Diurnal variations in absorption and translocation of a ferrated phytosiderophore in barley as affected by iron deficiency

The release of phytosiderophore (PS) from roots of Fe-deficient graminaceous plants follows a distinct diurnal rhythm with maximum release rates occurring usually 3 to 4 hours after the onset of light. However, it remains to be determined whether absorption of the PS-Fe³⁺ complex shows a diurnal rhythmicity similar to that of PS release, Barley plants grown with or without 10 µM FeEDTA for 7 days were fed with ferreted PS (10 µM labelled with ⁵⁹Fe) at 4-h intervals to study the diurnal variations in the absorption and transloca tion of ⁵⁹Fe, The absorption of ⁵⁹Fe, irrespective of the Fe nutritional status of the plants, was higher during the day and lower during the night but did not show any peak throughout the day-night cycle. On the other hand, the translocation of ⁵⁹Fe into shoots of Fe-deficient plants was lower than that of Fe-sufficient plants, while the Fe nutritional status of the plants did not affect the absorption of ⁵⁹Fe by roots, The formation of root apoplastic ⁵⁹Fe was lower during the day and higher during the night, regardless of the Fe nutritional status of plants. Our results showed that the absorption of the PS-Fe³⁺ complex by roots did not follow the PS release pattern.     

Detection of the regions of phytosiderophore release from barley roots

Abstract

We devised a method to detect regions of phytosiderophore release from barley (Hordeum vulgare cv. Minorimugi) roots. Plants were grown in Fe-sufficient (+Fe) or Fe-deficient (?-Fe) water cultures for 14 d in a phytotron. Intact or excised roots were sampled and put between two sheets of filter papers just after the onset of the light period. The filter papers with roots were wrapped with vinyl film to avoid drying out and covered with aluminum foil to shade. The roots between the filter paper were kept in the phytotron for 4 h and phytosiderophores (PS) released from roots were absorbed by the filter paper. Then, the shape of the roots was preserved by photocopy and PS released on the filter paper were visualized by the method employed for detecting PS on thin layer chromatography (TLC). Gelatinous Fe solubilizing activity was employed for detecting PS on the filter paper. Released PS were detected as white spots on the orange-colored background and the regions of PS release from the roots were visible on the filter paper. It was evident that the apical zones of roots were the main regions of PS release. It was apparent that a distinct primary root newly formed on the basal parts had higher activity to release PS than the other roots of ?Fe plants. It was also shown that apical root zones of +Fe plants released PS.     

Iron-deficiency response and expression of genes related to iron homeostasis in poplars

Iron (Fe) deficiency is a serious agricultural problem, especially in calcareous soils, which are distributed worldwide. Poplar trees are an important biomass plant, and overcoming Fe deficiency in poplars will increase biomass productivity worldwide. The poplar Fe-deficiency response and the genes involved in poplar Fe homeostasis remain largely unknown. To identify these genes and processes, we cultivated poplar plants under Fe-deficient conditions, both in calcareous soil and hydroponically, and analyzed their growth rates, leaf Soil and Plant Analyzer Development (SPAD) values, and metal concentrations. The data clearly showed that poplars have notable growth defects in both calcareous soil and a Fe-deficient hydroponic culture. They exhibited serious chlorosis of young leaves after 3 weeks of Fe-deficient hydroponic culture. The Fe concentrations in old leaves with high SPAD values were markedly lower in Fe-deficient poplars, suggesting that poplars may have good translocation capability from old to new leaves. The Zn concentration in new leaves increased in Fe-deficient poplars. The pH of the hydroponic solution decreased in the Fe-deficient culture compared to the Fe-sufficient culture. This finding shows that poplars may be able to adjust the pH of a culture solution to better take up Fe. We also analyzed the expression of Fe homeostasis-related genes in the roots and leaves of Fe-sufficient and Fe-deficient poplars. Our results demonstrate that PtIRT1, PtNAS2, PtFRO2, PtFRO5, and PtFIT were induced in Fe-deficient roots. PtYSL2 and PtNAS4 were induced in Fe-deficient leaves. PtYSL3 was induced in both Fe-deficient leaves and roots. These genes may be involved in the Fe uptake and/or translocation mechanisms in poplars under Fe-deficient conditions. Our results will increase a better understanding of the Fe-deficiency response of poplars and hence improve the breeding of Fe-deficiency-tolerant poplars for improved biomass production, the greening of high pH soils, and combatting global warming.     

The effects of Fe deficiency on low molecular weight organic acid exudation and cadmium uptake by Solanum nigrum L.

Abstract

The influence of Fe-deficiency on the root exudation of low molecular weight organic acids (LMWOAs), pH alteration and cadmium (Cd) accumulation and translocation were investigated in morel (Solanum nigrum L.) in hydroponic culture experiments. Tartaric, citric, malic and acetic acids were monitored because these acids were abundant and often detected as root exudates. Results showed that Fe-deficient plants excreted large amounts of LMWOAs in comparison with Fe-sufficient plants across all Cd treatments (p <0.05). In both cases the concentrations of the four organic acids were tartaric > citric > malic > acetic. The results showed that the Fe-deficient plants with higher concentrations of LMWOAs accumulated more Cd (p <0.05) and induced a decrease in solution pH compared with the Fe-sufficient plants. Cadmium accumulation in the Fe-deficient and Fe-sufficient plants had significant positive correlations with the exudation of malic and acetic acids (p <0.05 and p<0.01). Cadmium accumulation in the Fe-sufficient plants had a significant (p<0.01) positive correlation with the exudation of tartaric acid, whereas there was a negative correlation (p<0.01) between Cd accumulation and the exudation of tartaric acid in the Fe-deficient plants. No significant correlation between the exudation of citric acid and Cd accumulation was obtained. Our results indicate that Fe-deficiency could induce Cd accumulation and translocation through an increase of LMWOAs exudation and pH alteration, both of which enhance Cd bioavailability.     

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.     

影响菜豆体内铁再利用效率的因素及其机理

本文在人工气候室中，用营养液培养方法，并结合同位素示踪技术研究了铁的供应状况，两种形态氮素（ＮＯ＾－３－Ｎ和ＮＨ＾＋４－Ｎ）及叶处遮光对菜豆体内铁再利用效率的影响，并对其有关机理进行了深入的研究。结果表明，铁的缺乏有利于累积在根和初生叶中的铁身新生组织中转移，铁的再利用效率明显提高。无论有缺铁还供铁条件下，ＮＨ＾＋４－Ｎ的供应使得菜豆新叶中活性铁含量、新叶叶绿素含量及体内铁的再利用效率都明显高于Ｎ     

缺铁水稻根表铁膜对硒的转运和吸收的影响

Under anaerobic conditions, ferric hydroxide deposits on the surface of rice roots and affects uptake and translocation of certain nutrients. In the present study, rice plants were cultured in Fe-deficient or sufficient solutions and placed in a medium containing selenium （Se） for 2 h. Then, FeSO4 was added at the various concentrations of 0, 10, 40, or 70 mg L-1 to induce varying levels of iron plaque on the root surfaces and subsequent uptake of Se was monitored. The uptake of Se was inhibited by the iron plaque, with the effect proportional to the amount of plaque induced. The activity of cysteine synthase was decreased with increasing amounts of iron plaque on the roots. This may be the important reason for iron plaque inhibition of Se translocation. At each level of iron plaque, Fe-deficient rice had more Se than Fe-sufficient rice. Furthermore, with plaque induced by 20 mg Fe L-1, plants from Fe-deficient media accumulated more Se than those from Fe-sufficient media, as the Se concentration was increased from 10 to 30 or 50 mg L^-1. We found that phytosiderophores, highly effective iron chelating agents, could desorb selenite from ferrihydrite. Root exudates of the Fe-deficient rice, especially phytosiderophores in the exudates, could enhance Se uptake by rice plants with iron plaque.     

Physiological basis of iron chlorosis tolerance in rice (Oryza sativa) in relation to the root exudation capacity

Micronutrient deficiency in cultivable soil, particularly that of iron (Fe) and zinc (Zn), is a major productivity constraint in the world. Low Fe availability due to the low solubility of the oxidized ferric forms is a challenge. An experiment was, thus, executed to assess the performance of eight genetically diverse rice genotypes on Fe-sufficient (100 µM) and Fe-deficient (1 µM) nutrient solution, and their ability to recover from Fe deficiency was measured. Fe efficiency under Fe deficiency in terms of biomass production showed a significant positive correlation with the root release of phytosiderophore (PS) (R² = 0.62*). This study shows that the Fe deficiency tolerance of Pusa 33 was related to both a high release of PS by the root and an efficient translocation of Fe from the root to the shoot as the Fe–PS complex, which could be useful for improving the Fe nutrition of rice particularly under aerobic conditions.     

Diurnal rhythm of release of phytosiderophores and uptake rate of zinc in iron-deficient wheat

Abstract

The diurnal rhythm of release of phytosiderophores and uptake rate of zinc (Zn) was studied in iron (Fe) deficient wheat (Triticum aestivum L. cv. Ares) plants grown in nutrient solution under controlled environmental conditions. Different forms of Zn (e.g. ZnSO₄, ZnEDTA) were used to obtain different degrees of loading of the root apoplasmic pool with Zn.

In the Fe-deficient plants the release of phytosiderophores from the roots followed a distinct diurnal rhythm with a steep peak about 4 h after the onset of the light period. These plants also showed a similar pattern in the rates of Zn uptake over the 24 h day-night cycle. During the light period there was a steep transient peak (factor 3.8) in Zn uptake rate in the Fe-deficient plants supplied with ZnSO₄. This transient peak was much less distinct in plants supplied with ZnEDTA (factor 1.8) and absent in plants supplied with ZnEDTA plus free chelator (+ NaEDTA) in excess. The peak in Zn uptake coincided with the maximum rate of phytosiderophore release in the Fe-deficient plants. In the Fe-sufficient plants the release of phytosiderophores was very low and no such peak in Zn uptake rates could be observed.

These results demonstrate that phytosiderophores mobilize Zn not only in the rhizosphere, but also from the root apoplast. Thus, the apoplasmic pool of micronutrient cations has to be taken into account as potential source for both uptake and diurnal variation in uptake rates of Micronutrient cations.     

Effects of iron nutritional status and time of day on concentrations of phytosiderophores and nico‐tianamine in different root and shoot zones of barley

The diurnal pattern in concentrations of phytosiderophores (PS) and its precursor nicotianamine (NA) was studied in different root and shoot zones of iron (Fe)‐sufficient and Fe‐deficient barley (Hordeum vulgare L. cv. Europa) grown in nutrient solution. Roots were separated into apical (0–3 cm) and basal zones (>3 cm) and shoots into young (3 cm basal zones of youngest two leaves) and old (remaining zones of youngest two leaves and oldest leaf) parts. The main PS in barley was identified as epi‐hydroxymugineic acid (epi‐HMA). Regardless of the sampling zone and time of day, epi‐HMA concentrations were several times higher in Fe‐deficient than in Fe‐sufficient plants and several times higher in the roots than in the shoots. In roots and shoots, epi‐HMA concentrations were always higher in the younger compared with the older zones. In both root zones of Fe‐deficient plants, an inverse diurnal rhythm occurred in epi‐HMA concentrations and in its release by the roots. In contrast, such a rhythm was absent in roots of Fe‐sufficient plants and in the shoots regardless of the Fe nutritional status. Nicotianamine concentrations in roots were not affected by the Fe nutritional status in apical zones but slightly enhanced under Fe deficiency in basal zones. In contrast to roots, NA concentrations in both shoot parts were lower in Fe‐deficient than in Fe‐sufficient plants. Regardless of the Fe nutritional status in roots and shoots, NA concentrations were higher in young than in old parts and no consistent diurnal variations were observed. The results suggest that PS are also synthesized in the shoot, although at much lower rates than in roots. As with roots, PS synthesis in the shoot is enhanced under Fe deficiency and is mainly localized in young growing tissue. The distinct diurnal rhythm in PS release in roots is apparently not regulated by variation in the rate of PS synthesis during the day.     

Arsenic–iron interaction: Effect of additional iron on arsenic-induced chlorosis in barley grown in water culture

Abstract

The effect of additional iron (Fe) on arsenic (As) induced chlorosis in barley (Hordeum vulgare L. cv. Minorimugi) was investigated. The treatments were: (1) 0?μmol?L^?1 As?+?10?μmol?L^?1 Fe³⁺ (control), (2) 33.5?μmol?L^?1 As?+?10?μmol?L^?1 Fe³⁺ (As-treated) and (3) 33.5?μmol?L^?1 As?+?50?μmol?L^?1 Fe³⁺ (additional-Fe³⁺) for 14?days. Arsenic and Fe³⁺ were added as sodium-meta arsenite (NaAsO₂) and ethylenediaminetetraacetic acid-Fe³⁺, respectively. Chlorosis in fully developed young leaves was observed in the As-treated plants. The chlorophyll index and the Fe concentration decreased in shoots of the As-treated plants compared with the control plants. Arsenic reduced the concentration of phosphorus, potassium, calcium, magnesium, manganese, zinc and copper. The additional-Fe³⁺ treatment increased the chlorophyll index in plants compared with the As-treated plants. Among the elements, Fe concentration and accumulation specifically increased in the shoots of additional-Fe³⁺ plants compared with As-treated plants, indicating that As-induced chlorosis was Fe-chlorosis. Arsenic and Fe were mostly concentrated in the roots of the As-treated plants. Despite inducing chlorosis in the As-treated plants, phytosiderophores (PS) accumulation in the roots and release from the roots did not increase, rather PS accumulation decreased, indicating that As toxicity hindered PS production in the roots. The PS accumulation in the roots was further reduced in the additional-Fe³⁺ treatment.     

IRON IS REQUIRED FOR THE INDUCTION OF ROOT FERRIC CHELATE REDUCTASE ACTIVITY IN IRON-DEFICIENT TOMATO

Two mutants of tomato and their corresponding wild-type genotypes, Tfer/TFER and chloronerva/Bonner Beste, were grown in nutrient solution under conditions leading to iron (Fe) deficiency. Iron deficiency caused decreases in growth, leaf chlorosis, and changes in the morphology of roots. Ferric chelate reductase activities of whole roots were generally lower in Fe-deficient plants than in control, Fe-sufficient plants. Plants grown for 7 days without Fe, however, had transient increases in whole root ferric chelate reductase activity after the addition of small amounts of Fe (2 μM) to the nutrient solution. Also, adding sequential 0.5 μM Fe pulses to the nutrient solution led to high whole root ferric chelate reductase activities. Similar results were obtained with a protocol using excised root tips instead of whole root systems to measure ferric chelate reductase activities. The protocol using root tips generally gave higher ferric chelate reductase rates than the method using whole roots, due to the localized expression of the enzyme in the distal root zones.     

Water- and pyrophosphate-extractable humic substances fractions as a source of iron for Fe-deficient cucumber plants

The capacity of Fe-deficient cucumber plants to utilise water-extractable and pyrophosphate-extractable humic substances as a source of Fe was investigated. Plants were grown for 13 days in nutrient solution in the presence or absence of Fe and during the last 7 days water-extractable and pyrophosphate-extractable humic substances were added to the solution at a final concentration of 5 μg organic C ml^–1. The water-extractable humic fraction did not significantly modify leaf area and dry matter accumulation, leaf total Fe or chlorophyll content of cucumber plants adequately supplied with Fe. In contrast, pyrophosphate-extractable humic substances caused a slight but significant decrease of all the leaf parameters considered, with the exception of the chlorophyll content. Root Fe content of Fe-sufficient plants was decreased by more than 50% in the presence of each humified fraction. Addition of each humic fraction to Fe-deficient plants led to a partial disappearance of leaf chlorosis symptoms with a significant increase in chlorophyll and leaf Fe content. Fe content of roots was also significantly increased in Fe-deficient plants by the addition of humic substances to the nutrient solution. These results show that Fe-deficient cucumber plants can utilise Fe contained in the two fractions of humified organic matter. However, by calculating the amount of total Fe accumulated per plant in the presence of water-extractable or pyrophosphate-extractable humic substances, it could be seen that Fe contained in the water-extractable humic fraction was almost totally used by Fe-deficient cucumber plants, while that present in the pyrophosphate-extractable fraction could only be partially absorbed. The results strongly support a role of humified organic matter in Fe nutrition of plants and are discussed in terms of a possible interaction between soil humic substances and the biochemical mechanisms involved in the plant response to Fe deficiency. Received: 6 November 1996     

ALLEVIATION OF CADMIUM-TOXICITY BY APPLICATION OF ZINC AND ASCORBIC ACID IN BARLEY

ABSTRACT

Effect of cadmium (Cd) on biomass accumulation and physiological activity and alleviation of Cd-toxicity by application of zinc (Zn) and ascorbic acid in barley was studied, using semisolid medium culture including 15 treatments [four Cd concentration treatments: 0.1, 1, 5, 50?µmol?L^?1, four treatments with addition of 300?µmol?L^?1 Zn or 250?mg?L^?1 ascorbic acid (ASA) based on these four Cd concentrations, respectively, and three controls: basic nutrient medium, and with Zn or ASA, respectively]. Cadmium addition to semisolid medium, at a concentration of 1, 5, and 50?µmol?L^?1, inhibited biomass accumulation and increased malondialdehyde (MDA) content of barley plants, while the addition of 0.1?µmol?L^?1 Cd increased slightly dry mass. There was a tendency to a decrease in Zn, copper (Cu) concentrations both in shoots and roots and iron (Fe) in shoots of barley plants exposed to 1 to 50?µmol?L^?1 Cd. In addition, there were indications of a stress repose characterized by increased superoxide dismutase (SOD) and peroxidase (POD) activities relative to plants not subjected to Cd. The physiological changes caused by Cd toxicity could be alleviated to different extent by application of 300?µmol?L^?1 Zn or 250?mg?L^?1 ASA in Cd stressed plants. The most pronounced effects of adding Zn or ASA in Cd stressed medium were expressed in the decreased MDA and increased biomass accumulation, e.g., MDA contents were reduced (p≤0.01) by 4.8%–17.8% in shoots and 0.5%–19.7% in roots by adding 300?µmol?L^?1 Zn, in 50?µmol?L^?1 Cd stressed plants, and by 1.3%–7.4% in shoots and 2.6%–4.5% in roots by application of 250?µmol?L^?1 ASA, respectively. However, ASA addition may enhance Cd translation from root to shoot, accordingly, ASA would be unsuitable for the edible crops grown in Cd contaminated soils to alleviate phytotoxicity of Cd.     

Alien cytoplasm effects on phytosiderophore release in two spring wheats (Triticum aestivum L.)

Iron (Fe) deficiency is a difficult nutrient problem particularly in crop plants grown on calcareous soils. Recently, phytosiderophore (PS) release has been linked to the ability of graminaceous species and genotypes to withstand Fe-deficiency chlorosis. So enhancing PS release is a critical step to improve iron efficiency of plants grown on iron stressed soils. The effects of alien cytoplasm on PS release in spring wheat were studied by analyzing PS release from twenty wheat genotypes, including two spring wheat 881 and 352-35, and their 18 alloplasmic lines with the participation of cytoplasms from the Aegilops and Triticum species. Different genotypes were grown in iron sufficient and deficient nutrient solution under controlled environmental conditions. PS release rates were determined at two or three days intervals after onset of iron deficiency symptoms by the measurement of iron mobilizing capacity of root exudates from freshly precipitated Fe^III hydroxide. High amounts of phytosiderophores were released from roots of all wheat genotypes without iron supplied, and the amount progressively increased with the development of iron deficiency chlorosis. The results revealed that (1) the release rate of phytosiderophores from roots of common wheat could be considerably influenced by alien cytoplasms. Some alien cytoplasms exerted positive effects, some ones did negative effects, and the other ones had no significant effects. (2) the same alien cytoplasm could affect similarly or oppositely the phytosiderophores release from different wheat. (3) some alien cytoplasms, such as Chinese Spring, Ae. speltoides Tausch and Ae. cylindrica Host showed promising and potential in improving the rate of phytosiderophore release in common wheat. These cytoplasms which showed the desired effect should be given priority in interspecific and intergeneric hybridization to develop and reconstruct the needed wheat cultivars.     

A rice FRD3-like (OsFRDL1) gene is expressed in the cells involved in long-distance transport

We identified four putative AtFRD3-like genes (OsFRDL) in the rice genome that exhibited 39.1 to 56.7% amino acid sequence similarities to Arabidopsis FRD3. Of these, we cloned three OsFRDL genes from a cDNA library prepared from iron-deficient rice roots: OsFRDL1, OsFRDL2, and OsFRDL3. OsFRDL1 was expressed weakly in Fe-sufficient roots, and slight expression was induced in the roots of Fe-deficient plants. OsFRDL2 was expressed constitutively in both roots and leaves, and Fe deficiency reduced its expression in leaves. OsFRDL3 was expressed in leaves, but not in roots; Fe deficiency induced slight expression in leaves. An OsFRDL1-sGFP fusion protein was localized in the plasma membrane in onion epidermal cells. The promoter GUS analysis showed that OsFRDL1 was localized in the cells involved in long-distance transport, in both Fe-sufficient and Fe-deficient plants. Furthermore, OsFRDL1 expression was observed during the reproductive stage. These results suggest that OsFRDL1 is a transporter that resides in the plasma membrane of cells involved in long-distant transport.     

钙对镉胁迫下玉米生长及生理特性的影响

采用溶液培养试验 ,研究不同的钙和镉处理对玉米植株生长、叶绿素含量、硝酸还原酶和ATPase酶活性以及叶片中丙二醛含量、活性氧清除酶系统活性的影响。结果表明 ,根部未供钙或叶面喷施CaCl2时 ,加镉处理玉米根、地上部生物量降低 ,根冠比加大 ;而根部供钙 ,植株生长较好 ,生物量较高 ,根冠比相对较小。营养液中加镉 ,玉米植株中镉浓度显著增加 ,根部镉浓度明显比地上部高 ,根中镉约占 65%～ 78% ,地上部镉占到 22%～35%左右。根部供钙比未供钙处理 ,根中镉含量虽没有显著性差别 ,但地上部镉浓度明显较低。叶片喷施CaCl2 4次比喷施 2次处理 ,地上部镉浓度增加。供钙明显增加了玉米植株中钙浓度。未供钙的玉米叶片叶绿素含量下降 ,但叶绿素a/叶绿素b比基本不变 ;加镉处理 ,玉米叶片叶绿素a、叶绿素b及叶绿素总量下降更甚 ,叶绿素a/叶绿素b比升高 ;叶面喷施CaCl2 ,叶绿素含量也较低。前期和后期根部供钙处理 ,叶绿素下降程度有所缓解。而根部一直供钙 ,玉米叶片中叶绿素a、叶绿素b和叶绿素总量明显提高。镉抑制了玉米植株叶片硝酸还原酶活性、ATPase活性 ;根中ATPase活性以及活性氧清除酶系统超氧化物歧化酶 (SOD)、愈创木酚过氧化物酶 (Gua POD)、抗坏血酸过氧化物酶 (AsA POD)、过氧化氢酶 (CAT)受镉的诱导而增加，叶片中丙二醛(MDA)含量升高。与未供应钙加镉处理相比，根部供钙加镉处理的玉米叶片硝酸还原酶活性、ATPase活性显著增加，也明显减轻了镉对根中ATPase活性、叶片中丙二醛含量、活性氧清除酶系统SOD，POD，CAT 活性的诱导效应。间隔供钙，在一定程度上缓解了镉的毒害，但是叶片喷施CaCl2，对减轻镉毒害无明显效果。因此在本试验条件下，根部供钙对缓解玉米镉毒害有重要作用。关键词:钙；镉；玉米；生理特性     

Genotypic differences in effects of cadmium on growth and nutrient compositions in wheat

Abstract

A solution culture study was conducted to determine the genotypic difference in the effects of cadmium (Cd) addition on growth and on the uptake and distribution of Cd and other 11 nutrients in wheat plants. Cadmium addition at a rate of 1 mg L^?1 significantly reduced root and shoot dry matter production, shoot height, root length, chlorophyll content, and tillers per plant. On the average of 16 wheat genotypes used in study, Cd concentrations of Cd‐treated plants were 48.1 and 459 μg g^?1 dry weight (DW) in shoots and roots, respectively, and retained 77.91% of total Cd taken up in the roots. On the whole, Cd addition reduced the concentration of sulfur (S), phosphorus (P), magnesium (Mg), molybdenum (Mo), manganese (Mn), and boron (B), and increased iron (Fe), irrespective of the plant parts. The effect of Cd on the concentration of potassium (K), calcium (Ca), and copper (Cu) differed in shoots and roots. The significant difference existed among 16 wheat genotypes in their response to Cd in terms of growth and nutrient concentrations. Genotype E81513, which showed relatively less inhibition in growth, had the lowest shoot Cd concentration and more Cd accumulation in roots, while Ailuyuang had the highest Cd concentration and accumulation in shoot with lower Cd concentration in root. The significant interaction was found between Cd treatment and genotype for all nutrient concentrations in both shoot and root, except S and Zn in root.     

镉处理根表铁膜对水稻吸收镉锰铜锌的影响

本试验利用营养液和土壤培养系统,研究不同Fe、 Cd处理下根表铁膜对水稻吸收Cd、 Mn、 Cu、 Zn的影响。土壤中Fe的水平为0、 1、 2 g/kg Fe（以FeSO47H2O的形式供应）,Cd 的水平为0、 2、 10 mg/kg Cd（以3CdSO48H2O的形式供应）。营养液中Fe和Cd的水平分别为0、 10、 30、 50、 80、 100 mg/L Fe 和 0、 0.1、 1.0 mg/L Cd。收获后测定水稻根表、 根中和地上部Cd、 Fe、 Mn、 Cu、 Zn 含量。试验结果表明,两种培养方式下,随着介质中Fe浓度的增加,水稻根表铁膜（DCB-Fe）逐渐增多。土壤培养方式下,根表铁膜中Cd 和 Mn 含量随铁膜量增加而略有增加,所有元素含量均表现为根中大于铁膜中。营养液培养条件下,根表铁膜中Mn和Cu含量在高量 Fe 供应时有所增加, Mn、 Cu、 Zn表现为铁膜中大于根中。根表铁膜中Zn含量在两种培养方式下均未呈现一定规律性变化。根中和地上部 Cd、 Mn、 Cu、 Zn 含量一般都随介质中Fe浓度的增加而下降,Cu和Zn含量在加Cd处理中下降。以上结果证明,铁膜对Cd 的吸附阻挡能力有限,对Mn、 Cu、 Zn 的吸附作用因培养方式和元素种类不同而有所差异,植株体内微量元素含量的下降主要与它们之间的相互抑制作用有关。     

Iron deficiency enhances cadmium uptake and translocation mediated by the Fe2+ transporters OsIRT1 and OsIRT2 in rice

Abstract

Cadmium (Cd) accumulation in rice grains is enhanced if ponded water is released from paddy fields during the reproductive stage (intermittent irrigation). The release of ponded water creates aerobic soil conditions under which Cd becomes soluble and iron (Fe) solubility decreases. We hypothesized that Fe shortage in rice induces Fe uptake and translocation and that Cd is also taken up and translocated throughout this process. Hydroponically cultured Fe-deficient rice absorbed more Cd than did Fe-sufficient rice, and the presence of Fe enhanced the translocation of Cd to the shoots. Yeast mutants expressing OsIRT1 and OsIRT2, which encode the rice Fe²⁺ transporter, became more sensitive to Cd, suggesting that Cd was absorbed by OsIRT1 and OsIRT2. We discuss the possibility that Cd accumulation in rice grains during the reproductive stage is mediated by the Fe transport system.