Pattern of supply affects boron toxicity in barley

Barley (Hordeum vulgare L., cv. Stirling) was grown in pots of a sandy soil to which six levels of boron (B) were added presowing, during stem elongation, or during ear emergence. The pattern of B supply affected the development of leaf injury and other symptoms of B toxicity, the accumulation of B in the grain and in the whole shoots (WS) at maturity, and the relationships between the concentrations of B in the grain and in the WS at maturity and yield. Critical toxic concentrations (CTC) of B in plant tissues were found to vary from approximately 2 to 15 μg/g, and from approximately 50 to 420 μg/g, respectively. The findings of this experiment suggest that barley plants can accumulate relatively high levels of B and express severe levels of leaf injury and other symptoms of B toxicity in the latter stages of growth with relatively small effects on grain yield. They also suggest that the grain and the WS sampled at maturity are not suitable tissues for the diagnosis of yield depressions due to B toxicity in Stirling barley.     

Boron uptake and toxicity in maize genotypes in relation to boron and phosphorus supply

The effect of increasing levels of applied phosphorus (P) and boron (B) on the growth and the concentration and uptake of P and B were examined in eight maize genotypes (Furio, Riogrande, Sele, DK 743, Helix, Missouri, Betor, and Poker) with two individual greenhouse experiments. Phosphorus was applied at 0, 50, and 100 mg kg^‐1 in Experiment I and B at 0, 10, and 30 mg kg^‐1 levels in Experiment II. Application of B resulted in increased concentration and uptake of B and a decreased P concentration and uptake in all genotypes. The dry weight of all genotypes was decreased by application of B. However, applied P decreased B concentration and uptake and increased P concentration and uptake of the genotypes. The dry weight of all genotypes was increased by application of P. These experiments show that B is more toxic in the absence of rather than the presence of P, and that this toxicity could be alleviated with applications of P in the calcareous soils of semiarid areas.     

Nitrogen source and aluminum toxicity of two sorghum genotypes differing in aluminum susceptibility

After a 35 days growth on nutrient solutions with NO^‐ ₃ NH₄NO₃ and NH⁺ ₄ as nitrogen source (pH 4.2) dry matter yield of the sorghum genotype SC0283 was much less affected by Al (1.5 mg‐¹) than that of the genotype NB9040. With NO^‐ ₃ as the sole nitrogen source only growth of the NB9040 plants was significantly reduced. Since OH^‐ efflux, shoot Al content and concentrations of all major nutrients of both genotypes were almost equal, a higher sensitivity to Al may underlie the lower Al tolerance of the NB9040 genotype. In the presence of NH.‐N Al again lowered d.m. yield of the NB plants. With SCO283 significant Al effects on d.m. yield were observed only with NH₄NO₃. Aluminum drastically increased the amount of protons released per unit of root surface area, especially with the NB9040 line. This shift in proton flux density was partly the result of a decrease of the specific root surface area and partly due to enhanced excess of catlonic nutrients taken up. With NH₄NO₃‐fed plants the latter could almost completely be attributed to a changed N preference brought about by inhibited uptake of NO^‐ ₃ and a simultaneous enhanced NH, absorption. Although both proton efflux and NH⁺ ₄ preference of the NB plants were severely increased by Al, relative yields of this genotype were not lowered by NH⁺ _4. This can probably be explained by (1) the high NH, sensitivity of this cultivar through which Al effects can be masked and (2) the continuous adjustment of the solution pH through which rhizosphere conditions were prevented.     

Selection for ryegrass genotypes with tolerance to aluminum toxicity

Abstract

This study reports on a procedure where ryegrass (Lolium multiflorum Lam.) varieties are screened for tolerance to aluminum toxicity. The procedure utilized was a solution‐paper method where seedlings were grown on filter paper which transported nutrient solution from a reservoir. Mean root length for genotypes was the character utilized to determine tolerance to aluminum toxicity. Ryegrass genotypes were subjected to [Al] between 0 to 8 mM with the most useful concenrations being from 2 to 4 mM. Genotypes which demonstrated some tolerance to higher [Al] were North American Plant Breeders R. 0051, ‘Aubade’, ‘Urbana’, Fla 1977B, ‘Tetragulf, Mommersteeg Lmw 96. Considerable variation in root length due to genotypic effect tended to obscure the [Al] effect. The relative rankings of root growth ratios of 4 mM [Al] to 2 mM [Al] tolerance of ryegrass cultivars is questionable. Further work to establish a more reliable screening technique for this specie needs to be undertaken.     

The effect of cobalt stress on growth and physiological traits and its association with cobalt accumulation in barley genotypes differing in cobalt tolerance

Cobalt (Co) is beneficial for legume plants and not an essential element for most plants. There is no sufficient information about the effect of Co stress on barley growth. The current experiment was carried out to investigate the effects of different Co levels (25, 50, 75, and 100 µM) on growth and physiological traits of three barley genotypes (B325, J36, and B340) differing in Co tolerance. The results showed that Co stress inhibited plant growth, decreased chlorophyll content and photosynthetic rate, and enhanced oxidative stress. However, the effects differed among genotypes, with B325 and B340 being the most and the least affected, respectively. Co stress caused decrease and increase of manganese (Mn) and phosphorus (P) concentrations in both roots and shoots, respectively; iron (Fe) concentration had little change in shoots and a significant decrease in roots. The current results showed a close association of Co tolerance and its accumulation in plant tissues.     

Methods of assessing boron availability in potting media with special reference to toxicity

Abstract

Hot water, water and 2M DTPA (room temperature), all at 1:1.5 volume ratio, and saturation extracts with and without added DTPA, were compared for their ability to assess the availability of B in pottting media. In three experiments, B concentrations in the extractants were highly linearly correlated with one another, although medium components and pH affected the slopes of the relationships. Hot water extracted between 38 and 77% of the B in Pinus radiata‐based media and 58 to 97% of that in peat. The proportion was little affected by the pH of the medium. The solutions at room temperature extracted considerably less B than did hot water and the proportion extracted decreased with increasing pH. B in extracts at room temperature was more highly correlated ( r² = 0.90–0.97) with B uptake by a range of plants with widely differing tolerance of high concentrations of B than was hot water soluble B (r² = 0.79–0.94). No symptoms typical of B deficiency were observed at the lowest concentrations of extractable B attained in these experiments, which were 0.08 and 0.27 mg/L B in 2 mM DTPA (1:1.5 by volume) and saturation extracts containing DTPA respectively. Other evidence suggests that concentrations at the detection limit (about 0.03 mg/L) of the analytical technique used are adequate for normal flowering of Chrysanthemum morifolium cv. Yellow Mandalay. For absence of foliar toxicity symptoms in horticultural plants sensitive to B, 2 mM DTPA (1:1.5 by volume) and saturation extracts containing DTPA should not contain more than about 0.6 and 1 mg B/L, respectively. Tolerant species can remain symptom‐free in media giving up to about 5 and 8.3 mg B/L in the two extracts, respectively. These results will be particularly useful for checking for potential B toxicity in potting media containing composted waste materials.     

Root morphology of wheat genotypes differing in zinc efficiency

The root morphology (root length, diameter) of the three wheat genotypes (Triticum aestivum L. cvs Excalibur and Gatcher, and T. turgidum conv. durum (Desf.) McKay cv Durati) grown in zinc (Zn)‐deficient, sandy soil under controlled conditions has been measured by a root scanner coupled to a computer. Wheat plants were supplied with 0, 0.025, 0.05, 0.1, 0.2, or 0.4 mg Zn/kg soil. Excalibur has previously been identified as the Zn‐efficient genotype which can take up more Zn and has higher yield in soils with low plant‐available Zn. Durati is Zn‐inefficient and Gatcher an intermediate genotype with respect to Zn efficiency. Root and shoot dry matter significantly increased at 0.1 mg Zn/kg soil compared to the 0 Zn level. Zinc content in shoots was lower in Durati than in Excalibur and Gatcher at sufficient supply of Zn. Zinc applications had no significant effect on root morphology at two weeks after sowing. At that time, however, the Zn‐efficient genotype Excalibur developed a longer and thinner roots (greater proportion of fine roots with diameter <0.2 mm) than the less efficient Gatcher and Zn‐inefficient Durati. Hence, growing longer and thinner roots and having a greater proportion of thinner roots in the total root biomass early in the growth period may be the two characters associated with the Zn‐efficient genotypes.     

Difference in response to aluminum stress among Tibetan wild barley genotypes

Wild barley (Hordeum sp.) germplasm is rich in genetic diversity and provides a treasure trove of useful genes for crop improvement. We carried out a comprehensive program combining short‐term hydroponic screening via hematoxylin‐staining of root‐regrowth procedure and filter paper–based evaluation of diverse germplasm in response to Al/acid stress using 105 annual Tibetan wild barley and 45 cultivated barley genotypes. Root elongation among the 105 Tibetan wild barley genotypes varied significantly after Al exposure, ranging from 62.9% to 80.0% in variation coefficients and 4.35 to 4.45 in diversity index. These genotypic differences in Al resistance were fairly consistent in both the hydroponic and filter paper–based evaluations: XZ16, XZ166, and XZ113 were selected as Al‐resistant genotypes, and XZ61, XZ45, and XZ98 as Al‐sensitive wild genotypes. Furthermore, significantly lower Al concentrations in roots and shoots were detected in the three selected Al‐resistant genotypes than in the three sensitive genotypes in the filter paper–based experiment. Meanwhile, XZ16 was the least affected by Al toxicity in regard to reduced SPAD value (chlorophyll meter readings), plant height, root length, dry biomass, tillers per plant, and chlorophyll fluorescence (Fv/Fm) in the long‐term hydroponic experiment compared with the Al‐resistant cultivated barley cv. Dayton, while XZ61 had the severest stress symptoms.     

Evaluating quantitative screening methods for manganese toxicity in cotton genotypes 1

Identification of cotton genotypes more tolerant of toxic concentrations of soil solution manganese (Mn²⁺) would integrate well with soil ameliorations of that problem. Several quantitative and semi‐quantitative methods to determine the amount of Mn toxicity were evaluated on three genotypes of Gossypium hirsutum (LaDSIS 12513, LaDASS 5175, and Coker gl 79–501) and one genotype of Gossypium barbadense (Pitnas S‐5). Specific leaf weight (SLW) and the semi‐quantitative, ‘percentage of leaves that were damaged’ (PLD) correlated the least with other methods of Mn toxicity determination. Neither SLW or PLD provided more separation between genotypes than area/leaf (AL), peroxidase (POD) activity, and indole‐3‐acetic acid oxidase (IAAO) activity. Similar genotype separations occurred for AL, POD, and IAAO at 10 mg/L Mn in solution, but POD and IAAO produced more genotype separations than AL at 5 mg/L of Mn. There were differences in enzyme activity between genotypes at control (0.25 mg/L) Mn solution concentration, making assessment difficult, especially between species. Barring this caveat, the relatively fast POD activity assay was considered to be the best method since it paralleled activity of IAAO, the functional enzyme of Mn toxicity, which had a relatively slow assay method.     

Critical toxic concentrations of boron are variable in barley

The use of leaf symptoms and plant analysis in diagnosing and predicting yield depressions associated with boron (B) toxicity in barley was examined. Barley (Hordeum vulgare L., cv. Stirling) was grown in pots of a sandy soil to which six levels of B were added. With increasing additions to the soil, B accumulated in the older leaves, increasing leaf injury and senescence. Leaf injury symptoms at high levels of B supply appeared in time well before dry mailer was depressed. Root weight was decreased more than shoot weight. Grain filling was affected only at severe levels of B toxicity. Critical toxic concentrations (CTC) of B in shoots were found to vary between approximately 40 and 150 μg, depending on the stage of plant growth at the lime of B analysis and the yield parameter chosen. A distinction is made between CTC values of B that are diagnostic or prognostic.     

硅对大麦铝毒的消除和缓解作用研究

在温室和实验室进行了施硅对消除或缓解大麦酸害铝毒的土培和溶液培养试验。结果表明,施硅后大麦幼苗的地上部茎、叶和地下部根的生物量均比不施硅明显增加。施硅能有效地促使植株吸收的铝在根部积累,抑制铝向地上部分运转;施硅还能调节根吸收的磷向地上部分运移,以减轻因伴随铝毒而产生的缺磷症状。施硅消除或缓解酸害铝毒的可能机理是:铝与硅形成无毒的铝硅酸复合离子(HAS),降低活性铝的浓度,及硅能调节大麦幼苗地上部和根内铝和磷的再分配。     

两种冬小麦对铝毒响应的敏感性差异研究

A experiment was carried to evaluate the effects of Al on growth, accumulations of free proline and amino acid in 2 wheat cultivars (Triticum aestivum L.), Yangmai No.5 and Jian 864, differing in Al sensitivity. Plants grew initially in a nutrient solution without Al for 13 days before the addition of Al and finally in a nutrient solution containing 0.5mmol Al (L^-1) for 19 days. The results showed that there were marked decreases in dry weight, relative growth rate (RGR) and net assimilation rate (NAR) of Al-treated seedlings compared with control plants. The Al effects were more evident in Yangmai No.5 than Jian 864. Leaf area ratio(LAR) was little affected by Al. RGR was highly correlated with NAR rather than LAR. Aluminum increased the concentrations of free proline and total free amino acid in shoots of both the cultivars. The increases were greater in Yangmai No.5 than in Jian 864. The percentage of free proline in total amino acid in shoots was not affected by Al treatment. It was possible that accumulation of proline was merely a symptom of Al injury. The concentrations of total nitrogen in Al-treated plants did not significantly differ from those of control plants. Nitrate reductase activity (NRA) in leaves was severely decreased by Al, and a greater decrease was noted in Yangmai No.5 than in Jian 864, but NRA in roots of both the cultivars was not affected. The decreases in NRA might be an indirect (accumulation of amino acid) rather than a direct result of Al toxicity.     

Changes in total protein profiles of barley cultivars in response to toxic boron concentration

In this study, ten‐day‐old seedlings of barley {Hordeum vulgare L. cultivar Anadolu [boron (B)‐tolerant] and Hamidiye (B‐sensitive)} were used. Boron‐treated plants were grown on H₃BO₃ solution (final concentration of 10 mM) for five days. Control plants received no B treatment during this period. Total protein patterns were obtained by analysis of total protein extract from root and leaf tissues of control and B‐treated plants using two‐dimensional gel electrophoresis followed by silver staining. The protein profile of B‐treated seedlings of each cultivar was compared to the profile of control (no stress treatment) plants of the same cultivar. Silver‐stained gels showed that B stress caused increases or decreases in a number of proteins in root and leaf tissues. Moreover, as a result of B treatment, one newly synthesized protein with relative molecular weight (M_r) of 35.0 kDa was detected in root profile of the tolerant cultivar. This protein failed to show up in root profile of the B‐treated sensitive cultivar. Three proteins were quantitatively increased in B‐treated root profile of both cultivars. Following B treatment, three proteins were increased in root profile of the tolerant cultivar, but were not changed in the sensitive one. In leaf tissues, however, there were remarkable changes in total protein profiles after B treatment, relative to the control. Following B treatment, in leaf tissues, at least seven proteins were increased in amount in tolerant cultivar but were unchanged in the susceptible one. In tolerant and sensitive cultivars, amounts of two proteins were increased in B‐treated plants, relative to control seedlings. In addition, four proteins (M_r:29, 58, 58, and 22 kDa) were unchanged in control and B‐treated seedlings of the tolerant cultivar. In the susceptible cultivar however, among these four proteins, the first one (M_r:29) was very much reduced and the others (M_r: 58, 58, and 22 kDa) were completely lost in B‐treated seedlings. Moreover, following B treatment, a set of high‐molecular‐weight proteins was quantitatively decreased in the susceptible cultivar but was unchanged in the tolerant cultivar. These results indicate that in barley, certain proteins may be involved in tolerance to B toxicity. In this study, changes in polypeptide composition as a result of B toxic concentration in leaf tissues were more abundant than in roots. Therefore, it is suggested that these changes, especially at shoot level may form the basis of the tolerance mechanism to B toxicity.     

Salicylic acid or thiamin increases tolerance to boron toxicity stress in wheat

Boron (B) toxicity is an important environmental constraint that limits crop productivity. Salicylic acid (SA) and thiamin participate in the processes underlying plant adaptations to certain types of abiotic and biotic stress. This study aimed to investigate the individual and combined effects of SA or thiamin and B on physiological attributes of wheat under normal and B-toxicity conditions. Seeds were soaked in SA or thiamin and excess B was applied for 10-day after planting the seedlings. Growth parameters, photosynthetic pigments, B and some elements concentrations, hydrogen peroxide (H₂O₂), proline, other free amino acids, soluble proteins and carbohydrates were measured. Application of SA or thiamin showed an increase in tolerance towards high B as indicated by H₂O₂, amino acids, soluble proteins and carbohydrates contents. The results support the conclusion that SA and thiamin alleviate B toxicity not at the level of B content but by affecting other elements and osmo-protective metabolite.     

Classification of rice genotypes based on their mechanisms of adaptation to iron toxicity

Iron (Fe) toxicity is a nutritional disorder that affects lowland rice (Oryza sativa L.). The occurrence of excessive amounts of reduced Fe(II) in the soil solution, its uptake by the rice roots, and its transpiration‐driven transport result in elevated Fe(II) concentrations in leaf cells that catalyze the formation of reactive oxygen species. The oxidative stress causes rusty brown spots on leaves (bronzing) and the reduction of biomass and yield. While the use of resistant genotypes is the most promising approach to address the problem, the stress appears to differentially affect rice plants as a function of plant age, climatic conditions, stress intensity and duration, and the prevailing adaptation mechanism. We comparatively assessed 21 contrasting 6‐week‐old rice genotypes regarding their response (symptom score, biomass, Fe concentrations and uptake) to a 6 d iron pulse of 1500 mg L^–1 Fe(II). Eight selected genotypes were further compared at different stress intensities (0, 500, 1000, and 1500 mg L^–1 Fe(II)) and at different developmental stages (4‐, 6‐, and 8‐week‐old plants). Based on Fe‐induced biomass reduction and leaf‐bronzing score, the tested spectrum was grouped in resistant and sensitive genotypes. Linking bronzing scores to leaf iron concentrations allowed further differentiation into includer and excluder types. Iron precipitation on roots and organ‐specific iron partitioning permitted to classify the adaptation strategies into root exclusion, stem and leaf sheath retention, and leaf blade tissue tolerance. The effectiveness of these strategies differed with stress intensity and developmental stage. The reported findings improve the understanding of Fe‐stress response and provide a basis for future genotype selection or breeding for enhancing Fe‐toxicity resistance in rice.     

Phenolics in maize genotypes differing in susceptibility to Gibberella stalk rot (Fusarium graminearum Schwabe)

The relationship between phenolic compounds and maize pith resistance to Fusarium graminearum, the causal agent of Gibberella stalk rot, was investigated. The phenolic acid profiles in the stalks of six maize inbred lines of varying susceptibility were evaluated from silking to grain maturity. Four different fractions of phenolic compounds were extracted from inoculated and non-inoculated (control) pith tissues: insoluble cell-wall-bound, free, soluble ester-bound, and soluble glycoside-bound phenolics. Analysis by HPLC revealed that p-coumaric acid and ferulic acid were the most abundant compounds in the soluble and cell-wall-bound fractions. The quantity of free, glycoside-bound, and ester-bound phenolics in the pith was lower than the level required for the inhibition of Fusarium growth or mycotoxins production; however, significant negative correlations between diferulic acid contents in the cell walls and disease severity ratings 4 days after inoculation were found. The results indicated that future studies should focus on the levels of diferulic acids during the early infection process. Diferulates may play a role in genotypic resistance of maize to Gibberella stalk rot as preformed barriers to infection.     

Manganese availability and microbial populations in the rhizosphere of wheat genotypes differing in tolerance to Mn deficiency

Plant genotypes differ in their capacity to grow in soils with low manganese (Mn) availability. The physiological mechanisms underlying differential tolerance to Mn deficiency are poorly understood. To study the relationship between Mn content in soil, plant genotypes, and rhizosphere microorganisms in differential Mn efficiency, two wheat (Triticum aestivum L.) cultivars, RAC891 (tolerant to Mn deficiency) and Yanac (sensitive), were grown in a Mn‐deficient soil to which 5, 10, 20 or 40 mg Mn kg^–1 were added. The shoot dry matter of both cultivars increased with increasing Mn addition to the soil. At all soil Mn fertilizer levels, the tolerant RAC891 had a greater shoot dry matter and a higher total shoot Mn uptake than the sensitive Yanac. The concentration of DTPA‐extractable Mn in the rhizosphere soil of RAC891 at Mn20 and Mn40 was slightly lower than in the rhizosphere of Yanac. The population density of culturable microorganisms in the rhizosphere soil was low (log 6.8–6.9 cfu (g soil)^–1) in both cultivars and neither Mn oxidation nor reduction were observed in vitro. To assess the non‐culturable fraction of the soil microbial community, the ribosomal intergenetic spacer region of the bacterial DNA in the rhizosphere soil was amplified (RISA) and separated in agarose gels. The RISA banding patterns of the bacterial rhizosphere communities changed markedly with increasing soil Mn level, but there were no differences between the wheat cultivars. The bacterial community structure in the rhizosphere was significantly correlated with the concentration of DPTA‐extractable Mn in the rhizosphere, fertilizer Mn level, shoot dry matter, and total shoot Mn uptake. The results obtained by RISA indicate that differential tolerance to Mn deficiency in wheat may not be related to changes in the composition of the bacterial community in the rhizosphere.     

Differences in growth and yield in response to cadmium toxicity in cotton genotypes

A greenhouse hydroponic experiment was conducted to study the effects of cadmium (Cd; 0, 0.1, 1.0, 10 μM in nutrient solution) on yield and yield components as well as Cd concentration and accumulation in three cotton genotypes (Simian 3, Zhongmian 16, Zhongmian 16–2). The results showed that Cd concentration in different organs increased with increasing Cd levels in the nutrient solution in the following order: root > petiole > xylem > fruiting branch, leaf > phloem in vegetative organs and seed coat, seed nut > boll shell > fiber in reproductive organs. There were significant genotypic differences in functional leaf and petiole Cd concentrations at 1 and 10 μM Cd treatments, with the cultivar Simian 3 showing higher Cd concentrations and greater reductions in lint yield than the other two genotypes.     

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.