Ectomycorrhizal Association Enhances Al Tolerance by Inducing Citrate Secretion in Pinus densiflora

To investigate the effects of ectomycorrhizal association on the aluminum (Al) tolerance of Pinus densiflora Sieb. & Zucc., seedlings with or without ectomycorrhizal association with the fungus Pisolithus tinctorius (Pers.) Coker & Couch were exposed to 1 mM Al. Association with P. tinctorius alleviated Al-induced inhibition of root elongation and biomass growth in the mycorrhizal seedlings. Secretion of malate and citrate, both low-molecular-weight organic acids that could detoxify Al by the formation of stable complexes, was investigated in P. tinctorius mycelia and in pine roots with and without P. tinctorius association. Citrate secretion from the P. tinctorius mycelia in vitro was stimulated by Al. Citrate secretion from the roots of the ectomycorrhizal seedlings was also stimulated by Al, but was not detected in the non-mycorrhizal seedlings. These results suggest that citrate secreted from the roots of the ectomycorrhizal seedlings was produced in the hyphae of P. tinctorius. Citrate secretion may play a role in enhancing the Al tolerance of host seedlings.     

Uptake of Al,Ca, and P in black spruce seedlings: Effect of organic versus inorganic al in nutrient solutions.

Two-year old black spruce seedlings (Picea mariana [Mill.] B.S.P.) of greenhouse-grown paper-pot stock were subjected to chemically well-characterized nutrient solutions for 28 days to assess the elemental uptake (A1,P,Ca) of these plants in response to organic versus inorganic Al in the rooting medium (pH=3.0; 0 ≤ total Al ≤ 48 mg L^?1). Oxalate additions to the nutrient solutions (0 ≤ Ox ≤ 2.4 mmol) served as organic Al-complexing agent. The results indicated that the plants took up Al in proportion to the Al concentration of the rooting medium, with Al uptake from the Al-Ox treatments somewhat more extensive than the Al uptake from the inorganic Al treatments. Furthermore, root Al ? shoot Al for both cases. The pattern of P uptake was similar to that of Al uptake but for the roots only, i.e. root P was proportional to root Al.Increased root P was not associated with increased shoot P. Calcium content of the roots was slightly reduced with increased inorganic and organic Al, but increased strongly with increasing oxalate in the rooting medium.     

铝胁迫下萹蓄与饭豆根系有机酸分泌特性比较

以蓄和饭豆为试验材料,从对Al胁迫的响应时间、蛋白质合成抑制剂的影响、体内有机酸含量变化及阴离子通道抑制剂的影响等方面,比较研究了Al诱导根系分泌有机酸的差异,以进一步明确铝(Al)诱导植物根系有机酸分泌的过程。结果表明,萹蓄根系在Al胁迫后30.min内分泌出草酸,而Al胁迫至少4.h后饭豆根系才开始分泌柠檬酸;蛋白质合成抑制剂环己亚酰胺(Cycloheximide,CHM)不影响萹蓄根系草酸的分泌,但抑制了84%Al诱导的饭豆根系柠檬酸的分泌,表明前者不需要新蛋白质的诱导合成,却是后者所必需的。Al处理不改变萹蓄根尖草酸的含量,但明显提高了饭豆根尖柠檬酸的含量;阴离子通道抑制剂苯甲酰甲醛(Phenylglyoxal,PG)和蒽-9-羧酸(Anthrancene-9-carboxylic.acid,A-9-C)分别有效抑制Al诱导萹蓄根系草酸的分泌及饭豆根系柠檬酸的分泌,再次证明两者有机酸的分泌是通过某种被Al所诱导或激活的阴离子通道所实现的。     

Aluminum-Enhanced Proton Release Associated with Plasma Membrane H+-Adenosine Triphosphatase Activity and Excess Cation Uptake in Tea (Camellia sinensis) Plant Roots

Cultivated tea (Camellia sinensis) plants acidify the rhizosphere, and Aluminum (Al) toxicity is recognized as a major limiting factor for plant growth in acidic soils. However, the mechanisms responsible for rhizosphere acidification associated with Al have not been fully elucidated. The present study examined the effect of Al on root-induced rhizosphere acidification, plasma membrane H⁺-adenosine triphosphatase (H⁺-ATPase) activity, and cation-anion balance in tea plant roots. The exudation of H⁺ from tea plant roots with or without Al treatment was visualized using an agar sheet with bromocresol purple. The H⁺-ATPase activity of plasma membranes isolated from the roots was measured after hydrolysis using the two-phase partition system. The Al treatment strongly enhanced the exudation of H⁺, and the acidification of tea plant roots by Al was closely associated with plasma membrane H⁺-ATPase activity. The root plasma membrane H⁺-ATPase activity increased with Al concentration. The Al content, amount of protons released, and H⁺-ATPase activity were significantly higher in roots treated with Al than in those untreated. The results of the cation-anion balance in roots showed an excess of cations relative to anions, with the amount of excess cation uptake increasing with increasing Al concentrations. These suggest that Al-enhanced proton release is associated with plasma membrane H⁺-ATPase activity and excess cation uptake. Findings of this study would provide insights into the contributing factors of soil acidification in tea plantations.     

Distribution of Accumulated Aluminum and Changes in Cell Wall Polysaccharides in Eucalyptus camaldulensis and Melaleuca cajuputi under Aluminum Stress

Distribution of aluminum (Al) within plant components and Al-induced changes in cell wall polysaccharides in root tips of Eucalyptus camaldulensis Dehnh. seedlings were compared with those of Melaleuca cajuputi Powell. In E. camaldulensis , 0.5 mM Al (pH 4.2 for 40 d) reduced plant dry weight by 50%, increased callose concentration in the root tips and induced leaf necrosis. In comparison with M. cajuputi , Al concentrations were higher in roots and leaves of E. camaldulensis on both a fresh weight basis and in the cell sap, but were lower in the cell wall. Al increased pectin, hemicellulose and cellulose concentration in the cell walls of E. camaldulensis root tips. Al-induced leaf necrosis and growth reduction in E. camaldulensis is discussed in the context of potentially toxic concentrations of Al in plant tissue and changes in polysaccharide content which could reduce water and nutrient uptake and cell wall extensibility in roots.     

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.     

Effect of aluminum on callose synthesis in root tips of tea (Camellia sinensis L.) plants

Aluminum (Al) toxicity is a major factor limiting yield production on acid soils (Foy 1983). The initial symptom of Al toxicity in many plants is manifested by the inhibition of root elongation (Ownby and Popham 1990; Llugany et al. 1994; Sasaki et al. 1994; Horst et al. 1997), which occurs during a very short period of time after exposure to Al (Llugany et al. 1994; Staß and Horst 1995). In a large number of recent reports, it was shown that the root apex plays a major role in the Al-sensitivity and response mechanisms (Zhang et al. 1994; Sasaki et al. 1997; Sivaguru and Horst 1998). However, it is interesting to note that stimulatory effects of Al on the growth of plants have also been reported in some studies (Chenery 1955; Konishi et al. 1985; Huang and Bachelard 1993; Osaki et al. 1997). In tea plant (Camellia sinensis L.) a stimulatory effect of Al on the growth was also demonstrated in some experiments, using intact plant (Chenery 1955; Konishi et al. 1985), cultured roots (Tsuji et al. 1994), and pollen tubes (Yokota et al. 1997). The growth of tea roots was typically more stimulated than that of shoots by Al (Konishi et al. 1985). It was assumed that Al effects might be due to the amelioration of phosphorus absorption (Konishi et al. 1985), secretion of malic acid from roots to dissolve aluminum phosphate in the rhizosphere (Jayman and Sivasubramaniam 1975), stimulation of growth of microorganisms on the root surface (Konishi 1990) or replacement of some functions of boron (Konishi 1992; Yokota et al. 1997). However, the stimulatory effects of Al on tea plant growth have not yet been el ucidated.

The formation of callose (1,3-β-glucan) has been reported as a common plant response to a variety of stresses, as well as mechanical, biophysical, chemical, and biological injury (Jaffe and Leopold 1984; Zhang et al. 1994). Increased synthesis of callose has been observed upon exposure to excess amounts of some elements, such as boron (McNairn and Currier 1965), cobalt, nickel, zinc (Peterson and Rauser 1979), and manganese (Wissemeier and Horst} 1987, 1992). Callose synthesis was also induced by Al in the roots of Triticum aestivum (Zhang et al. 1994) and Zea mays (Horst et al. 1997; Sivaguru and Horst 1998), suspension-cultured cells of Glycine max (Staß and Horst 1995), and protoplasts of Avena sativa (Schaeffer and Walton 1990) and Zea mays (Wagatsuma et al. 1995). Induction of callose synthesis in roots seems to be a very rapid physiological indicator of Al-induced injury or genotypical differences in Al sensitivity (Wissemeier and Horst 1992; Zhang et al. 1994; Horst et al. 1997). Nevertheless, Al-induced callose synthesis in tea plant, whose growth is stimulated by suitable Al concentrations, has not been described yet. Therefore, to elucidate the physiological basic effects of Al on tea plant, callose synthesis affected by Al in the root tips of intact plants was analyzed in the present study.     

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.     

Boron amelioration of aluminum toxicity in mungbean seedlings

Boron (B) amelioration of aluminum (Al) toxicity was studied for growth of mungbean (Phaseolus aureus Roxb.) seedlings and cuttings (without roots) in a growth chamber. Mungbean seedlings and cuttings were grown in the solution with combinations of three concentrations of B (0,5, and 50 μM) and three concentrations of Al (0, 2, and 5 mM) in randomized complete block design experiments for 16 days. Results showed that B significantly promoted elongation of epicotyls and hypocotyls, and increased height of seedlings grown under Al stress. Boron also increased fresh weight of seedlings in high Al solution. Treatment of plants grown with high B and Al stress had no apparent effect on fresh and dry weights of seedling roots. Seedling dry weight increased significantly by adding high B to solutions with 2 mM or 5 mM Al. No significant differences were observed between the high B treatment and the control (normal B, 5 μM) in lengths of epicotyls and fresh and dry weights of mungbean cuttings grown under Al stress. High concentrations of B decreased soluble protein and increased chlorophyll in seedlings treated with 2 mM Al. Boron had no amelioration effect on cuttings grown with Al, although Al increased soluble protein. Our results suggested that B alleviation of Al toxicity was related to root function and Al toxicity may possibly be due, in part, to B deficiency.     

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.     

模拟酸雨和外源铝对茶树铝及一些营养元素吸收积累的影响

采用盆栽方法,研究了模拟酸雨和外源铝对茶树铝及一些营养元素吸收积累的影响,以期为酸沉降区茶园管理提供资料。结果表明,随着外源铝浓度的增加,茶树根、茎和叶中铝含量增加,在适度浓度外源铝处理下,模拟酸雨促进茶树根、茎和叶对铝的吸收与积累,高酸高铝则抑制茶树各器官中铝的积累。外源铝促进茶树根、茎和叶对磷、铜和铁的吸收与积累,促进茶树茎和叶对钾的吸收与积累,对茶树根中钾含量没有明显的影响,外源铝抑制茶树根对钙、镁和锌的吸收与积累,但不影响它们在茶树中的运输,茎和叶中含量增加。模拟酸雨对茶树根和茎中磷含量没有明显影响,pH4.5的模拟酸雨有利于茶叶磷的积累,模拟酸雨对茶树根、茎和叶中钾、钙、镁、铜和锌含量没有明显的影响。无外源铝处理下,模拟酸雨降低茶树根系中铁的含量,对茎和叶中铁含量没有明显影响,外源铝处理下,模拟酸雨明显降低茶树根、茎和叶中铁的含量,并且外源铝处理浓度越高,模拟酸雨对根、茎和叶中铁含量的降低幅度越大。     

Organic acids in root exudates from Picea abies seedlings influenced by mycorrhiza and aluminum

Organic acid anions exuded from roots of Picea abies (Norway spruce) seedlings grown on glass beads in the presence and absence of mycorrhiza (Laccaria bicolor) and aluminum (Al) at pH 3.9 were measured. We wanted to test if the roots exuded more organic acid anions when exposed to Al and if mycorrhization influenced the exudation. Oxalate was exuded in far higher amounts than any other organic acid anion, with a maximum rate of 1.7 nmol (mg root DW)^–1 d^–1. Mycorrhizal roots exuded significantly more oxalate than nonmycorrhizal roots. The presence of Al did not enhance oxalate exudation. We conclude that the oxalate exuded constitutively by Picea abies/Laccaria bicolor may lead to rhizosphere oxalate concentrations that are relevant for Al resistance.     

Differential Aluminum Resistance and Organic Acid Anions Secretion in Triticale

Abstract

Triticale (X Triticosecale Wittmack), a hybrid of wheat and rye, shows a high degree of aluminum (Al) tolerance, but variation in Al resistance between cultivars does exist. The mechanisms responsible for differential Al resistance in 10 triticale cultivars were investigated in this study. Triticale roots secreted both malate and citrate in response to Al stress. The amount of organic acid anions secreted was correlated positively to the relative root elongation (an index for Al resistance) and negatively to the Al content in root apices under Al stress, suggesting that the secretion of malate and citrate seems to be involved in the exclusion of Al from root tip. The Al‐induced secretion of malate and citrate was characterized using an Al‐resistant cultivar (ZC 237) and an Al‐sensitive cultivar (OH 1621). Root elongation was significantly inhibited in both ZC 237 and OH 1621 after 24 h of exposure to 30, 50, or 100 µM Al but was more strongly in OH 1621 than in ZC 237 at all Al concentrations tested. A marked lag phase (3 h) between the addition of Al and the secretion of organic acid anions was observed in both triticale cultivars, and the secretion increased with increasing external Al concentration. The two anion‐channel inhibitors, phenylglyoxal and niflumic acid, significantly inhibited the secretion of malate and citrate in ZC 237, with the degree of the inhibition of niflumic acid greater than that of phenylglyoxal. The Al‐induced secretion of malate and citrate decreased to a very low level at low temperature (4°C) in both cultivars. These results indicate that Al‐induced malate and citrate secretion from roots play important roles in excluding Al and thereby detoxifying Al in triticale. The Al‐induced organic acid anions were inhibited by anion‐channel inhibitors and were dependent on temperature.     

Mechanisms of Aluminum Tolerance in Phosphoenolpyruvate Carboxylase Transgenic Rice

Transgenic rice, in which C4-phosphoenolpyruvate carboxylase (PEPC) is overexpressed, was grown in hydroponic culture to evaluate its tolerance for high aluminum (Al) content in relation to organic acid synthesis and exudation into the rhizosphere. With regard to root growth in short-term experiments, PEPC-transgenic rice was more tolerant of Al than the wild type. At increased Al levels in the root medium, root tips of the transgenic rice accumulated less Al than those of the wild type. Aluminum-induced oxalate exudation from roots occurred at increased rates in the transgenic line. Overexpression of C4-PEPC drastically increased PEPC activity in leaves of the transgenic rice, causing higher organic acid concentrations in leaves and roots. The increased organic acid concentrations seemed to cause higher exudation rates of oxalate from roots, leading to a detoxification of Al in the root apoplast and rhizosphere.     

Effects of nitrogen source and aluminum on growth of tropical tree seedlings adapted to low pH soils

The effects of N-source and Al on the growth of seedlings of Melastoma malabathricum, Acacia mangium, and Melaleuca cajuputi, which are tropical woody plants and are very tolerant to Al, and barley (Hordeum vulgare), which is a typical Al-sensitive plant, were investigated. The Al and N treatments consisted of the application of either 0 or 0.5 mM Al, and 2 mM NH₄ ⁺ or N0₃ ^-, respectively. Growth of the tropical plants was enhanced by Al and NH₄ application. In all the plant species, the pH of the culture solution decreased and the concentrations of soluble Al and P increased with the + NH₄ treatment, which positively affected the growth of the tropical plant species. Excised roots of M. malabathricum dissolved insoluble Al with NH₄ application and absorbed Al mainly from root tips. Al did not affect the leaf N concentration except in the case of barley. Roots of M. cajuputi exuded a large amount of citrate, which slightly increased by the + Al treatment. In A. mangium, the reactivity of soluble Al to PCV (pyrocatecholviolet) decreased in the culture solution of the + Al + NH₄. treatment and Al concentration of roots in this treatment was very low. Roots of M. malabathricum released H+ along with Al uptake as well as NH₄ ⁺ uptake. It is concluded that Al and NH₄ ⁺ exert beneficial effects on the growth of tropical tree seedlings.     

一种新型根系分泌物收集装置与收集方法的介绍

根系分泌物在养分活化、改善环境胁迫方面具有重要作用,很多科技工作者对根系分泌物的研究表现出极大兴趣,取得了一系列进展。但土壤栽培条件下,根系分泌物收集是一个难点。本文介绍了一种新型根系分泌物的收集装置与收集方法。该装置由根系生长箱和分泌物收集箱组成,植物在生长箱土壤中生长,通过定向引导作用,根系从生长箱穿过琼脂层进入收集箱中生长,待收集箱内积累一定根系后,通过淋洗收集箱内的介质,实现根系分泌物收集。研究发现,利用该装置收集分泌物,植物总根尖数的90%分布在收集箱。外源有机酸加样回收率可达70%以上。土壤栽培条件下,随生长时期延长,大豆有机酸分泌量逐渐增加,苹果酸分泌量高于柠檬酸。而且土壤栽培条件下大豆柠檬酸和苹果酸分泌量是溶液栽培时的11.4倍和6.7倍。上述研究表明,该装置可以用于土壤栽培条件下根系有机酸的分泌研究。     

油茶根系吸收铝导致生长介质酸化

选用油茶为试验材料,采用固体琼脂培养和溶液培养两种试验体系,研究了油茶根系吸收铝离子与生长介质pH变化的关系。琼脂培养试验结果表明,在钙离子和铝离子介质中,油茶根际区域均发生了明显的酸化;溶液培养试验结果进一步表明,阳离子的吸收尤其是铝离子的吸收是介质酸化的原因,铝与钙同时存在时,溶液酸化主要是由铝离子的吸收引起的。另外,随着溶液铝浓度的增加,溶液pH下降幅度增加,二者之间呈现极显著正相关关系,且油茶培养时间越长,溶液pH下降越多。所有这些结果表明油茶吸收铝会降低生长介质pH。     

铝胁迫下黑麦根尖分泌有机酸和钾离子的研究

采用药理学研究方法,研究了几种抑制剂和脱落酸对铝诱导黑麦根尖分泌有机酸和钾离子的影响。结果表明,在铝(100、200、300μmol/L AlCl3)胁迫下,根尖分泌柠檬酸、苹果酸和钾离子,且随着铝处理浓度的增加其分泌量显著增加。阴离子通道抑制剂苯甲酰甲醛(0.1、0.2 mmol/L)抑制根尖在铝(200μmol/L AlCl3)胁迫下分泌有机酸的同时,也抑制根尖分泌钾离子;钾离子通道抑制剂四乙基铵(20、40 mmol/L)和铯(10、20 mmol/L CsCl)在抑制根尖分泌钾离子的同时,也抑制铝诱导的有机酸分泌。25、50μmol/L的ABA处理后,铝诱导的有机酸分泌和钾离子的分泌均显著增加。但是,铝诱导的有机酸分泌在受到阴离子通道抑制剂尼氟灭酸(0.4、0.8 mmol/L)处理抑制后,钾离子的分泌并不减少;铝胁迫下根尖分泌的钾离子在ATP酶抑制剂钒酸钠(0.25、0.50、2.00 mmol/L)处理后受阻的同时,有机酸的分泌却显著增加。这些结果说明,钾离子是铝诱导黑麦根尖分泌有机酸的陪伴离子,而并非有机酸分泌的调控因子。     

Aluminum and nutrient interplay across an age-chronosequence of tea plantations within a hilly red soil farm of subtropical China

Aluminum (Al) and nutrients are key factors to influence tea (Camellia sinensis L.) productivity and quality, while how they interplay in tea plantations under the pressure of global change and increasing fertilization is little studied. In this study, we selected the tea plantations along an age-chronosequence to study Al fractions using a sequential extraction procedure, and nutrient concentrations in topsoil and subsoil and various plant organs. Our results indicated that Al levels and nutrient concentrations in soils and plants generally increased with planting year (P < 0.05), and soil Al bioavailability was positively correlated with Al concentrations in most plant organs. Significant negative relations among pH and most extractable Al fractions in both soil layers suggested that decreased pH would directly alter soil-plant Al cycling due to exogenous nitrogen (N) fertilizer and atmospheric acid deposition. Topsoil total phosphorus (P) was positively correlated with most Al fractions, and root P was positively correlated with root Al concentration, both of which indicate that P and Al were synchronously absorbed by roots in acid tea soils. In addition, topsoil organic carbon was positively correlated with both active and inert Al fractions, indicating that above-ground organic litters would be the main source of elevated Al levels in older tea plantations. Clearly, Al enrichment in tea leaves with increasing planting year needs to be considered under management practices with heavy N and P fertilizers and increasing atmospheric acid deposition in subtropical China.