Studies on photosynthetic electron transport,photophosphorylation and CO2 fixation in zinc deficient leaf cells of Zea mavs. L.

The effect of Zn deficiency on rate of photosynthesis of leaf discs, isolated mesophyll and bundle sheath cells and chloroplasts of maize (Zea mays. L) was studied. The yield of mesophyll and bundle sheath cells obtained by enzymic digestion of the leaf tissues from Zn deficient plants is lower than the identical tissues from normal plants which suggests that Zn deficiency brings about some structural changes in the leaf cell. Photosynthetic oxygen evolution measured in the leaf discs is low due to Zn deficiency. Photosystem‐II dependent Hill reaction and non cyclic photophosphorylation of chloroplasts were also affected by Zn deficiency. Rate of photosynthetic carbon dioxide fixation by both bundle sheath and mesophyll cells obtained from Zn deficient leaf‐tissue waslower than the cells free from Zn deficiency. Addition of various metabolites like NADPH, ATP and PEP to Zn deficient mesophyll cells whowed marked enhancement in 14‐CO₂ fixation. However, addition of NADPH, ATP and RuBP to Zn deficient bundle sheath cells showed no or very little enhancement in the rate of 14‐Cu₂ fixation. Addition of exogenous Zn ions to isolated cells inhibited the CO₂ fixation both in the non‐deficient and Zn deficient cell types. It is suggested that Zn deficie ‐ncy affects the primary electron transport and phospho‐rvlation ability for chloroplasts which in turn affects CO₂ fixation in leaf cells.     

Immobilization of Zinc Fertilizer in Flooded Soils Monitored by Adapted DTPA Soil Test

Zinc (Zn) deficiency is a persistent problem in flooded rice (Oryza sativa L.). Severe Zn deficiency causes loss of grain yield, and rice grains with low Zn content contribute to human nutritional Zn deficiencies. The objectives of this study were to evaluate the diethylenetriaminepentaacetic acid (DTPA) extraction method for use with reduced soils and to assess differences in plant availability of native and fertilizer Zn from oxidized and reduced soils. The DTPA‐extractable Zn decreased by 60% through time after flooding when the extraction was done on field‐moist soil but remained at original levels when air‐dried prior to extraction. In a pot experiment with one calcareous and one noncalcareous soil, moist‐soil DTPA‐extractable Zn and plant Zn uptake both decreased after flooding compared with the oxidized soil treatment for both soils. In the flooded treatment of the calcareous soil, both plant and soil Zn concentrations were equal to or less than critical deficiency levels even after fertilization with 50 kg Zn ha^?1. We concluded that Zn availability measurements for rice at low redox potentials should be made on reduced soil rather than air‐dry soil and that applied Zn fertilizer may become unavailable to plants after flooding.     

Zinc uptake and distribution in tomato plants in response to foliar supply of Zn hydroxide‐nitrate nanocrystal suspension with controlled Zn solubility

The present study investigated the foliar uptake rate, distribution, and retranslocation patterns of novel, synthesized zinc hydroxide‐nitrate nanocrystals (ZnHN; solubility 30–50 mg Zn L^?1) applied on to the adaxial surface of tomato leaves (Solanum lycopersicum L. cv. Roma). The total Zn absorption from ZnHN suspension positively increased with ZnHN application rates, but the relative efficacy started to decline at > 400 mg Zn L^?1. Within the 3 weeks, total Zn recovery in the ZnHN‐treated plants was 16% of the total ZnHN‐Zn applied, compared to the near 90% total Zn recovery in the Zn(NO₃)₂‐plants at the same Zn rate. Foliar‐absorbed ZnHN‐Zn was distributed from the treated leaves into other plant parts and preferentially translocated into the roots. Distribution of Zn from ZnHN‐treated leaves to apical parts was not limited by Zn deficiency. These results demonstrate that ZnHN crystals with controlled solubility provided some sort of slow‐release Zn over a certain growth period at a rate slower (but quantitatively effective) than the soluble Zn(NO₃)₂. The efficacy of the prolonged foliar Zn supply could be enhanced if the ZnHN suspension is sprayed over a large leaf surface area at the peak vegetative or early flowering stage.     

Response of corn to plowed‐down and disked‐in Zn as zinc sulfate

Abstract

A field investigation was conducted to compare the efficacy of plowed‐down and disked‐in Zn as ZnSO₄.H₂O in correcting Zn deficiency of corn (Zea mays L.). The soil, Buchanan fine sandy loam, was nearneutral in pH and contained 0.7 ppm of EDTA‐extractable Zn and 1.4 ppm of dilute HCl‐H₂SO₄ extractable P. Application of 6.72 kg Zn/ha as ZnSO₄.H₂O corrected Zn deficiency of corn plants on the soil. Corn grain yields and Zn concentrations in tissue samples indicated that the plowed‐down and disked‐in Zn were about equally effective in correcting Zn deficiency where the level of Zn application was 6.72 kg/ha.     

螯合-缓冲营养液中不同磷锌配比对小麦苗期磷-锌关系的影响

采用螯合-缓冲营养液培养方法对小麦进行了苗期培养试验,在3个磷水平(0、0.6 mmol·L-1、3.0mmol·L-1)和3个锌水平(0、3μmol·L-1、30 μmol·L-1)的完全组合下对小麦苗期的磷-锌关系进行了研究,以期为提高小麦籽粒锌的生物有效性提供理论依据.结果表明,与正常磷锌供应比较,磷锌的缺乏与过量均不利于小麦生长,缺磷比过量供磷的抑制程度更大,而过量供锌比缺锌的影响更为强烈,缺磷和过量供锌主要影响小麦幼苗的分蘖和地上部干物质的积累.过量供磷时,小麦根部存在明显的磷-锌拮抗,抑制了根部对锌的吸收,但磷的供应却提高了锌在小麦植株体内向地上部的转运;缺锌时,小麦叶片会积累大量磷,而供锌后则会抑制磷在小麦植株体内向地上部的转运.在小麦苗期,磷、锌均处于正常水平时其交互作用有利于锌的吸收和向地上部转运,但抑制了磷向叶部的转运.此外,磷、锌的缺乏均降低了叶绿素SPAD值,而磷的正常供应和锌的供应促进了叶绿素的合成.缺磷胁迫时小麦叶片的SOD和POD活性较高,而CAT活性较低;锌缺乏和过量时叶片SOD活性较低,而缺锌时POD和CAT活性较高,供锌后二者活性降低.总之,磷-锌拮抗作用主要发生在小麦根部,但在其他器官内也会发生;且不仅在二者配比不合理时发生,即使在配比合理时也会发生.     

Zinc‐deficiency resistance and biofortification in plants

Zinc (Zn) deficiency is a well‐documented problem in plants, causing decreased yields and nutritional quality. When facing a shortage in Zn supply, plants acclimatize by enhancing the Zn acquisition. In this review, we highlight recent progress in understanding of plant resistance to Zn deficiency and discuss the future challenges to fully unravel its molecular basis of regulation. Emphasis is given on the physiological and molecular basis of Zn acquisition, the long‐distance transport of Zn and the genotypic variations in Zn use efficiency of plants. Prospects of Zn biofortification strategies as well as further efforts for crop improvement to overcome Zn deficiency are also addressed.     

Effects of sulfur supply on soybean plants exposed to zinc toxicity

Application of most waste or by‐product material increases the zinc (Zn) concentration in soils markedly. This investigation was conducted to determine if enhanced sulfur (S) supplied as sulfate (SO₄) would modify the toxic effects of excess Zn. Soybean (Glycine max [L.] Merf. cv. Rarisorri) was grown for two weeks in nutrient solutions containing ranges in Zn (0.8 to 80 μM) and S (0.02 to 20 mM). Root and shoot conditions were observed, dry weights measured, and Zri concentration determined. Zinc‐toxicity symptoms started about one week after transplanting young plants to nutrient solutions. Symptoms including chlorosis, especially in the trifoliate leaves, and change in orientation of unifoliate leaves were mild in 20 μM‐, intermediate in 40 μM‐, and severe in 80 μM Zn‐containing solutions. Dry weight was reduced in plants exposed to 20, 40, and 80 μM Zn. Plants grown in 40 μM Zn and 20 mM S survived longer than those grown in lower S concentrations and showed alleviation of the chlorosis in trifoliate leaves. The change in the orientation of the unifoliate leaves due to Zn toxicity, however, was not affected by S. Zinc contents in shoots grown at toxic Zn levels were higher in 20 mM‐ than in lower S‐containing nutrient solutions. High S supply (20 mM) increased Zn translocation from roots to shoots. Besides increasing the Zn translocation from roots to shoots, it seems that S nutrition may also be a factor helping the plants to cope with high levels of Zn in their tissues.     

Plant growth,phosphorus nutrition,and acid phosphatase enzyme activity in three tomato cultivars grown hydroponically at different zinc concentrations

Three tomato cvs., Blizzard, Liberto, and Calypso, were grown hydroponically in a controlled temperature (C.T.) room for six weeks at three zinc (Zn) concentrations (0.01, 0.5, and 5.0 mg Zn L^‐1) in the nutrient solution. There were significant reductions in the dry matter and chlorophyll contents of all three cultivars grown at both low (0.01 mg L^‐1) and high (5 mg L^‐1) Zn as compared to 0.5 mg Zn L^‐1. The concentration of Zn at 0.01 mg L^‐1 was not sufficient to provide for optimal plant growth, while 5 mg Zn L^‐1 in the nutrient solution was detrimental to plant growth for all three cultivars. The best results for all parameters tested were for the plants grown at 0.5 mg Zn L^‐1. The concentration of phosphorus (P) was at an excess level in leaves of plants grown in 0.01 mg Zn L^‐1, while it was deficient in the 5 mg Zn L^‐1 treatment. Acid Phosphatase Enzyme [EC.3.1.3.2.] (APE) activity was significantly higher in both the leaves and roots of P‐deficient plants, i.e., plants receiving high (5 mg L^‐1) Zn. Acid Phosphatase Enzyme activity was slightly higher in the mature leaves than those in developing leaves, where P concentration was higher. Concentration of P and, in particular Zn, increased in the roots with increasing Zn in the nutrient solution. The APE activity increased in the roots of P‐deficient plants receiving high Zn (5 mg L^‐1).     

Exogenous succinate increases resistance of maize plants to copper stress

The effect of copper (Cu) excess (1.5, 4.7, 31, 78, 156 μM) and exogenously supplied succinate on plant growth, chlorophyll content, chlorophyll fluorescence, and isoenzym profiles of some antioxidant enzymes in maize plants was studied. Excessive Cu supply led to a reduction in the relative growth rate (RGR), tolerance index (TI), chlorophyll a and chlorophyll b contents, and the quantum yield of PSII electron transport in the light‐adapted state (ΦPSII). Copper treatment induced several changes in the anionic and cationic peroxidases (PODs), as well as superoxide dismutase (SOD) isoenzyme profiles. After 8 d of 78 μM–Cu treatment, two new anionic and two new cationic peroxidase isoenzymes in the roots were registered. Copper applied at concentrations above 31 μM resulted in higher levels of manganese superoxide dismutase (Mn‐SOD) in the roots and Cu,Zn‐superoxide dismutase (Cu,Zn‐SOD) in the leaves. However, the addition of Na‐succinate (200 μM) to the root medium prior to Cu treatment increased the capacity of the plants to partially overcome Cu toxicity.     

The Cd‐tolerant rice mutant cadH‐5 is a high Cd accumulator and shows enhanced antioxidant activity

To investigate the mechanism of cadmium (Cd) detoxification in rice (Oryza sativa L.), a Cd‐tolerant mutant cadH‐5, obtained by an Agrobacterium tumefaciens‐based gene‐delivery system, was used for a Cd‐tolerance and accumulation study. After 15 d of exposure to 0.75 mM CdCl₂, significant phenotypic differences were observed between the wild type (WT) and cadH‐5. When exposed to 0.5 mM CdCl₂, higher Cd levels were accumulated in cadH‐5 root cell wall, root cytosol, and membranes than those in WT. However, Cd concentrations in root tissues varied in both WT and cadH5. No significant difference of hydrogen peroxide (H₂O₂) concentrations was observed between WT and cadH‐5, while contents of cell‐wall polysaccharides and phytochelatins (PCs) in the mutant were higher compared to WT. The ratios of reduced glutathione to oxidized glutathione (GSH : GSSG) and ascorbate to dehydroascorbate (ASC : DHA) were lower in WT than in cadH‐5, while the NADPH : NADP⁺ ratio was different to the ratios of GSH : GSSG and ASC : DHA; the ascorbate peroxidase (APX, EC 1.11.1.11), glutathione peroxidase (GR, EC 1.6.4.2), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and monodehydroascorbate reductase (MDHAR, EC 1.6.5.4) activities were lower in WT compared to cadH‐5. Our results indicate that under long‐term Cd stress, cadH‐5 plants can accumulate more Cd with more PC. Also, the redox status of ASC‐GSH cycle was more inhibited in WT than in cadH‐5 plants, rendering WT less able to scavenge reactive oxygen species (ROS). The cadH‐5 mutant maintains relatively high ASC, GSH, and NADPH concentrations, ratios of ASC : DHA, GSH : GSSG, and NADPH : NADP⁺, as well as antioxidative enzymatic activities and PC concentrations. Thus, it is tolerant of relatively high Cd accumulation.     

Quantitative methods for estimating foliar uptake of zinc from suspension‐based Zn chemicals

The present study developed methods for quantifying foliar Zn uptake from suspension‐based Zn chemicals of low solubility, which were ZnO (particle size: 0.15^–1.34 μm) and a newly synthesized Zn hydroxide nitrate crystal (Zn‐HNC) (50^–100 nm thickness and 0.2^–1 μm lateral dimension). Recently matured leaves of citrus (Citrus aurantium L. cv. Valencia), capsicum (Capsicum annume L. cv. Giant Bell), and/or tomato (Solanum lycopersicum L. cv. Roma) were in vitro–treated with microdroplets (5 μL per droplet) of Zn‐HNC‐ and ZnO‐suspension solutions on the adaxial surface and incubated under controlled conditions for up to 72 h. Leaf‐washing protocols were compared, including: dilute ethanol (3%), dilute nitric acid (2%), and their combination. The methods for quantifying Zn uptake were: (1) whole‐leaf loading by which droplets of the Zn suspension solutions were loaded onto central regions of both left and right sides of leaf blades and (2) half‐leaf loading by which soluble‐Zn (ZnSO₄) droplets were loaded onto only one side of leaf blades while the other was used as the background Zn control. Foliar‐surface characteristics of the plant species affected the effectiveness of the washing methods. The dilute nitric acid (2%; ± 3% ethanol) was required to remove residue particles of the ZnO and Zn‐HNC suspensions from foliar surfaces of capsicum and tomato (highly trichomatic), but the residue Zn chemicals on citrus leaves (nontrichomatic and highly waxy) were similarly and effectively removed by the three washing methods. For quantifying Zn uptake by the leaves, the half‐leaf loading method showed its advantages over the whole‐leaf loading method, because it did not stringently require similar background Zn concentrations in the control and treated leaves at the start and had little risks of secondary absorption of soluble Zn in the washing solution.     

利用螯合–缓冲营养液对小麦苗期磷–锌关系的研究

采用螯合缓冲营养液培养技术（Chelator-buffer culture solution）,对小麦幼苗植株的磷锌营养进行了探讨。结果表明,高磷条件下小麦出现的缺锌黄化与磷中毒症状之间存在着明显区别,本研究结果支持高磷条件下作物出现的黄化是锌缺乏症状而非磷中毒的观点。与缺磷相比,正常供磷促进了小麦的生长,但过量磷对小麦生长有阻碍作用,而且锌的供应加剧了促进或抑制的程度。正常供应磷、锌条件下,小麦幼苗根系或地上部的磷、锌含量、吸收量及转运率均处于相对较高的水平,其余各处理则因为磷或锌供应量不适宜而使植株的磷、锌营养受到不同程度的影响。另外,磷锌相互拮抗的作用方式及大小程度不同:磷主要影响小麦根系对锌的吸收,而锌对小麦磷营养的影响主要是通过对其从根系向地上部转运的抑制来实现的;磷对锌的影响要明显大于锌对磷的影响,磷素水平在小麦的磷、锌营养平衡中起着更为重要的作用。磷锌拮抗作用只在双方供应不适宜的情况下发生,而且相互作用的方式及程度存在明显差异。     

Foliar Symptomology and Tissue Concentrations of Nutrient‐Deficient Vegetative Strawflower Plants

Abstract

Elemental deficiencies of nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, manganese, copper, zinc, or boron (N, P, K, Ca, Mg, S, Fe, Mn, Cu, Zn, or B) were induced in plants of Florabella Pink strawflower [Bracteantha bracteata (Vent.) A. A. Anderberg]. Rooted stem cuttings were planted in 4.87‐L plastic containers and fertilized with a complete modified Hoagland's solution or this solution minus the element that was to be investigated. Plants were harvested for tissue analyses as well as dry weights when initial foliar symptoms were expressed and later under advanced deficiency symptoms. Deficiency symptoms for all treatments were observed within 7 weeks. The most dramatic expression of foliar symptoms occurred with N (chlorotic lower foliage leading to necrotic margins on the mature leaves), Ca (black necrotic spots on the tips of the young leaves), S (uniform chlorosis of young leaves and recently mature leaves), B (thick, leathery, and deformed young leaves), Fe (uniform yellowish‐green chlorosis on the young leaves), and Zn (brownish‐gray necrosis on the tips of the mature leaves). At the initial stage, only Fe‐deficient plants weighed less than the control, whereas K‐, Ca‐, and Mg‐deficient plants had greater dry weights than plants receiving the complete modified Hoagland's solution (control plants). Dry weights of plants treated with solutions not containing N, P, Ca, S, Cu, or Mn were significantly lower when compared with the control plants under an advanced deficiency. Foliar‐tissue concentration data will assist plant‐tissue analysis laboratories in establishing foliar symptom standards for growers.     

Zinc‐efficient wild grasses enhance release of phytosiderophores under zinc deficiency

The effect of the zinc (Zn) nutritional status on the rate of phyto‐siderophore release was studied in three wild grass species (Hordeum murinum, Agropyron orientale, and Secale cereale) grown in nutrient solution under co‐trolled environmental conditions. These wild grasses are highly “Zn‐efficient”; and grow well on severely Zn‐deficient calcareous soils in Turkey (DTPA‐extractable Zn was 0.12 mg/kg soil and CaCO₃ was 37%). In all wild grasses studied, Zn deficiency reduced shoot growth but had no effect on root growth. Low amounts of phytosiderophores were released from roots of all wild grasses adequately supplied with Zn. In plants grown without Zn, release of phytosiderophores progressively increased with the onset of visual Zn deficiency symptoms, such as inhibition of shoot elongation and appearance of chlorotic and necrotic patches on leaves. Compared to Zn‐sufficient plants, phytosiderophore release increased 18–20‐fold in deficient plants. HPLC analysis of root exudates showed that the dominating phytosiderophore in Zn‐deficient Agropyron and Hordeum was 3‐epi‐hydro‐xymugineic acid (epi‐HMA) and was 3‐hydroxy‐mugineic acid (HMA) in Secale. Besides HMA, epi‐HMA and mugineic acid (MA) were also detected in exudates of Zn‐deficient Secale. The results indicate the importance of phytosiderophores in adaptation of wild grasses to Zn‐deficient calcareous soils. Phytosiderophores might enhance mobilization of Zn from sparingly soluble Zn pools and from adsorption sites, both in the rhizosphere and within the plants.     

Response of carboxylate metabolism to zinc deficiency in Lactuca sativa and Brassica oleracea plants

Species or genotypes differ in their zinc use efficiency (ZnUE) under low Zn availability in the soil. Organic acids (OAs) synthetized by plant carboxylate metabolism may play a role in Zn‐deficiency tolerance. The main objective of the present work was to assess the response of two species of great agronomic interest such as Lactuca sativa and Brassica oleracea to Zn deficiency focusing on OAs and carboxylate metabolism. For this, L. sativa and B. oleracea plants were grown in hydroponic culture with two different Zn‐application rates: 10 µM Zn as control and 0.1 µM Zn as deficiency treatment. ZnUE parameters, concentrations of OAs and enzymes of carboxylate metabolism were analyzed. L. sativa showed better Zn uptake efficiency (ZnUpE), while B. oleracea demonstrated better Zn utilization efficiency (ZnUtE). In L. sativa, citrate and oxaloacetate concentrations and phosphoenolpyruvate carboxylase and citrate synthase activities increased, while fumarase and malate dehydrogenase activities declined. In B. oleracea no significant response was found in concentrations of carboxylate metabolism or enzyme activity except for a decrease in fumarase activity. These results suggest that a possible factor that induces the tricarboxylic acid cycle could be the low ZnUtE rather than the low Zn concentration under Zn‐deficiency conditions. In L. sativa citrate, oxaloacetate, phosphoenolpyruvate carboxylase, and citrate synthase may play a key role to face Zn deficiency, while in B. oleracea the higher ZnUtE cannot be explained in terms of a rise in OAs synthesis.     

缺锌玉米植株的傅立叶变换红外光谱研究

【目的】傅里叶变换红外光谱（fourier transform infrared spectroscopy, FTIR）是一种基于化合物中官能团和极性键振动的结构分析技术。本文利用傅立叶变换红外光谱仪检测缺锌和正常供锌玉米植株不同器官的组分变化,同时比较两个玉米品种植株不同部位的生物量和锌含量,以期为缺锌影响玉米生长与生理代谢的机理研究提供参考。【方法】选取农大108和郑单958两个玉米品种,利用营养液培养方式,设置缺锌和正常处理。1）当玉米出现缺锌症状后,将地上部和根系分开,测量株高和根长,烘干至恒重测干重。2）烘干至恒重的植株样品用HNO3-HClO4（3∶1）消煮,原子吸收分光光度计（型号WFX-120C,北京瑞利分析仪器公司）测定消煮液中锌浓度,计算植株中锌含量和锌积累量。3）收获玉米根系放入FAA固定液（70%酒精∶38%甲醛∶乙酸体积=90∶5∶5）中,利用扫描仪（EsponV700）扫描根系样品获取数字化图像,利用WinRHIZO根系分析软件（Regent Instruments Inc., Canada）对图像进行分析,获得根长、 根面积、 根体积等指标。4）取玉米根、 茎、 叶部分烘干样品,磨碎过0.2 mm筛,采用溴化钾压片法,利用傅立叶变换红外光谱仪（VERTEX 70,Bruker）检测不同部位的光谱特性,OPUS 6.5软件采集数据并进行基线校正。【结果】缺锌胁迫下, 植株地上部锌含量明显下降,低于临界水平（20 g/g）,生物量降低; 缺锌根系面积与体积变小,总根长变小。用缺锌与施锌植株生物量比来表征玉米对缺锌敏感性,品种农大108较郑单958对缺锌更为敏感。缺锌玉米根系和叶片FTIR谱在波数3410、 2920、 1650、 1380、 1055 cm-1附近处透过率较高,茎FTIR谱在这些波数处透过率较低,表明缺锌导致根系和叶片中碳水化合物、 脂类、 蛋白质及核酸含量下降,而在茎中有所积累。农大108植株中各组分变化受缺锌影响较大。【结论】缺锌导致玉米植株生长受抑,利用FTIR技术研究发现缺锌植株中碳水化合物、 脂类、 蛋白质及核酸组分发生变化,农大108植株中各组分变化受缺锌影响较大,品种农大108可能较郑单958对缺锌更为敏感。     

Effect of Zinc Humate on Growth of Soybean and Wheat in Zinc‐Deficient Calcareous Soil

Abstract

Humic acids have many benefits for plant growth and development, and these effects may be maximized if these materials are combined with micronutrient applications. In the present study, pot experiments were conducted to evaluate the effects of zinc (Zn) humate and ZnSO₄ on growth of wheat and soybean in a severely Zn‐deficient calcareous soil (DTPA‐Zn: 0.10 mg kg^?1 soil). Plants were grown for 24 (wheat) and 28 days (soybean) with 0 or 5 mg kg^?1 of Zn as either ZnSO₄ or Zn humate. Zinc humate used in the experiments was obtained from Humintech GmbH, Germany, and contained 5% of Zn. When Zn was not supplied, plants rapidly developed visible symptoms of Zn deficiency (e.g., chlorosis and brown patches on young leaves in soybean and necrotic patches on middle‐aged leaves in wheat). Adding Zn humate eliminated Zn‐deficiency symptoms and enhanced dry matter production by 50% in soybean and 120% in wheat. Zinc‐humate and ZnSO₄ were similarly effective in increasing dry matter production in wheat; but Zn humate increased soybean dry matter more than ZnSO₄. When Zn was not supplied, Zn concentrations were 6 mg kg^?1 for wheat and 8 mg kg^?1 for soybean. Application of Zn humate and ZnSO₄ increased shoot Zn concentration of plants to 36 and 34 mg kg^?1 in wheat and to 13 and 18 mg kg^?1 in soybean, respectively. The results indicate that soybean and wheat plants can efficiently utilize Zn chelated to humic acid in calcareous soils, and this utilization is comparable to the utilization of Zn from ZnSO₄. Under Zn‐deficient soil conditions, plant growth and yield can be maximized by the combined positive effects of Zn and humic acids.     

高钾供应加剧了水稻叶片缺镁诱导的氧化胁迫

Magnesium （Mg） deficiency in plant affects photosynthesis and many other metabolic processes. Rice （Oryza sativa L. cv. ＇Wuyunjing 7＇） plants were grown in hydroponics culture at three Mg and two potassium （K） levels under greenhouse conditions to examine the induction of oxidative stress and consequent antioxidant responses in rice leaves due to Mg deficiency. At low Mg （0.2 mmol L 1 Mg supply for two weeks after transplanting） and high K （6 mmol L^-1） for 21 days, the rice plants showed severe Mg deficiency and a significant decreases in the dry matter production. The Mg deficiency in leaves decreased chlorophyll concentrations, photosynthetic activity, and soluble protein, but significantly increased the concentrations of soluble sugars and malondialdchyde （MDA） and the activities of superoxide dismutase （SOLD, EC 1.15.1.1）, catalase （CAT, EC 1.11.1.6） and peroxidase （POD, EC 1.11.1.7）. In addition, Mg concentrations in the leaves and in the shoot biomass were negatively related to the activities of the three antioxidative enzymes and the concentration of MDA in leaves. There were very significant interactive effects between Mg and K supplied in the culture solution on shoot biomass yield, chlorophyll content, photosynthesis rate, the activities of SOD, CAT and POD, and MDA content in the leaves of rice. It is suggested that the high K level in the nutrient solution aggravated the effect of low Mg supply-induced Mg deficiency and created the oxidative damage in rice plants.     

不同供Zn量对三种小麦基因型幼苗生长和养分吸收的影响

采用溶液培养方法,研究了不同供Zn量(0、0.5、104、0.mg/L,分别用Zn0、Zn0.5、Zn10、Zn40表示)对三种亲缘关系很远的半冬性小麦基因型郑麦9023、陕512、西农979幼苗生长发育及Zn、Fe、Mn吸收的影响,以期为筛选耐高锌的小麦基因型提供理论依据。结果表明,不供Zn时小麦幼苗未出现缺Zn症状;Zn0.5对小麦的正常生长影响较小。三种基因型小麦的幼苗在过量供Zn(Zn10、Zn40)时均受到严重伤害:抑制小麦分蘖、根系及地上部生长,叶片叶绿素SPAD值显著降低,小麦植株尤其是根部的耐性指数降低;施入的Zn的转运率显著降低,却大大提高了小麦植株尤其是根部的Zn含量和吸收量,但Zn10时幼苗体内Zn含量和吸收量大于Zn40,且Zn10比Zn40更能在根部积累Zn。Zn与Fe的吸收在根部似乎表现为互助作用,而地上部表现为颉颃作用;Zn与Mn之间表现出强烈的颉颃作用。过量供Zn时以西农979耐性指数最大,Zn转运率最高,植株体内的Fe、Mn含量也高。总之,供Zn量为通常配方的51～0倍时对小麦幼苗的生长尚无明显影响;1002～00和4008～00倍时则能对小麦幼苗造成严重伤害,三种供试小麦基因型中以西农979对过量Zn毒害的耐性最强。     

Influence of zinc on the growth,distribution of elements,and metabolism of one‐year old American ginseng plants

Using a water culture technique, 0.05 ppm zinc (Zn) was found to be the critical deficiency concentraction for one‐year American ginseng (Panax quinquefolium L) plants, 0.3 ppm was optimum, 0.5 ppm the critical Zn‐toxicity concentration, and 10 ppm the concentration when severe toxicity occurs. Therefore, the optimum Zn concentration for the growth of American ginseng plants was between 0.1 ppm ‐ 0.3 ppm. Zinc deficiency symptoms of one‐year old American ginseng plants were indicated by the inhabition of root growth, with little fibrous root development, and smaller leaves compared to normal leaves. The symptoms of toxicity were also indicated by the inhibition of root growth, and when seedlings were suffering from an acute toxicity, no fibrous roots appeared, and eventually the roots yellowed and leaves grew slowly or even entirely ceased to grow, the final result being very small leaves which are also chlorotic. Zinc maintained within the 0.1 ppm to 0.3 ppm sufficiency range promoted the synthesis and accumulation of ginsenosides by American ginseng plants, and both low and high Zn concentrations restrained the synthesis and accumulation of ginsenosides. Both Zn deficiency and the optimum Zn concentration (0.3ppm) are beneficial to the accumulation of amino acids in the roots of American ginseng plants. Close to the optimum Zn concentration, the ratios of P/Zn and Fe/Zn in the shoot of American ginseng plants were maintained at 77 and 9.4, respectively.