Effects of Cd2+ on the physiological state and photosynthetic activity of young barley plants

Barley plants (Hordeum vulgare L. cv. Obzor) were grown as a water culture in a climatic room. One part of them was subjected to a long-term Cd²⁺ stress - 12 d with 5.4×10⁻⁵ M Cd. The Cd²⁺ stress inhibited formation of the photosynthetic apparatus and its capacity for ¹⁴C photoassimilation, decreased the content of soluble proteins, increased the dark respiration rate and the free amino acids content, disturbed plant water relations, as well as the distribution of ¹⁴C within primary photoproducts of the treated barley plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of Cd2+ on the physiological state and photosynthetic activity of young barley plants

Barley plants (Hordeum vulgare L. cv. Obzor) were grown as a water culture in a climatic room. One part of them was subjected to a long-term Cd²⁺ stress - 12 d with 5.4×10^?5 M Cd. The Cd²⁺ stress inhibited formation of the photosynthetic apparatus and its capacity for ¹⁴C photoassimilation, decreased the content of soluble proteins, increased the dark respiration rate and the free amino acids content, disturbed plant water relations, as well as the distribution of ¹⁴C within primary photoproducts of the treated barley plants.

     

Effect of bioaccumulation of cadmium on biomass productivity,essential trace elements,chlorophyll biosynthesis,and macromolecules of wheat seedlings

Soil contamination with heavy metals has become a worldwide problem, leading to losses in agricultural yield and hazardous human health effects as they enter the food chain. The present investigation was undertaken to examine the influence of cadmium (Cd²⁺) on the wheat (Triticum aestivum L.) plant. Cd²⁺ accumulation and distribution in 3-wk-old seedlings grown in nutrient medium containing varying concentrations of Cd²⁺ (control, 0.25, 0.50, 1.0, 2.5, and 5.0 mg/L) was monitored. The effect of varying Cd²⁺ concentrations up to 21 d on biomass productivity, plant growth, photosynthetic pigments, protein, amino acids, starch, soluble sugars, and essential nutrients uptake was studied in detail to explore the level up to which the plant can withstand the stress of heavy metal. Plants treated with 0.5, 1.0, 2.5, and 5.0 mg/L Cd²⁺ showed symptoms of heavy-metal toxicity as observed by various morphological parameters which were recorded with the growth of plants. The root, shoot-leaf length and the root, shoot-leaf biomass progressively decreased with increasing Cd²⁺ concentration in the nutrient medium. Cd²⁺ uptake and accumulation was found to be maximum during the initial growth period. Cd²⁺ also interfered with the nutrients uptake, especially calcium (Ca²⁺), magnesium (Mg²⁺), potassium (K⁺), iron (Fe²⁺), zinc (Zn²⁺), and manganese (Mn²⁺) from the growth medium. Growth reduction and altered levels of major biochemical constituents such as chlorophyll, protein, free amino acids, starch, and soluble sugars that play a major role in plant metabolism were observed in response to varying concentrations of Cd²⁺ in the nutrient medium. In the present study, the effects of Cd²⁺ on growth, biomass productivity, mineral nutrients, chlorophyll biosynthesis, protein, free amino acid, starch, and soluble sugars in wheat plants was estimated to establish an overall picture of the Cd²⁺ toxicity at structural and functional levels.     

Effect of cadmium and nickel on photosynthesis and the enzymes of the photosynthetic carbon reduction cycle in pigeonpea (Cajanus cajan L.)

The effect of Cd²⁺ and Ni²⁺ on the rate of photosynthesis and activities of key enzymes of the photosynthetic carbon reduction cycle was examined in leaves from pigeonpea (Cajanus cajan L., cv. UPAS-120) grown in nitrogen free sand culture. Two different concentrations of Cd²⁺ and Ni²⁺ were applied through the rooting medium at two growth stages. The application of Cd²⁺ and Ni²⁺ (0.5 and 1.0 mM) at an early vegetative stage (30 days after sowing) resulted in about 50% and 32% reduction in net photosynthesis, respectively. However, enzyme activities were decreased to different levels (2–61%) depending upon the enzyme and the concentration of the metal ion.These concentrations (0.5 and 1.0 mM of Cd²⁺ and Ni²⁺) had no effect when applied at a later vegetative stage i.e. 70 days after sowing. However, when the concentration of Cd²⁺ was increased to 10 mM, there was about an 86% reduction in the rate of photosynthesis but the enzyme activities were reduced by only about 40%. Although Ni²⁺ reduced the photosynthetic rate by 65%, it had little effect on enzyme activities. The reduction in photosynthesis seems to occur indirectly through a decrease in chlorophyll content and stomatal conductance but not due to decreased enzyme activities. Oxygen evolution by leaf discs was inhibited by Cd²⁺ and Ni²⁺ in parallel with a reduction in photosynthesis. These data confirm the earlier reported effects of Cd²⁺ and Ni²⁺ on O₂ evolution in isolated chloroplasts.Abbreviations FBPase Fructose-1,6-bisphosphatase - PCR Photosynthetic carbon reduction - 3-PGA 3-Phospho-glycric acid - RUBP Ribulose, 1,5-bisphosphate     

Effect of cadmium and calcium treatments on phytochelatin and glutathione levels in citrus plants

Industry residues, phosphate fertilisers and wastewater as a source of irrigation have considerably increased levels of heavy metals in the soil, mainly cadmium (Cd²⁺). To test the effects of a calcium (Ca²⁺) treatment on Cd²⁺ accumulation and plant tolerance to this heavy metal, plants of two citrus genotypes, Cleopatra mandarin (CM) and Carrizo citrange (CC), were watered with increasing concentrations of Cd²⁺, and phytochelatin (PC) and glutathione (GSH) content were measured. Both genotypes were able to synthesise PCs in response to heavy metal intoxication, although CM seems to be a better Cd²⁺ excluder than CC. However, data indicate that CC plants had a higher capacity for regenerating GSH than CM plants. In this context, the effects of Ca²⁺ treatment on Cd²⁺ accumulation, plant survival and PC, GSH and oxidised glutathione (GSSG) content were assessed. Data indicate that treatment with Ca²⁺ had two positive effects on citrus physiology: it reduced Cd⁺² uptake into roots and also increased GSH content (even in the absence of Cd²⁺). Overall, the data indicate that although Cd²⁺ exclusion is a powerful mechanism to avoid heavy metal build‐up into photosynthetic organs, the capacity to maintain optimum GSH levels to feed PC biosynthesis could also be an important factor in stress tolerance.     

Effect of NaCl,water stress or both on gas exchange and growth of wheat

Responses of wheat (Triticum aestivum L.) to various concentrations of NaCl and levels of drought were followed. With the rise of NaCl or drought, or NaCl and drought together, growth was retarded. The water content of shoots and roots was mostly unchanged. The chlorophyll and carotenoid contents were increased in plants subjected to salinity or drought or both. Only high salinity level induced a considerable decrease in net photosynthetic rate (P_N) and dark respiration rate (R_D). P_N and R_D were decreased with the decrease of soil moisture content. The content of Na⁺ in the shoots and roots of wheat plants increased with increasing salinity or decreasing soil moisture content or both treatments. Considerable variations in the content of K⁺, Ca²⁺ or Mg²⁺ were induced by the NaCl, drought or both treatments.     

Effects of Cadmium on Chlorophyll Content,Photochemical Efficiency,and Photosynthetic Intensity of Canna indica Linn.

The effects of cadmium (Cd²⁺) on growth status, chlorophyll (Chl) content, photochemical efficiency, and photosynthetic intensity were studied on Canna indica Linn. Plant specimens that were produced from a constructed wetland and precultivated hydroponically in 20 L of 1/10 Hoagland solution under greenhouse conditions for 1 week were exposed to cadmium in concentrations of 0, 0.4, 0.8, 1.6 and 3.2 mg L^―1 Cd²⁺, respectively. The results show that leaves were injured in the Cd²⁺ solution by the third day of exposure and the injury became more serious with an increase in the applied heavy metal. Under 3.2 mg L^―1 Cd²⁺ treatment, growth retardation, the decrease of chlorophyll content from 0.70 to 0.43 mg g^―1 FW, and a decrease in Chl a/b ratio from 2.0 to 1.2 were observed. Chl a was more sensitive than Chl b to Cd²⁺ stress. The decrease was the same with photochemical efficiency. Photosynthetic intensity decreased by 13.3% from 1.5×10⁴ μmol m^―2s^―1 CO₂ in control to 1.3×10⁴ μmol m^―2s^―1 CO₂ in the treatment of 3.2 mg L^―1. Because Canna species are used in heavy metal phytoremediation, these results show that C. indica can tolerate 0.4 to 0.8 mg L^―1 Cd²⁺. Therefore, it is a potential species for phytoremediation of cadmium with some limitations only at higher concentrations.     

The Relationship between Salinity and Cadmium Stress in Barley

Distribution of cadmium between roots and shoots of barley was manipulated by the cadmium concentration (0.01 and 0.005 mM Cd²⁺), pH (4.6 and 5.9) as well as treatment duration. The prolongation of treatment increased dry mass and content of cadmium in plants. The cadmium is accumulated mainly in roots. Presence of both, 0.005 mM Cd²⁺ and 100 mM NaCl in medium at pH 5.9 (Cd-NaCl plants) resulted in the most severe growth inhibition of plants, but about one half accumulation of cadmium in roots then in a case of only Cd-treated plants. In the Cd-NaCl plants, the net photosynthetic and transpiration rates were less reduced then in a case of only NaCl-treated plants. The treatments also influenced uptake of Ca, Cd, Cu, K, Mg, Na and Zn predominantly in roots. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of NaCl salinity on growth,pigment and mineral element contents,and gas exchange of broad bean and pea plants

Increasing salinity of growth medium induced a reduction in growth and transpiration rate. The concentrations of chlorophylls and carotenoids were increased in most cases in broad bean leaves while in pea plants they remained more or less unchanged with the rise of salinization up to 80mM NaCl. Thereabove a significant decrease in these contents was observed. A stimulation of the net photosynthetic rate of pea was observed at the lowest levels of NaCl but at the highest levels inhibitory effect was recorded. In broad bean all salinization levels inhibited photosynthetic activity, but dark respiration of both plant species was stimulated. The content of Na⁺ in the roots and shoots of both species increased at increasing salinity. In broad bean, Ca²⁺ concentration in shoots and K⁺ and Ca²⁺ contents of roots increased at increasing salinization, while in pea plants, the content of K⁺ and Ca²⁺ was almost unaffected by salinity. Salinity induced an increase in the content of these ions in pea roots. Mg²⁺ content in shoots and roots of both broad bean and pea decreased at increasing salinity except in roots of pea, where it was generally increased.     

Does Cd2+ use Ca2+ channels to penetrate into chloroplasts? — a preliminary study

Effects of Cd²⁺ toxicity on the photochemistry of primary leaves at two different growth stages of runner bean plants were taken into consideration to study whether Cd²⁺ can use Ca²⁺ channels to get into chloroplasts. Different concentrations of Cd²⁺, ionophore A 23187 and Ca²⁺ were vacuum infiltrated into leaf discs. Toxicity of Cd²⁺ at the donor side of PSII depending on the metal concentration and age of the plants was confirmed. Application of ionophore caused an increase in the sensitivity of the PSII donor side to low Cd²⁺ concentrations. Additional supply of Ca²⁺ in the infiltration medium abolished toxic effect of Cd²⁺ on photochemical activity, except for older plants, where it was not observed for the highest Cd²⁺ concentration. In our opinion it is possible that Cd²⁺ penetrates into chloroplasts via Ca²⁺ channels. Age-dependent Ca²⁺ content in the primary leaves seems to be a very important factor protecting photochemical activity from the toxic action of Cd²⁺.     

Phosphorus content and growth of fenugreek as affected by cadmium application

Changes in growth and phosphorus content in plants and seeds of fenugreek with increasing cadmium concentration was evaluated. Root length and shoot length ranged from 11.63 to 27.72 and from 9.70 to 54.78 cm, respectively. With the increasing Cd²⁺ concentration there was a significant decrease in root and shoot length, and fresh mass. Various phosphorus fractions of shoot decreased with increasing Cd²⁺ concentration except lipid P and nucleic acid P which increased at 65 and 95 d after sowing and protein P only increased at vegetative stage. In seeds (60 d after flowering) lipid P increased except at 2.5 μg(Cd²⁺) g^?1 (soil) while protein P decreased.     

Effect of cadmium uptake and heat stress on root ultrastructure, membrane damage and antioxidative response in rice seedlings

Excess cadmium (Cd²⁺) in the soil environment is taken up by plants and can cause phytotoxicity. Elevated temperatures also lead to deleterious effects on plants. Plants are very often exposed to a combination of stresses rather than a single stress. The effect of Cd²⁺ and heat stress (HS) on the growth, root ultrastructure, lipid peroxidation (MDA), hydrogen peroxide accumulation and the activities of antioxidant enzymes peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) of rice roots from sensitive cv. DR-92 and tolerant cv. Bh-1 were investigated at 10 and 20 day of growth under controlled conditions. At day 10 under all Cd²⁺ treatments, the Cd²⁺ content between the two rice cultivars were almost similar. Application of 500 μM Cd²⁺ significantly increased metal concentrations at day 20 in the roots of rice seedlings resulting in a maximum accumulation of 44.25 μg Cd²⁺ g^-1 dry wt in cv. DR-92 and 30 μg Cd²⁺ g^-1 dry wt in cv. Bh-1 with a ~25 % decline in Relative Growth Index (RGI) in cv. DR-92. TEM studies revealed slight disorganization with cell wall ingrowths in root tissues from cv. DR-92 grown in 100 μM Cd²⁺ + HS. Uptake and accumulation of Cd²⁺ increased upon heat treatment in parenchyma, vacuoles and vascular cylinder of root tissues. Peroxidase primarily located in cell walls, the intensity being higher in sensitive cv. DR-92. Under Cd²⁺ stress alone, plants of sensitive cv. DR-92 significantly increased the H₂O₂ and MDA levels together with increased activities of the enzymes POD, CAT and APX at day 10 but remained almost stable at day 20. A strong increase in MDA levels was noted at day 20 in tolerant cv. Bh-1. Cd²⁺ + HS treatments in tolerant cv.Bh-1 led to a decreased H₂O₂ and MDA levels and decreased activities of the enzymes POD, CAT and APX. Results suggest stimulation of root antioxidant system under combination of two stresses and that heat stress seem to have a direct protective role by mitigating the effect of mild Cd²⁺ toxicity largely by enhanced Cd²⁺-MT formation contributing thereby towards the management of Cd²⁺ toxicity at cellular level that confers Cd²⁺ tolerance to rice cv. Bh-1.     

The Activity of the Antioxidative System in Cadmium-Treated Arabidopsis thaliana

Changes in the content of reactive oxygen species (ROS) and activity of the antioxidant system were measured in leaves of Arabidopsis thaliana (L.) Heynh exposed to Cd²⁺. Mature plants growing in the nutrient solution were treated with Cd²⁺ at different concentrations (0, 5, 25, 50, 100 μM). An increase of content in leaves was observed at 5, 25 and 50 μM Cd²⁺. A strong accumulation of H₂O₂ was found only at the lowest Cd²⁺ concentration. The content of OH^*. was high at 50 and 100 μM Cd²⁺. Superoxide dismutase (SOD) activity was always higher in Cd²⁺-treated plants than in control. Catalase (CAT) activity decreased with increasing Cd²⁺ concentration in the nutrient solution. Guaiacol peroxidase (POX) activity was particularly high at the lowest and highest Cd²⁺ concentrations and ascorbate peroxidase (APX) activity additionally at 50 μM Cd²⁺. Enhanced activity of monodehydroascorbate reductase (MDHAR) and strong reduction in ascorbate (AA) content were observed at 25 μM Cd²⁺. Glutathione reductase (GR) activity was always higher than in control but decreased as Cd²⁺ concentration increased. However, it was accompanied by gradual content increase of SH-groups. This revised version was published online in July 2006 with corrections to the Cover Date.     

Attenuation of cadmium toxicity in mycorrhizal celery (<Emphasis Type="Italic">Apium graveolens</Emphasis> L.)

A pot-culture experiment was carried out to investigate the effect of arbuscular mycorrhizal (AM) fungus (Glomus macrocarpum Tul. and Tul.) on plant growth and Cd²⁺uptake by Apium graveolens L. in soil with different levels of Cd²⁺. Mycorrhizal (M) and non-mycorrhizal (NM) plants were grown in soil with 0, 5, 10, 40 and 80 Cd²⁺ mg kg⁻¹soil. The infectivity of the fungus was not affected by the presence of Cd²⁺ in the soil. M plants showed better growth and less Cd²⁺ toxicity symptoms. Cd²⁺ root : shoot ratio was higher in M plants than in NM plants. These differences were more evident at highest Cd²⁺ level (80 mg kg⁻¹ soil). Chlorophyll a and chlorophyll b concentrations were significantly higher in AM-inoculated celery leaves. The dilution effect due to increased biomass, immobilization of Cd²⁺ in root and enhanced P-uptake in M plants may be related to attenuation of Cd²⁺toxicity in celery.     

镉胁迫下硒对罗汉果组培苗光合特性的影响

实验以罗汉果组培苗为材料,室内栽培在内装市售营养土的塑料盆中,以0、10、50、100、200mg·kg-1浓度镉离子和1mg·kg-1浓度硒处理,培养20d后分析罗汉果幼苗的相关光合生理指标。结果表明:低浓度Cd2+对叶片叶绿素含量、光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)影响不大或稍有上升,但高浓度镉离子处理植株叶片的叶绿素含量、光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)明显下降;随Cd2+处理浓度的增加,叶片胞间CO2浓度(Ci)呈现上升趋势;加硒则延缓叶绿素下降,促进光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)上升,降低叶片胞间CO2浓度(Ci)。表明高浓度镉离子的毒害导致罗汉果组培苗叶片光合性能受到伤害,从而影响罗汉果幼苗生长。镉硒混合处理反映出硒对镉的毒害有缓解作用。     

Effects of Combined Abiotic Stresses on Growth,Trace Element Accumulation,and Phytohormone Regulation in Two Halophytic Species

Trace element contamination of lands is a serious environmental problem that limits yield and threatens human health. To study the combined effect of high salinity and toxic levels of trace elements on halophytes, the performance of two marsh species, Atriplex halimus and Suaeda fruticosa, grown for 1 month with an irrigation solution supplemented with 200 mM NaCl and 400 μM Cd²⁺ or 400 μM Cu²⁺ was evaluated. The effect of the combined stress conditions on hormone signaling was also assessed. Biomass production and chlorophyll content decreased under Cd²⁺ stress in both species, whereas Cu²⁺ had a lower impact on plant performance. The different plant sensibilities to the two trace elements assayed indicate that each metal has a different effect on plants. Furthermore, the deleterious effect of metal toxicity was alleviated when NaCl was added to the irrigation solution, demonstrating that NaCl improves plant performance and tolerance of halophytic species to cope with trace element intoxication. Results show that both species accumulated important quantities of Cd²⁺ and Cu²⁺ in roots (Cd²⁺: 2,690–3,130 μg g^?1 DW and Cu²⁺: 2,070–2,770 μg g^?1 DW); this finding allows us to classify these species among the hyperaccumulator plants. Cd²⁺ and Cu²⁺ differently affected endogenous phytohormone contents in both species. Data suggest an essential involvement of roots on the regulation of tolerance to trace elements. Therefore, indole-3-acetic acid levels increased in roots of both species irrigated with high levels of Cd²⁺, which suggests that the auxin may stimulate root promotion and growth under these stress conditions. Other compounds, classically considered as “stress hormones” showed very different patterns of accumulation. Whereas, salicylic acid (SA) levels in roots and leaves increased in response to Cd²⁺, root contents of jasmonic acid (JA), and abscisic acid (ABA) decreased. In leaves, the rambling pattern of accumulation observed for JA and ABA suggested the lack of a specific role in regulation against trace element toxicity. Together, data suggest that SA could act as a specific signal that detects trace element toxicity, whereas JA and ABA promote general responses against abiotic stress.     

Bioaccumulation and effect of cadmium in the photosynthetic apparatus of Prosopis juliflora

In the present study Prosopis juliflora plants grown in hydroponics solution were exposed to 50,100 and 1000 μM CdCl₂. The cadmium uptake, transport and toxicity on the photosynthetic activities in the plants were measured at 48 h after starting cadmium treatments. The results showed that the concentration of Cd²⁺ in P. juliflora tended to increase with addition of Cd²⁺ to hydroponics solution. However, the increase of Cd²⁺ in roots and leaves varied largely. In this sense, the accumulation of Cd²⁺ in P. juliflora roots increased significantly in proportion with the addition of this metal. In contrast a relatively low level of Cd²⁺ transportation index, and bioaccumulation factor were found in P. juliflora at 48 h after of treatments. On the other hand the maximum photochemical efficiency of photosystem II (Fv/Fm) and the activity of photosystem II (Fv/Fo) ratios in P. juliflora leaf treated with Cd²⁺ not showed significantly changes during the experiment. These results suggested that the photosynthetic apparatus of P. juliflora was not the primary target of the Cd²⁺ action. Further studies will be focused in understanding the participation of the root system in Prosopis plants with the rhizosphere activation and root adsorption to soil Cd²⁺ under natural conditions.     

Effects of Cd2+ and EDTA on young sugar beets (Beta vulgaris). II. Net uptake and distribution of Mg2+, Ca2+ and Fe2+/Fe3+

Levels of Mg²⁺, Ca²⁺ and Fe²⁺/Fe³⁺ were determined in roots and shoots of sugar beet seedlings (Beta vulgaris L. cv. Monohill) cultured for 5 weeks in a complete nutrient solution to which either Cd²⁺ (0, 5 or 50 μM), EDTA (0, 10 or 100 μM) or a combination of both was added. The plants subjected to the various treatments showed a variety of deficiency symptoms. Leaves of the Cd²⁺-treated plants became thin and chlorotic (Mg- and Fe-deficiency symptoms). The plants showed reduced growth and developed only a few brownish roots with short laterals (Ca-deficiency symptoms). EDTA treatment resulted in green, stunted, hard leaves and reduced growth (Ca-deficiency symptoms). The deficiency symptoms observed correspond well with the observed uptake rates and distributions of Mg²⁺, Ca²⁺ and Fe²⁺/Fe³⁺. Increases in either Cd²⁺, EDTA or a combination of both in the growth medium, were correlated with increasing Mg²⁺ levels in the roots and with decreasing Mg²⁺ levels in the shoots. Cd²⁺ alone or in combination with EDTA had little influence on Ca²⁺ levels in the shoots but decreased Ca²⁺ levels in the roots. Thus, Cd²⁺ affects Mg²⁺ and Ca²⁺ transport in opposite ways: Mg²⁺ transport to the shoots is inhibited while that of Ca²⁺ is facilitated. Treatment with EDTA alone did not affect Ca²⁺ concentrations in either the shoots or the roots. Treatment with Cd²⁺ lowered Fe²⁺ concentrations in both roots and shoots.     

Mechanism of cadmium tolerance in Salicornia europaea at optimum levels of NaCl

• Many saline-alkali soils around the world are polluted by the heavy metal Cd, restricting the development of agriculture and ecology in those regions. The halophyte Salicornia europaea L. is capable of growing healthily in Cd-contaminated saline-alkali soil, suggesting that the species is tolerant to stress caused by both salt and heavy metals. In this study, the mechanism of Cd tolerance in this species was explored under 200 mM NaCl.
• Flame spectrophotometric assays for ions content and spectrophotometric for organic soluble substances, antioxidant enzyme activity, phytochelatins (PCs) content and phytochelatin synthase (PCS) activity, the photosynthetic parameters by portable photosynthesis measurement system, genes expression by qRT-PCR analysis were carried out.
• Cd treatment significantly decreased the dry weight, photosynthetic rate, K⁺, Zn²⁺, and Fe^2+/3+ content, while significantly increasing Na⁺ and Cd⁺, soluble organic matter, and reactive oxygen species (ROS) levels. Compared with Cd treatment at 0 mM NaCl, Cd treatment at 200 mM NaCl significantly increased dry weight and photosynthetic rate while significantly decreasing ROS content through increased antioxidant enzyme activity. When exposed to Cd stress, treatment with 200 mM NaCl significantly increased PCs content and PCS activity and up-regulated the expression of the phytochelatin synthase genes CDA1 and PCS1 were, thereby increasing resistance to Cd.
• NaCl treatment increases the tolerance of S. europaea to the heavy metal Cd by growing rapidly, reducing the quantity of Cd²⁺ from entering the plant shoots, increasing the levels of PCs that chelate Cd²⁺, thereby reducing its toxicity.

     

Responses of elongation growth rate,turgor pressure and cell wall extensibility of stem cells of Impatiens balsamina to lead,cadmium and zinc

Elongation growth rate of stem cells of Impatiens balsamina was inhibited by the heavy metals Pb²⁺, Cd²⁺ and Zn²⁺ due to their suppression on cell wall extensibility. Effective turgor was also inhibited by Pb²⁺ and Cd²⁺ but it played a secondary role in reducing the stem cell elongation growth rate. The major rate-limiting factor for cell elongation growth was the cell wall extensibility. Furthermore, Cd²⁺ was found to be more toxic than Pb²⁺, while Pb²⁺ was more toxic than Zn²⁺.