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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 cytoplasm,wh
2、ich 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 activation;Adaptat
3、ion 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 plants,K+is involved
4、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 chlorophyll synthesis;Improving chl
5、oroplast 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 for turgor changes in the guard
6、 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,Improving the tolerance of plants to
7、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 quality;-,Quality element!,缺素症状植株生长缓慢,矮化;下
8、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，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 t
9、he 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.Potassium chloride is the major sort of potassium fer
10、tilizer.,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
11、 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 the plant:()Mineral K-almost completely unavailable,9098%;()Fixed K-sl
12、owly 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 NH4+ions by soil clay,Section 2Molecular and physiological aspects of potassium u
13、ptake 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 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 Earl
14、y 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 first to treat mineral ion transporters as enzyme kinetics to studies of concentration-depen
15、dent 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 operated 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
16、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 component.,High-affinity K+uptake system exhibited several properties:Increasing gene expression or tran
17、sport 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 for K+and Rb+;Less influenced by changes in the K+status of the plant.,2.2 Mechanistic basis for High-and low-affi
18、nity 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+。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，
19、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各H+由ATP酶运出细胞后，其中的1各又经由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，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
20、+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 trk1trk2 with an Arabidopsis cDNA library.,半乳糖,KAT1 and AKT1 shows the characteristics of inward current(K+influx),selectivity for
21、,time-dependent kinetics,lack of inactivation,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
22、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 Thr-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
23、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,Indicating a link between Ca2+-mediated signaling processes and K+transport by the channel.-binding motifs,KCO1 is expressed in
24、 low amounts in Arabdopsis and is not localized to any particulartissue,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,w
25、as 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 Xenopus oocytes gave rise to large inward currents in the present of K+.,Expression of HKT1 in yeast shows Km=29M,Expression of HKT1 i
26、n 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 high-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;Facilitating a low-affinity system,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,
