhizal inoculation reduced As concentration in roots and shoots. This study shows that growing lentil with compatible AM inoculum can minimise As toxicity and increase growth and P uptake.     

Phenanthrene toxicity and dissipation in rhizosphere of grassland plants (Lolium perenne L. and Trifolium pratense L.) in three spiked soils

Rhizodegradation is a technique involving plants that offers interesting potential to enhance biodegradation of persistent organic pollutants such as polycyclic aromatic hydrocarbons (PAHs). Nevertheless, the behaviour of PAHs in plant rhizosphere, including micro-organisms and the physico-chemical soil properties, still needs to be clarified. The present work proposes to study the toxicity and the dissipation of phenanthrene in three artificially contaminated soils (1 g kg^-1 DW). Experiments were carried out after 2 months of soil aging. They consisted in using different systems with two plant species (Ryegrass—Lolium perenne L. var. Prana and red clover—Trifolium pratense L. var. fourragère Caillard), three kinds of soils (a silty-clay-loam soil “La Bouzule”, a coarse sandy-loam soil “Chenevières” and a fine sandy-loam soil “Maconcourt”). Phenanthrene was quantified by HPLC in the beginning (T ₀) and the end of the experiments (30 days). Plant biomass, microbial communities including mycorrhizal fungi, Rhizobium and PAH degraders were also recorded. Generally phenanthrene contamination did not affect plant biomass. Only the red clover biomass was enhanced in Chenevières and La Bouzule polluted soils. A stimulation of Rhizobium red clover colonisation was quantified in spiked soils whereas a drastic negative phenanthrene effect on the mycorrhization of ryegrass and red clover was recorded. The number of PAH degraders was stimulated by the presence of phenanthrene in all tested soils. Both in ryegrass and red clover planted soils, the highest phenanthrene dissipation due to the rhizosphere was measured in La Bouzule soils. On the contrary, in non-planted soils, La Bouzule soils had also the lowest pollutant dissipation. Thus, in rhizospheric and non-rhizospheric soils the phenanthrene dissipation was found to depend on soil clay content.     

Early taproot development of a xeric shrub (<Emphasis Type="Italic">Larrea tridentata</Emphasis>) is optimized within a narrow range of soil moisture

Effects of watering amount and frequency on root biomass accumulation and taproot elongation were examined 16–17 days post-germination in seedlings of Larrea tridentata, a dominant shrub in North American hot deserts. Two experimental variables manipulated in a full factorial design greenhouse study were (i) number of “triggering” days: consecutive days (2, 3, 4 or 5) at the start of the experiment on which seedlings received 10 mm of water per day; and (ii) “post-trigger” watering frequency: 5 mm of water either daily or every other day. We hypothesized that taproot elongation would increase with greater numbers of triggering days, whereas higher post-trigger watering frequency would enhance root biomass development. Increasing the number of triggering days from two to four promoted taproot extension without affecting root biomass, and higher watering frequency in the post-trigger phase generally increased root biomass, as expected. Contrary to expectations, root biomass and taproot length were significantly reduced when daily watering followed five consecutive triggering days. Taproot length correlated with root biomass, but irrigation regime also had a biomass-independent effect: with either two or five triggering days, taproots were shorter than expected based on root biomass. Thus, both too little and too much water stymied taproot extension. In natural settings, the adverse response of taproots to too little or too much water could reduce seedling survivorship and restrict establishment to a narrow range of environmental conditions.     

德国鸢尾对Cd胁迫的生理生态响应及积累特性

通过盆栽研究了Cd胁迫下德国鸢尾的生长状况、生态效应、生理特性及吸收和富集Cd的能力.结果表明:德国鸢尾对小于5 mg/kg的Cd有较强的耐性,适用于城区土壤修复;Cd浓度大于5 mg/kg时抑制德国鸢尾生长,降低了其生态效应.随着Cd浓度的增大,德国鸢尾根系活力、叶绿素含量和含水量逐渐降低,游离脯氨酸和可溶性糖含量先升高后降低,细胞膜透性逐渐升高.Cd在德国鸢尾体内分布为根系＞地上部分,随着Cd浓度的增大,德国鸢尾根系和地上部分Cd积累浓度逐渐升高、富集系数和转运系数逐渐降低;Cd浓度为20 mg/kg时德国鸢尾对Cd的积累量最大,为2.122 mg/plant.     

丛枝菌根真菌对砂培玉米幼苗根系特征、光合生理与镉累积的影响

【背景】丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)是一类重要的土壤微生物,能显著影响植物对镉(cadmium,Cd)的耐性与累积,但其对不同形态Cd胁迫的响应尚不清楚。【目的】探讨不同形态Cd胁迫下接种AMF对玉米(Zea mays L.)生长和Cd累积的影响。【方法】采用30 cm高的培养容器填装石英砂(0.2 mm),开展室内砂培玉米试验,研究溶解态和胶体态Cd (1 mg/kg)胁迫下,接种摩西斗管囊霉(Funneliformis mosseae)对玉米幼苗生长、根系特征、光合生理及Cd累积的影响。【结果】双因素分析表明,AMF和Cd形态均对玉米生长(株高和生物量)、根系特征、光合生理(叶绿素含量和光合速率)与Cd累积量存在显著的影响,但二者之间没有显著交互作用。与未接种处理相比,接种AMF显著降低玉米株高、生物量、叶片叶绿素含量和光合速率,抑制玉米根长、根表面积、根体积和根尖数;同时增加了玉米根系Cd含量,但减少玉米地上部Cd含量以及地上部与根系Cd累积量;与胶体态Cd处理相比,溶解态Cd显著降低玉米的根长、根表面积、平均根系直径、根尖数和地上部Cd累积量,但增加了植株叶片光合速率、根系Cd含量和累积量。相关分析发现,玉米根长、根表面积和根尖数与地上部Cd含量呈显著或极显著正相关,与根系Cd含量呈极显著负相关。【结论】溶解态Cd比胶体态Cd对砂培玉米幼苗的毒害效应严重,而且接种AMF加重溶解态和胶体态Cd对玉米幼苗的损伤,但降低了植株对Cd的累积。     

Tissue partitioning of cadmium in transgenic tobacco seedlings and field grown plants expressing the mouse metallothionein I gene

Since agricultural crops contribute >70% of human cadmium (Cd) intake, modification of crops to reduce accumulation of this pollutant metal during plant growth is desirable. Here we describe Cd accumulation characteristics of seedlings and field grown tobacco plants expressing the Cd-chelating protein, mouse metallothionein I. The objective of the transformation is to entrap Cd in roots as Cd-metallothionein and thereby reduce its accumulation in the shoot. Transformed and control seedlings were exposed for 15 days in liquid culture at a field soil-solution-like Cd concentration of 0.02 μm. Transformed seedlings ofNicotiana tabacum cultivar KY 14 contained about 24% lower Cd concentration in shoots and about 5% higher Cd concentration in roots than control seedlings. Dry weights of transformed and control tissues did not differ significantly. In the field in 1990, mature transformedN. tabacum cv. KY 14 plants exposed only to endogenous soil Cd contained about 14% lower leaf lamina Cd concentration than did controls. Differences were significant at thep≤0.1 level in 13 of 16 leaf positions. Leaf dry weight did not differ significantly but transformed field plants had 12% fewer leaves and were 9% shorter than the controls. Copper (Cu) concentration was significantly higher (ca10%) in the bottom nine leaf positions of transformed plants suggesting that reduced leaf number and plant height may be due to Cu deficiency or toxicity. Alternatively, somaclonal variation or gene position effects may be involved. No differences were found in zinc levels. WithN. tabacum cv. Petit Havana, transformed seedlings contained no less Cd in shoots but 48% higher Cd concentration in roots. However, dry weights of shoots and roots of transformed seedlings were 25% and 26%, respectively, greater than in controls. In the field, transformed and control plants of this cultivar showed little significant differences in leaf Cd content, plant height or leaf number. Although comparison of additional metallothionein-expressing tobaccos and other plants is needed, results obtained with cultivar KY 14 support the hypothesis that sequestration of Cd in roots as Cd-metallothionein may have potential for reducing Cd content of above root tissues of certain plants.     

Application of sulfur fertilizer reduces cadmium accumulation and toxicity in tobacco seedlings (<Emphasis Type="Italic">Nicotiana tabacum</Emphasis>)

Greenhouse pot experiments were carried out to illuminate the mitigation effects of sulfur (S) on cadmium (Cd) uptake and toxicity in tobacco using two levels of exogenous sulfur of S1 and S2 containing 47 and 38% total S. Results showed that Cd1 and Cd2 treatments of 1 and 5 mg Cd kg^?1 soil increased leaf Cd concentration and accumulation but reduced plant height, net photosynthetic rate (Pn) and biomass, with a much severe response in Cd2 treatment. Application of S2 fertilizer alleviates Cd toxicity, markedly decreased Cd concentration and improved photosynthesis, compared with Cd1 and Cd2 alone treatment; but S1 only alleviated Cd toxicity when tobacco was subjected to Cd1 stress. Our results suggest that S2 fertilizer was more effective in reducing Cd accumulation and toxicity in Tobacco than S1, and highlights a promising approach of S fertilizer application to lower leaf Cd accumulation in order to ensure product safety of tobacco grown in Cd polluted soils.     

Exogenous nitric oxide enhances cadmium tolerance of rice by increasing pectin and hemicellulose contents in root cell wall

To study the mechanisms of exogenous NO contribution to alleviate the cadmium (Cd) toxicity in rice (Oryza sativa), rice plantlets subjected to 0.2-mM CdCl₂ exposure were treated with different concentrations of sodium nitroprusside (SNP, a NO donor), and Cd toxicity was evaluated by the decreases in plant length, biomass production and chlorophyll content. The results indicated that 0.1 mM SNP alleviated Cd toxicity most obviously. Atomic absorption spectrometry and fluorescence localization showed that treatment with 0.1 mM SNP decreased Cd accumulation in both cell walls and soluble fraction of leaves, although treatment with 0.1 mM SNP increased Cd accumulation in the cell wall of rice roots obviously. Treatment with 0.1 mM SNP in nutrient solution had little effect on the transpiration rate of rice leaves, but this treatment increased pectin and hemicellulose content and decreased cellulose content significantly in the cell walls of rice roots. Based on these results, we conclude that decreased distribution of Cd in the soluble fraction of leaves and roots and increased distribution of Cd in the cell walls of roots are responsible for the NO-induced increase of Cd tolerance in rice. It seems that exogenous NO enhances Cd tolerance of rice by increasing pectin and hemicellulose content in the cell wall of roots, increasing Cd accumulation in root cell wall and decreasing Cd accumulation in soluble fraction of leaves.     

Hairy root type plant in vitro systems as sources of bioactive substances

“Hairy root” systems, obtained by transforming plant tissues with the “natural genetic engineer” Agrobacterium rhizogenes, have been known for more than three decades. To date, hairy root cultures have been obtained from more than 100 plant species, including several endangered medicinal plants, affording opportunities to produce important phytochemicals and proteins in eco-friendly conditions. Diverse strategies can be applied to improve the yields of desired metabolites and to produce recombinant proteins. Furthermore, recent advances in bioreactor design and construction allow hairy root-based technologies to be scaled up while maintaining their biosynthetic potential. This review highlights recent progress in the field and outlines future prospects for exploiting the potential utility of hairy root cultures as “chemical factories” for producing bioactive substances.     

Podophyllotoxin content in <Emphasis Type="Italic">Podophyllum hexandrum</Emphasis> Royle plants of known age of seed origin and grown at a lower altitude

Podophyllum hexandrum Royle, an important alpine herb, and a source of the highly valued aryltetralin-type lignan, podophyllotoxin, has been subjected to heavy collection from the wild due to ever increasing demand. The present study deals with an attempt to bring this plant under cultivation at a relatively lower altitude and to evaluate (1) various growth parameters including above and below ground biomass accumulation, net assimilation rate and relative growth rate, etc., and (2) podophyllotoxin content from the resulting above and below ground biomass in seed raised plants of a known age series of 1–5 years. The podophyllotoxin content was estimated on the basis of HPLC analyses. The levels were found to increase with the plant age and the maximum amount was found in 5-year old plants. This study demonstrates that (1) seeds can be conveniently used for raising healthy propagules in easily approachable locations at a relatively lower altitude, and that the plants can be maintained in such sites over long periods, and (2) this approach of “conservation through cultivation” can be suggested as an effective tool for the management of this “critically endangered status” species.     

Iron nutrition affects cadmium accumulation and toxicity in rice plants

The effect of iron (Fe) nutrition on cadmium (Cd) toxicity and accumulation in rice plants was studied using a hydroponic system. The inhibitory effect of Cd on plant growth and chlorophyll content (SPAD value) was dependent on Fe level and the genotype. Malondialdehyde (MDA) content in leaves and roots was not much affected by an increased Cd stress at 0.171 mg l⁻¹ Fe, but it showed a rapid increase when the plants were exposed to moderate (1.89 mg l⁻¹) and high (16.8 mg l⁻¹) Fe levels. High Fe nutrition caused a marked reduction in Cd content in both leaves and roots. Fe content in plants was lower at high Cd (5.0 μM) stress than at low Cd (<1.0 μM) stress. Cd stress increased both superoxide dismutase (SOD) and peroxidase (POD) activities at low and moderate Fe levels. However, with high Fe level, it increased the POD activity, but reduced the SOD activity. Our results substantiate the hypothesis that cell membrane-bound iron transporter (carrier) involved in high-affinity iron transport systems can also transport Cd, and both these ions may compete for this common carrier. The study further showed that there were significant correlations between MDA and Fe contents in leaves and roots of rice plants. It is suggested that the occurrence of oxidative stress in plants exposed to Cd stress is mediated by Fe nutrition. The present results also show that Cd stress affects the uptake of Cu and Zn.     

Indian rice “Kasalath” contains genes that improve traits of Japanese premium rice “Koshihikari”

Rice (Oryza sativa L.) chromosome segment substitution lines (CSSLs), in which chromosomal segments of the Indian landrace “Kasalath” replace the corresponding endogenous segments in the genome of the Japanese premium rice “Koshihikari”, are available and together cover the entire genome. Chromosome regions affecting a trait (CRATs) can be identified by comparison of phenotypes with genotypes of CSSLs. We detected 99 CRATs for 15 agronomic or morphological traits. “Kasalath” had positively acting alleles in 53 CRATs. Its CRATs increased panicle number per plant by up to 23.3%, grain number per panicle by up to 30.8%, and total grain number by up to 15.1%, relative to “Koshihikari”. CRATs were identified for grain size (grain thickness and width), with positive effects of about 5.0%. A CRAT on chromosome 8 almost doubled the weight of roots in uppermost soil layers compared to “Koshihikari”. Additionally, “Kasalath” possessed CRATs for higher lodging resistance (reduction in plant height and increase in stem diameter). In some cases, multiple CRATs were detected in the same chromosome regions. Therefore, CSSLs with these chromosome segments might be useful breeding materials for the simultaneous improvement of multiple traits. Five CRATs, one for plant height on chromosome 1, one for stem diameter on chromosome 8, and three for heading date on chromosomes 6, 7, and 8 overlapped with the corresponding QTLs that already had been mapped with back-crossed inbred lines of “Nipponbare” and “Kasalath”. In both “Koshihikari” CRATs and “Nipponbare” QTLs, “Kasalath” had similar effects. Both Y. Madoka and T. Kashiwagi have contributed equally to this article.     

Glutathione in adaptation of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> to cadmium stress

The role of glutathione (GSH) in the adaptation of wild type Arabidopsis thaliana plants to Cd stress was investigated. The nutrient solution (control or containing 50 or 100 μM Cd) was supplemented with buthionine sulfoximine (BSO; 50, 100, 500 μM, to decrease the GSH content in plants) or GSH (50, 100, 500 μM, to increase its content in plants) in order to find how GSH content could regulate Cd stress responses. BSO application did not influence plant biomass, while exogenous GSH (especially 500 μM) reduced root biomass. BSO (500μM) in combination with Cd (100 μM) increased Cd toxicity on root growth (by over 50 %), most probably due to reduced GSH content and phytochelatin (PC) accumulation (by over 96 %). On the other hand, combination of exogenous GSH (500 μM) with Cd (100 μM) was also more toxic to plants than Cd alone despite a significant increase in GSH and PC accumulation (up to 2.7 fold in the roots). This fact could indicate that the natural content of endogenous GSH in wild type A. thaliana plants is sufficient for Cd-tolerance. A decrease in this GSH content led to decreased Cd-tolerance of the plants but an increase in GSH content did not enhance Cd-tolerance, and it showed even toxic effect on the plants.     

Contributions of apoplasmic cadmium accumulation,antioxidative enzymes and induction of phytochelatins in cadmium tolerance of the cadmium-accumulating cultivar of black oat (<Emphasis Type="Italic">Avena strigosa</Emphasis> Schreb.)

The contributions of cadmium (Cd) accumulation in cell walls, antioxidative enzymes and induction of phytochelatins (PCs) to Cd tolerance were investigated in two distinctive genotypes of black oat (Avena strigosa Schreb.). One cultivar of black oat ‘New oat’ accumulated Cd in the leaves at the highest concentration compared to another black oat cultivar ‘Soil saver’ and other major graminaceous crops. The shoot:root Cd ratio also demonstrated that ‘New oat’ was the high Cd-accumulating cultivar, whereas ‘Soil saver’ was the low Cd-accumulating cultivar. Varied levels of Cd exposure demonstrated the strong Cd tolerance of ‘New oat’. By contrast, low Cd-accumulating cultivar ‘Soil saver’ suffered Cd toxicity such as growth defects and increased lipid peroxidation, even though it accumulated less Cd in shoots than ‘New oat’. Higher activities of ascorbate peroxidase (EC 1.11.1.11) and superoxide dismutase (EC 1. 15. 1. 1) were observed in the leaves of ‘New oat’ than in ‘Soil saver’. No advantage of ‘New oat’ in PCs induction was observed in comparison to Cd-sensitive cultivar ‘Soil saver’, although Cd exposure increased the concentration of total PCs in both cultivars. Higher and increased Cd accumulation in cell wall fraction was observed in shoots of ‘New oat’. On the other hand, in ‘Soil saver’, apoplasmic Cd accumulation showed saturation under higher Cd exposure. Overall, the present results suggest that cell wall Cd accumulation and antioxidative activities function in the tolerance against Cd stress possibly in combination with vacuolar Cd compartmentation.