1、第四章 植物大量元素（钾）,Section 1 General,In general, K20 content in plants is about 0.35% of dry weight.,Potassium is characterized by high mobility in plants at all levels (cells, tissues, long-distance transport) , which is easily transported from roots to shoots.,There is a stable K concentration in cytop
2、lasm, which is about 100200 mM, the other K stores at the vacuole.,Unlike N and P, K exists in plant as an ion(K+), and does not form stable complexes.,Nutrition function of K+ involves :neutralizing the soluble and insoluble anion;Stabling pH between 7 and 8;Regulating osmotic pressure;Enzyme activ
3、ation;Adaptation to stress-,Enzyme activation,There are more than 60 enzymes which either completely depend on or are stimulated by K+.,ATPase, pyruvate kinase （果糖激酶）6-phosphofructokinase （6-磷酸果糖激酶）,Protein Synthesis,It is now well established that K+ is required for protein synthesis in higher plan
4、ts,K+ is involved in several steps of the translation process, including the binding of tRNA to ribosome.,So the accumulation of soluble nitrogen compounds (aa, amide, and nitrate) when K+ is deficient.,Photosynthesis,In higher plants K+ affects photosynthesis at various levels:, Enhancing chlorophy
5、ll synthesis; Improving chloroplast structure; Increasing CO2 fixation; Improving carbohydrate transport.,Osmoregulation,K+ is the dominant osmotic substances.,Cell extension is the consequence of the accumulation in the cells of K+.,Stomatal Movement,In most species K+ has the major responsibility
6、for turgor changes in the guard cells during stomata movement.,An increase in the K+ concentration in the guard cells results in the uptake of water from the adjacent cells and a corresponding increase in turgor in the guard cells and thus the stomata opening.,Improving organic acid metabolism,Impro
7、ving the tolerance of plants to stress,Drought; High temperature; Cold; Disease; Salt; Lodging - -,Suitable K can Improve crop quality:Increasing protein and ammonia acid composition Increasing sugars and starch content ;Enhancing vitamins in vegetables;Delaying storage period;Improving commercial q
8、uality;-,Quality element!,缺素症状 植株生长缓慢,矮化; 下部老叶叶缘先发黄，然后变褐、焦枯； 有些作物叶片呈青铜色，向下卷曲，叶表叶肉突起，叶脉下陷； 根系生长不良，色泽黄褐； 种子、果实小，产量低，品质差； 早衰。,水稻：叶片披散，下部老叶沿叶尖、叶缘焦枯并逐渐扩散呈“V”型，老叶片上有棕褐色斑点。,yellowing, followed by tissue death, progressing inward along the margins of older leaves.,烟草：叶片小、叶尖端黄化，叶缘间失绿发黄，有褐色坏死斑点。,缺钾油菜,从叶缘开始黄化，
9、沿叶脉间失绿，有褐色斑点或局部有白色干枯组织,soybean are chlorosis of the leaf edges of older, lower leaves,芹菜缺钾,严重缺钾时，叶缘发焦，似灼伤状,番茄缺钾,左为正常果实， 右为缺钾果实，有绿背,缺钾果实着色不均匀，有时有棱角，果实发育不良，汁液少，内空，多为等外果,上为缺钾叶片， 下为缺镁叶片， 缺钾的叶缘症状更为明显,萝卜缺钾叶片,自右至左缺钾加重，叶缘呈灼伤状,Potassium mineral bed is the major source for manufacture of potassium fertilizer.
10、 Potassium chloride is the major sort of potassium fertilizer.,我国钾肥目前的市场需求在600万吨以上，而且这一数字还将以每年5%左右的速度递增。但目前我国的钾肥产量仅有5060万吨。,中国最大的钾镁盐湖察尔汗盐湖(面积达5000多平方公里的大盐湖，是世界上海拔最高的内陆盐湖), 氯化钾储量为.45亿吨。,1996年生产能力达万吨。,青海万吨钾肥项目建设工程完成？,据农民日报2001.9.21报道：罗布泊钾盐储量1.74亿吨，被国家计委确定为国内两大钾肥生产的化工基地。,这一产量将占中国年度进口钾肥总量的三分之一。目前中国农田里施用
11、的钾肥90%是进口的。,中国最大钾肥生产基地的第一步，一期建成20万吨硫酸钾厂，最终计划是年产220万吨钾肥。,K is the seventh most abundant element in the earths crust ranging from 0.5 to 2.5%. But the available K is only 1-2% of total K.,Potassium in soil,Forms: Total K consists of four distinct forms in the soil, each of different availability to th
12、e plant: () Mineral K-almost completely unavailable, 9098%; () Fixed K-slowly available, 1-10%; () Exchangeable K-readily available, 1-2%; () Soil solution K-readily available, 0.1-0.2%.,There is an equilibrium between the various forms,Organic K is only a small part.,Release and fixation of K+ and
13、NH4+ ions by soil clay,Section 2 Molecular and physiological aspects of potassium uptake in plants,K is the most abundant cellular cation, with cytoplasmic concentrations regulated between 80 and 200 mM, and total tissue concentrations of approximately 20 mM.,The transport of K+, which is mobile in
14、plant, has been studied intensively for the last 50 years.,K+转运进入植物和在植物中运输的模式图,2. 1 Early Physiological and biochemical studies indicated the existence of multiple K+ transporters,Excited roots (Hoaglant and Broyer， 1936）,Epstein was first to treat radioisotopes to quantify ion efflux.,Epstein was f
15、irst to treat mineral ion transporters as enzyme kinetics to studies of concentration-dependent root K+ uptake.,Dual isotherm of K absorption,High-affinity K+ transport was thought to dominate at low concentration of K+ in soil, whereas as higher K+ concentrations, a low-affinity K+ transporter oper
16、ated that was less specific for K+ over other alkali cations.,硫基修饰的N 乙基马来亚铵（NEM）:抑制髙亲和力转运蛋白但不影响低亲和力转运蛋白。,Physiological studies provided further evidence for separate high and low-affinity K+ transporters,The application of a K+ -channel blocker TEA (四乙铵) inhibited the linear, low-affinity transport
17、component.,High-affinity K+ uptake system exhibited several properties:Increasing gene expression or transport activity induced by K+ starvation;A very high affinity for K+ (Km=5 to 30 M ) ;A strong selectivity for K+ and Rb+ over other alkali cations.,Low-affinity K+ uptake system:Less selective fo
18、r K+ and Rb+;Less influenced by changes in the K+ status of the plant.,2.2 Mechanistic basis for High- and low-affinity K+ uptake system,利用电生理技术， 将玉米低盐根置于低钾（220M）溶液中将引起膜电位的强烈的去极化。而在更髙的浓度（0.5mM）时，去极化减弱。,植物中存在两种类型的K+通道：内流型通道（inward rectify K进）和外流型通道（outward rectify K出）内流型通道（K进）在Em（50150 mV）超极化时打开促使吸收K
19、+。而外流型通道（K出）在Em去极化时打开并将K+运出细胞。,研究表明低亲和性钾吸收的1个主要成分是内向整流通道（K进）。,植物中内流型通道（K进）不易失活，可以长时间保持开放。,内流型通道和外流型通道均具有较高的K+/Na+选择性，受TEA和Ba2+的抑制。,拟南芥akt1突变体的AKT1内向整流通道缺陷，低钾时生长慢。,K+ /H+ cotransport system,毎2个H+由ATP酶运出细胞后，其中的1个又经由K+ /H+同向共运转蛋白返回细胞中。,High-affinity K+ uptake is an active process involved ion pump.,总之，
20、 植物中存在几种截然不同的K+转运蛋白，它们在转运途径的不同位点起着作用。在根部， 可能存在一种或几种髙亲和力K+转运蛋白，它们由H+ATP酶提供能量，以 K+ /H+同向共运转的形式发挥功能。同样，也可能存在一种或几种K+通道，介导着低亲和力的K+吸收。,2.3 Many plant genes encode K+ transporters,KAT1 and AKT1 were the first K+ transporter gene to be cloned by complementation of the yeast K+ transport-detective mutant trk
21、1trk2 with an Arabidopsis cDNA library.,半乳糖,KAT1 and AKT1 shows the characteristics of inward current ( K+ influx) , selectivity , time-dependent kinetics, and response to the TEA.,Current-voltage relationship for uninjected and injected Xenopus oocytes with KAT1 mRNA 4 d.,KAT1 和马铃薯中的同源基因KST1位于叶片保卫细
22、胞中，推测它们编码的是参与气孔作用的K进通道。,AKT1 位于根表皮和（芽孢）皮层中。 AKT2 在叶子中表达。,KAT1在拟南芥幼苗的保卫细胞、成熟的根、侧根和排水器中表达。,Shaker 钾通道的结构， 侧面图（左）和俯视图（右）,2.5 The structure of transporters and its function,AKT1,A highly conserved tripeptide (Gly-Tyr-Gly ) was found in P-domains of all highly selective K+ channels.,A highly conserved Th
23、r-X-Gly-Tyr-Gly-Asp motif was found in P-domains of the K+out channel gene: KCO1 . The first K+out channel gene cloned from Arabidopsis by searching an EST database.,KCO1-activated K+ currents were influenced strongly by the concentration of cytosolic Ca2+ (150 nM),EF hand : Ca2+- binding motifs,Ind
24、icating a link between Ca2+-mediated signaling processes and K+ transport by the channel.- binding motifs,KCO1 is expressed in low amounts in Arabdopsis and is not localized to any particular tissue, being found in whole seedlings, leaves, and flowers.,通过酶消化，特异性地将原生质体从木质部导管周围的木薄壁组织种释放出来，利用膜片钳技术研究确定3
25、种类型的离子通道：K进通道和另外两种通道一种对K有选择性，另一种无选择性。,2.6 The cloning of high-affinity K+ transporters,The first high-affinity K+ transporter, HKT1, was cloned by complementation of yeast trk1trk2 K+ transport mutant with a cDNA library,a mass of 59 kDa and contain 12 membrane-spanning domains,Expression of HKT1 in
26、 Xenopus oocytes gave rise to large inward currents in the present of K+.,Expression of HKT1 in yeast shows Km=29 M,Expression of HKT1 in plant is localized to root cortex, stele and leaves, but not in root epidermis.,The expression of HKT1 was proposed to be a K+- Na+ cotransporter that mediates hi
27、gh-affinity K+ uptake.,AtKUP1 and AtKUP2 are the members of another family of genes encoding high-affinity K+ transporters.,Concentration-dependent kinetics of Rb+ uptake in transgenic Arabidopsis suspension cells with 35S-AtKUP1 (red) and an empty vector (blue ). Mediating a high-affinity system; F
28、acilitating a low-affinity system,Topological Model of AtKUP1,克隆到的编码K+转运蛋白的植物基因小结,Low K+ : 40 M, High K+: 20 mM,Root,Cell 125, 13471360, 2006,All evidence supports the conclusion that there exists an AKT1-mediated and CBL/CIPK (a Ser/Thr protein kinase)-regulated K+ uptake pathway in higher plants t
29、hat plays crucial roles in plant K+ uptake, particularly under K+-deficient conditions.,(A) Phenotype comparison between WT and lks1, F1,(B) Positional cloning of LKS1, identified as encoding CIPK23,Overexpression of LKS1 Enhances Arabidopsis Tolerance to Low-K+ Stress by Increasing K+ Uptake,CIPK23
30、 Interacts with AKT1,Interaction of CIPK23 with CBL1 and CBL9 CBL1 and CBL9 Are Involved in Upstream Regulation of CIPK23,Schematic Model for the CBL1/9- and CIPK23- Mediated Regulatory Pathway of AKT1,the protein kinase CIPK23 encoded by LKS1 CIPK23 directly phosphorylates the K+ transporter AKT1 CIPK23 is activated by the binding of two calcineurin B-like proteins, CBL1 and CBL9.,
