高等植物水分胁迫诱导的基因及其表达调控

高等植物在生长发育过程中经常受到恶劣环境的胁迫,很多环境胁迫如干旱、盐渍、低温和高温等都表现为不同程度的对植物体内水分状况的影响,因此,水分胁迫是高等植物面临的主要环境问题。在长期进化过程中,高等植物通过一系列的生理或发育的变化来响应环境的水分胁迫。高等植物对水分胁迫的耐受性在一定程度上具有相同的分子基础,很多基因的表达     

植物根表铁膜的形成及其营养与生态环境效应

论述了根表铁膜的形成条件、形态和矿物学组成及在根表的沉积位置,讨论了根表铁膜作为铁库改善植物Fe营养、影响P、Zn等营养状况的植物营养效应以及铁膜通过吸附或共沉淀的外在抗性机制和竞争代谢敏感位点的内在抗性机制,在提高植物抵抗Cu、Ni、Cd、As等重金属毒害和强酸、低碳的逆境环境等方面的生态环境效应．     

高等植物含钼酶与钼营养

就高等植物中的含钼酶,钼与植物碳氮及其它元素代谢的关系,钼与激素合成及植物抗性的关系,以及植物钼营养基因型差异的研究进展作了介绍.     

植物对Si的吸收、运输和沉积

本文综述了植物中的S i及其吸收、运输和沉积的研究进展:(1)植物含S i量因植物种、品种甚至无性系与器官的不同而有较大差异,S i在细胞中呈现区隔化分配;(2)植物中沉积的S i主要是非晶态的S iO2.nH2O(又称硅胶、植物蛋白石、植硅石等),是有机物质矿质化的产物,不同植物所形成的S i化结构及其形态不同,可用于植物分类、鉴定及古气候与环境变化的研究;(3)硅藻和高等植物主要吸收S i(OH)4,高等植物中存在S i主动吸收机制;(4)有机大分子物质(包括多胺、碳水化合物、纤维素)作为有机衬质参与了植物的S i沉积过程;(5)突变体的鉴定和应用,对S i营养研究具有重要作用.     

植物硒同化的研究进展及其耐硒突变体的筛选

简要叙述了高等植物对硒元素吸收、同化的过程和特点。对近年来植物硒蛋白存在状态、硒相关突变体的筛选和应用硒代谢关键酶基因的转基因植物研究等方面的最新进展作了扼要综述。在此基础上对植物硒营养研究的发展提出了几点设想。     

作物铁生物强化

铁是植物必需的微量元素。缺铁不仅影响植物的生长,更影响作物的营养品质。铁营养摄入不足是导致人体缺铁性贫血的主要原因。在膳食结构中,以谷物为主食,特别是发展中国家的人群,缺铁性贫血更为严重。因此,以提高作物食用部分铁含量为目标的"铁生物强化"意义重大。首先,介绍了植物铁吸收、转运和储存的分子机制;其次,总结了提高作物铁含量和生物有效性的方法 ;最后,对未来作物铁生物强化的研究方向提出了展望。     

植物硒同化的研究进展及其耐硒突变体的筛选

简要叙述了高等植物对硒元素吸收、同化的过程和特点。对近年来植物硒蛋白存在状态、硒相关突变体的筛选和应用硒代谢关键酶基因的转基因植物研究等方面的最新进展怍了扼要综述。在此基础上对植物硒营养研究的发展提出了几点设想。     

植物吸收利用铁的机理

根据植物铁营养的一些研究进展,论述了植物对铁的吸收和运输机理以及HCO3^-,N、P等因素对铁利用效率的影响。     

第十四届国际植物铁营养与相互作用及中国生物强化2008年年会联合研讨会

“植物铁营养与相互作用国际研讨会”是一个国际例会,从上世纪七十年代开始,每两年举办一次。其目的是聚集各国从事植物铁营养研究方面的科学家进行交流,讨论植物铁营养所影响同时受之影响的各种因素（包括土壤、微生物、植物、动物等）及其相互之间的作用,促进该领域的国际交流和发展,揭示植物对土壤中铁的活化、吸收、代谢以及积累的生理及分子机制,     

高等植物体内铁运输机制研究进展

铁是植物所必需的微量矿质元素,在光合作用、呼吸作用等过程中发挥着重要的作用。虽然铁在地壳中含量丰富,但生物有效获取率非常低。因此,探索高等植物铁吸收及运输机制一直是植物铁营养领域研究的热点问题。近几年来,人们对于高等植物体内铁运输,尤其是细胞内铁运输又有了新的认识。本文主要对高等植物体内长距离铁运输(木质部,韧皮部)和细胞内的铁运输(液泡,叶绿体和线粒体)两方面的运输机制进行了综述,这将帮助我们进一步了解植物铁代谢机制,对我们培育高铁含量作物和提高植物抗逆性有着重要意义。     

根系活动对湿地植物根际铁异化还原的影响及机制研究进展

根系活动是影响湿地植物根际铁异化还原速率的关键因素之一。以往国内外湿地铁异化还原的研究多为分析和比较各类中宏观生境中铁异化还原能力的差异。近年来,湿地植物根际微域铁的生物地球化学行为也日益成为该领域的研究热点。综述了根际铁异化还原研究概况,梳理了根系活动对根际铁异化还原关键因子的作用机制,分析了根际铁异化还原和其他有机质代谢途径的竞争关系,探讨了根际铁异化还原对根系活动动态变化和异质性的响应,提出了根际铁异化还原的概念模型,并指出了未来我国湿地植物根际铁异化还原研究应加强的工作。     

Soil-dependent variability of leaf iron accumulation in transgenic tobacco overexpressing ferritin

Ferritin overexpression in transgenic plants has been recently reported to increase leaf and seed iron content. We investigated the influence of various soil conditions on this increase in leaf iron content. One control transgenic tobacco and two transgenic tobaccos overexpressing ferritin in the plastids or in the cytoplasm, respectively, were grown on five different soils, two of them being amended with sewage sludge. Although a significant increase in leaf iron concentration was measured in transgenics overexpressing ferritin grown on three out of five soils, this increase was not a general rule. On some soils, leaf iron concentration of control plants was as high as in transgenics grown on other soils. In addition, an increased phosphorus concentration in the two sewage sludge amended soils correlated with a high leaf iron concentration in control plants, similar to the one measured in ferritin transformed plants. Indeed, growing plants in vitro with various increasing phosphate concentrations revealed a direct P involvement in iron loading of control plants, at a similar level as overexpressing ferritin plants. Also, with one of the soil tested, not only iron but also manganese, zinc and cadmium, and to a much lesser extent copper, nickel and lead were found more abundantly in ferritin transformed plants than in control plants. These data indicate that the iron fortification of leaves, based on ferritin overexpression, could be limited in its biotechnological application because of its high soil dependence.     

Goethite Dissolution in the Presence of Phytosiderophores: Rates, Mechanisms, and the Synergistic Effect of Oxalate

The purpose of this study was the elucidation of the chemical mechanism of an important process in iron acquisition by graminaceous plants: the dissolution of iron oxides in the presence of phytosiderophores. We were particularly interested in the effects of diurnal root exudation of phytosiderophores and of the presence of other organic ligands in the rhizosphere of graminaceous plants on the dissolution mechanism. Phytosiderophores of the type 2′-deoxymugineic acid (DMA) were purified from the root exudates of wheat plants (Triticum aestivum L. cv. Tamaro). DMA-promoted dissolution of goethite under steady-state and non-steady-state conditions and its dependence on pH, adsorbed DMA concentration, and the presence of the organic ligand oxalate were studied. We show that dissolution of goethite by phytosiderophores follows a surface controlled ligand promoted dissolution mechanism. We also found that oxalate, an organic ligand commonly found in rhizosphere soils, has a synergistic effect on the steady-state dissolution of goethite by DMA. Under non-steady-state addition of the phytosiderophore, mimicking the diurnal exudation pattern of phytosiderophore release, a fast dissolution of iron is triggered in the presence of oxalate. To investigate the efficiency of these mechanisms in plant iron acquisition, wheat plants were grown on a substrate amended with goethite as only iron source. The chlorophyll status of these plants was similar to iron-fertilized plants and significantly higher than in plants grown in iron free nutrient solutions. This demonstrates that wheat can efficiently mobilize iron, even from well crystalline goethite that is usually considered unavailable for plant nutrition.     

OsYSL16 plays a role in the allocation of iron

Graminaceous plants acquire iron by secreting mugineic acid family phytosiderophores into the rhizosphere and taking up complexes of iron and phytosiderophores through YSL (yellow stripe 1-like) transporters. Rice OsYSL15 is a transporter of the iron(III)-2'-deoxymugineic acid complex. OsYSL16 has 85?% similarity to both OsYSL15 and the iron(II)-nicotianamine transporter OsYSL2. In the present study, we show that OsYSL16 functionally complemented a yeast mutant defective in iron uptake when grown on medium containing iron(III)-deoxymugineic acid, but not when grown on medium containing iron(II)-nicotianamine. OsYSL16-knockdown seedlings were smaller than wild-type seedlings when only iron(III)chloride was supplied as an iron source. The iron concentration in shoots of OsYSL16-knockdown plants was similar to that of the wild type; however, they showed more severe chlorosis than wild-type plants under iron-deficient conditions. Furthermore, OsYSL16-knockdown plants accumulated more iron in the vascular bundles of the leaves. Expression of the OsYSL16 promoter fused to the β-glucuronidase gene showed that OsYSL16 is expressed in the root epidermis and vascular bundles of whole plants. The expression was typically observed around the xylem. In the vascular bundles of unelongated nodes, it was detected in the xylem of old leaves and the phloem of new leaves. Graminaceous plants translocate iron from the roots to old leaves mainly via the xylem and to new leaves mainly via the phloem. Our results suggest that OsYSL16 plays a role in the allocation of iron(III)-deoxymugineic acid via the vascular bundles.     

Reduction-based iron uptake revisited: On the role of secreted iron-binding compounds

With the exception of the grasses, plants rely on a reduction-based iron (Fe) uptake system that is compromised by high soil pH, leading to severe chlorosis and reduced yield in crop plants. We recently reported that iron deficiency triggers the production of secondary metabolites that are beneficial for Fe uptake in particular at high external pH when iron is present but not readily available. The exact function of these metabolites, however, remains enigmatic. Here, we speculate on the mechanism by which secondary metabolites secreted by roots from Fe-deficient plants improve Fe acquisition. We suggest that the production and excretion of Iron Binding Compounds (IBCs) constitute an integrative, pH-insensitive component of the reduction-based iron uptake strategy in plants.     

Nitric oxide improves internal iron availability in plants

Iron deficiency impairs chlorophyll biosynthesis and chloroplast development. In leaves, most of the iron must cross several biological membranes to reach the chloroplast. The components involved in the complex internal iron transport are largely unknown. Nitric oxide (NO), a bioactive free radical, can react with transition metals to form metal-nitrosyl complexes. Sodium nitroprusside, an NO donor, completely prevented leaf interveinal chlorosis in maize (Zea mays) plants growing with an iron concentration as low as 10 microM Fe-EDTA in the nutrient solution. S-Nitroso-N-acetylpenicillamine, another NO donor, as well as gaseous NO supply in a translucent chamber were also able to revert the iron deficiency symptoms. A specific NO scavenger, 2-(4-carboxy-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, blocked the effect of the NO donors. The effect of NO treatment on the photosynthetic apparatus of iron-deficient plants was also studied. Electron micrographs of mesophyll cells from iron-deficient maize plants revealed plastids with few photosynthetic lamellae and rudimentary grana. In contrast, in NO-treated maize plants, mesophyll chloroplast appeared completely developed. NO treatment did not increase iron content in plant organs, when expressed in a fresh matter basis, suggesting that root iron uptake was not enhanced. NO scavengers 2-(4-carboxy-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and methylene blue promoted interveinal chlorosis in iron-replete maize plants (growing in 250 microM Fe-EDTA). Even though results support a role for endogenous NO in iron nutrition, experiments did not establish an essential role. NO was also able to revert the chlorotic phenotype of the iron-inefficient maize mutants yellow stripe1 and yellow stripe3, both impaired in the iron uptake mechanisms. All together, these results support a biological action of NO on the availability and/or delivery of metabolically active iron within the plant.     

Effect of salt on physiological responses of barley to iron deficiency.

Iron chlorosis is very common on alkaline soils such as calcareous ones, since iron availability is limited by high pH. Under these conditions of iron deficiency, graminaceous plant species induce special mechanisms for iron acquisition, involving enhanced release of iron chelators called phytosiderophores. On the other hand, it is known that most of salt soils have alkaline pH. So, plants growing on this kind of soils are often subjected simultaneously to salinity and iron deficiency. This work aimed at (i) studying the physiological responses of barley (Hordeum vulgare L.) to iron deficiency, and (ii) evaluating the effect of salt on the iron nutrition and the phytosiderophore release. For this purpose, seedlings of Hordeum vulgare L. were cultivated under controlled conditions, either in a complete nutrient solution with or without NaCl, or in an iron free nutrient solution containing or not NaCl. The plant morphological aspect, chlorophyll content of young leaves, iron status, biomass production, and phytosiderophore release by roots were assessed. Plants subjected to Fe deficiency exhibited a severe chlorosis, accompanied by a significant biomass reduction. These plants developed more lateral roots than the control with a highly stimulated phytosiderophore release. However, the latter was greatly diminished when iron deficiency was associated to salinity. A depressive effect of salt on iron acquisition in plants subjected only to salt stress which was also observed and further confirmed by the important decrease of efficiency in iron acquisition. These results suggest that salinity may reduce capacity of plants to acquire iron from alkaline soils by inhibiting phytosiderophore release.     

The effect of calcium bicarbonate on iron absorption and distribution byChrysanthemum morifolium, (Ram.)

Summary Plants grown for two weeks in high-bicarbonate nutrient solution with iron became chlorotic, absorbed less iron, and translocated a lower percentage of absorbed iron than did green plants grown under low bicarbonate with iron. Chlorotic plants, pretreated in low-bicarbonate solutions lacking iron, absorbed more iron and translocated a higher percentage to leaves than the green plants. Plants induced to chlorosis by high bicarbonate absorbed less iron after transfer to low-bicarbonate solution containing iron than did chlorotic plants pretreated with low-carbonate solution lacking iron. Initial localization of iron occurred in the roots. A considerable amount of the iron initially found on the roots was translocated to developing shoots over a nine-week period unless the plants were grown in high bicarbonate solutions. More iron was translocated from roots of plants in minus-iron solutions following initial absorption than when iron was supplied in the nutrient solutions. Journal Series Paper736. University of Georgia, College of Agriculture Experiment Stations, College Station, Athens, Ga. 30601.     

Iron sulfide formation on root surfaces controlled by the life cycle of wild rice (<Emphasis Type="Italic">Zizania palustris</Emphasis>)

Iron sulfide plaques have been observed on roots of wild rice (Zizania palustris) and other wetland plants grown in sulfur-impacted freshwater ecosystems, but the mechanism of their formation and ramifications for plants have not been investigated. We exposed a model annual wetland plant, Zizania palustris, to elevated sulfate concentrations (3.1 mM) and quantified the development of iron oxide and iron sulfide precipitates on root surfaces throughout the plant life cycle. During the onset of seed production, root surfaces amended with sulfate transitioned within 1 week from iron (hydr)oxide plaques to iron sulfide plaques. During the same week, Fe(III) decreased on roots of plants not amended with sulfate but FeS did not accumulate. Prior to FeS accumulation, sulfate-amended plants had taken up the same amount of N as unamended plants. After FeS accumulation, total plant nitrogen did not increase further on sulfate-amended plants, indicating a cessation in nitrogen uptake, whereas total plant N continued to increase in unamended plants. Sulfate-amended plants produced fewer and lighter seeds with less nitrogen than unamended plants. FeS precipitation on roots may be associated with elevated sulfide and inhibited nitrogen uptake before the end of the plant’s life cycle, thus affecting the populations of this annual aquatic plant. We propose a mechanism by which a physiologically-induced decline in radial oxygen loss near the end of a plant’s life cycle initiates a precipitous decline in redox potential at the root surface and in adjacent porewater, initiating accumulation of iron sulfide plaques. These plaques could be an important locus for iron sulfide accumulation in wetland sediments.