Silicon effects on aluminum toxicity to mungbean seedling growth

The effects of silicon (Si) on the toxicity of aluminum (Al) to mungbean (Phaseolus aureus Roxb.) seedlings were studied in a growth chamber. Mungbean seedlings were grown in a nutrient solution with combinations of three concentrations of Si (0,1, and 10 mM) and three concentrations of Al (0, 2, and 5 mM) in randomized completely block design experiments for 16 days. Silicon at 1 mM in the solution decreased root length, fresh and dry weights, and chlorophyll content, and showed no significant effect on epicotyl length and seedling height, and protein contents of shoots or roots in mungbean seedling under no Al stress. But, Si at 10 mM showed marked toxic effects on mungbean seedling growth and increased protein contents of the shoots or roots. In contrast, under 2 mM Al stress, Si addition at 1 mM had significant increasing effect on root length, fresh and dry weights, and chlorophyll content. It also had decreasing effect on protein contents of the shoots or roots, and had no effect on epicotyl length and seedling height. Silicon addition at 10 mM showed no effect on morphological and physiological measurements of mungbean seedling. However, Si at 1 mM added to solution only increased seedling height, epicotyl length, fresh weight, and chlorophyll content, but decreased dry weight and protein content of the roots under 5 mM Al stress, significantly. Silicon addition at 10 mM showed similar toxic effects on mungbean seedling growth under 5 mM Al stress to that under no Al stress.     

Effects of Boron on Aluminum Toxicity on Seedlings of Two Soybean Cultivars

Boron (B) is an essential micronutrient for higher plants. It has been suggested that addition of B at an optimal concentration might alleviate Al toxicity. Little information is available about B effects on soybean seedling growth under Al stress and differential alleviation of B on Al toxicity. In the present study, the seedlings of two soybean cultivars (Williams and Nanrong 73-935) were grown in a solution with factorial combinations of Al (0, 2, and 5 mM) and B (0, 5, and 50 μM) in a randomized complete block design experiment for 18 days. The results showed that high B was found to ameliorate Al toxicity by significantly increasing the growth characters including root length under 2 mM Al stress, and epicotyl length and fresh weight under 5 mM Al stress of the two cultivars. However, high B concentration did not significantly increase chlorophyll content under Al stress. Williams was more sensitive than Nanrong 73-935 on the growth characters and chlorophyll content under double stresses (B deficiency combined with Al toxicity), although they had similar sensitivity to B deficiency stress alone for growth characters. In addition, high B concentration was found to cause toxicity symptoms on root length and older leaves of both cultivars under no Al stress.     

ALLEVIATION EFFECT OF DIFFERENT RATIOS OF Al TO Ca ON Al TOXICITY FOR MORPHOLOGICAL GROWTH OF MUNGBEAN SEEDLING

Aluminum (Al) is one of the major factors limiting plant production in acid soils. Calcium (Ca) plays a very important role in the response of plants to salt stress. Little information is available about ratios of Al/Ca on the growth of mungbean seedlings under Al stress. Mungbean seedlings were grown in solution with combined concentrations of Al (0, 2, and 5 mM) and Ca (0–10 mM) in a randomized complete block design experiment for 16 days, to evaluate effects of the ratios on alleviation of Al toxicity for the morphological growth under Al stress. The results showed that Al0 + CaO significantly decreased the epicotyl length, seedling height, root length, fresh weight, and dry weight by 25%, 15%, 16%, 16%, and 16%, respectively, compared with a control (Al0 + Ca0.5). At 2mM Al without Ca in the solution (Al2 + Ca0), the epicotyl length, seedling height, root length, fresh weight, and dry weight were decreased by 26%, 12%, 12%, 14%, and 12%, respectively, compared with a control (Al2 + Ca0.5). At 5mM Al without Ca in the solution (Al5 + Ca0), the epicotyl length, seedling height, root length, fresh weight, and dry weight were also decreased by 16%, 8%, 4%, 9%, and 7%, respectively, compared with a control (Al5 + Ca0.5). At 2mM Al stress, with the ratio of Al/Ca = 1:2 (Al2 + Ca4), the epicotyl length, seedling height, and fresh weight increased 13%, 5%, and 15%, respectively, compared with the control (Al2 + Ca0.5). While at 2mM Al stress, the root length at Al/Ca = 2:1 (Al2 + CA1) and dry weight at Al/Ca = 1:1 (Al2 + Ca2) were shown to be increased by 4% and 5%, respectively. At 5mM Al stress, with the ratio of Al/Ca = 2:1 (Al5 + Ca2.5), the epicotyl length, seedling height, and fresh weight increased 12%, 4%, and 7%, respectively, compared with the control (Al5 + Ca0.5). However, the root length and dry weight with the ratio either of Al/Ca = 2:1, 1:1 or 1:2, had no ameliorating effect, but was shown to have a negative effect, compared with the control (Al5 + Ca0.5). This suggests that the alleviation effect and its extent of Ca on Al toxicity for the seedling morphological growth are dependent on characters, the degree of Al stress, and the ratio of Al to Ca.     

PHYSIOLOGICAL EFFECTS OF ALUMINUM/CALCIUM RATIOS ON ALUMINUM TOXICITY OF MUNGBEAN SEEDLING GROWTH

Mungbean seedlings were grown in a nutrient solution with combined concentrations of aluminum (Al) (0, 2, and 5 mM) and calcium (Ca) (0–10 mM) in a randomized complete block design experiment for 16 days. The results showed that under no Al stress, Al0 + Ca0 decreased chlorophyll content by 10%, increased soluble protein, free proline content, and electrolyte leakage by 51%, 533%, and 111%, respectively, compared with a control (Al0 + Ca0.5). Under 2mMAl stress, Al2 + Ca0 decreased chlorophyll content by 19%, increased soluble protein, free proline content, and electrolyte leakage by 48%, 405%, and 55%, respectively, compared with a control (Al2 + Ca0.5). The ratio of Al/Ca = 1:2 increased chlorophyll content by 3%, decreased free proline content and electrolyte leakage by 64% and 34%, respectively. However, all of Al/Ca = 2:1, 1:1 and 1:2 at 2AlmM significantly increased soluble protein, compared with Al2 + Ca0.5. Under 5mMAl stress, Al5 + Ca0 decreased chlorophyll content by 11%, and increased soluble protein, free proline content, and electrolyte leakage by 77%, 85%, and 30%, respectively, compared with a control (Al5 + Ca0.5). The ratio of Al/Ca = 1:2 increased chlorophyll content by 14%, decreased free proline content by 80%, and electrolyte leakage by 34%, compared with Al5 + Ca0.5. However, all ratios of Al/Ca = 2:1, 1:1 and 1:2 at 5mMAl also significantly increased soluble protein, compared with the control. Furthermore, it was observed that Al/Ca = 1:2 could accumulate more Al and Ca in the seedlings than Al/Ca = 2:1 and 1:1 regardless of Al stress (2mM or 5mMAl). Lack of Ca affected the synthesis of chlorophyll, increased soluble protein and free proline, and enhanced electrolyte leakage. Al/Ca = l:2 might be an appropriate ratio for physiological alleviation of Al toxicity to mungbean seedling growth. High concentration of Ca in the solution at appropriate Al/Ca ratio (e.g. Al/Ca = 1:2) could increase chlorophyll content, an indication of alleviation effect. On the contrary, the high Ca caused a significant increase of soluble protein. It suggests the involvement of various proteins that have properties to resist Al toxicity for mungbean seedling growth.     

Effect of aluminium and calcium on growth of wheat seedlings and germination of seeds

Two separate experiments were conducted to investigate the aluminium (Al) and calcium (Ca) effects on wheat seedling growth and on seed germination. Wheat (Tritcum aestivum L, cs Yangmai No. 5) seedlings were grown for a 15‐day period and treated with 0.5 mM Al with low Ca (1 mM Ca) or high Ca (5 mM Ca). The growth of seedlings was signficantly inhibited by Al. Supplement of Ca improved the growth of Al‐treated plants, increased dry matter weight of plant and leaf area, and decreased shoot/root ratio. This showed that Ca ameliorated Al toxicity in wheat. In experiments on seed germination, Al concentrations less than 2 mM in the germinating medium had little or no visible effect on length of shoot and root of germinating seed. The germinating rate of seed was not affected significantly by Al, when Al concentrations lower than 5 mM Al. The addition of 3 mM Ca did not increase the length of shoot and root and germination rate of seeds. Both pretreatments with 6 mM Ca and 1 μM GA had no significant effect on the length of shoot and root and amylolytic activity of Al‐treated germinating seeds. No significant differences were found in the total amylolytic activity in Al‐treated and control seeds two days and five days after germination. The results of Al and Ca effects on seedlings and seed germination showed that Al‐toxicity on germinating seeds was different from on seedling growth. The high concentrations of Al inhibit growth of roots and shoots of germinating seeds by other toxicity mechanism rather than interaction of Al with Ca and mobilization of carbohydrate reserves.     

INFLUENCE OF ALUMINUM ON MINERAL NUTRIENT UPTAKE AND ACCUMULATION IN URTICA PILULIFERA L.

Pollutants can have detrimental effects on living organisms. They can cause toxicity, damaging cells, tissues and organs because of their high concentrations or activities. Plants provide a useful system for screening and monitoring environmental pollutants. Among pollutants, aluminum is considered as a primary growth limiting factor for plants resulting in decreased plant growth and development. Although considered to be a non-essential and highly toxic metal ion for growth and development, aluminum (Al) is easily absorbed by plants. Urticaceae family members have high nutrient requirements demonstrated by leaves containing high levels of calcium (Ca), iron (Fe), magnesium (Mg), and nitrogen (N). Urtica pilulifera is one of the important traditional medicinal plants in Turkey. In this study, U. pilulifera was used as a bioindicator to investigate the possible differences in the absorption and accumulation of mineral nutrients at different levels of the Al exposure and examine the mineral nutrition composition of U. pilulifera under Al stress. Also, some growth parameters (leaf-stem fresh and dry weights, root dry weights, stem lengths and leaf surface area) were investigated. U. pilulifera seedlings were grown for two months in growth-room conditions and watered with spiked Hoagland solution, which contained 0, 100, and 200 μM aluminium chloride (AlCl₃). It was observed that macro- and micro-nutritional status of roots and leaves was altered by Al exposure. The concentrations of some macro- and micronutrients were reduced while concentrations of others were increased by excess of Al. Some macro- and micronutrients were increased at low level of Al whereas reductions were observed at high level of Al, and vice versa. The patterns were dependent on the macro- or micronutrient and the plant part.     

Subcellular compartmentation of sugars in wheat leaves under the influence of salinity and boron toxicity

In this study, long-term effects of salinity and high boron (B) on subcellular distribution of sugars in wheat leaves were investigated. Four treatments with three replications of each; control, high B, sodium chloride (NaCl) and NaCl + high B, respectively were established according to completely randomized design. Plants were grown hydroponically and harvested after 6 weeks onset of experiment. NaCl treatment markedly decreased the shoot fresh and dry weight compared to high B or NaCl + high Boron. It increased the sugar concentrations in subcellular compartments, whereas decreased in NaCl + high B. Contrary, NaCl either alone or in combination with high B decreased the sugar contents in whole leaf compared to control or high B. Overall, higher concentrations of sugars were observed in symplast compared to apoplast indicating the symplast as major compartment for sugar transport. Furthermore, wheat plants accumulate sugars in subcellular compartments to maintain their growth under stress conditions.     

Effect of aluminum uptake on growth and enzyme activity in Pisum sativum var. ‘Alaska’ and ‘Little Marvel’

It is usually assumed that plant tissue responses to nutritional elements are due to specific genetic differences that may exist either between inbred or closely related species. Little Marvel (dwarf) and Alaska (normal) varieties of 14‐day old pea seedlings were treated with four different concentrations of Al‐containing nutrient solution (0.0mM, 0.2mM, 0.6mM and distilled H₂O), prior to being exposed for 14 days to either DARK, LIGHT, or UV. Selected tissues (root tip, main root, main stem and proximal stem) were bioassayed for peroxidase and polyphenol oxidase enzyme activities, fresh wt vs. dry wt, water uptake and stem growth. The present study suggests that Little Marvel and Alaska pea tissue responds to high toxicity levels of Al by demonstrating an enhancement of enzymic activity. Tissue weight, growth and water uptake also show differential tissue specificity in both Little Marvel and Alaska tissue, in terms of Al toxicity response, given a particular external exposure.     

Differences in aluminium tolerance of ryegrass and white clover plants grown from seed or propagated vegetatively

The effect of aluminium (Al) on the relative yield of plants grown from seeds of ryegrass (Lolium perenne L.) or white clover (Trifolium repens L.) and either tillers (ryegrass) or stolon tip cuttings (white clover) were investigated using a low ionic strength (2.7 x 10^‐3 M) solution culture technique. In ryegrass, plants grown from tillers had higher relative yields than plants grown from seedlings in the tops when solution Al concentrations were greater than 16 μM and in the roots when solution Al concentrations were greater than 7 μM. In white clover, relative yields in the tops and roots plants were higher in plants grown from stolon tip cuttings than from seedlings when solution Al concentrations were greater than 10 μM. There were no significant cultivar effects. The results indicate that plants used in Al‐tolerance experiments can be grown from seed or vegetatively propagated, provided solution Al rates are adjusted to reflect differences in Al tolerance.     

MITIGATION EFFECTS OF SILICON ON TOMATO PLANTS BEARING FRUIT GROWN AT HIGH BORON LEVELS

Interactive effects of silicon (Si) and high boron (B) on growth and yield of tomato (Lycopercison esculentum cv. ‘191 F1’) plants were studied. Treatments were: 1) control (B1), normal nutrient solution including 0.5 mg L^?1 B (boron), 2) B1 +Si treatment: 0.5 mg L^?1 boron plus 2 mM Si, 3) B2 treatment: 3.5 mg L^?1 B, 4) B2 +Si treatment: 3.5 mg L^?1 B plus 2 mM Si, 5) B3 treatment: 6.5 mg L^?1 B, and 6) B3 +Si: 6.5 mg L^?1 B plus 2 mM Si. High B reduced dry matter, fruit yield and chlorophyll (Chl) in tomato plants compared to the control treatment, but increased the proline accumulation. Supplementary Si overcame the deleterious effects of high B on plant dry matter, fruit yield and chlorophyll concentrations. High B treatments increased the activities of superoxide dismutase (SOD; EC 1.15.1.1), peroxidase (POD; EC. 1.11.1.7) and polyphenol oxidase (PPO; EC 1.10.3.1). However, supplementary Si in the nutrient solution containing high B reduced SOD and PPO activities in leaves, but POD activity remained unchanged. These data suggest that excess B-induced oxidative stress and alterations in the antioxidant enzymes. Boron (B) concentrations increased in leaves and roots in the elevated B treatment as compared to the control treatment. Concentrations of calcium (Ca) and potassium (K) were significantly lower in the leaves of plants grown at high B than those in the control plants. Supplementing the nutrient solution containing high B with 2 mM Si increased both nutrients in the leaves. These results indicate that supplementary Si can mitigate the adverse effects of high B on fruit yield and whole plant biomass in tomato plants.     

Exogenous application of zinc mitigates the deleterious effects in eggplant grown under salinity stress

The present study was conducted to investigate the effects of Zn application to salt stressed eggplant (Solanum melongena L.) seedlings grown in vitro and whether it can alleviate the deleterious effects of salinity or not. Zinc (0, 5, 10 and 20?mg/L) and sodium chloride (NaCl) at different concentrations (0, 50, 100 and 150?mM) were added to solidified half strength MS medium placed in 250?mL glass jars. The treatments were arranged in a 4?×?4 factorial experiment in a completely randomized design with four replications. Application of Zn to growing seedlings at different concentrations (5, 10 or 20?mg/L) increased the length of shoot and root and their dry weights, as well as enhanced the photosynthetic pigment contents and leaf relative water content compared to control. However, the application of NaCl to growing seedlings at different concentrations (50, 100 and 150?mM) significantly reduced the above mentioned attributes compared to control and those of Zn treatments alone. Treatment of seedlings with either Zn (5, 0 or 20?mg/L) or NaCl (50, 100 or 150?mM) significantly increased the proline content and the antioxidant enzyme activities of superoxide dismutase (SOD), peroxidase (POX) and ascorbate peroxidase (APX) in growing seedlings. However, the application of Zn to salt stressed seedlings mitigated the deleterious effects of salt stress in growing seedlings and increased the tolerance of seedlings to its deleterious effects.     

Differential response of two taro cultivars to aluminum: I. Plant growth

Abstract

Aluminum (Al) toxicity is one of the major factors limiting plant growth in acid soils. To determine the response of taro [Colocasia esculenta (L.) Schott] to Al‐toxicity, cultivars (cv.) Lehua maoli and Bun long were grown in hydroponic solution at six initial levels of Al (0, 110, 220, 440, 890, and 1330 uM Al). Increasing Al levels significantly depressed fresh and dry weights of taro leaf blades, petioles, and roots, as well as leaf areas and root lengths. No significant cultivar differences were found for plant dry weights. However, significant cultivar differences were found for expansion growth parameters, with cv. Lehua maoli exhibiting greater leaf fresh weights and root lengths in the presence of Al, compared to cv. Bun long. Apparently, differential response of taro cultivars to Al is related to the ability of the Al‐tolerant cultivar to maintain water uptake and cell expansion in the presence of Al. The initial solution Al level that resulted in the greatest separation of growth differences between taro cultivars in their response to Al was 890 μM Al.     

In vitro aluminum effects on ectomycorrizal fungi

This study investigates the effects of soluble Al on different ectomycorrhizal fungi in vitro. Al was added to the medium as A1₂(SO₄)₃ · 18H₂O in the concentration range from 0 to 20 mM Al. The lateral growth, fresh and dry weights of mycelia showed dependance on fungal species and the concentrations of Al. Concentrations from 1 to 20 mM of Al reduced the growth of most species but one strain of Pisolithus tinctorius showed a higher tolerance to all Al concentrations studied. The growth of Suillus variegatus showed the most marked sensitivity to and also changes in the morphology of mycelia grown on 15 mM Al, Lactarius piperatus growth was stimulated at the same Al concentrations and showed no differences from the control with SEM observations.     

Effect of simulated acid rain on the growth of Japanese conifers grown with or without fertilizer

Three-year old cuttings of Japanese cedar (Cryptomeria japonica), Japanese cypress (Chamaecyparis obtusa) and Sawara cypress (Chamaecyparis pisifera) were grown in pots with andosol and were exposed to simulated acid rain (SAR) at pH 2.0, 3.0, and 4.0 for 23 months. Total precipitation was 2460, 3960, or 5450 mm and SAR contained sulfuric, nitric and chloric acid at equivalent ratio of 5∶2∶3. Deionized water of pH 5.6 was a control. Exposure to SAR at pH 2.0 induced visible foliar injuries, but not any visible symptoms at pH 3.0 or higher. Total dry weights of 3 conifer cuttings grown with fertilizer were about two fold of those in plants grown without fertilizer and they reduced significantly by the exposure to SAR at pH 2.0. However, Cryptomeria japonica without fertilizer increased dry weights even though plants developed reddish-brown necrosis in large parts of tops. These 3 coniferous cuttings did not show any significant growth reduction at pH 3.0 and 4.0. Soil pH after receiving 5450 mm of SAR at pH 2.0 was 4.0 and molar ratio of (K+Ca+Mg)/Al in water and 1M ammonium acetate soluble fraction of the soil was about 0.3 and 0.4. respectively. However, dry weight of root in plants grown without fertilizer did not decrease. This suggested that growth reduction in plants fertilized and exposed to pH 2.0 was due to a reduction in photosynthetic organs associated with visible injuries, but not direct linkage with root growth inhibition due to soil acidification stress.     

Effect of water stress on aluminum toxicity in pitch pine seedlings

A decrease in soil water content during droughts may increase aluminum (Al) to concentrations that are toxic to the growth of trees. The effects of water stress (WS) on the response of ectomycorrhizal pitch pine (Pinus rigida Mill.) seedlings to aluminum was determined by growing seedlings in sand irrigated with nutrient solution (pH 3.8) containing 0, 5, or 10 mg L^‐1 Al. Water stress was imposed for 41 days by withholding nutrient solution for five consecutive days each week. At harvest time, seedlings at high WS had 72% of mean gravimetric water contents of seedlings at low WS. Aluminum decreased growth of seedlings at high WS, but had no effect on growth of seedlings at low WS. Aluminum toxicity symptoms in roots (e.g., dark thickened tips) were observed at lower Al levels at high WS than at low WS. Stem dry weight was the only plant part decreased by water stress alone. Across Al levels, Al concentration in roots was higher at low WS than at high WS. Water stress alone reduced root [phosphorus (P), potassium (K), and calcium (Ca)] and foliar [P, K, and magnesium (Mg)] concentrations of mineral nutrients. Decreases of nutrients in roots with increasing Al was greater at low than at high WS. Calcium was the only foliar nutrient decreased by Al treatment.     

Effect of Foliar Salicylic Acid Applications on Growth,Chlorophyll, and Mineral Content of Cucumber Grown Under Salt Stress

The objective of this study was to determine the effect of foliar salicylic acid (SA) applications on growth, chlorophyll, and mineral content of cucumber grown under salt stress. The study was conducted in pot experiments under greenhouse conditions. Cucumber seedlings were treated with foliar SA applications at different concentrations (0.0, 0.25, 0.50, and 1.00 mM). Salinity treatments were established by adding 0, 60, and 120 mM of sodium chloride (NaCl) to a base complete nutrient solution. The SA was applied with spraying two times as before and after transplanting. Salt stress negatively affected the growth, chlorophyll content and mineral uptake of cucumber plants. However, foliar applications of SA resulted in greater shoot fresh weight, shoot dry weight, root fresh weight, and root dry weight as well as higher plants under salt stress. Shoot diameter and leaf number per plant increased with SA treatments under salt stress. The greatest chlorophyll content was obtained with 1.00 mM SA treatment in both saline and non-saline conditions. Leaf water relative content (LWRC) reduced in response to salt stress while SA raised LWRC of salt stressed cucumber plants. Salinity treatments induced significant increases in electrolyte leakage. Plants treated with foliar SA had lower values of electrolyte leakage than non-treated ones. In regard to nutrient content, it can be interfered that foliar SA applications increased almost all nutrient content in leaves and roots of cucumber plants under salt stress. Generally, the greatest values were obtained from 1.00 mM SA application. Based on these findings, the SA treatments may help alleviate the negative effect of salinity on the growth of cucumber.     

Boron Toxicity Alters Nitrate Reductase Activity,Proline Accumulation,Membrane Permeability,and Mineral Constituents of Tomato and Pepper Plants

ABSTRACT

Boron (B) toxicity is an important disorder that can limit plant growth on soils of arid and semi arid environments throughout the world. Although of considerable agronomic importance, our understanding of B toxicity is rather fragmented and limited. The effects of increasing levels of B (0, 0.5, 5, 50 mg kg^{? 1}) on plant growth, proline accumulation, membrane permeability, nitrate reductase activity (NRA), and mineral nutrient interactions of tomato and pepper plants were investigated in greenhouse conditions. Increasing levels of B increased the B contents of plants. Boron toxicity symptoms occurred at 5 and 50 mg kg^{? 1} levels. Fresh and dry weights of the plants clearly decreased with the application of the 50 mg kg^{? 1} level of B. Membrane permeability and proline accumulation were significantly increased by the 50 mg kg^{? 1} level of B. Nitrate reductase activity of tomato plants was increased with increasing levels of B. With the exception of potassium (K) and calcium (Ca) in pepper and magnesium (Mg) in tomato, B treatments significantly affected nutrient concentrations of tomato and pepper. Except for sulfur (S) and Ca in tomato, the highest rate of B applied increased the N, phosphorus (P), and K concentrations of tomato and N, P, Mg, and S concentrations of pepper.     

Micronutrient toxicity in buffalograss

The growth responses of buffalograss [Buchloe dactyloides (Nutt.) Engelm.] to elevated micronutrient levels in the fertilizer solution were investigated. Seedling plants established in peat‐lite mix in 11‐cm (0.6 L) pots in the greenhouse were irrigated with solutions containing 0.5, 1, 2, 4, 6, 8, or 12 mM of boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), or zinc (Zn). The control solution contained (in μM): 20 B, 0.5 Cu, 40 Fe, 10 Mn, 0.5 Mo, and 4 Zn. A standard macronutrient concentration was used for all treatment solutions. Boron and Mo induced visual toxicity symptoms more readily than other micronutrients. Boron toxicity was characterized by chlorosis often accompanied by bleached leaf tips, while Mo toxicity resulted in leaf necrosis. The lowest levels that induced visual foliar toxicity were 0.5 mM B, 2 mM Cu, 4 mM Fe, 6 mM Mn, 1 mM Mo, and 4 mM Zn. Chloride did not induce foliar abnormalities in the concentration range tested. Biomass yield was reduced when the nutrient solution contained 2 mM B, 6 mM Cu, or 2 mM Mo. Elevated levels of Cl, Fe, Mn, and Zn did not alter dry matter yield. The relationship between the nutrient and tissue concentrations was determined for each microelement.     

Toxicity of copper and zinc in seedlings of Mung bean and inducing accumulation of polyamine

A solution culture was conducted to investigate the effects of copper (Cu) and zinc (Zn) toxicity on growth of mung bean (Phaseolus aures Roxb. cv VC‐3762) and accumulation of polyamine. Eight‐day‐old seedlings were grown in diluted nutrient solution with different concentrations of Cu and Zn for 6 days. Results showed that elongation of epicotyl and fresh weight of plants were decreased by 10 μM Cu and 100 μM Zn significantly compared to control (0.03 μMCu and 0.1 μMZn). Accumulation of polyamine, especially putrescine (Put) was found in the epicotyl of mung bean seedlings. Addition of 5 mM calcium (Ca) into nutrient solution improved the growth of 10 μM Cu‐treated seedling, and decreased the concentration of Put and increased concentrations of spermine and spermidine in epicotyl of plants. Moreover, supplying Put did not increase tolerance of plant to Cu or Zn. It was suggested that Put accumulation resulting from toxicity of Cu and Zn might merely be a symptom of stress injury.     

Aluminium toxicity with sorghum genotypes in nutrient solutions and its amelioration by magnesium

Effects of Al toxicity and interaction of Al and Mg on growth of twelve sorghum (Sorghum bicolor (L.) Moench) genotypes have been studied in nutrient solutions (pH 4.2). Aluminium at 30 μM decreased biomass (dry matter yield) of the individual genotypes by factors between 1.27 and 7.36, with identical sensitivity grouping of genotypes as obtained in an earlier pot experiment with an acid soil. Resembling acid-soil stress, Al toxicity was simultaneously expressed in two independent ways, i.e. impairment of root development and induced Mg deficiency. The effect of Al on total dry matter production of the genotypes was correlated more closely with changes in specific root length (m g⁻¹ dry root) than with changes in internal Mg status. Increased Mg concentrations in the solutions (2.5 and 7.5 instead of 0.25 mM) not only decreased Al-induced Mg deficiency but also reduced the concentrations of Al in/on the roots and its damaging effect on root development. Therefore, the sorghum genotypes were less sensitive to Al at the higher Mg levels. At a high Mg concentration in the solution (7.5 mM) dry matter yield of two genotypes was even stimulated by Al.