Effects of Cd2+ and EDTA on young sugar beets (Beta vulgaris). I. Cd2+ uptake and sugar accumulation

Sugar beets ( Beta vulgaris L. cv. Monohill) grown in a complete nutrient solution, were treated with Cd²⁺ (5 or 50 μ M ) and/or EDTA (10 or 100 μ M ) in different combinations. The Cd contents of five-week-old roots and shoots were determined by atomic absorption spectrophotometry, and the sucrose, glucose and fructose contents were measured enzymatically. The Cd²⁺ uptake in both roots and shoots shows a linear relationship to the concentration of free Cd²⁺ in the nutrient solution. This uptake is diminished in the presence of EDTA, suggesting that the Cd-EDTA complex is unable to penetrate the membranes. The contents of glucose, fructose and sucrose in both roots and shoots decrease with increasing uptake of free Cd²⁺. This may be a secondary effect caused by the inhibition of photosynthesis in the presence of Cd²⁺. EDTA reduces the inhibition of Cd²⁺ on sugar formation and accumulation. In the presence of EDTA alone the sugar content increases somewhat. EDTA slightly influences the dry weights of whole plants. The ratio roots:whole plants increases. Cd²⁺ (≤ 50 μ M ) increases the dry matter portion of roots by ca 30%, but not that of shoots.     

Direct and indirect effects of Cd2+ on photosynthesis in sugar beet (Beta vulgaris)

Sugar-beet plants ( Beta vulgaris L. cv. Monohill) were cultivated for 4 weeks in a complete nutrient solution. Indirect effects of cadmium were studied by adding 5, 10 or 20 μ M CdCl₂ to the culture medium while direct effects were determined by adding 1, 5, 20, 50 or 2 000 μ M CdCl₂ to the assay media. The photosynthetic properties were characterized by measurement of CO₂ fixation in intact plants, fluorescence emission by intact leaves and isolated chloroplasts, photosystem (PS) I and PSII mediated electron transport of isolated chloroplasts, and CO₂-dependent O₂ evolution by protoplasts. When directly applied to isolated leaves, protoplasts and chloroplasts. Cd²⁺ impeded CO₂ fixation without affecting the rates of electron transport of PSI or PSII or the rate of dark respiration. When Cd²⁺ was applied through the culture medium the capacity for, and the maximal quantum yield of CO₂ assimilation by intact plants both decreased. This was associated with: (1) decreased total as well as effective chlorophyll content (PSII antennae size), (2) decreased coupling of electron transport in isolated chloroplasts, (3) perturbed carbon reduction cycle as indicated by fluorescence measurements. Also, protoplasts isolated from leaves of Cd²⁺-cultivated plants showed an increased rate of dark respiration.     

Excretion of ions (Cd2+, Li+, Na+ and Cl−) by Tamarix aphylla

Excretion of minerals by the NaCl-resistant and comparatively cadmium-resistant tree Tamarix aphylla (L.) Karst, was investigated. Cd²⁺ was excreted by plants exposed for 1–10 days to 9 or 45 μ M Cd²⁺ solutions. Excretion of this toxic ion increased considerably with time but was less than 5% of the quantities that had been accumulated in the shoots. Excretion of Na⁺ and Cl⁻ was positively correlated with NaCl concentration (1.5, 10, 50 m M ) of the medium. The Na⁺/Cl⁻ ratios of the excrete were positively correlated with the concentration of the treatment solution. Ca²⁺ excretion decreased with increasing NaCl concentrations of the solution. Excretion of K⁺ and Mg²⁺ was only little affected by NaCl. Excretion of Li⁺ occurred whenever this element was supplied in the uptake solution; daily excretion rates of Li⁺ increased with time. The ecological significance of excretion is discussed in relation to the low selectivity of the mechanism in T. aphylla .     

Uptake of Cd2+ and Fe2+ by excised roots of Tamarix aphylla

The uptake of Cd²⁺ by excised roots of Tamarix aphylla (L.) Karst, was investigated using roots of hydroponically grown plants. The concentration isotherm of Cd²⁺ uptake approached saturation with a single phase hyperbola. The time course of Cd²⁺ absorption was generally hyperbolic, with an apparent linear section between 2 and 30 min. The temperature response varied among different temperature ranges: a Q₁₀ of approximately 1.9 was found between 10 and 20°C, but at higher and lower temperatures Q₁₀ values were only 1–1.3. It is concluded that Cd²⁺ uptake by the roots of T. aphylla at moderate temperatures is mediated by a metabolic process, combined with a passive influx component that becomes dominant at higher and lower temperatures. The distribution of the absorption sites for Cd²⁺ and for Fe²⁺ along the roots of T. aphylla was also investigated. Cadmium uptake showed no apparent pattern, whereas a distinct pattern of uptake was observed for Fe²⁺, with the highest rates at the root tip. Iron absorption was stimulated in the presence of nutrients, whereas that of Cd²⁺ was inhibited. Adsorption and absorption of Cd²⁺ were strongly inhibited by Ca²⁺ and by Mg²⁺, but were unaffected by Fe²⁺. Monovalent ions (Na⁺, K⁺, Li⁺) also reduced Cd²⁺ absorption, but to a lesser extent than Ca²⁺ and Mg²⁺. Uptake of Cd⁺ was reduced at lower pH of the medium. The importance of interfering cations for Cd²⁺ tolerance of T. aphylla is emphasized.     

Influence of NaCl, Cd(NO3)2 and air humidity on transpiration of Tamarix aphylla

Transpiration rates of young Tamarix aphylla (L.) Karst, plants grown in hydroponics were measured under NaCl- and Cd(NO₃)₂-stress. Transpiration rates were negatively correlated with the relative humidity of the ambient air at all NaCl concentrations investigated. Low and intermediate concentrations of Cd²⁺ (45 and 90 μ M , respectively) in the medium caused an increase in transpiration rates. This was particularly pronounced at low levels of relative humidity. At 180 μ M Cd²⁺, transpiration rates dropped, probably as a result of root damage due to Cd²⁺ toxicity. Since the transpiration rates differed by a factor of ca 3 between day and night, it is concluded that the stomata did not lose their ability to regulate transpiration under the influence of NaCl or of Cd(NO₃)₂. The transpiration behaviour of T. aphylla indicates that the effect of water vapour pressure (presented as relative humidity) on the degree of stomatal opening is small. Under conditions of ample water supply transpiration follows the evaporative demand of the ambient air and is influenced by the water uptake capacity of the root system as well as by other environmental factors, e.g. light.     

Cadmium and copper change root growth and morphology of Pinus pinea and Pinus pinaster seedlings

Heavy metal loads in forest soils have been increasing over time due to atmospheric inputs. Accumulation in the upper soil layers could affect establishment of seedlings and forest regeneration. Mediterranean species show a high initial root development, allowing seedlings to reach the moisture of deeper soil layers. In the present work seedlings of stone pine ( Pinus pinea L.) and maritime pine ( Pinus pinaster Ait.), were grown in culture solution supplied with 0.0, 0.1, 1 or 5 μ M CdSO₄ or with 1 μ M CdSO₄ and 1 μ M CuSO₄ combined. In both species tap-root elongation was drastically reduced in the 5 μ M Cd²⁺ and in the (Cd²⁺+ Cu²⁺) treatments. A supply of 0.1 or 1 μ M Cd²⁺, however, enhanced root elongation in Pinus pinea without significantly influencing root elongation in Pinus pinaster . In both species the root density (weight per unit length) and the width of the cortex increased in response to Cd²⁺ exposure. In Pinus pinaster the mitotic index decreased at the higher Cd²⁺ concentrations and when Cd²⁺ and Cu²⁺ were combined. The data suggest that cell elongation is more sensitive to Cd²⁺ than cell division. The number and length of the lateral roots were also affected by Cd²⁺ treatment to a higher degree in Pinus pinaster than in Pinus pinea, reflecting the different Cd- tolerance of the two species.     

The nature and localization of superoxide dismutase in fronds of Lemna gibba L. and the effect of copper and zinc deficiency on its activity

Superoxide dismutase (SOD) is present in the fronds of Lemna gibba L. Differential centrifugation showed that ca. 90% of the enzyme is present in the 140,000 g soluble cell fraction. Lemna SOD is sensitive to cyanide and is probably a Cu-Zn metallo-protein. Gel filtration showed the SOD to have a mass of 31,000 daltons. In Zn-defizient culture media, the activity of Lemna SOD was less than in fronds grown in complete nutrient media whereas in Cu-deficient media little change was found in the enzyme activity. The SOD activity in Zn-deficient plants could be partly restored to the level of Zn-sufficient fronds by adding Zn²⁺ to the enzyme assay solution.     

Effects of cadmium on growth of Helianthus annuus seedlings: physiological aspects

Sunflower seedlings ( Helianthus annuus hybrid Select) were grown in a complete nutrient solution in the absence or presence of Cd²⁺ (10 and 20 μM). Analyses were performed to establish whether there was a differential effect of Cd²⁺ on mature and young leaves. After 7 d the growth parameters as well as the leaf area had decreased in both mature and young leaves. Accumulation of Cd²⁺ in the roots exceeded that in the shoots. Seedlings treated with Cd²⁺ exhibited reduced contents of chlorophyll and CO₂ assimilation rate, with a greater decrease in young leaves. The photochemical efficiency of photosystem II (PSII) was not altered by Cd²⁺ treatment in either mature or young leaves, although during steady-state photosynthesis in young leaves there was a significant alteration in the following parameters: quantum yield of electron transport by PSII (Φ_PSII), photochemical quenching ( q _P), non-photochemical quenching ( q _NP), and excitation capture efficiency of PSII (Φ_exc).     

The Pmr1 protein, the major yeast Ca2+-ATPase in the Golgi, regulates intracellular levels of the cadmium ion

Cadmium is a nonessential, highly toxic heavy metal that shows ionic properties similar to calcium. These ionic similarities imply that the cadmium ion, Cd²⁺, is a calcium ion, Ca²⁺, receptor-agonist, affecting the same biochemical pathways involved in Ca²⁺ homeostasis. In the yeast Saccharomyces cerevisiae , the PMC1 and PMR1 genes encode vacuolar and Golgi Ca²⁺-ATPases, respectively. The PMR1 protein product Pmr1p is involved in both Ca²⁺ and Mn²⁺ homeostasis. This study investigated the importance of Pmc1p and Pmr1p for Cd²⁺ cellular detoxification. Using the standard techniques of yeast molecular research and a multielemental procedure named particle-induced X-ray emission, Pmr1p was identified as a protein that directly participates in the detoxification of Cd²⁺, possibly through the secretory pathway. The results allow us to posit a model of Cd²⁺ detoxification where Pmr1p has a central role in cell survival in a Cd²⁺-rich environment.     

Interaction between a copper-tolerant and a copper-sensitive population of Silene cucubalus

Interactions between copper-tolerant and copper-sensitive plants of Silene cucubalus (L.) Wib. were absent when grown in mixed culture in a nutrient solution with a normal Cu²⁺ concentration (0.5 μ M ). When grown in mixed culture in a nutrient solution with 40.5 μ M CuSO₄, however, the biomass production of the sensitive plants was less affected than when grown in monoculture. At 40.5 μ M Cu²⁺, in the presence of tolerant plants, the concentration of copper in both roots and shoots of sensitive plants was significantly diminished in comparison to a monoculture without tolerant plants. At the same time the copper concentration in the roots of the tolerant plants was higher in the presence of sensitive plants. The possibility of external detoxification of the copper by tolerant plants as a mechanism of heavy metal resistance is discussed.     

Studies on the accumulation of cadmium by a strain of Proteus mirabilis

Abstract A bacterium isolated from a wastewater plant sludge, identified as Proteus mirabilis , was tested for cadmium tolerance and accumulation capacity. The organism was able to grow in the presence of Cd²⁺ up to 300 mg l⁻¹.
Accumulation of cadmium is reported for growing and non-growing cells of the organism. In non-growing cultures a 70% removal of cadmium was observed when the initial concentration of Cd²⁺ was 1 mg l⁻¹ whereas at the same concentration the removal by growing cells was only 22%. The metal was shown to be associated with the cell envelope (80%) and accumulated in the cytoplasm (20%).     

Chlorophyll fluorescence and photoacoustic characteristics in relationship to changes in chlorophyll and Ca2+ content of a Cu-tolerant Silene compacta ecotype under Cu treatment

The effect of Cu toxicity on photosynthetic function, chlorophyll and Ca²⁺ content of Cu-tolerant Silene compacta plants grown in nutrient solution was studied. Since, in plants grown under 8 μ M Cu, the chlorophyll and Ca²⁺ concentration as well as the photosystem II (PSII) photochemistry were increased, compared to the control, the development of an adaptive mechanism of the Cu-tolerant ecotype of S. compacta to 8 μ M Cu is suggested. Increased Cu tolerance of the S. compacta ecotype reflects modulation of the photosynthetic apparatus to optimize photosynthesis. However, exposure of plants to 160 μ M Cu resulted in a marked increase of the fraction of closed PSII centres and decreased quantum yield of PSII electron transport (Φ_PSU) which was accompanied by a significant decline of relative quantum yield for O₂ evolution (A_ox/A_pt). The concentration of chlorophyll and Ca²⁺ in leaves also decreased significantly under 160 μ M Cu treatment. Photochemical quenching (q_p) displayed a reduction as a result of perturbation of the photosynthetic electron transfer chain, while non-photochemical quenching (q_N) increased. High Cu treatment reduced photosynthetic productivity of S. compacta plants which can be attributed, in part, to pertubation of photosynthetic process and photosynthetic pigments as well as to Ca²⁺ loss.     

Effect of chelating agents on bud induction and accumulation of iron and copper by the moss Bartramidula bartramioides

The chelating agents, EDDHA, its iron salt, EDTA, and salicylic acid enhance bud formation in Bartramidula bartramioides (Griff.) Wijk & Marg. Salicylic acid elicits optimal response at 10^–4 M , whereas the other substances do so at 10^–7 M . Increased concentration of ferric citrate and cupric sulphate also stimulate bud induction. The accumulation of Fe³⁺ and Cu²⁺ is facilitated by chelators. The endogenous iron content is maximum at 10^–7 M EDDHA or EDTA, which is also the concentration optimal for bud induction.     

Chlorophyll-protein levels and degree of thylakoid stacking in radish chloroplasts from high-light, low-light and bentazon-treated plants

Lemna gibba plants were incubated aseptically on medium containing labelled 10^-7 M indole-3-acetic acid (IAA-1-¹⁴C). Most of the radioactivity disappeared from the culture medium during a 24 h light period. A high percentage of the loss was due to photolysis and only a low percentage of the radioactivity was recovered in the plants. Uptake of ¹⁴C by the plants was strongly stimulated by light. The radioactivity taken up by the plants was the sum of photosynthetically taken up ¹⁴CO₂ and ¹⁴C taken up in IAA. Analyses with the indolo-α-pyrone fluorescence method revealed that the free IAA content was almost the same in plants grown in control and in IAA media for 5 h, whereas the amount of IAA which could be liberated by alkaline hydrolysis was doubled by the presence of IAA in the medium.     

Inhibition of the glucose and amino-acid carriers of Lemna gibba by pretreatment with HgCl2

The electrical resting potential across the plasmalemma of Lemna gibba L. (G 1) cells is −230 to −250 mV and the diffusion potential in the presence of 1 mol m⁻³ KCN + 1 mol m⁻³ salicylhydroxamic acid is about −100 mV. A concentration of 0.01 mol m⁻³ HgCl₂ depolarises the transmembrane electrical potential in a largely reversible way. When the cells after 16 min of HgCl₂-application are returned to Hg-free solution, the transmembrane electrical potential is only depolarised by 24 × 13 mV (SD, n = 13) compared with the potential prior to HgCl₂ treatment. In contrast, a 16 min pretreatment with HgCl₂ followed by a wash with mercury-free solution reduces the transient depolarisations of transmembrane potential observed after addition of 5 mol m⁻³ D-glncose or 1 mol m⁻³ L-alaoine to about 60% of controls. These transient depolarisations are due to the onset of solute uptake. Accordingly, HgCl₂-pretreatment inhibits uptake of ¹⁴C-3-O-methyl- d -glucose by more than 50% and uptake of ¹⁴C- l -alanine by more than 70%. Washing with 1 mol m⁻³ 1,4-dithiothreitol does not reverse this inhibition. It is, therefore, concluded that Hg²⁺ irreversibly binds to essential SH-groups of the H⁺-hexose and the H⁺-amino-acid cotransport carriers of Lemna gibba and inhibits these carriers without appreciably affecting the electrogenic proton-extrusion pump.     

Photoinhibition of photosynthesis in Lemna gibba as induced by the interaction between light and temperature. I. Photosynthesis in vivo

The floating angiosperm Lemna gibba L. was exposed for 2 h to various combinations of photosynthetic photon flux densities and temperature. The extent of photoinhibition of photosynthesis was assayed by measuring the net CO₂ uptake before and after a photoinhibitory treatment, and the time course for photoinhibition was studied. It was found that the maximum quantum yield and the light-saturated rate of CO₂ uptake were affected by the interaction between light and temperature during the photoinhibitory treatment. At a constant photon flux density of 650 μmol m⁻² s⁻¹ the extent of photoinhibition increased with decreasing temperature showing that even a chilling-resistant plant like L. gibba is much more susceptible to photoinhibition at chilling temperatures. About 60% photoinhibition of the quantum yield for CO₂ uptake could be obtained either by a high photon flux density of 1 750 μmol m⁻² s⁻¹ and 25°C or by a moderate photon flux density of 650 μmol m⁻² s⁻¹ and 3°C. The time courses of recovery from 60% photoinhibition produced by either of these two treatments were similar, indicating that the nature of the photoinhibition was intrinsically similar. The extent of photoinhibition was related to the amount of light absorbed in excess to what could be handled by photosynthesis at that temperature. The vital importance of photosynthesis in alleviating photoinhibition is discussed.     

Phytotoxicity of cadmium ions on germinating seedlings of mung bean (Phaseolus vulgaris): Involvement of lipid peroxides in chlorphyll degradation

Germinating seedlings of mung bean ( Phaseolus vulgaris L. cv. K-16) were treated with different concentrations of cadmium acetate (10, 50 and 100 μ M ). Cd²⁺ lowered the chlorophyll and heme levels. The level of lipid peroxides were higher on day 3 than on day 6. However, Cd²⁺ treatment significantly enhanced the level of lipid peroxides. Similarly, a dose-dependent induction of lipoxygenase (EC 1.13.11.12) activity was observed with Cd²⁺ treatment. Further, the activities of antioxidant enzymes such as superoxide dismutase (EC 1.15.1.1) and catalase (EC 1.11.1.6) were decreased. Our results suggest that lipoxygenase-mediated accumulation of lipid peroxides on the one hand and inhibition of free radical scavenging enzymes like superoxide dismutase and catalase on the other caused a pronounced reduction in the chlorophyll and heme levels of the seedlings. The experiments conducted on the effect of Cd²⁺ on dark-grown seedlings did not conform with the result of light-grown seedlings. Though chlorophyll and heme levels decreased in a dose-dependent manner, no accumulation of lipid peroxides was observed, suggesting that the inhibition of chlorophyll synthesis by Cd²⁺ is achieved both by reaction with constituent biosynthetic enzymes as well as peroxide-mediated degradation.     

An effect of Na+ on K+ uptake in intact seedlings of Zea mays

Models for the regulation of K⁺ uptake in higher plant roots have become more complex as studies have moved from the level of excised low-salt roots to that of intact plants grown under fully autotrophic conditions. In this paper we suggest that some of the differences between the conditions are qualitative, possibly requiring fundamental changes to the model, rather than simply quantitative.
The uptake of K⁺ by low-salt roots of Zea mays L. [(A619 x Oh 43) x A632], was independent of Na⁺ concentration over a wide range. However, independence of Na⁺ was not the case in plants grown on complete nutrient medium in the light: inclusion of Na⁺ in the uptake medium enhanced K⁺ uptake. In the presence of Na⁺, K⁺ uptake rates were similar in whole plants with high root K⁺ contents to rates in excised or intact, low-salt roots.     

Effect of potassium status on K+ (Rb)+ uptake and transport in sunflower roots

Young sunflower plants ( Helianthus annuus L. cv. Halcón), grown in nutrient solution at two K⁺ levels (0.25 and 2.5 m M ) were used to study the effect of K⁺ content in the root on uptake and transport of K⁺ to the exuding stream of decapitated plants. Roots of plants grown in low K⁺ gave higher exudation flux, higher K⁺ concentration in exudate and higher K⁺ flux than high K⁺ roots. After 6 h of uptake the K⁺ flux in low K⁺ roots was about three times that in high K⁺ roots. When the roots were kept in a nutrient solution in which Rb⁺ replaced K⁺, low K⁺ roots exuded much more Rb⁺ than K⁺ after the first 2 h, whereas high K⁺ roots exuded about similar amounts of K⁺ and Rb⁺. In intact plants grown at three different K⁺ levels (0.1, 1.0 and 10.0 m M ), there was an inverse relationship between the K⁺ level in the nutrient solution and the Rb⁺ accumulated in the roots or transported to the shoot. The results suggest that the transport of ions from xylem parenchyma to stele apoplast may be controlled by ions coming down from the shoot in sieve tubes.     

Isolation of cadmium sensitive mutants in Chlamydomonas reinhardtii by transformation/insertional mutagenesis

Abstract An arg7, cw15, mt⁺ strain of Chlamydomonas reinhardtii (CC1618) was transformed with pARG7.8, a plasmid containing the wild-type ARG7 gene. Over 2300 arg⁺ transformants were selected on TAP media. Upon subsequent analysis on TAP plus cadmium plates, five of the transformants failed to grow at a level of 400 μM cadmium and were designated as cadmium sensitive (Cd^s) mutants. Hybridization data indicated that vector (pBR329) sequences were present in these five mutants, but not in the untransformed parental strain. Two of the mutants have been back crossed to an arg7, cw15, Cd⁺, mt⁻ strain (CC425) and found to have progeny which always cosegregate the arg⁺ and Cd^s phenotypesin these two mutants results from the insertion of the plasmid pARG7.8 into a gene involving cadmium detoxification, and it provides a method by which to clone the interrupted gene(s).