Enhancing phytoremediative ability of Pisum sativum by EDTA application

The aim of our research was to demonstrate how the presence of EDTA affects resistance of pea plants to Pb and Pb-EDTA presence, and to show the effectivity of lead ions accumulation and translocation. It was determined that EDTA not only increased the amount of Pb taken up by plants but also Pb ion transport through the xylem and metal translocation from roots to stems and leaves. It can be seen in the presented research results that addition of the chelator with Pb limited metal phytotoxicity. We also demonstrated a significant effect of EDTA not only on Pb accumulation and metal transport to the aboveground parts but also on the profile and amount of thiol compounds: glutathione (GSH), homoglutathione (hGSH) or phytochelatins (PCs), synthesized by the plants. We observed a significant effect of the synthetic chelator on increasing the level of Pb accumulation in roots of plants treated with Pb including EDTA (0.5 and 1 mM). Pisum sativum plants treated only with 1 mM Pb(NO3)2 accumulated over 50 mg Pb x g(-1) dry wt during 4 days of cultivation. Whereas in roots of pea plants exposed to Pb+0.5 mM EDTA 35% more Pb was observed. When 1 mM EDTA was applied roots of pea accumulated over 67% more metal. The presence of EDTA also increased metal uptake and transport to the aboveground parts. In pea plants treated only with 1 mM lead nitrate less than 3 mg Pb x g(-1) dry wt was transported, whereas in P. sativum treated with Pb-EDTA doubled amount of Pb was observed in stems and leaves.     

Toxicity of arsenic (III) and (V) on plant growth, element uptake, and total amylolytic activity of mesquite (Prosopis juliflora x P. velutina)

The effects of arsenite [As(III)] and arsenate [As(V)] on the growth of roots, stems, and leaves and the uptake of arsenic (As), micro- and macronutrients, and total amylolytic activity were investigated to elucidate the phytotoxicity of As to the mesquite plant (Prosopis juliflora x P. velutina). The plant growth was evaluated by measuring the root and shoot length, and the element uptake was determined using inductively coupled plasma optical emission spectroscopy. The root and leaf elongation decreased significantly with increasing As(III) and As(V) concentrations; whereas, stem elongation remained unchanged. The As uptake increased with increasing As(III) or As(V) concentrations in the medium. Plants treated with 50 mg/L As(III) accumulated up to 920 mg/kg dry weight (d wt) in roots and 522 mg/kg d wt in leaves, while plants exposed to 50 mg/L As(V) accumulated 1980 and 210 mg/kg d wt in roots and leaves, respectively. Increasing the As(V) concentration up to 20 mg/L resulted in a decrease in the total amylolytic activity. On the contrary, total amylolytic activity in As(III)-treated plants increased with increasing As concentration up to 20 mg/L. The macro- and micronutrient concentrations changed in As-treated plants. In shoots, Mo and K were reduced but Ca was increased, while in roots Fe and Ca were increased but K was reduced. These changes reduced the size of the plants, mainly in the As(III)-treated plants; however, there were no visible sign of As toxicity.     

Accumulation, speciation, and coordination of arsenic in an inbred line and a wild type cultivar of the desert plant species Chilopsis linearis (Desert willow)

This study investigated the absorption of arsenic (As), sulfur (S), and phosphorus (P) in the desert plant Chilopsis linearis (Desert willow). A comparison between an inbred line (red flowered) and wild type (white flowered) plants was performed to look for differential responses to As treatment. One month old seedlings were treated for 7 days with arsenate (As₂O₅, As^V) at 0, 20, and 40 mg As^V L⁻¹. Results from the ICP-OES analysis showed that at 20 mg As^V L⁻¹, red flowered plants had 280 ± 11 and 98 ± 7 mg As kg⁻¹ dry wt in roots and stems, respectively, while white flowered plants had 196 ± 30 and 103 ± 13 mg As kg⁻¹ dry wt for roots and stems. At this treatment level, the concentration of As in leaves was below detection limits for both plants. In red flowered plants treated with 40 mg As^V L⁻¹, As was at 290 ± 77 and 151 ± 60 mg As kg⁻¹ in roots and stems, respectively, and not detected in leaves, whereas white flowered plants had 406 ± 36, 213 ± 12, and 177 ± 40 mg As kg⁻¹ in roots, stems, and leaves. The concentration of S increased in all As treated plants, while the concentration of P decreased in roots and stems of both types of plants and in leaves of red flowered plants. X-ray absorption spectroscopy analyses demonstrated partial reduction of arsenate to arsenite in the form of As-(SX)₃ species in both types of plants.     

Effect of mercury and gold on growth,nutrient uptake,and anatomical changes in Chilopsis linearis

Plants of Chilopsis linearis were grown with 0, 50, 100, and 200 μM Hg [as Hg(CH₃COO)₂] and 0 and 50 μM Au (as KAuCl₄) in hydroponics. The results showed that seedling grown with 50 μM Au + 50 μM Hg and 50 μM Au + 100 μM Hg had roots 25 and 55% shorter than control roots, respectively. The element uptake determination using ICP/OES demonstrated that Hg at 50 and 100 μM (with and without Au) significantly increased (p < 0.05) the S concentration in leaves. On the other hand, the concentration of Fe significantly increased in roots of plants treated with Au–Hg. In addition, the stems of plants treated with Hg at 100 μM, with and without Au, had 239 and 876 mg Hg/kg dry biomass (d wt), respectively. Also, at 50 μM Hg, with and without Au, stems accumulated 375 and 475 mg Hg/kg d wt. The Hg concentration in leaves (287 mg Hg/kg d wt) was higher (p < 0.05) for the treatment containing 50 μM Au + 100 μM Hg. Without Au, the Hg concentration in leaves decreased to 75 mg Hg/kg d wt. Toxicity symptoms induced by Hg in cortex cells and the vascular system were lower in plants exposed to 50 μM Au + 50 μM Hg compared to plants exposed to 50 μM Hg only. Further, the SEM micrographs revealed deposition of Au–Hg particles inside the root. Although the concentrations of Hg used in this study showed different degree of toxicity, the plants displayed good agronomic value.     

The effect of nitrogen nutrition on cluster root formation and proton extrusion by Lupinus albus

Nitrogen nutrition can influence cluster root formation in many wild species, but the effect of N form on cluster root formation and root exudation by white lupin is not known. In a solution culture study, we examined the effect of N nutrition (ammonium, nitrate, both or N2 fixation) on cluster root formation and H+ extrusion by white lupin plants under deficient and adequate P supply. The number of cluster roots increased greatly when plants were supplied with I microM P compared with 50 microM P, the increase being 7.8-fold for plants treated with (NH4)2SO4, 3-fold for plants treated with KNO3 and NH4NO3, and 2-4-fold for N2-fixing plants. Under P deficiency. NH4+-N supply resulted in production of a greater number and biomass of cluster roots than other N sources. Dry weight of cluster roots was 30 % higher than that of non-cluster roots in P-deficient plants treated with (NH4)2SO4 and NH4NO3. In plants treated with sufficient P (50 microM), the weight of non-cluster roots was approx. 90 % greater than that of cluster roots. Both total (micromol per plant h(-1)) and specific (micromol g(-1) root d. wt h(-1)) H+ extrusions were greatest from roots of plants supplied with (NH4)2SO4, followed by those supplied with NH4NO3 and N2 fixation, whereas plants receiving KNO3 had negative net H+ extrusion between the third and fifth week of growth (indicating uptake of protons or release of OH- ions). The rate of proton extrusion by NH4+-N-fed plants was similar under P-deficient and P-sufficient conditions. In contrast, proton exudation by N2-fixing plants and KNO3-treated plants was ten-fold greater under P deficiency than under P sufficiency. In comparison with P deficiency, plants treated with 50 microM P had a significantly higher concentration of P in roots, shoots and youngest expanded leaves (YEL). Compared with the N2 fixation and KNO3 treatments, total N concentration was highest in roots, shoots and YEL of plants supplied with (NH4)2SO4 and NH4NO3, regardless of P supply. Under P deficiency, K concentrations in roots decreased at all N supplies, especially in plants treated with (NH4)2SO4 and NH4NO3, which coincided with the greatest H+ extrusion at these P and N supplies. In conclusion, NH4-N nutrition stimulated cluster root formation and H+ extrusion by roots of P-deficient white lupin.     

Biomass allocation is an important determinant of the tannin concentration in growing plants

BACKGROUND AND AIMS: Condensed tannins (CTs) in the diet affect consumers in a concentration-dependent manner. Because of their importance in plant defence against herbivores and pathogens as well as their potential application against gastrointestinal parasites of ruminants in agronomy, an understanding of the seasonal dynamics of CT concentrations during plant growth is essential. METHODS: Over a vegetation period, CT concentrations in leaves, stems and roots and the biomass proportions between these organs were investigated in Onobrychis viciifolia, Lotus corniculatus and Cichorium intybus. Based on the experimental data, a model has been suggested to predict CT concentrations in harvestable biomass of these species. KEY RESULTS: During the experiment, leaf mass fractions of plants decreased from 85, 64, 85 to 30, 18, 39 % d. wt in Onobrychis, Lotus and Cichorium, respectively, and proportions of stems and roots increased accordingly. While CT concentrations almost doubled in leaves in Onobrychis (from 52 to 86 mg g(-1) d. wt, P<0.001) and Lotus (from 25 to 54 mg g(-1) d. wt, P<0.001), they were stable at low levels in expanding leaves of Cichorium (5 mg g(-1) d. wt) and in stems and roots of all investigated species. Due to an inverse effect of the increasing CT concentrations in leaves and simultaneous dilution from increasing proportions of 'CT-poor' stems, CT concentrations in harvestable biomass were stable over time in all investigated species: 62, 26 and 5 mg g(-1) d. wt for Onobrychis, Lotus and Cichorium, respectively. CONCLUSIONS: As a consequence of the unequal distribution of tannins in different plant parts and due to the changing biomass proportions between them, various herbivores (e.g. a leaf-eating insect and a grazing ruminant) may find not only different concentrations of CT in their diets but also different CT dynamics during the season. For the prediction of seasonal variations of CT concentrations, biomass allocation and accumulation of none-CT plant material are likely to be as important predictors as the knowledge of CT synthesis and its regulation.     

Nitric oxide potentiates oligosaccharide-induced artemisinin production in Artemisia annua hairy roots

The purpose of the present study was to characterize the generation of nitric oxide （NO） in Artemisia annua roots induced by an oligosaccharide elicitor （OE） from Fusarium oxysporum mycelium and the potentiation role of NO in the elicitation of artemisinin accumulation. The OE （0.3 mg total sugar/mL） induced a rapid production of NO in cultures, which exhibited a biphasic time course, reaching the first plateau within 1.5 h and the second within 8 h of OE treatment. Artemisinin content in 20-day-old hairy roots was increased from 0.7mg/g dry wt to 1.3 mg/g dry wt by using the OE treatment for 4d. In the absence of OE, the NO donor sodium nitroprusside （SNP） at 10, 50 ~1 and 100 ~1 enhanced the growth of hairy roots, but had no effect on artemisinin synthesis, The combination of SNP with OE increased artemisinin content from 1.2 mg/g drywt to 2.2 mg/g dry wt, whereas the maximum production of artemisinin in cultures was 28.5 mg/L, a twofold increase over the OE treatment alone. The effects of SNP on the OE-induced artemisinin were suppressed strongly by the NO scavenger 2-（4- carboxyphenyl）-4,4,5,5-tetramethylimidazoline-l-oxyl-3-oxide （cPTIO）. The results suggest that NO can strongly potentiate elicitor-induced artemisinin synthesis in A. annua hairy roots.     

N,beta-D-Glucopyranosyl vincosamide, a light regulated indole alkaloid from the shoots of Psychotria leiocarpa

From leaves of Psychotria leiocarpa, an indole alkaloid was isolated to which the structure N,beta-D-glucopyranosyl vincosamide (1) was assigned. This represents the first report of an N-glycosylated monoterpenoid indole alkaloid. In field-grown plants highest amounts of 1 were found in the leaves (2.5% of dry wt) and fruit pulp (1.5% dry wt). Lower amounts were found in the stems (0.2% dry wt) and the seeds (0.1% of dry wt), whereas the alkaloid was not detected in the roots. The accumulation of 1 in aseptic seedlings was also restricted to the shoots and increased with plant age and light exposure, independent of the supply of sucrose in the culture medium.     

Use of synchrotron- and plasma-based spectroscopic techniques to determine the uptake and biotransformation of chromium(III) and chromium(VI) by Parkinsonia aculeata

In this study, a combination of inductively coupled plasma optical emission spectroscopy and X-ray absorption spectroscopy (XAS) was used to study the uptake and speciation of chromium in Parkinsonia aculeata, commonly known as Mexican Palo Verde. Plants were treated for 14 days in a modified Hoagland solution containing chromium(III) or chromium(VI) at several concentrations. The results showed that plants treated with 70 mg Cr(III) L(-1) and 30 mg Cr(VI) L(-1) had similar Cr concentrations in leaves (～200 mg kg(-1) dry weight, DW). The results also showed that neither Cr(III) nor Cr(VI) affected the uptake of phosphorus and sulfur. However, the concentration of calcium in the stems of plants treated with Cr(VI) at 40 mg L(-1) (about 6000 mg Ca kg(-1) DW) was significantly higher compared to the Ca concentration (about 3000 mg kg(-1) DW) found in the stems of plants treated with 150 mg Cr(III) L(-1). However, no differences were observed in potassium and magnesium concentrations. The iron concentration (about 1000 mg kg(-1) DW) in roots treated with 40 mg Cr(VI) L(-1) was similar to the iron concentration found in the roots of plants treated with 110 mg Cr(III) L(-1). The XAS data showed that Cr(VI) was reduced to Cr(III) in/on the plant roots and transported as Cr(III) to the stems and leaves. The XAS studies also showed that Cr(III) within plants was present as an octahedral complex.     

Adventitious root growth and ginsenoside accumulation in Panax ginseng cultures as affected by methyl jasmonate

Adventitious roots of ginseng were treated with methyl jasmonate (MJ) up to 150 microM and cultured for 40 days. Up to 100 microM MJ inhibited the root growth but increase ginsenoside accumulation. In a two-stage bioreactor culture, total ginsenosides, after elicitation with 100 microM MJ peaked after 10 days at 48 mg g(-1) dry wt and then dropped sharply. Of the two groups of ginsenosides (Rb and Rg), higher amounts of Rb accumulated in the adventitious roots.     

Mepiquat chloride seed treatment and germination temperature effects on cotton growth, nutrient partitioning, and water use efficiency

Cotton seed (Gossypium hirsutum L. cv. Stoneville 825), treated with 0, 0.2, 1.0, and 2.0 g active ingredient (a.i.) mepiquat chloride (MC) kg^–1, was evaluated for the effect of MC on early plant growth. Emergence rate and total emergence of MC-treated seed and control were similar regardless of germination temperature. However, the number of leaves and squares and the dry weight of leaves, stems, and roots for hydroponically grown cotton plants were significantly lower at lower germination temperatures (15°C for 3 day/30°C for 1 day and 15°C for 4 days) than at higher germination temperatures (30°C for 4 days and 30°C for 3 days/15°C for 1 day). All MC treatments significantly decreased the number of nodes, leaves, and squares, as well as dry weight of leaves, stems, and roots, as compared to control plants at 28 days after emergence. MC seed treatments also significantly reduced plant height and total leaf area compared to controls. Water-use efficiency (WUE) was significantly lower for the 1.0 g a.i. MC treatment than for control plants. In general, the highest rate of MC seed treatment resulted in greater concentrations of calcium, phosphorus, and nitrogen in plant leaves and stems and also in greater concentrations of magnesium, phosphorus, and nitrogen in roots than in controls.     

Application of sodium selenate to cowpea (Vigna unguiculata L.) increases shoot and grain Se partitioning with strong genotypic interactions

BackgorundCowpea is a crop widely used in developing countries due its rusticity. Besides its rich genotypic variability, most breeding programs do not explore its potential to improve elements uptake. Selenium (Se) is a scarce element in most soils, resulting in its deficiency being common in human diets. This study aimed to evaluate the interaction between biofortification with Se and genotypic variation in cowpea, on the concentrations of Se in roots, leaves + stem and grains.MethodsTwenty-nine cowpea genotypes were grown in a greenhouse in the absence (control) and presence of Se (12.5 μg Se kg⁻¹ soil) as sodium selenate, in fully randomized scheme. The plants were cultivated until grains harvest. The following variables were determined: roots dry weight (g), leaves + stems dry weight (g), grains dry weight (g), Se concentration (mg kg⁻¹) in roots, leaves + stems and grains, and Se partitioning to shoots and grains.ResultsSelenium application increased the Se concentration in roots, leaves + stems and grains in all genotypes. At least twofold variation in grain Se concentration was observed among genotypes. Selenium application did not impair biomass accumulation, including grain dry weight. Genotype “BRS Guariba” had the largest Se concentration in grains and leaves + stems. Genotype MNC04-795 F-158 had the largest partitioning of Se to shoots and grain, due to elevated dry weights of leaves + stems and grain, and high Se concentrations in these tissues.ConclusionThis information might be valuable in future breeding programs to select for genotypes with better abilities to accumulate Se in grain to reduce widespread human Se undernutrition.     

Morphological and anatomical variations ofCajanus cajan (Linn.) huth raised in cadmium-rich soil

Different concentrations of cadmium in the growing media affected morphological parameters ofCajanus cajan. Over time, the amount of increase in shoot and root lengths, number of branches and leaves per plant, single and total leaf areas, and dry mass of leaves, was significantly lower for treated plants compared with controls. The root-shoot length ratio, which varied little over time, was relatively low for the treated plants. Although dry mass of both stems and roots increased, the rates were considerably low under Cd stress. The root-shoot dry mass ratio in the controls was highest during flowering and lowest in the post-flowering stage, but continually declined over time for the stressed plants. Compared with the controls, treated plants had fewer pods, with the number decreasing as the Cd concentration increased. Cd content was greater in roots than in stems or leaves, and leaves had greater amounts than did stems at higher doses. For all plants, the width and density of vessel elements and the length of fibers in the wood of stems and roots increased with plant age. However, the rate of increase was generally lower in the treated plants, the difference being more pronounced with higher doses of Cd. This indicated a reduced ascent of sap and, hence, less available water for tissues in treated plants.     

Changes in chemical composition of hydrophyte leaves during adaptation to aquatic environment

Leaf chemical composition of 19 hydrophytes was studied. The content of carbon, nitrogen, nonstructural carbohydrates, organic acids, minerals, and water was determined. Hydrophytes were shown to contain less carbon (below 410 mg/g dry wt in 60% species) than terrestrial plants. Hydrophytes and terrestrial plants did not differ in the nitrogen concentration in the leaves (33 and 29 mg/g dry wt, respectively). Hydrophytes were characterized by a low content of organic acids (40–90 mg/g dry wt in 60% species) and high content of mineral compounds (90–170 mg/g dry wt in 50% species). Total amount of nonstructural carbohydrates was similar in the leaves of hydrophytes and terrestrial plants (from 120 to 190 mg/g dry wt), but the proportions of various carbohydrate fractions differed substantially. In the hydrophyte leaves, the content of soluble carbohydrates was 2.4-fold lower, whereas the content of nonstructural polysaccharides 1.2-fold higher than in terrestrial plant leaves. Two groups of correlations between parameters of leaf chemical composition were distinguished: the contents of carbon, nitrogen, and soluble sugars were positively correlated, and the negative correlation was observed between these parameters and the amounts of mineral compounds, organic acids, water, and nonstructural polysaccharides. We concluded that hydrophyte leaf chemical composition reflects a specificity of plant adaptation to aquatic environment.     

重金属镉在番茄及其害虫西花蓟马中的积累与传递

重金属镉(Cd)是农田土壤中的重要污染源,可在植物和植食性昆虫中积累与传递。本文采用水培法,研究了不同浓度的Cd在番茄Solanum lycopersicum不同组织和在其重要害虫西花蓟马Frankliniella occidentalis体内的积累量。结果表明,随着水培营养液中Cd浓度的增加,番茄植株的根、茎和叶中Cd含量呈增长趋势。根中Cd的积累量远高于茎和叶,当水培溶液中Cd含量为20 mg/L时,根、茎和叶中的积累量分别达19 333.67±233.38、122.67±6.84和147.33±2.96 mg/Kg(干重)。随着Cd浓度的增加,番茄根、茎和叶的鲜重和干重均显著下降。西花蓟马取食Cd处理的番茄叶片后,体内Cd显著积累,最高达1.95±0.36 mg/Kg。同时,Cd积累量的提高进一步影响了以番茄叶片为食的西花蓟马的适合度,降低了其存活率。除对照外,番茄茎-叶的转移系数和叶片对Cd的富集系数均大于1,叶片表现出较强的富集能力。而在所有的试验浓度处理中,西花蓟马对Cd的富集系数和转移系数均小于1,表明Cd未在其体内产生生物放大作用。研究结果明确了Cd在番茄各组织及其害虫中的积累和传递水平,为揭示重金属在农业生态系统食物链中的富集效应提供了基础数据。     

卡拉麦里南部工业区梭梭和琵琶柴重金属空间分布及污染评价

对五彩湾工业区周边21个采样点的梭梭(Hadoxylon)和琵琶柴(Reaummuria soongorica)的Zn、Cu、Cr、Pb、As、Hg 6种重金属元素含量测定,运用统计学方法和地统计插值法分析其茎叶和根部重金属含量变化情况和空间分布特征,并综合评价其污染程度和潜在生态危害性。结果表明:梭梭和琵琶柴植株Hg含量的最大值和均值都超出新疆土壤背景值0.017 mg/kg,除梭梭根部的均值0.060 mg/kg未超出国家土壤背景值0.065 mg/kg,在二者其他部位的最大值和均值都已超出;琵琶柴整株中Cr最大值72.62 mg/kg和Zn最大值97.61 mg/kg均超出新疆土壤背景值49.3 mg/kg和国家土壤背景值61 mg/kg,Pb元素未被检出。插值精度方面,Hg、As的RMSE较小,分别为0.263和0.443,预测模型中Hg的R~2为0.72,Cu的R~2为0.67,能较好地估计预测样点的重金属含量,Zn的R~2为0.31,精度较低;插值结果,琵琶柴中的Zn、Cr、As、Hg含量较高的区域均在工业园区内部及周围,受人为扰动程度较大。梭梭和琵琶柴中Hg元素分别为中度污染和重度污染;Hg元素为中等潜在危害程度高于其他4种元素。     

广藿香毛状根多倍体诱导及其植株再生

为了提高药用植物广藿香的次生物质广藿香醇含量,采用秋水仙素人工诱导染色体加倍技术,进行了广藿香毛状根多倍体诱导及其植株再生、倍性鉴定和挥发油组分广藿香醇含量的测定。结果表明,广藿香毛状根多倍体诱导的最佳条件为0.05%秋水仙素处理36 h,其多倍体诱导率可达40%以上;经秋水仙素加倍的广藿香毛状根在MS+6-BA 0.2 mg/L+NAA 0.1 mg/L培养基中培养60 d后可获得毛状根多倍体再生植株。与对照(二倍体植株)相比,广藿香毛状根多倍体再生植株根系更发达、茎更粗、节间变短、叶片的长度、宽度和厚度均较二倍体明显增大。根尖细胞染色体压片观察证实,所获得的广藿香毛状根多倍体再生植株为四倍体,其根尖细胞染色体数约为128;同时,其叶片的气孔保卫细胞体积及其叶绿体数目均约为对照的两倍;但其气孔密度则随着倍性增加而下降,二倍体植株叶片的气孔密度约为四倍体植株叶片的1.67倍。GC-MS测定结果表明,广藿香毛状根多倍体再生植株的广藿香挥发油组分广藿香醇的含量为4.25 mg/g干重,约为二倍体植株的2.30倍。该结果证实毛状根多倍体化可提高药用植物广藿香的广藿香醇含量。     

Nitrogen dioxide at an ambient level improves the capability of kenaf (Hibiscus cannabinus) to decontaminate cadmium

As reported previously, atmospheric nitrogen dioxide (NO2) at an ambient level increased plant size and the contents of cell constituents. We investigated this effect of atmospheric NO2 on decontamination of cadmium (Cd) by kenaf (Hibiscus cannabinus). Seventeen-day-old seedlings of kenaf were grown in air either with NO2 or without NO2. (Plants were exposed to 100 +/- 50 ppb NO2 for 10 d under irrigation of 0.1% Hyponex supplemented with 20 microM CdCl2.) Plants were then harvested and the biomass of stems, leaves, and roots, as well as the content of Cd in the organs, was determined. The stem and root biomass per plant were 1.25-1.27-fold greater in +NO2 plants than in -NO2 plants. The Cd content per stem was more than 30% greater in +NO2 plants than in -NO2 plants.     

Differential antioxidative responses to cadmium in roots and leaves of pea (Pisum sativum L. cv. Azad).

Pea (Pisum sativum L. cv. Azad) plants exposed to 4 and 40 microM of Cd for 7 d in hydroponic culture were analysed with reference to the distribution of metal, the accumulation of biomass and the metal's effects on antioxidants and antioxidative enzymes in roots and leaves. Cd-induced a decrease in plant biomass. The maximum accumulation of Cd occurred in roots followed by stems and leaves. An enhanced level of lipid peroxidation and an increased tissue concentration of hydrogen peroxide (H2O2) in both roots and leaves indicated that Cd caused oxidative stress in pea plants. Roots and leaves of pea plants responded differently to Cd with reference to the induction of enhanced activities of most of the enzymes monitored in the present study. These differential responses to Cd were further found to be associated with levels of Cd to which the plants were exposed. Cd-induced enhancement in superoxide dismutase (SOD) activity was more at 40 microM than at 4 microM in leaves. While catalase (CAT) prominently increased in leaves both at 4 and 40 microM Cd, ascorbate peroxidase (APX) showed maximum stimulation at 40 microM Cd in roots. Enhancement in glutathione reductase (GR) activity was also more at 40 microM than at 4 microM Cd in roots. While glutathione peroxidase (GPOX) activity decreased in roots and remained almost unmodified in leaves, glutathione S-transferase (GST) showed pronounced stimulation in both roots and leaves of pea plants exposed to 40 microM Cd. Increased activities of antioxidative enzymes in Cd-treated plants suggest that they have some additive function in the mechanism of metal tolerance in pea plants.     

Salicylic acid-induced adaptive response to copper stress in sunflower (Helianthus annuus L.)

The ameliorative effect of salicylic acid (SA: 0.5 mM) on sunflower (Helianthus annuus L.) under Cu stress (5 mg l⁻¹) was studied. Excess Cu reduced the fresh and dry weights of different organs (roots, stems and leaves) and photosynthetic pigments (chlorophyll a, b and carotenoids) in four-week-old plants. There was a considerable increase in Chl a/b ratio and lipid peroxidation in both the roots and leaves of plants under excess Cu. Soluble sugars and free amino acids in the roots also decreased under Cu stress. However, soluble sugars in the leaves, free amino acids in the stems and leaves, and proline content in all plant organs increased in response to Cu toxicity. Salicylic acid (SA) significantly reduced the Chl a/b ratio and the level of lipid peroxidation in Cu-stressed plants. Under excess Cu, a higher accumulation of soluble sugars, soluble proteins and free amino acids including proline occurred in plants treated with 0.5 mM SA. Exogenous application of SA appeared to induce an adaptive response to Cu toxicity including the accumulation of organic solutes leading to protective reactions to the photosynthetic pigments and a reduction in membrane damage in sunflower.