植物生理学英文课件：chapter09 senescence

1、Chapter 9 Plant Senescence and Organ Abscission,Section 1 Plant Senescence and its program 1.1 Concept and types of plant senescence 1.1.1 Senescence:A program in which the function of organ or whole plant naturally declines to death. This is an essential phase of the growth and development in plant

2、。 For nutrition transfer, such as seed，tuber and bulb。Leaf abscission in fallsprout，leaf and flower grow in next spring。Fruits mature and fallseeds spread。,1.1.2 types of plant senescence,(1) Overall Senescence Senescence occurs in whole plant body, such as annuals which senesces to death after flow

3、er and setting.,(2)Top Senescence The part aboveground dies with the end of growth season,but the part underground is alive for several years. Perennial weeds , corm(球茎) and bulb（鳞茎）lily 。,In summer,In winter,(3) Deciduous senescence The leaf falls in specious season, in summer or winter. Deciduous

4、trees,(4)Progressive senescence Senescence only occurs in older organ or tissue.New organ or tissue develops while old ones are senescing. Green trees。,衰老有其积极的生物学意义，不仅能使植物适应不良环境条件，而且对物种进化起重要作用。温带落叶树的叶片，在冬前全树叶片脱落，从而降低蒸腾作用，有利于安 全越冬。通常植物在衰老时，其营养器官中的物质降解、撤退并再分配到种子、块茎和球茎等新生器官中去。如花的衰老及其衰老部分的养分撤离，能使受精胚珠正 常

5、发育；果实成熟衰老使得种子充实，有利于繁衍后代。,1.2 Program for plant senescence Senescence can occur at different levels: cell, tissue, organs and whole plant. 1.2.1 Cell senescence Membrane and organelle senescence。 、Senescence in cell membrane。 (1)Lipid phase change。Biomembrane changes its phase from liquid-crys

6、talline state to solid-gel state. Hard and inextensive，fluidity decreases and cohesion increases。,液晶相,凝固相,衰老、低温,六方晶相I,六方晶相II,混合相,衰老,生物膜几种相变示图,liquid-crystalline state,solid-gel state,（2）Degradation and peroxidation of lipid lead to decrease in lipid content Synthesis , lipase , phospholipase、lipoxyg

7、enase and active O2 MDA (malonyldialdehyde ） 。,（3） Phospholipase 。磷脂酶A1、磷脂酶A2、磷脂酶B、磷脂酶C、磷脂酶D等。其中，磷脂酶D主要存在于高等植物组织中。,CH2OCR1 C H CH2OPO-X,R2CO,O,O,O,OH,A1,A2,B,C,D,The dehydration bound for different phospholipases,Phospholipid phospholipase A or B Poly double-bound fat acid Lox (lipoxygenase ) Organi

8、c free radicals,顺，顺甲叉间二烯,O2,OOH,夺取氢，形成过氧自由基,自由基：反，顺共轭二烯,重排,OOH,OOH,过氧化作用,反，顺共轭二烯过氧化物,（4）Biomembrane degradation and leakage. Loss equilibrium of ions and disorder of metabolism 。 、Organelle senescence。 Ribosome and rough ER chloroplasts breakdown mitochondria cristae swollen vacuole broken .

9、Autophagy occurs and cell senesces and degrades.,1.2.2 Programmed cell death (PCD，程序性细胞死亡) The organism controls the initiation and execution of the cell death process, these types of cell death are referred to as programmed cell death (PCD) PCD可发生在植物的各种细胞。 过程： DNA断裂、染色质固缩、胞泡形成、凋亡小体形成。 动物细胞PCD后产物被其他

10、细胞吞噬利用，植物细胞PCD后产物用于本身细胞次生壁的构成。,One of the important functions of PCD in plants is protection against pathogens.When a pathogen infects a plant,cells at the site of the infection quickly accumulate high concentrations of toxic phenolic compounds and die.The dead cells form a small circular island cal

11、led a necrotic lesion,which isolates and prevents the infection from spreading to surrounding healthy tissues.This rapid and locaized death due to pathogen attack is called the hypersensitive response, which is a genetically programmed process.,PCD发生过程,启动阶段（initiation stage) 启动细胞死亡信号的产生和传递 效应阶段(effe

12、ctor stage) caspase的活化和线粒体通透性的改变。 Caspase属于半胱氨酸蛋白酶家族，直接导致PCD细胞原生质解体 酶解清除阶段(degradation stage),Fig 20.4 Cell death occurs in almost all plant cells and tissues. PCD is involved in numerous processes, inclu-ding the following illustrat-ed in this figure gamete formation, including megaspore formation

13、(1); embryo development(2); degeneration of tissues in the seed and fruit (3); tissue and organ development (4 ) through (6); senescence(7); and responses to environ-mental signals and path-ogens(8 and 9).,Fig 20.9 Senescence in Arabidopsis thaliana.,(A) Development of Arabidopsis thaliana plants is

14、 shown at various times after germination. Photographs show plants at 14, 21, 37, and 53 days after germination ( left to right). Note the yellowing of shoots of the 53-day-old plant. (B) Age-related changes in rosette leaves of Arabidopsis 7, 9, and 11 days after leaf expansion had ceased. Note the

15、 progressive yellowing of leaves, beginning farthest from the main veins,Fig 20.2 (A)Saccharromyces cereoisiae undergoes autophagy(自体吞噬) when starved of nutrients. The yeast shown in this figure was nitrogen-starved, bringing about autophagy, in which autophagic bodies(AB) engulf the cytoplasm and t

16、ransport it to the vacuole (V), where proteases and other lytic enzymes release nitrogen to compensate for the lack of nitrogen in the medium.(B)Autophagy occurs in dying plant cells as in the senescing Impomea tricolor corolla cell diagrammed here. Autophagic bodies engulf a portion of cytoplasm, i

17、ncluding the nucleus(N), to the vacuole(s), where breakdown of the cells contents occurs. The three cells shown represent different stages of PCD, A being the earliest, and B and C later stages of autophagy.,A,B,Fig 20.5 The inflorescences of maize contain flowers that are initially bisexual, but PC

18、D results in the death of male or female tissues to give rise to female inflore-scence (ear) or male inflorescence (tassel), respectively. In the tasselseed2 mutant (A),female tissues in the tassel do not undergo PCD, and the resulting tassel flowers are mostly pistilate. A wild-type tassel in inclu

19、ded for comparison (B).,Fig 20.6 One visible example of PCD in plants is seen in the ornamental plant Mon-stera deliciosa. The leaves of this plant exhibit deep indentations and hole in the lamina, which result from the pro-grammed death of specific regions of tissue in the developing promor-dia. As

20、 the leaf expands, these areas are not replaced, and the resulting leaf lamina has the characteristic pattern that inspires the common name, Swiss cheese plant,Fig 20.8 Aerechyma formation in maize roots in response to hypoxia. Roots were grown under areobic (A) and hypoxic (B) conditions. Under low

21、-oxygen conditions, cortical cells between the endodermis and hypodermis undergo lysogenic to form air spaces that are continuous throughout the root, thereby allowing submerged roots access to atmospheric gases obtained by above-ground tissues.,1.2.3 Organ Senescence Leaf senescence。 （1）Pho

22、tosynthesis declines-slower phase and faster phase。 Decrease in activity and content of photosynthetic key enzyme (Rubisco) Decrease in activity of photoelectron transport and photophosphorylation. Decrease in stomatal conductance. Decrease in chlorophyll. Leaf yellow. Organelle degradation:叶绿体内基粒（脂

23、类小体）内质网核糖体线粒体液泡膜。,相对值大小,呼吸速率,可溶性氮化物,蛋白质,叶绿素含量,光化学活性,光合速率,Rubisco活力,天,叶片衰老期间的生理变化示意图,脂质小体,Fig 20.13 Impact of senescence on plastid ultrastructure in leaves of wild-type and a stay-green mutant of the C3 grass X. Festulolium. (A) Prior to senescence, the chloroplasts of a wild-type and mutant plants

24、contain numerous grana, stacks of appressed thylakoid membranes. (B) These internal membrane structures are lost during senescence of a wild-type mesophyll cell, and electron-dense lipid droplets known as plastoglobuli accumulate. (C) Retention of intrinsic thylakoid membrane proteins, pigments, and

25、 other hydrophobic components gives the gerontoplasts(老年质体) of mutant tissues a distinctive appearance, with persistent grana stacks and few plastoglobuli.,Fig 20.15 Chlorophyll a and its breakdown products. Subcellular compart-mentation of the pheo-phorbide a pathway of chlorophyll catabolism in le

26、af mesophyll cells.,Fig 20.19 (A) Activity of key chlorophyll-catabolizing enzyme PaO is strongly induced in senescing tissues of wild-type X. Festulolium but undetectable in presenescent leaves and in a stay-green mutant.(B) Induction of chlorophyll degradation in wild-type tissue is accompanied by

27、 loss of the pigment-binding membrane protein LHCP, as shown by Western blotting analysis. In the mutant a second form of LHCPII progressively accumulates as senescence proceeds. As illustrated in the cartoon, degradation of LHCPII which protrudes from the thylakoid membrane into the stroma. (C) Sta

28、bility of Rubisco, the major stromal protein, is enhanced very slightly in the mutant compared to wild type.,Changes in mRNAs of rbcS (A) and rca (B) in flag leaf after heading, Seed aging。 The viability of seed loss inversely from mature to death。 Degradation and leakage of biomembrane: Mito

29、chondria and ER become swollen, plasmic membrane contacts and depart from cell wall. DNA injury，broken。 Enzyme activity decreases: dehydrase。 Storage matter exhausting, free fat acid rising.,1.2.4 Senescence in whole plant： One setting plants Poly setting plants-gradually senescing,Section2 Senescen

30、ce Mechanism and regulation 2.1 Senescence caused by nutrition exhaustion Nutrition exhaustion theory： Senescence caused by reproductive organ . Such as tomato, if setting, survives for one season, if flower removed off, survives for several year. Root tissue culture, more than 30 years. 龙舌兰 does no

31、t flower, live for several decades, and flowering alive8-10 years。 Opposite views: Sunflower senesces prior to flower initiation. Removing flower accelerates senescence in maize and popper 自由基损伤学说： 自由基有细胞杀手之称。1955年哈曼（Harman）就提出，衰老过程是细胞和组织中不断进行着的自由基损伤反应的总和。,2.2 Physiology and biochemistry during sene

32、scence 2.2.1 Senescence-associated genes（SAGs） expression。 Senescence is controlled by special genes. Two kinds of genes can be found during senescence. (1) Senescence-downward genes，most of genes code enzymes relevant to photosynthesis, energy metabolism and other synthesis。 (2) Senescence-upward g

33、enes，most of genes code enzymes for hydrolase, such as DNase, RNase, Protease, phospholipase。,Senescence-associated genes（SAGs） refers to their mRNA levels increase with senescence proceeding. They function in metabolism of biomacromolecule degradation and mobilization. More than 40 genes have been

34、cloned: Proteases in Maize, A.thaliana,rape. SAG2, See1, LSC7，SAG12，LSC790，LSC760； RNS1，RNS2，RNS3 in A.thaliana ； PEPC，MDH，MS，ICL，GAPDH,F-1,6-P, aldolase and galactosidase in rape, corn and cucumber.,Stages in Brassica napus leaf senescence. SAGs are divided into 10 classes according to their tempor

35、al pattern of expression.,2.2.2 Degradation of biomacromolecules。 (1).DNA degrades，RNA changes in quality and quantity. RNA break down faster than DNA does during senescence, especially rRNA, which is more sensitive to senescence. RNase activity rises and DNARNA polymerase activity declines。,(2).Pro

36、tein synthesis decreases and its degradation increases。 Soluble protein-Rubisco decreases in 85%, thylakoid membrane protein decrease50%, and cytochromef,b decreases fast。,Two possible mechanisms are illustrated.In one case (left side of fig.),occupation of binding sites by cofactors (e.g.,enzyme su

37、bstrates) or allosteric effectors locks the protein into a conformation resistant to proteolysis,and the equilibrium between this structure and the susceptible conformation is thus determined by the abundance of these ligands.In the other case (right side),the protein is marked for degradation by th

38、e addition of a tag such as ubiquitin and is thereby made available for proteolysis.,Fig 20.20 Comparison of the foliar senescence-as-sociated protease SEE1 from maize with other cysteine endopeptidases. (A)The amino acid sequence inferred from See1 cDNA aligned with the sequences of other proteases

39、 from the same family. Conserved structure fea-tures including a putative vacuole sorting motif (residues 29 through 34; red line), potential glyco-sylation sites (125 throu-gh 127, 256 through 258; blue lines), and the likely cleavage point that removes the prodomain (between 142 and 143; arrowhead

40、). Open circles indicate the cysteine-,histidine-asparagine triad of the active site, and the green lines identitify the surrounding conserved regions. (B) Dendrogram locating SEE1 in the same subfamily as the cereal germination proteases aleurain and oryzain.Note that SAG12 of gree of conservation

41、of cysteine protease structural motifs in SEE1 allows a three-dimensional model to be devised.,Gluconeogenesis in senescingle leaf cells The glyoxylate bypass is activated,(3).biomembrane breakdowns and losses its function.,2.2.3 Disorder of plant growth substance （1）、CTK content decreases。 Detached

42、 (in vitro)leaf -aggravating senescence; Rooting - Regreening Higher CTK contents of the bleeding sap in the resist-senescing cultivars in sunflower and rice,CTK functions: Blocking some senescence-associated genes(SAGs) expression; Preventing high biomolecules from degradation; Delaying declination

43、 of photosynthesis and maintaining regular respiration; Making the stomata open; Cleaning free radicals and changing assimilate distribution. （2）Eth. It induces“Cyanide-resistant pathway”，and stimulate active O2 formation as well as hydrolase synthesis and activation。,Fig 20.26 Ethylene promotes lea

44、f senescence in wild-type (WT) Arabidopsis, but not in the ethylene-insensitive etr1 mutant.,Fig 20.28 Ethylene production (A) and the expression of ethylene-induced genes (B) in ripening tomato fruit. MG1 through MG4 refer to sequential stages in tomato fruit development. MG, mature green; Imm, imm

45、ature.,The inflorescence in (B) is from a plant carrying the never ripe mutation, which is insensitive to ethylene because of a mutation in an ethylene receptor. As a result, ethylene does not trigger senescence and abscission in these flowers. In untreated wild-type flowers, floral senescence follo

46、ws pollination (C), whereas in the ethylene-insensitive mutants, the flowers do not senesce after pollination but instead remain intact, even as the fruit begin to develop(D). Thus,ethylene is a key signal in inducing floral senescence after pollination in tomato. As the name implies, in the never r

47、ipe mutant, the fruit do not ripen. The two tomato fruits in (E) are of approximately the same age and were grown under the same conditions. However, the fruit on the left is from a never ripe mutant, whereas the fruit on the right is from the wild-type plant, thus emphasizing the importace of ethyl

48、ene signaling in the induction of repening,Fig 20.29 Exogenous treatment with ethyle-ne induces senescence in many plants. The tomato inflorescence on the left in (A) was treated with ethylene, causing the flowers to senesce and abscise.,w,w,w,nr,nr,nr,Ethylene synthesis by leaves of control (Blue)

49、or antisenesce(red) tomato plants expressing ACC synthase.,Fig Synthetic competition of ployamine to Eth,(3)ABA. Stomatal closure and hydrolase synthesis (4)JA JA (Me-JA) : chlorophyll degradation and Eth promotion.,2.2.4 Equilibrium loss of Ca2+ between intro- and extra-cell 。 Usually Ca2+8-15mmol/

50、L in apoplast and 0.1-1mol/L in cytoplasm. Ca2+ enters the cytoplasm and causes senescence,2.2.5、Free radicals burst and the capacities of scavenger systems decline. feed radical Free radicals : ion , atom and molecule with free electron. Characters：instable, active , strongly oxidative capa

51、city and chain-reactions Inorganic free redicals : 、1O2 and OH； Organic free redicals: ROO、RO。,Most of inorganic free radicals from the illuminated chroloplast (1)Photochemical free redicals - hv PSII PSI,(3)Fenton reaction：,(4)Haber-Weiss reaction, Free radical scavenging systems in plant (1

52、)Non- protective enzyme system antioxidant: Cytf、glutathione、ascorbic acid、ubiquinone, vitamin E and carotenoids。 (2)Protective enzyme systems SOD、AAO、 glutathione reductase、 catalase and glutathione peroxidase. SOD is most important.,SOD types: (1)Cu and ZnSOD，dimmer with subunit 32kD，and each with

53、 one Cu2+ and Zn+，mainly distributes in higher plant chloroplast (2) MnSOD mainly distributes in prokaryotic bacteria as well in eucaryotic mitochondria (3) FeSOD is a basic type，mainly locates in green alga. SOD catalytic reaction：,Fig 20.24 The associate- glutathione redox cycle in senescence. Asc

54、orbate is regenerated from oxidized forms by a cycle catalyzed by ascorbate peroxidase (APX), monodehydroascor-bate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR). Superoxide dimutase (SOD) is one of the enzymatic defenses against the buildup of reac-tive oxygen

55、 species. In ma-ture leaves, photosynthetic electron transfer generates NADPH,which donates,electrons to ascorbate by way of reduced glutathione (GSH). In senescing leaves, NADPH production decreases, resulting in increased ratios of oxidized glutathione (GSSG) to GSH and of dehydroascorbate to asco

56、rbate. These relatively subtle changes can result in substantial changes in cellular redox conditions and signal new patterns of gene expression. PSI, Photosystem I;*,nonenzymatic reaction.,Section3 Mechanism for Abscission Abscission: a process during which the cells, tissues or organs, such as flo

57、wers, fruits and small braches, are detached from the plant body. Normal abscission caused by senescence or ripening . Abnormal abscission caused by stresses:higher or lower temperature, drought or flood, insects or diseases. Physiological abscission caused by disorders in physiology itself:such as

58、nutritional competition between vegetation and regeneration, sink and source.,Bud in cotton is 70 abscission，flowers or fruits in soybean is 60-70% abscission。 3.1 Abscission in anatomy and physiology 3.1.1 Abscission in anatomy A specific Part for abscissionabscission zone。,One or several layers of

59、 cell locate in the petiole in which cells have a small in size, a close connection with each other, a dense cytoplasm and starch grains. Division cell,Change in cell wall during abscission,中胶层,3.1.2 Enzymes relative to abscission (1)、Cellulase。 Cellulase activity increases in bean, cotton and citrus during leaf abscission。,(2)、Pectinase. In bean pectinase, abscission . Pectin compound Pectinase (PEM,果胶甲酯酶) Pectin Pectinase (PG,多聚半乳糖醛酸酶) Small subunit (sugar, C5) (3)、Catalase , abscission 。,3.1.3 Ab