Effects of Manganese on Uptake and Translocation of Nutrients in a Hyperaccumulator

The effects of manganese (Mn) on the growth and Mn-induced changes in nutrients uptake and translocation in Mn hyperaccumulator Phytolacca acinosa was investigated in this study. Results showed that high Mn (5000 μ M) in culture solution lead to typical Mn toxicity symptoms in leaves of P. acinosa and decrease of dry matter accumulation in shoots whereas there are no obvious toxicity symptoms and significant decrease of dry weight in roots. Manganese accumulation in roots, stems, and leaves increased with the increment of Mn concentration at the medium level. Calcium (Ca), magnesium (Mg), and iron (Fe) concentration in organs of P. acinosa decreased as the Mn concentration in the nutrient solution increased, but the Ca and Mg concentrations were still at a normal level and the Fe concentration at a sufficient level when compared with the normal plants. The Zn concentration affected by higher Mn level occurred only in roots of P. acinosa and the P concentration affected only in stems, whereas there were no significant influences of excess Mn on the potassium (K) and copper (Cu) concentration in organs of P. acinosa.     

不同柑橘砧木对锰过量胁迫的耐受性及生理响应

  【目的】  土壤pH影响土壤锰 (Mn) 有效性,酸性土壤易出现Mn过量问题,我国柑橘主要分布在南方红黄壤区,柑橘园酸性或强酸性土壤比例高,柑橘园土壤Mn过量较普遍。为此,我们研究了4种柑橘砧木对Mn过量胁迫的耐受性和生理响应,以期为Mn过量土壤上适宜砧木的选择提供依据。  【方法】  选用枳、资阳香橙、红橘和沙田柚4种常用柑橘砧木苗为材料,采用蛭石与珍珠岩1∶1的基质进行了营养液栽培试验,营养液中Mn处理包括0.01 (对照)、0.05、0.25、1.25和6.25 mmol/L 5个浓度。观察砧木苗的生长反应和中毒症状,处理60天时,测定叶绿素含量和光合参数;处理67天终止处理,测定砧木苗生长量、生物量、过氧化物酶活性、营养元素含量等生理生化指标,并用隶属函数对砧木过量锰的耐受性进行综合评价。  【结果】  柑橘砧木苗出现锰中毒的症状为叶片失绿,出现褐色坏死斑点;根量变少,呈现褐色斑点。4种砧木苗均在Mn 0.25 mmol/L处理时出现Mn中毒症状,其中枳最先出现症状且最严重,资阳香橙最迟出现症状且最轻;4种砧木在Mn 0.05 mmol/L处理时即出现Mn过量胁迫,表现为地上部和地下部鲜重和干重显著下降,根冠比升高 (红橘除外)、叶绿素含量下降、净光合速率降低、气孔开度下降、胞间CO₂浓度上升。Mn过量 (> 0.05 mmol/L) 胁迫使4种砧木叶片细胞膜受损,相对电导率和MDA含量上升;清除活性氧的SOD和POD活性上升,CAT活性下降。Mn过量胁迫影响柑橘砧木的营养元素吸收和转运,叶片和根系Mn含量上升,但随Mn胁迫浓度升高,Mn从根系到叶片的迁移率先降低后升高;Mn过量胁迫使砧木叶片K、P、Ca、Mg、Fe、Zn元素含量下降,根系K、P、Fe、Zn含量上升而Ca、Mg含量下降。  【结论】  不同砧木对Mn过量胁迫耐受性存在明显的差异,综合评价耐性强弱顺序为:资阳香橙 > 沙田柚 > 红橘 > 枳,高锰土壤的柑橘园可选用资阳香橙做砧木以减轻锰害。     

Influence of phosphorus on the growth and nutrient contents of the rice plant

A greenhouse experiment was conducted to study the effect of phosphorus application on the growth of rice and the concentration of P, N, K, Ca, Mg, Fe, Mn, Cu, B and Al in leaves, stems and roots. The results showed that application of phosphorus substantially increased the dry matter of leaves, stems and roots upto 30 ppm of P level. Application of phosphorus caused a decrease in the concentration of Fe, Cu and Al in leaves and stems and increased concentration in roots. Phosphorus concentration increased in all plant fractions, while N and Mn increased in leaves but decreased in stems and roots. Similarly Ca, Mg and B concentration decreased in leaves, stems and roots.     

Patterns of mineral nutrient fluctuations in soybean leaves in relation to their position

Dry weight accumulation in blades for the trifoliolate leaf as well as the concentration per gram of dry weight and accumulation of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) were determined during the vegetative and reproductive phases at different leaf positions of soybean [Glycine max (L) Merrill, var. Halle] grown in the field without fertilization. The leaf blades at each position were sampled three times at seven day intervals. Mature (middle) leaves showed a higher rate of dry weight accumulation particularly during the vegetative stage in comparison to the older (lower) and younger (upper) leaves. These differences increased with the progress of plant growth. The minimization to zero of the rate of dry weight accumulation in blades after the development of pods is differentiated in leaves of different age. The N, P, and K concentration in leaf blades increase and those of Ca and Mg decrease from older (lower) to mature (middle) and younger (upper) leaves. Rates of N and P accumulation at the vegetative stage are greater than the rate of dry weight accumulation. During the reproductive stage, P mobilization and transport to reproductive sinks was observed. Older and mature leaves sustain significant levels of N and P up to the end of the plant life cycle. In the upper leaves, the decline of N and P concentration during the same period is ascribed to dilution and change of the carbon/nitrogen (C/N) ratio due to the late increase of dry weight. Potassium in blades of mature and upper leaves seems to be mobilized to reproductive sinks. This did not seem likely for the lower leaves. High Ca concentration in the blades was attributed to the high level of available Ca in the soil, combined with the prevalence of dry growth conditions during the summer. The rate of Ca accumulation is smaller than the rate of dry weight accumulation during the vegetative stage and greater during the reproductive one. The Mg fluctuations indicate a small influence of reproductive sinks on Mg concentration in the blades. The older leaves have the greatest Ca and Mg concentrations compared to the mature and upper leaves. In lower leaves, indications of faster Mg redistribution are found. Iron, Cu, and Zn concentrations in the blades are higher before flowering, then afterwards in a contrary manner than that for Mn. A decline of Fe, Cu, Zn, and Mn concentration in blades from the lower to the mature and upper leaves was determined. Iron shows the greatest change with the highest concentration being during the early vegetative stage and a rapid decline shortly afterwards. Older leaves were found to be significant Fe reserves during the vegetative stage, while after pod development, they present an impressive accumulation of Zn and Mn.     

Effects of soil type,mineral nutrition and salinity on greenhouse‐grown muskmelon in winter 1

Greenhouse experiments under winter conditions were conducted to examine the effects of soil type, mineral nutrition and salinity on vegetative growth and. fruit yield of ‘Galia’ muskmelon (Cucumis melo L.). Growth in a calcareous soil or in sand, under low nutrition level or with 200 mM NaCl added during fruit maturation, imposed significant stresses on the plants expressed by (a) a decrease in dry matter accumulation in vegetative organs, in fruit number and size, and (b) an increase in dry matter percentage in leaf blades and stems. Despite the significant differences in vegetative growth of plants grown in heavy soil vs sandy soil, and in high nutrition vs low nutrition levels, the distribution of dry matter among vegetative organs (leaves, stems and roots) was affected only slightly. Sandy soil, low nutrition and high salinity decreased branching, and thus the distribution of dry matter between the main shoot and the branches. Dry matter percentage in leaf blades and stems was a sensitive parameter which increased under soil, nutrition or salinity stresses. Fruit netting and total soluble solids (TSS) content were significantly decreased by sandy soil and low nutrition level. Application of salinity during fruit growth increased both netting and TSS.     

不同供锌水平对苹果幼树干物质和锌积累及分配的影响

采用盆栽砂培试验,研究了低、中、高3个供锌水平(Zn 0.013、0.254和5.070 mg/L)对苹果幼树干物质和锌积累、分配动态的影响。结果表明,锌的过量及缺乏均对果树的生长及养分吸收产生影响。生长初期,苹果幼树根系活动较晚,枝叶的快速生长主要利用根茎中的养分,锌的积累量呈快速增加趋势,处理间差异显著;低锌处理,除根系明显增加外,其他器官变化较小,根系的锌分配比例明显高于中锌、高锌处理。说明生长后期,低锌、高锌抑制了树体的生长,且低锌处理的树体锌主要分布于地下,上运明显受阻;而中锌、高锌处理,地上部锌含量要高于根系。     

Effect of manganese on endomycorrhizal sugar maple seedlings

Abstract

Manganese (Mn) toxicity may play an important role in the poor survival of seedlings in declining sugar maple (Acer saccharum Marsh.) stands in northern Pennsylvania. To determine the effect of Mn on the growth of sugar maple seedlings, 1‐year‐old seedlings inoculated with vesicular‐arbuscular mycorrhizal (VAM) fungi and growing in sand‐vermiculite‐peat moss medium were irrigated for 7 weeks with nutrient solution (pH 5) containing 0.1 (control), 1, 2, 4, 8, or 16 mg L^?1 Mn. Total seedling dry weight was negatively correlated with Mn, becoming significantly different than the control at 2 mg L^?1 Mn. Stem and root dry weight were reduced by lower Mn levels than leaf dry weight. Manganese had no effect on the root/shoot ratio. The concentration of Mn in roots and leaves increased as the level of Mn in the nutrient solution increased, with the concentration in the leaves 2.2‐ to 3.7‐fold greater than the concentration in the roots. Except for a reduction of P in the roots, Mn had little effect on the concentration of nutrient elements in the roots or leaves. Colonization of the roots by VAM fungi was increased by Mn, with a maximum percentage at 4 mg L^?1 Mn. Manganese toxicity symptoms in the leaves, small discrete chlorotic spots, began to appear at 1 mg L^?1 Mn. The sensitivity of sugar maple seedlings to Mn found in this study supports the hypothesis that Mn may affect regeneration in declining sugar maple stands. However, evaluation of the effects of Mn on seedlings in native soils under field conditions will be necessary before the role of Mn in sugar maple regeneration can be understood.     

Interaction Between Ozone Exposure and Iron Nutrition in Two Tobacco Cultivars

The initial objective was to confirm evidence, obtained from field grown plants, for iron (Fe) accumulation in leaves under ozone exposure. Tobacco plants were grown in pots under either open air or growth chamber conditions. The ozone-sensitive cultivar Bel W3 showed symptoms of ozone injury only when grown outside, while the cultivar Virginia never developed symptoms. In both cultivars, basal leaves of plants grown outside had higher concentration of Fe, but not of manganese (Mn) or zinc (Zn), than those from the growth chamber. Results suggest an interference of the oxidative stress with the mechanisms regulating Fe homeostasis. A second objective was to test whether differences in tolerance to ozone correspond with differences in tolerance to Fe toxicity. Iron toxicity was induced by supplying an excess of Fe-EDTA to plants, grown hydroponically in a growth chamber, upon partial root cutting. Symptoms in leaves were more severe in Bel W3 than in Virginia, which suggested that mechanisms of tolerance to ozone were also effective against Fe toxicity. In both cultivars, a good correlation was determined between Fe accumulation and ethylene production in the leaves.     

大豆磷酸烯醇式丙酮酸磷酸酯酶(PEPP)研究:I.对非生物胁迫的反应

对缺磷、铝毒、盐、干旱、Fe、Mn、Cu、Zn胁迫下大豆根系和叶片磷酸烯醇式丙酮酸磷酸酯酶(PEPP)活性进行了测定,结果表明:(1)长期缺磷和铝毒胁迫可显著提高大豆根系的PEPP活性,并表现出加成效应;(2)长期铝毒、缺磷和铝毒耦合胁迫也显著提高大豆敏感品种BL2叶片的PEPP活性;(3)盐胁迫、干旱以及长期Fe、Mn、Cu、Zn过量都显著提高大豆根系的PEPP活性,Fe、Cu、Zn缺乏则对根系和叶片的PEPP活性影响不大,长期缺Mn显著降低大豆根系及叶片的PEPP活性。     

Diagnosis of zinc deficiency in canola by plant analysis

Abstract

Canola plants (Brassica napus cv. Eureka) were grown in soil culture with seven levels of zinc (Zn) supply (0, 67, 133, 200, 267, 533, and 1,067 μg Zn/kg soil) for 39 days. Critical Zn concentrations in young leaf blades and petioles were established for the diagnosis of Zn deficiency in canola plants during vegetative growth by assessing the relationship between the Zn concentration in the leaves and shoot dry matter on 22 and 39 days after sowing (DAS). Zinc concentrations in leaf blades and petioles increased with increasing Zn supply, but Zn concentrations were always 50% higher in the youngest open leaf (YOL) than in the youngest mature leaf (YML). The relationship between shoot dry matter and Zn concentrations in leaf petioles exhibited Piper‐Steenbjerg curvature, indicating their unsuitability for Zn‐deficiency diagnosis either alone or by inclusion with leaf blades. By contrast, inclusion of leaf mid‐ribs with leaf blades did not alter the relationship between shoot dry matter and Zn concentrations, nor the critical Zn concentration. Critical Zn concentrations in the YOL, YOL+1, and YOL+2 blade on 39 DAS, corresponding with the stem elongation stage, were 15–17, 9–10, and 7–8 mg Zn/kg dry matter, respectvely. In comparison, the critical Zn concentration in the YOL+2 leaf blades with mid‐ribs was 7–8 mg Zn/kg dry matter. In conclusion, during the vegetative stage up to stem elongation, YOL+2 leaf blades which are also the YML are recommended for the diagnosis of Zn deficiency in canola plants with the critical Zn concentration being 7–8 mg Zn/kg dry matter.     

Phytosiderophore release from manganese‐induced iron deficiency in barley

An experiment was conducted in the phytotron with barley (Hordeum vulgare L. cv. Minorimugi) grown in nutrient solution to compare iron (Fe) deficiency caused by the lack of Fe with manganese (Mn)‐induced Fe deficiency. Dark brown spots on older leaves and stems, and interveinal chlorosis on younger leaves were common symptoms of plants grown in either Mn‐toxic or Fe‐deficient treatments. Dry matter yield was affected similarly by Fe deficiency and Mn toxicity. The Mn toxicity significantly decreased the translocation of Fe from roots to shoots, caused root browning, and inhibited Fe absorption. The rate of Fe translocated from roots to shoots in the 25.0 μM Mn (toxic) treatment was similar to the Fe‐deficient treatment. Manganese toxicity, based on the release of phytosiderophore (PS) from roots, decreased from 25.0>250>2.50 uM Mn. The highest release of PS from roots occurred 7 and 14 days after transplanting (DAT) to Mn‐toxic and Fe‐deficient treatments, respectively; but was always higher in the Fe‐deficient treatment than the Mn‐toxic treatments. The release of PS from roots decreased gradually with plant age and with severity of the Mn toxicity symptoms. The PS content in roots followed the PS release pattern.     

Sorghum genotypic differences in tolerance to excess manganese

Manganese (Mn) toxicity can be a growth limiting constraint for many plants grown on acid soil. Plant species/genotypes tolerant to Mn could help overcome detrimental Mn toxicity effects on plants grown on high Mn soils. Thirty‐seven sorghum [Sorghum bicolor (L.) Moench] genotypes from a broad germplasm base were grown in solution culture (pH 4.5) with 0, 3.0, and 6.0 mM of added Mn above the basic solution concentration (18 μM) to determine genotypic differences in tolerance to excess Mn. Dry matter (DM) was used to evaluate 24‐day‐old plants (10 days in Mn treatments) for Mn toxicity responses. Wide variability among genotypes for differential DM was noted at 3.0 and 6.0 mM Mn. Sorghum generally tolerated high levels of Mn. Genotypes showing relatively high tolerance to excess Mn in solution were NB 9040, Wheatland, IS 7180, IS 7755, and IS 7809. Those genotypes showing relatively low tolerance to high Mn were ICA‐Nataima, Martin, IS 7173c (SC 283), IS 7321, IS 9187, IS 9785, and IS 9828. IS 7173c, an aluminum (Al)‐tolerant standard genotype, was sensitive to high Mn. Wide variability was noted among tissue culture generated lines derived from a common parent. Laboratory screening for tolerance to Mn toxicity was effective with sorghum, but results need to be verified in the field.     

INDUCTION OF OXIDATIVE STRESS AND ANTIOXIDANT ENZYMES BY EXCESS COBALT IN MUSTARD

This study focuses on induction of oxidative stress and antioxidative defense mechanism on exposure to excess cobalt (Co) in mustard (Brassica campestris L.; cv. ‘T-59’) plants grown in refined sand. Plants were grown for 40 days at normal (0.1 μM) Co. Additional cobalt was supplied from d 41 at 6 levels, i.e., 0.1 (control), 100, 200, 300, 400 and 500 μM as cobalt sulfate. The primary site of Co toxicity was shoots where middle leaves developed interveinal chlorosis after three days of excess cobalt supply (>100 μM). At severity these chlorotic spots became necrotic and affected areas appeared dry and papery, at this stage, growth of the plants were completely checked, the upper part of the stem became dry and hanged down. The toxicity of cobalt at d 46, i.e., six days after metal supply, (DAMS) reduced the dry weight, concentrations of chlorophyll a, b and carotenoids in leaves and tissue Fe with decreased activity of catalase and lipid peroxidation. Enhancement in proline concentration and elevated activities of antioxidant enzymes peroxidase, superoxide dismutase and ascorbate peroxidase were observed in leaves and roots in response to excess Co supply in mustard. Cobalt concentration of mustard in leaves and roots, ranged from 200 to 397 μg g^?1 at excess Co as compared to 1.1 to 2.5 μg Co g^?1 dry matter in control (0.1 μM Co).     

Uptake and utilization of applied phosphorus in oilseed rape (Brassica napus L. cv. Hayola) plants at vegetative and reproductive stages: Comparison of root with foliar phosphorus application

ABSTRACT

In order to compare plants’ response to phosphorus (P) application through roots and leaves, oilseed rape (Brassica napus L. cv. Hayola) plants were cultivated until vegetative or reproductive stages and were pretreated with an adequate (+P) or low (?P) supply of P. Thereafter, these plants were treated with 0.3 mM P as sodium dihydrogen phosphate (NaH₂PO₄) either through roots (root application, RA) or leaves (leaf application, LA). Shoot biomass was observed to be suppressed under ?P conditions at both stages, whereas root growth was comparatively improved in ?P plants at the vegetative stage but not at the reproductive stage. Both RA and LA were able to compensate for the growth of vegetative shoot and roots at both stages; however, LA reduced P and dry matter partitioning into the fruits. At the vegetative stage, recovery of applied P was similar between RA and LA treatments, and was extensive in ?P plants compared with the +P ones. At the reproductive stage, in contrast, significantly lower recovery of P was observed likely due to the lower capacity of leaves for P absorption and/or their lower re-translocation ability through the phloem. Data of P utilization efficiency showed that ?P plants, at both vegetative and reproductive stages, efficiently use leaf-applied P for biomass production when compared with the +P plants. Activity of acid phosphatase was sharply inhibited by RA in ?P plants, whereas it was preferably increased by LA in both +P and ?P plants. Results indicated that under P-deficiency conditions, plants had higher ability to utilize foliar-applied P, and in contrast to RA, LA may enable plants for a continuous higher capacity of P uptake from P-deficient soil; however, RA was superior to LA in terms of fruit growth.     

Variation of tolerance to manganese toxicity in Australian hexaploid wheat

High concentrations of manganese (Mn), iron (Fe), and aluminium (Al) induced in waterlogged acid soils are a potential constraint for growing sensitive wheat cultivars in waterlogged‐prone areas of Western Australian wheat‐belt. Tackling induced ion toxicities by a genetic approach requires a good understanding of the existing variability in ion toxicity tolerance of the current wheat germplasm. A bioassay for tolerance to high concentration of Mn in wheat was developed using Norquay (Mn‐tolerant), Columbus (Mn‐intolerant), and Cascades (moderately tolerant) as control genotypes and a range of MnCl₂ concentrations (2, 250, 500, 750, 1000, 2000, and 3000 μM Mn) at pH 4.8 in a nutrient solution. Increasing solution Mn concentration decreased shoot and root dry weight and intensified the development of toxicity symptoms more in the Mn‐intolerant cv. Columbus than in Norquay and Cascades. The genotypic discrimination based on relative shoot (54% to 79%) and root dry weight (17% to 76%), the development of toxicity symptoms (scores 2 to 4) and the shoot Mn concentration (1428 to 2960 mg kg^–1) was most pronounced at 750 μM Mn. Using this concentration to screen 60 Australian and 6 wheat genotypes from other sources, a wide variation in relative root dry weight (11% to 95%), relative shoot dry weight (31% to 91%), toxicity symptoms (1.5 to 4.5), and shoot Mn concentration (901 to 2695 mg kg^–1) were observed. Evidence suggests that Mn tolerance has been introduced into Australian wheat through CIMMYT germplasm having “LERMO‐ROJO” within their parentage, preserved either through a co‐tolerance to Mn deficiency or a process of passive selection for Mn tolerance. Cultivars Westonia and Krichauff expressed a high level of tolerance to both Mn toxicity and deficiency, whereas Trident and Janz (reputed to be tolerant to Mn deficiency) were intolerant to Mn toxicity, suggesting that tolerance to excess and shortage of Mn are different, but not mutually exclusive traits. The co‐tolerance for Mn and Al in ET8 (an Al‐tolerant near‐isogenic line) and the absence of Mn tolerance in BH1146 (an Al‐tolerant genotype from Brazil) limits the effectiveness of these indicator genotypes to environments where only one constraint is induced. Wide variation of Mn tolerance in Australian wheat cultivars will enable breeding genotypes for the genetic solution to the Mn toxicity problem.     

外源水杨酸对锰污染红壤中玉米的生长与抗氧化酶活性的调节作用

采用盆栽实验方法研究了外源水杨酸（SA）对锰污染红壤中玉米的生长、脂质过氧化程度、活性氧水平以及抗氧化酶活性的影响。结果表明,过量锰明显降低玉米植株干重,显著提高了茎叶和根中锰的含量。SA促进锰胁迫下玉米的生长,但对植株中锰的含量与分布无影响。过量锰处理下,玉米叶片超氧阴离子（O.2-）和过氧化氢积累显著增加,脂质过氧化、电解质渗透率和脯氨酸含量显著升高;而SA和过量锰复合处理下,这些指标则显著降低。过量锰诱导超氧化物歧化酶（SOD,EC1.15.1.1）、过氧化物酶（POD,EC1.11.1.7）活性升高,抑制过氧化氢酶（CAT,EC1.11.1.6）和抗坏血酸过氧化物酶（APX,1.11.1.11）活性;SA处理促进锰胁迫下SOD和POD活性进一步升高,减小CAT和APX活性下降的程度。这些结果提示,SA调节抗氧化酶活性,保护组织细胞免遭氧化损伤,是SA缓解过量锰对玉米毒害作用的重要生理原因。     

Tolerance of rice plants to trace metals

Abstract

The tolerance of rice (Oryza sativa L. C.V. Earlirose) to various trace metal excesses was tested to determine if high levels of the trace metals found in some field‐grown plants were at toxicity levels. In one experiment, levels of 2200 μg Zn/g dry weight, 44 μg Cu/g dry weight, 4400 μg Mn/g dry weight, and 32 μg Pb/g dry weight in shoots of young plants had no adverse effects on vegetative yields. A level of 3160μgZn/ g dry weight decreased yields about 40% (P = . 05). In another test 51 μg Cu/g dry weight or 94 μg Pb/g dry weight did not decrease vegetative yields. Boron supplied at 10^‐3 MH₃BO₃ not only caused no toxicity but resulted in only 144 μg B/g dry weight in shoots. Root levels of Zn were about equal to those in shoots; Mn levels were lower in roots than in shoots (1/4 to 1/10); B levels were generally low in both shoots and roots with roots 1/10 that of shoots; Cu levels were higher in roots than in shoots. Rice was tolerant of a high level of Cr. The tolerance of rice to high levels of some trace metals in these experiments may be related to high P levels in plants.     

Effect of lead treatment on the distribution of essential elements in cucumber

Changes in the fresh and dry weight of leaf blades, petioles, internodes, and their ion concentrations as well as rates of root exudation were investigated in cucumber grown in hydroponic culture and treated with physiological concentrations of lead (Pb). The growth of flowering cucumber supplied with FeCl₃ shows a typical bell‐shaped curve derived from leaf dry weights, where the 4th, 5th, and 6th leaves are the largest ones. Lead inhibited growth up to 20% (except the youngest leaves which were stimulated), but did not cause morphological changes. Whereas root growth was also retarded by about 20%, exudation was inhibited to 50%, that is, the root resistance to water transport was increased by Pb. In spite of that the dry matter yield of internodes and petioles hardly reached 10 and 5% of that of leaf blades, respectively, their calcium (Ca), magnesium (Mg), and zinc (Zn) concentrations were almost the same. Similarly, the concentrations of these metals in the specific leaf blades are equal despite their different growth characteristics but the concentration of Mn is independent of the growth of the examined tissues. Lead was the only cation to accumulate in the largest leaves. The inhibitory effect of Pb on ion uptake was proportional to the growth inhibition of the tissues except manganese (Mn), the accumulation of which was stimulated by Pb in all the analyzed tissues and copper (Cu) which increased only in the internodes. We could not explain the extremely different ion distributions observed during the growth of cucumber. However, it is evident that the measurement of ion concentrations at whole shoot level is not enough to characterize ion interactions because only some ions accumulate at the same rate as tissues grow. These ions maintain stable concentration levels in shoot parts whereas others decrease or increase independently from growth.     

Genotypic Variation of Sweetpotatoes Grown Under Low Potassium Stress

Abstract

Ninety‐four sweetpotato (Ipomoea batatas L.) genotypes were compared under low potassium (K) stress (35 mg kg^?1 dry soil) over two growing seasons. Potassium utilization efficiency ratio (KER), defined as the dry matter weight/K content, was significantly different among genotypes. Genotypes were divisible into four KER categories: high efficient, efficient, fairly efficient and inefficient with most of the genotypes falling in the efficient and fairly efficient groups. The K contents varied significantly within individual plants. Potassium concentration on a dry weight basis was greatest in the petioles followed by leaves, stems, and roots. On a total plant basis, K content in roots was greatest followed by stems, leaves, and petioles. Several genotypes (including 602 × 81‐3, Zhe15‐47 and Xushu18) were selected as most suitable for growth on soils low in available K due to their appreciable yields and higher KER under low K stress.     

Manganese toxicity in bush bean as affected by concentration of manganese and iron in the nutrient solution

An experiment was conducted to clarify the relationship between Mn toxicity and Fe deficiency in bush snap bean (Phaseolus vulgaris L. cv. ‘Wonder Crop No. 2'). Seedlings were grown in full strength Hoagland No. 2 solution at pH 6.0 for ten days. Six concentrations of Mn as MnCl₂.4H₂O were used in combination with three concentrations of Fe as FeEDTA.

Toxicity symptoms, induced by low levels of Mn (0.1 ppm and above), included: small brown necrotic spots and veinal necrosis on primary leaves; necrosis on primary leaf petioles; interveinal chlorosis, with or without brown necrotic spots, on trifoliate leaves; and brown necrotic spots on stipules. Manganese toxicity symptoms were alleviated or prevented by increasing Fe concentration in the nutrient solution.

Manganese concentration in the leaves increased with increasing Mn and decreased with increasing Fe concentration in the nutrient solution, Iron concentration in the roots increased with increasing Fe concentration in the nutrient solution; however, Fe concentration in the leaves was not significantly affected by increasing Mn concentration in the solution culture. Manganese toxicity symptoms developed when Mn concentration in the leaves reached about 120 ppm.

A decrease in the Fe/Mn ratio in the nutrient solution resulted in a proportionate decrease in that of the leaves. Manganese toxicity symptoms occurred when the Fe/Mn ratio in the solution was 10.0 and below, or when the ratio in the leaves was less than 1.5. The ratio of Fe/Mn in the solution required for optimum growth of ‘Wonder Crop No. 2’ bean, without Mn toxicity symptoms, was in the range of 20.0 to 25.0.

Results indicate that the chlorosis on bush bean leaves induced by excessive Mn in the nutrient solution was due to excessive accumulation of Mn and not to Fe deficiency.