Kinetics of Ion Uptake in Higher Plants

Single, multiphasic mechanisms located in the plasmalemma and the tonoplast are proposed to mediate ion uptake in cells of higher plants. There are no parallel uptake mechanisms and, normally, little or no free diffusion across the plasmalemma. The plasmalemma controls the rate of uptake at low external salt concentrations, while the tonoplast may become rate-limiting at high concentrations.     

Structural Basis for Silicic Acid Uptake by Higher Plants

Many of the world's most important food crops such as rice, barley and maize accumulate silicon (Si) to high levels, resulting in better plant growth and crop yields. The first step in Si accumulation is the uptake of silicic acid by the roots, a process mediated by the structurally uncharacterised NIP subfamily of aquaporins, also named metalloid porins. Here, we present the X-ray crystal structure of the archetypal NIP family member from Oryza sativa (OsNIP2;1). The OsNIP2;1 channel is closed in the crystal structure by the cytoplasmic loop D, which is known to regulate channel opening in classical plant aquaporins. The structure further reveals a novel, five-residue extracellular selectivity filter with a large diameter. Unbiased molecular dynamics simulations show a rapid opening of the channel and visualise how silicic acid interacts with the selectivity filter prior to transmembrane diffusion. Our results will enable detailed structure–function studies of metalloid porins, including the basis of their substrate selectivity.     

Fe型超氧物歧化酶在高等维管植物中分布的研究

应用聚丙烯酰胺浓度梯度胶电泳,ＳＯＤ活性染色,特异性抑制制定位鉴定和活区带密度扫描,对１８个科５８种维管植物ＳＯＤ粗酶提取液进行研究。研究结果表明,２５种植物在含有ＣｕＺｎ－ＳＯＤ和Ｍｎ－ＳＯＤ的同时还检测出Ｆｅ－ＳｏＤ,主要分布在茄科、芸香料等６个科中。维管植物的Ｆｅ－ＳＯＤ同工酶区带一般为１～３条,Ｆｅ－ＳＯＤ活性在总ＳＯＤ活性中所占比例大多在１５％以下。实验结果表明改进测定方法会在越来越多的     

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。     

Inhibitory Effect of Pseudobactin on the Uptake of Iron by Higher Plants

Purified pseudobactin inhibits the uptake of ferric iron by the roots of peas and maize plants sufficiently to reduce the synthesis of chlorophyll. This inhibition is interpreted as competitive binding, as described for synthetic chelating compounds.     

Update on Boron in Higher Plants - Uptake, Primary Translocation and Compartmentation

Abstract: This review focuses on the uptake and primary translocation of boron (B), as well as on the subcellular compartmentation of B and its role in cell walls of higher plants. B uptake occurs via passive diffusion across the lipid bilayer, facilitated transport through major intrinsic proteins (MIPs), and energy-dependent transport through a high affinity uptake system. Whereas the first two represent passive uptake systems, which are constitutively present, the latter is induced by low B supply and is able to establish a concentration gradient for B between the root symplasm and the external medium. At high B supply, a substantial retention of B can be observed at xylem loading, and passive processes are most likely responsible for that. At low B supply, another energy-dependent high affinity transport system for B seems to be induced which establishes an additional concentration gradient between root symplasm and the xylem. The possible significance of all these processes at various B supplies is discussed. The role of soluble B complexes in uptake and primary translocation of B has been evaluated, but the few data available do not allow comprehensive conclusions to be drawn. In any case, there are no indications that soluble B complexes play a major role in either uptake or primary translocation of B. The subcellular compartmentation of B still remains a matter of controversy, but it is unequivocally clear that B is present in all subcellular compartments (apoplasm, cell wall, cytosol and vacuole). The relative distribution of B between these is dependent on plant species and experimental conditions and may vary greatly. Recent results on the well-established role of B in cell walls are summarized and their physiological significance discussed.     

Mercury Uptake by Modified Mackinawite

This study investigated the mercury uptake capacity of synthetic mackinawite regarding its surface modification with L-cysteine. Mackinawite (FeS) is an excellent material for mercury uptake from anoxic-contaminated sediments. However, one limitation to its use is the low oxidation stability; it is easily transformed when applied to natural sediments. The modification of mackinawite with L-cysteine improves its oxidation stability, making it a promising material to be used in sediment remediation by in-situ capping. The results showed that L-cysteine does not affect the mercury-uptake capacity of mackinawite (around 490 mg/g for modified and unmodified mackinawite). The Hg (II) uptake decreased as the solution pH changed from acid to alkaline range, especially in solutions with low Hg (II) concentrations. Sorption curves for Hg (II) on modified mackinawite, as a function of initial concentration of Hg (II) and mackinawite, showed the same pattern as that on unmodified mackinawite, indicating no significant difference in the mercury-sorption mechanism. The solids before and after Hg (II) uptake were analyzed by X-ray powder diffraction (XRPD) by noting the composition of both modified and unmodified mackinawite, and the results were in agreement with the sorption experiments.     

Ion Uptake in Higher Plants and KCl Stimulation of Plasmalemma Adenosine Triphosphatase: Comparison of Models

Criteria for the acceptance or rejection of the dual, the cooperative, and the multiphasic model of ion uptake are given and are used to evaluate the models on the basis of previously published analyses. In addition, mathematical representations of the models are fitted to concentration-dependence data for various ions and plant tissues by a general curve fitting program. The calculated parameters are evaluated for biological relevance, and the fit is compared by statistical analysis. The kinetics of ion uptake in higher plants are found to be consistent with the concept of multiphasic uptake mechanisms, while the dual and the cooperative model must be rejected. KCl stimulation of plasmalemma-bound ATPases is also shown to obey multiphasic kinetics, thus strengthening the correlation between ion uptake and membrane-bound ATPases.     

Polyamine Uptake and Translocation in Plants

Recently, evidence has increased for both long- and short-distance transport of polyamines (PAs) in living organisms, but the mechanisms involved and physiological significance of PAs translocation are still not well understood. This review deals with various aspects of polyamine uptake and transport in higher plant tissues.     

植物钙素吸收和运转

近年来,钙素在植物体内的吸收和运输研究主要集中在细胞和分子水平,但整株水平上的研究也同样重要.整株水平上的钙吸收和运输包括根细胞的钙吸收、钙离子横向穿过根系并进入木质部、在木质部运输、从木质部移出并进入叶片或果实及在叶片或果实中运转分配等环节,既经过质外体也穿越共质体.钙离子通道、Ca2 -ATP酶和Ca2 /H 反向转运器等参与根细胞的钙吸收.在钙离子横向穿根进入木质部的过程中,需要穿越内皮层和木质部薄壁细胞组织.根系内皮层凯氏带阻挡了Ca2 沿质外体途径由内皮层外侧向内侧的移动,部分Ca2 由此通过离子通道流进内皮层细胞而转入共质体并到达木质部薄壁细胞组织,而由木质部薄壁细胞组织进入中柱质外体可能需要Ca2 -ATP酶驱动;还有一些Ca2 由内皮层细胞运出,沿内皮层内侧的质外体途径进入木质部导管,并通过导管运向枝干.钙离子以螯合态的形式在枝干导管运输;水流速率是影响钙离子沿导管运输的关键因子.钙离子在果实和叶片中的运输和分配不仅通过质外体途径也通过共质体途径.     

The Distribution of Substances similar to Gibberellic Acid in Higher Plants

Gibberellic-acid-like substances have been found in extractsfrom all parts of seedlings of tall and dwarf peas and in matureseeds of wheat, French bean and tall and dwarf peas. They werepresent in amounts equivalent to o‘1–0’3 µg-gibberellicacid in 100 plants (F.W. 100–200 g.). Immature runnerbean seed yielded larger quantities, equivalent to 0.25 µg.gibberellic acid per gram fresh weight, distributed betweentestas, cotyledons, and embryos.     

Function of Node Unit in Photosynthate Distribution to Root in Higher Plants

Leaf-root interaction is a critical factor for plant growth during maturation and activity of roots is maintained by a sufficient supply of photosynthates. To explain photosynthate distribution among organs in field crops, the node unit hypothesis is proposed. One node unit consists of a leaf and an upper adventitous root, as well as the axillary organs and the lower adventitious root, which is adjacent to one node. Using ¹⁴C as tracer, the carbon distribution system has been clarified using spring wheat, soybean, tomato, and potato. The interrelationship among organs from the strongest to the weakest is in the following order: (1) within the node unit > (2) between the node unit in the same or adjacent phyllotaxy > (3) in the main root or apical organs, which are adjacent to the node unit. Within the node unit, ¹⁴C assimilated in the leaf on the main stem tended to distribute to axillary organs in the same node unit. The ¹⁴C assimilated in the leaf of axillary organs tended to distribute within the axillary organs, including adventitious roots in the axillary organ and then translocated to the leaf on the main leaf of the same node unit. In different organs of the node unit in the same or adjacent phyllotaxy, ¹⁴C assimilated in the leaf on the main stem was also distributed to the organs (node unit) belonging to the same phyllotaxy in dicotyledons, while in monocotyledons, the effect of phyllotaxy on ¹⁴C distribution was not clear. Among roots/apical organs and node unit, ¹⁴C assimilated in the upper node unit was distributed to apical organs and ¹⁴C assimilated in the lower node unit was distributed to roots. Thus the node unit hypothesis of photosynthate distribution among organs is very important for understanding the high productivity of field crops.     

Release of Volatile Mercury from Vascular Plants

Volatile, organic solvent soluble mercury has been found in leaves and seeds of several angiosperms. Leaves of garlic vine (Pseudocallyma alliacium), avocado (Persea americana) and haole-koa (Leucaena glauca) release mercury in volatile form rapidly at room temperature. In garlic vine, the most active release is temperature dependent, but does not parallel the vaporpressure temperature relationship for mercury. Mercury can be trapped in nitric-perchloric acid digestion fluid, or n-hexane, but is lost from the hexane unless the acid mixture is present. Seeds of haole-koa also contain extractable mercury but volatility declines in the series n-hexane (90%) > methanol (50%) > water (10%). This suggests that reduced volatility may accompany solvolysis in the more polar media. Gas chromatographic analysis shows that the volatile compound is not dimethyl mercury.     

Oscillatory Transpiration and Water Uptake of Avena Plants

Xylem vessels in the lower part of the leaf of young Avena plants have been exposed to deformation by application of an external pressure. In this way a resistance to the water flow at the deformation site has been achieved, inducing undamped oscillations in transpiration and water uptake, even after removal of the root system.     

Oscillatory Transpiration and Water Uptake of Avena Plants

The transpiration rate of oat plants, 6 days old, has been investigated. Dependent on the irradiance level of the white light used in the experiments, the transpiration rate oscillated with different period times. In darkness or at low irradiances the period was about 100–110 min. At higher irradiances the period was about 40 min. At intermediate irradiances autocorrelation analysis was used to find the period content of the transpiration rate. It was concluded that two oscillatory systems were present in the plants, characterized by their different periods. When plants cultivated in a light/dark cycle were used, the transpiration oscillations were influenced by a circadian rhythm. Oscillations in darkness were then most pronounced in the mornings. Plants cultivated in continuous light did not show such a circadian rhythm, but the oscillations died out after about 20 h. Kinetin induced transpiration oscillations in darkness and made them sustain for a longer time.     

砷在植物体内的吸收和代谢机制研究进展

砷污染在全世界尤其是东南亚地区已成为一个严峻的环境问题,严重威胁着农业生产、生态环境及人体健康。植物是砷流入人体最主要的途径之一。揭示植物对砷吸收、转运和储存及阐明植物调控砷超积累和迁移的分子机制,对开发植物修复技术并有效控制砷向食物链迁移意义重大。该文综述了目前植物砷吸收与代谢机制的研究进展,并对植物体内参与砷运输过程的转运蛋白进行了重点阐述。     

Oscillatory Transpiration and Water Uptake of Avena Plants

The oscillatory transpiration of 6 days old Avena plants was investigated with respect to the water potential of the root medium. The desired water potential was obtained by means of mannitol solutions. When the water potential was lowered (“mannitol step”), the amplitude of the oscillations decreased. Below –3.0 bars no oscillations persisted. A detailed study was made of the phase changes of the oscillations caused by a short time decrease of the water potential of the root medium (“mannitol pulse”). The duration of these short term treatments was either 9.0, 3.0 or J.5 min. The experimental results are discussed on the basis of an electric analogue previously presented in the literature. Published simulations based on the model were in clear contrast to the present experimental results as well as to earlier results in the literature. However, simulations in the present paper showed that the model could explain the experimental results if suitable parameter values were chosen.