Effects of low aluminum activity in nutrient solutions on the organic acid concentrations in maize plants

The effects of low aluminum (Al) activity in nutrient solution on the concentrations of organic acids in two cultivars of maize (Zea mays L.), HS7777 Al‐sensitive and C525‐M Al‐tolerant, were studied. Aluminum stress increased total organic acid concentration in the roots and in the shoots for both cultivars. The relative increase of t‐aconitic, citric, formic, malic, and quinic acids was higher in the roots than in the shoots for both cultivars. The concentrations of c‐aconitic, isocitric, malonic, oxalic, and succinic organic acids were reduced by Al stress, principally for C525‐M. There were no consistent differences in organic acid concentrations between the cultivars to discriminate Al tolerance. The Al tolerance for C525‐M may be justified by lower Al concentrations in the root tips where cellular division takes place and/or by higher excretion of organic acids from roots to the rhizosphere for detoxification of Al by chelation.     

Tolerance of barley cultivars to an acid,aluminum‐toxic subsoil related to mineral element concentrations in their shoots

Abstract

Barley, Hordeum vulgare L., is extremely sensitive to excess soluble or exchangeable aluminum (Al) in acid soils having pH values below about 5.5. Aluminum tolerant cultivars are needed for use in rotations with potatoes which require a soil pH below 5.5 for control of scab disease. They are also potentially useful in the currently popular “low input, sustainable agriculture (LISA)”; in which liming even the plow layer of soil is not always possible or cost effective, or in situations where surface soils are limed but subsoils are acidic and Al toxic to roots. Ten barley cultivars were screened for Al tolerance by growing them for 25 days in greenhouse pots of acid, Al‐toxic Tatum subsoil (clayey, mixed, thermic, typic Hapludult) treated with either 750 or 4000 μg?g^‐1 CaCO₃ to produce final soil pH values of 4.4 and 5.7, respectively. Based on relative shoot dry weight (weight at pH 4.4/weight at pH 5.7 X 100), Tennessee Winter 52, Volla (England), Dayton and Herta (Denmark) were significantly more tolerant to the acid soil than Herta (Hungary), Kearney, Nebar, Dicktoo, Kenbar and Dundy cultivars. Relative shoot dry weights averaged 28.6% for tolerant and 14.1% for sensitive cultivar groups. Comparable relative root dry weights were 41.7% and 13.7% for tolerant and sensitive cultivars, respectively. At pH 4.4, Al concentrations were nearly three times as high in shoots of sensitive cultivars as in those of the tolerant group (646 vs. 175 μg?g^‐1), but these differences were reduced or absent at pH 5.7. At pH 4.4, acid soil sensitive cultivars also accumulated phosphorus concentrations that were twice as high as those in tolerant cultivars (1.2% vs. 0.64%). At pH 5.7, these P differences were equalized at about 0.7% for both tolerant and sensitive groups. At pH 4.4, shoots of the Al‐sensitive cultivar Nebar contained 1067 μg?g^‐1 Al and 1.5% P. Concentrations of Al and P in the shoots of acid soil sensitive cultivars grown at pH 4.4 exceeded levels reported to produce toxicity in barley. The observed accumulation of such concentrations of Al and P in the shoots of plants grown under Al stress is unusual and deserves further study.     

Differential response of two taro cultivars to aluminum: II. Plant mineral concentrations

Abstract

One proposed mechanism of aluminum (Al)‐tolerance involves the ability of plants to maintain uptake of essential mineral elements in the presence of Al. To examine this hypothesis, taro [Colocasia esculenta (L.) Schott] cultivars (cv.) Lehua maoli and Bun long were grown in hydroponic solution at six initial Al levels (0, 110, 220, 440, 890, and 1330 μM Al), and plant mineral concentrations were determined after 27 days. Increasing Al levels significantly increased Al concentrations in taro leaf blades, petioles, and roots. This increase in Al concentrations in the leaf blades as solution Al levels increased was greater for Al‐sensitive cv. Bun long compared to cv. Lehua maoli, resulting in significant interaction between Al and cultivar effects. However, no significant cultivar differences were found for Al concentrations in the petioles or roots. Increasing Al levels in solution significantly depressed concentrations of calcium (Ca), magnesium (Mg), manganese (Mn), and iron (Fe) in taro leaf blades, and significantly depressed concentrations of Ca, Mg, copper (Cu), and zinc (Zn) in taro roots. Aluminum‐induced Ca deficiency appeared to be one possible mechanism of Al phototoxicity in taro, becvasue Ca concentrations in the leaf blades and roots at the higher Al levels were within the critical deficiency range reported for taro. Significant cultivar differences were found, in which Al‐tolerant cv. Lehua maoli had significantly greater Ca and Cu concentrations in the roots, and significantly greater potassium (K) concentrations in the leaf blades across all Al levels. Our results show that Al‐tolerance in taro cultivars is associated with the ability to maintain uptake of essential mineral nutrients, particularly Ca and K, in the presence of Al.     

Responses of Kentucky bluegrass cultivars to excess aluminum in nutrient solutions

Kentucky bluegrass, Poa pratensis L., is generally regarded as an acid‐soil‐sensitive species. However, previous studies in our laboratory showed that cultivars within the species differed widely in tolerance to acid Tatum subsoil (pH 4.6) which is used routinely to screen plants for aluminum (Al) tolerance. In the early studies, specific differential Al tolerance was not demonstrated. The objective of the current study was to test the hypothesis of differential Al tolerance more precisely in nutrient solutions. In one experiment, acid‐soil‐tolerant Victa and Fylking and acid‐soil‐sensitive Windsor and Kenblue cultivars were grown for 35 days in nutrient solutions containing 0, 2, 4, 6, 12, and 24 mg Al L^‐1, at initial pH 4.5, with no subsequent adjustment. In a second experiment, Victa and Windsor were grown for 30 days in solutions containing 0, 4, and 6 mg Al L^‐1, at initial pH 4.5, with no further adjustment. For Victa and Windsor, tolerance to Al in nutrient solution corresponded with tolerance to acid Tatum subsoil, however, the cultivar difference in tolerance, based on relative root dry weight, was only about 2‐fold, compared with 20‐fold in acid Tatum subsoil. Fylking and Kenblue cultivars, which showed a wide difference in tolerance to acid Tatum subsoil, did not show distinct differences in tolerance to Al in nutrient solutions. Possible reasons for this discrepancy are discussed. Superior Al tolerance of Victa (compared with Windsor) was associated with a greater plant‐induced increase in the pH of its nutrient solutions and a corresponding decrease in concentrations of soluble Al in the filtered solutions at the end of the experiments. Greater Al sensitivity in Windsor (compared with Victa) was not related to reduced uptake of phosphorus (P) or excessive uptake of Al; neither cultivar accumulated appreciable Al concentrations in its shoots. The observed differential acid soil and Al tolerance among bluegrass cultivars appears worthy of further study. Improved understanding of Al tolerance mechanisms would contribute to fundamental knowledge of plant mineral nutrition and could aid plant breeders in tailoring plants for greater tolerance to acid subsoils.     

Varietal diversity of upland rice in sensitivity to aluminium

A rapid and simple nutrient addition technique was used for evaluating Al tolerance of six local upland rice (Oryza sativa L.) cultivars (BG35, BR21, DA25, DA26, DA14, and DA22) from Bangladesh and three IRRI rice, IR46, IR97, and IR45, cultivars from the Philippines. The plants were grown for 21 days with Al (0 μM, 140 μM, 280 μM or 560 μM) at pH 4.1. The roots were more affected by Al than the shoots. In rating cultivars for Al sensitivity, relative shoot weight (RSW) was found to be the best parameter due to the severe damage of the roots, irrespective of Al sensitivity. The cultivars were rated as Al tolerant (BG35, BR21, DA25, and DA26), mid‐tolerant (DA14, DA22, and IR46) and sensitive (IR97 and IR45) . More Al was retained in the roots of tolerant cultivars than in the mid‐tolerant or sensitive cultivars. In shoots, the Al concentration of tolerant cultivars was less than in the mid‐tolerant or in the sensitive cultivars and the inhibition of growth was proportional to Al concentration irrespective of Al tolerance. Therefore, the variation among cultivars in Al sensitivity could be related to the capacity of roots to retain Al from transport to the shoots.     

Differential response of citrus rootstocks to aluminum levels in nutrient solutions: II. Plant mineral concentrations 2

The objective of this study was to determine relations between Al effects and mineral concentrations in citrus seedlings. Six‐month‐old seedlings of five citrus rootstocks were grown for 60 days in supernatant nutrient solutions of Al, P, and other nutrients. The solutions contained seven levels of Al ranging from 4 to 1655 μM. Al and similar P concentrations of 28 μM P. Aluminum concentrations in roots and shoots increased with increasing Al concentration in the nutrient solution. Aluminum concentrations in roots of Al‐tolerant rootstocks were higher than those of Al‐sensitive rootstocks. When Al concentrations in nutrient solution increased from 4 to 178 μM, the K, Mg, and P concentrations in roots and the K and P levels in shoots increased. Conversely, Ca, Zn, Cu, Mn, and Fe in the roots and Ca, Mg, Cu, and Fe in the shoots decreased. The more tolerant rootstocks contained higher Fe concentrations in their roots than did the less tolerant ones when Al concentrations in solution were lower than 308 μM. Concentrations of other elements (Ca, K, P, Mg, Zn, and Mn) in roots or shoots exhibited no apparent relationship to the Al tolerance for root or shoot growth of the rootstocks. Calcium, K, Zn, Mn, and Fe concentrations in roots and Mg and K concentrations in shoots of all five rootstocks seedlings had significant negative correlations with Al concentrations in corresponding roots or shoots.     

Aluminum tolerances of two snapbean cultivars related to organic acid content evaluated by high‐performance liquid chromatography

High‐performance liquid chromatography (HPLC) was used to determine aluminum (Al)‐induced changes in organic acid (OA) concentrations of Al‐tolerant ‘Dade’ and Al‐sensitive ‘Romano’ snapbean cultivars. Two week old ‘Dade’ and ‘Romano’ snapbean were grown in 1/5‐strength Steinberg nutrient solution for 10 days and then subjected to 0, 2, 4, 6, and 8 mg L^‐1 Al treatments at pH 4.5 for an additional 3–15 days. Current studies confirmed earlier findings that the Dade cultivar was significantly more tolerant to Al than the Romano variety. Organic acid analyses were performed on extracts of root and leaf, and on stem exudates. The organic acids were separated on an ion exclusion column using a mobile phase of 0.01 N H₃PO₄. Individual OA were quantified with a variable wavelength detector operating at 210 nm. Aluminum stress tended to reduce the concentrations of citric, malonlc, malic, glycolic, fumaric, and acetic acids in the roots and increased the OA concentrations in stem exudates. In the presence or absence of Al stress, the Al tolerant Dade cultivar contained higher OA concentrations than did the Al‐sensitlve Romano. Aluminum stress reduced total OA levels in root extracts from Al‐sensltive Romano plants to a greater extent than in those of the Al‐tolerant Dade. Malic and citric acid concentrations were decreased more than those of the other organic acids examined. Results indicate that the Al‐tolerant Dade snapbean cultivar has a higher potential for Al‐chelation and detoxification than does the Al‐sensitive Romano. Hence, an Al‐chelation mechansism may be involved in differential Al tolerance within this species.     

Responses of forage grasses to aluminum in solution culture

Growth, nutrient uptake and nutrient uptake efficiency differences in orchardgrass (Dactylis glomerata L.), tall fescue (Festuca arundinacea Schreb), and timothy (Phleum pratense L.) were evaluated at 0, 100, 200, and 300 μM Al. In each of the species, cultivar differences were also compared. In the absence of Al stress, cultivars of orchardgrass outperformed other grasses. The presence of Al reduced shoot and root growth; however, the magnitude of the growth reduction depended upon the species and cultivars. The growth of shoots and roots showed a significant difference with respect to species, cultivars, treatment Al and their Interactions. Aluminum reduced the uptake of many essential nutrients. At 100 μM Al Potomac orchardgrass had the highest and climax timothy had the lowest mineral content. The efficiency ratio (ER) assisted in classifying grass entries into efficient and inefficient utilizers of the absorbed nutrients. The ER is defined as milligrams of dry shoot weight produced per milligram of element in the shoot. The ER for P, K, Cu and Zn gave a positive correlation with shoot weight; however, in general, negative relationships were observed for shoot growth and ER for Mg, Fe, and Mn. In all the species increasing Al concentration from 0 to 100 μM increased ER for Mg and decreased ER for K and Zn. With the exception of tall fescue cultivars, the ER for P was reduced by 100 μM Al. The species and cultivars used in this study showed inter‐ and intraspecific differences in growth, uptake, and ER for nutrients in the presence or absence of Al stress. Significant reduction in growth, even at 100 μM Al by all the three species of grass indicates that these grass species are far more sensitive to Al than the field crops. Therefore, experiments with levels of Al lesser than 100 μM would have given a better outlook on the performances of these grass species.     

Acid soil tolerances of two wheat cultivars related to soil Ph,KCl‐extractable aluminum and degree of aluminum saturation

Aluminum toxicity, associated with soil acidity, is a major growth‐limiting factor for plants in many parts of the world. More precise criteria are needed for the identification of potential Al toxicity in acid soils. The objective of the current study was to relate the acid soil tolerances of two wheat cultivars to three characteristics of an acid Tatum subsoil (clayey, mixed, thermic, typic Hapludult): pH in a 1:1 soil to water suspension; KCl‐extractable Al; and degree of Al saturation. Aluminum‐tolerant ‘BH 1146’ (Brazil) and Al‐sensitive ‘Sonora 63’ (Mexico) wheat cultivars were grown in greenhouse pots of soil treated with CaCO₃ to establish final soil pH levels of 4.1, 4.6, 4.7, 4.9, 5.2 and 7.3. Soil Al, Ca and Mg were extracted with 1 N KCl, and Al saturation was calculated as KCl‐Al/KCl Al + Ca + Mg%.

Within the soil pH range of 4.1 to 4.9, BH 1146 tops and roots produced significantly more dry matter than did those of Sonora 63; however, at pH 5.2 and 7.3, the top and root yields of the two cultivars were not significantly different. Significant cultivar differences in yield occurred over a range of 36 to 82% saturation of the Tatum soil. Graphs of relative top or root yields against soil pH, KCl‐extractable Al and Al saturation indicated that the two cultivars could be separated for tolerance to Tatum soil under the following conditions: pH less than 5.2 (1:1 soil‐water); KCl‐Al levels greater than 2 c mole kg^‐1 and Al saturations greater than 20%. Results demonstrated that any soil test used to predict Al toxicity in acid soils must take into account the Al tolerances of the plant cultivars involved.     

Aluminum toxicity and high bulk density: Role in limiting shoot and root growth of selected aluminum indicator plants and eastern gamagrass in an acid soil

Abstract

Shallow rooting and susceptibility to drought are believed to be caused, at least in part, by strongly acidic (pH <5.5, 1:1 soil‐water), aluminum (Al)‐toxic subsoils. However, this hypothesis has not been clearly confirmed under field conditions. The Al toxicity hypothesis was tested on a map unit of Matawan‐Hammonton loam (0–2% slope) on unlimed and limed field plots (pH range 5.1 to 5.8) at Beltsville, MD, during 1994 to 1998. Aluminum‐tolerant and sensitive pairs of barley (Hordeum vulgare L.), wheat [Triticum aestivum (L.)], snap bean (Phaseolus vulgaris L.), and soybean [Glycine max (L.) Merr.] cultivars were used as indicator plants. Eastern gamagrass [Tripsacum dactyloides (L.) L.], cultivar ‘Pete’, reported to tolerate both chemical and physical stress factors in soils, was grown for comparison. Shoots of Al‐sensitive ‘Romano’ snap beans showed a significant response to liming of the 0–15 cm surface layer, but those of Al‐tolerant ‘Dade’ did not, indicating that Al toxicity was a growth limiting factor in this acid soil at pH 5.1. Lime response of the Al‐tolerant and sensitive cultivars of barley, wheat, and soybean were in the same direction but not significant at the 5% level. Aluminum‐tolerant and sensitive cultivars did not differ in abilities to root in the 15–30 cm soil depth. Only 9 to 25% of total roots were in this layer, and 75 to 91% were in the 0–15 cm zone. No roots were found in the 30–45 cm zone which had a pH of 4.9. Soil bulk density values of 1.44 and 1.50 g cm^?3 in the 15–30 and 30–45 cm zones, respectively, indicated that mechanical impedance was a primary root barrier. Results indicated that restricted shoot growth and shallow rooting of the Al‐indicator plants studied in this acid soil were due to a combination of Al toxicity and high soil bulk density. Confounding of the two factors may have masked the expected response of indicator plants to Al. These two growth restricting factors likely occur in many, if not most acid, problem subsoils. Studies are needed to separate these factors and to develop plant genotypes that have tolerance to multiple abiotic stresses. Unlike the Al indicator cultivars, eastern gamagrass showed high tolerance to acid, compact soils in the field and did not respond to lime applications (pH 5.1–5.8).     

Tolerance of durum wheat lines to an acid,aluminum‐toxic subsoil

Durum wheat, Triticum durum Desf., is reportedly more sensitive to aluminum (Al) toxicity in acid soils than hexaploid wheat, Triticum aestivum L. em. Thell. Aluminum‐tolerant genotypes would permit more widespread use of this species where it is desired, but not grown, because of acid soil constraints. Durum wheat germplasm has not been adequately screened for acid soil (Al) tolerance. Fifteen lines of durum wheat were grown for 28 days in greenhouse pots of acid, Al‐toxic Tatum subsoil at pH 4.5, and non‐toxic soil at pH 6.0. Aluminum‐tolerant Atlas 66 and sensitive Scout 66 hexaploid wheats were also included as standards. Based on relative shoot and root dry weight (wt. at pH 4.5/wt. at pH 6.0 X 100), durum entries differed significantly in tolerance to the acid soil. Relative shoot dry weight alone was an acceptable indicator of acid soil tolerance. Relative dry weights ranged from 55.1 to 15.5% for shoots and from 107 to 15.8% for roots. Durum lines PI 195726 (Ethiopia) and PI 193922 (Brazil) were significantly more tolerant than all other entries, even the Al‐tolerant, hexaploid Atlas 66 standard. Hence, these two lines have potential for direct use on acid soils or as breeding materials for use in developing greater Al tolerance in durum wheat. Unexpectedly, the range of acid soil tolerance available in durum wheat appears comparable to that in the hexaploid species. Hence, additional screening of durum wheat germplasm for acid soil (Al) tolerance appears warranted. Durum lines showing least tolerance to the acid soil included PI 322716 (Mexico), PI 264991 (Greece), PI 478306 (Washington State, USA), and PI 345040 (Yugoslavia). The Al‐sensitive Scout 66 standard was as sensitive as the most sensitive durum lines. Concentrations of Al and phosphorus were significantly higher in shoots of acid soil sensitive than in those of tolerant lines, and these values exceeded those reported to cause Al and phosphorus (P) toxicities in wheat and barley.     

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.     

Effects of low aluminium levels on growth and nutrient relations in three rice cultivars with different tolerances to aluminium

Reports on varietal diversity of upland rice in relation to relatively low aluminium (Al) levels are limited. Therefore, effects were examined of 35, 70, and 140 μM Al on plant growth and uptake of macro‐ and micro‐nutrients (K, P, Ca, Mg, Fe, Zn, Cu, and Mn) and their distribution in three upland rice (Oryza saliva L.) cultivars (BG35, DA14, and IR45) with different Al sensitivity. After an initial growth period of 5 days without Al, the plants were grown for 21 days in nutrient solutions containing Al at pH 4.1. Cultivar BG35 showed the highest and IR45 the lowest tolerance to Al when fresh weights of shoots or roots were considered. Except for IR45 at 140 μM Al, total dry weight was unaffected by Al, and the cultivars could not be clearly distinguished with respect to Al tolerance. Net Al uptake rate was higher in Al tolerant BG35 than in DA14 or IR45. Conversely, in IR45 the absorbed Al was rapidly transported to the shoots and accumulated there. In BG35, net P and Ca uptake rates in Al‐treated plants were high enough to maintain the P and Ca status of the shoots at all Al levels. Irrespective of Al sensitivity, there was a general depression of internal Mg concentration in Al‐reated plants. The Fe, Zn, Cu, and Mn concentrations of the plants were not negatively affected by Al in any of the cultivars.     

Growth and macronutrient contents of faba bean plants: Effects of salinity and nitrate nutrition

The effects of the interaction between sodium chloride, nitrate, and concentrations on growth and internal ion content of faba bean (Vicia faba L.) plants were studied, to understand the relationship between the above parameters and salt tolerance. Increased salinity substantially reduced the dry weight of roots and shoots and increased the root/shoot biomass ratio. Additional nitrate‐N considerably moderated the salinity effects on these parameters. The promotive effects of nitrate‐N were more pronounced on shoot dry weight. These results suggest that an exogenous supply of nitrate‐N would improve the vegetative growth of V. faba plants by moderating the suppresive effects of salinity. The evolution of the root and shoot content in potassium (K), sodium (Na), magnesium (Mg), calcium (Ca), and nitrogen (N) was monitored during vegetative growth. A high correspondence between total N and Ca content was found. The acquisition of Ca and K in response to salt and nitrate was similar in shoots and roots, whereas Mg uptake showed notable differences in the two organs. In salt‐affected plants, the roots were found to be high in accumulated Na while the shoots exhibited the lowest Na concentration. Potassium accumulation was higher in the shoots. In this way, there was an antagonistic effect between Na and K uptake. Analyses of the nutrient contents in plant organs have provided a data base on salt‐tolerance mechanisms of V. faba plants.     

高铝低磷胁迫对胡枝子生长及矿质元素吸收的影响

限制酸性土壤作物生长的最重要、最普遍的因子是Al3+ 的毒害和 P 的缺乏.本文用溶液培养试验研究两种不同生态型的二色胡枝子在高Al低P胁迫下的矿质营养元素积累情况.试验表明,江西胡枝子比河北胡枝子更耐低 P 低 pH 的生长环境,但两者间耐Al性无显著差异;100 μm/L Al 处理显著地抑制了两种胡枝子对 Ca 的吸收,降低了根系 Mg 的积累量,对植株的 K、P、Fe、Zn、Cu 含量没有显著影响;低 P 处理没有显著降低两种胡枝子对 Ca、K、Fe、Zn、Cu 和江西胡枝子对 Mg 的吸收,但是低 P 处理显著降低了河北胡枝子对 Mg 的吸收和转运.二色胡枝子植株吸收的 Al 主要积累在根部,地上部分Al含量仅是根系的1% 左右.     

Mechanisms of aluminum tolerance in triticum aestivum L. (wheat) III. Long‐term pH changes induced in nutrient solutions by winter cultivars differing in tolerance to aluminum

Five winter cultivars of Triticum aestivum L., representing a known range of tolerance to aluminum (Al), were grown in nutrient solutions with and without Al for 41 days to determine long‐term changes in solution pH. Plant‐induced pH of the nutrient solutions declined for 16 to 17 days. Subsequently, the pH induced by Al‐sensitive plants grown without Al and Al‐tolerant plants grown with Al and without Al increased rapidly, presumably reflecting depletion of NH₄ ⁺ from the nutrient solutions. Aluminum‐sensitive plants grown with Al showed a less pronounced pH rise after 16 to 17 days of treatment.

After nutrient solutions were renewed on days 26 and 34, plant‐induced pH patterns were similar to those during days 1 to 26. However, the time required for the onset of the rapid rise in pH decreased. In these subsequent pH cycles, the pH patterns induced by Al‐tolerant plants grown with Al progressively approximated those induced by plants grown without Al. Aluminum‐sensitive plants grown with Al did not induce a rapid rise In pH of nutrient solutions.

Differential tolerance to Al was apparent visually after three to five days growth. Cultivar tolerance to Al was correlated with the initial rate of the pH decline (days 1 to 26) as well as final pH of solutions discarded on days 26, 34, and 41. These results support the hypothesis that differential uptake of NH₄ ⁺ and NO₃ ^‐ causes cultivar differences in plant‐induced pH of nutrient solutions and affects the relative growth of cultivars in Al‐toxic nutrient solutions.     

Low phosphate nutrition alters bean plants’ ability to assimilate and translocate nitrate

Bean plants (Phaseolus vulgaris L.) were cultured for 10 or 18 days on phosphate sufficient (+P) or phosphate deficient (‐P) nutrient medium. Nitrate and phosphate distribution between shoot and root, nitrate uptake, and nitrate reductase activity (NR activity, in vivo and in vitro) in root and leaves was estimated. The decrease in Pi concentration in leaves and roots led to decreased rate of NO₃ uptake and increased NO₃ accumulation in roots, accompanied by alterations in NO₃ distribution between shoot and roots. Nitrate reductase activity estimated in vitro was twice higher than estimated in vivo and both in +P and ‐P plants was lower in the roots than in the shoots. The decrease of NR activity in ‐P plants was more pronounced in the roots and after 2 weeks of phosphate starvation it was about 40% lower as compared with the control. The depression in nitrate uptake may be the result of feedback inhibition due to accumulation of nitrate in the roots. The increased NO₃ concentration in root tissue may be explained by decreased NR activity and lower transport of nitrate from roots to shoot.     

铝毒胁迫下磷对荞麦根系铝形态和分布的影响

以2个荞麦（Fagopyrum esculentum Moench）品种＂江西荞麦＂（铝耐性）和＂内蒙荞麦＂（铝敏感）为材料,采用水培法,研究铝毒胁迫下磷对荞麦根系总铝和单核2种形态以及Al在根尖和细胞壁中的分布情况的影响。结果表明,与200μmol/L Al处理相比,1.0mmol/L磷预处理分别使江西荞麦和内蒙荞麦的相对根长增加了24.4%和35.9%,根系总Al含量分别降低了18.2%和22.5%,根系单核Al含量分别降低了95%和63.2%。根尖细胞壁荧光检测结果为在单Al胁迫下细胞壁的荧光强度最大,1.0mmol/L磷预处理大幅度减弱细胞壁的荧光强度。表明外源磷供应可降低根系总Al和单核Al含量,使毒性形态的铝转化为无毒形态,以及减少Al在根尖以及细胞壁的积累,以缓解Al对根伸长的抑制,提高荞麦根系的抗铝毒害能力。     

Aluminum toxicity in tomato. Part 1. growth and mineral nutrition

Aluminum (Al) toxicity was studied in two tomato cultivars (Lycopersicon esculentum Mill. ‘Mountain Pride’ and Floramerica') grown in diluted nutrient solution (pH 4.0) at 0, 10, 25, and 50 μM Al levels. In the presence of 25 and 50 μM Al, significant reduction was found in leaf area, dry weight, stem length, and longest root length of both cultivars. Growth of ‘Floramerica’ was less sensitive to Al toxicity than growth of ‘Mountain Pride’. Elemental composition of the nutrient solutions were compared immediately after the first Al addition and four days later. The uptake of micronutrients copper (Cu), manganese (Mn), molybdenum (Mo), zinc (Zn), boron (B), and iron (Fe) from the nutrient solution was reduced in both cultivars with increasing Al levels. Nutrient solution Al gradually decreased in time for every treatment; less in cultures of ‘Floramerica’ than in ‘Mountain Pride’. Aluminum treatments decreased the calcium (Ca), potassium (K), magnesium (Mg), Mn, Fe, and Zn content in the roots, stems, and leaves. Aluminum treatment promoted the accumulation of P, Mo, and Cu in the roots, and inhibited the transport of these nutrients into stems and leaves. At 25 and 50 μM levels of Al, lower Al content was found in the roots of cv. “Floramerica’ than in the roots of cv. ‘Mountain Pride’.     

Tolerances of wheat germplasm to acid subsoil

Aluminum toxicity is a major growth limiting factor for plants in many acid soils of the world. Correcting the problem by conventional liming is not always economically feasible, particularly in subsoils. Aluminum tolerant plants provide an alternative and long‐term supplemental solution to the problem. The genetic approach requires the identification of Al tolerance sources that can be transferred to cultivars already having desirable traits. Thirty‐five cultivars and experimental lines of wheat (Triticum aestivum L. em. Thell) were screened for Al tolerance on acid Tatum soil (clayey, mixed thermic, typic Hapludult) receiving either 0 or 3500 mg CaCO₃/kg (pH 4.1 vs. pH 7.1). Entries showed a wide range of tolerance to the acid soil. On unlimed soil at pH 4.3, absolute shoot dry weights differed by 5‐fold, absolute root dry weights by 6.5‐fold, relative shoot weights (wt. at pH 4.3/wt. at pH 7.1 %) by 4.7‐fold and relative root dry weights by 7‐fold. Superior acid soil (Al) tolerance of ‘BH‐1146’ from Brazil and extreme sensitivities of cultivars ‘Redcoat’ (Indiana, USA) and ‘Sonora 63’ (Mexico) were confirmed. Seven experimental (CNT) lines from Brazil showed a range of acid soil tolerance but were generally more tolerant than germplasm from Mexico and the USA. One line, ‘CNT‐1’, was equal to BH‐1146 in tolerance and may be useful in transferring Al tolerance to existing or new cultivars. Five durum cultivars (Triticum, durum, Desf.) were extremely sensitive to the acid Tatum subsoil at pH 4.3 compared with pH 7.1.