Bài giảng Biology - Chapter 35: Plant Structure, Growth, and Development

Chapter 35Plant Structure, Growth, and DevelopmentOverview: No two Plants Are AlikeTo some peopleThe fanwort is an intrusive weed, but to others it is an attractive aquarium plantThis plant exhibits plasticityThe ability to alter itself in response to its environmentFigure 35.1In addition to plasticityEntire plant species have by natural selection accumulated characteristics of morphology that vary little among plants within the speciesConcept 35.1: The plant body has a hierarchy of organs, tissues, and cellsPlants, like multicellular animalsHave organs composed of different tissues, which are in turn composed of cellsThe Three Basic Plant Organs: Roots, Stems, and LeavesThe basic morphology of vascular plantsReflects their evolutionary history as terrestrial organisms that draw nutrients from two very different environments: below-ground and above-groundThree basic organs evolved: roots, stems, and leavesThey are organized into a root system and a shoot systemFigure 35.2Reproductive shoot (flower)Terminal budNodeInternodeTerminalbudVegetativeshootBladePetioleStemLeafTaprootLateral rootsRootsystemShootsystemAxillarybudRootsA rootIs an organ that anchors the vascular plantAbsorbs minerals and waterOften stores organic nutrientsIn most plantsThe absorption of water and minerals occurs near the root tips, where vast numbers of tiny root hairs increase the surface area of the rootFigure 35.3Many plants have modified rootsFigure 35.4a–e(a) Prop roots(b) Storage roots(c) “Strangling” aerialroots(d) Buttress roots(e) PneumatophoresStemsA stem is an organ consisting of An alternating system of nodes, the points at which leaves are attachedInternodes, the stem segments between nodesAn axillary budIs a structure that has the potential to form a lateral shoot, or branchA terminal budIs located near the shoot tip and causes elongation of a young shootMany plants have modified stemsFigure 35.5a–dRhizomes. The edible base of this ginger plant is an example of a rhizome, a horizontal stem that grows just below the surface or emerges and grows along thesurface.(d)Tubers. Tubers, such as these red potatoes, are enlarged ends of rhizomes specializedfor storing food. The “eyes” arranged in a spiral pattern around a potato are clusters of axillary buds that markthe nodes.(c)Bulbs. Bulbs are vertical,underground shoots consistingmostly of the enlarged bases of leaves that store food. You can see the many layers of modified leaves attached to the short stem by slicing an onion bulb lengthwise.(b)Stolons. Shown here on a strawberry plant, stolons are horizontal stems that grow along the surface. These “runners”enable a plant to reproduce asexually, as plantlets form at nodes along each runner.(a)Storage leavesStemRootNodeRhizomeRootLeavesThe leafIs the main photosynthetic organ of most vascular plantsLeaves generally consist ofA flattened blade and a stalkThe petiole, which joins the leaf to a node of the stemMonocots and dicotsDiffer in the arrangement of veins, the vascular tissue of leavesMost monocotsHave parallel veinsMost dicotsHave branching veinsIn classifying angiospermsTaxonomists may use leaf morphology as a criterionFigure 35.6a–cPetiole (a) Simple leaf. A simple leafis a single, undivided blade.Some simple leaves are deeply lobed, as in anoak leaf.(b) Compound leaf. In acompound leaf, theblade consists of multiple leaflets.Notice that a leaflethas no axillary budat its base.(c) Doubly compound leaf. In a doubly compound leaf, each leaflet is divided into smaller leaflets.Axillary budLeafletPetioleAxillary budAxillary budLeafletPetioleSome plant speciesHave evolved modified leaves that serve various functionsFigure 35.6a–e(a) Tendrils. The tendrils by which thispea plant clings to a support are modified leaves. After it has “lassoed” a support, a tendril forms a coil that brings the plant closer to the support. Tendrils are typically modified leaves, but some tendrils are modified stems, as in grapevines.(b) Spines. The spines of cacti, such as this prickly pear, are actually leaves, and photosynthesis is carried out mainly by the fleshy green stems. (c) Storage leaves. Most succulents, such as this ice plant, have leaves modified for storing water.(d) Bracts. Red parts of the poinsettia are often mistaken for petals but are actually modified leaves called bracts that surround a group of flowers. Such brightly colored leaves attract pollinators.(e) Reproductive leaves. The leaves of some succulents, such as Kalanchoe daigremontiana, produce adventitious plantlets, which fall off the leaf and take root in the soil.The Three Tissue Systems: Dermal, Vascular, and GroundEach plant organHas dermal, vascular, and ground tissuesFigure 35.8DermaltissueGroundtissueVasculartissueThe dermal tissue systemConsists of the epidermis and peridermThe vascular tissue systemCarries out long-distance transport of materials between roots and shootsConsists of two tissues, xylem and phloemXylemConveys water and dissolved minerals upward from roots into the shootsPhloemTransports organic nutrients from where they are made to where they are neededGround tissueIncludes various cells specialized for functions such as storage, photosynthesis, and supportCommon Types of Plant CellsLike any multicellular organismA plant is characterized by cellular differentiation, the specialization of cells in structure and functionSome of the major types of plant cells includeParenchymaCollenchymaSclerenchymaWater-conducting cells of the xylemSugar-conducting cells of the phloemParenchyma, collenchyma, and sclerenchyma cellsFigure 35.9Parenchyma cells60 m PARENCHYMA CELLS80 m Cortical parenchyma cellsCOLLENCHYMA CELLSCollenchyma cellsSCLERENCHYMA CELLSCell wallSclereid cells in pear25 m Fiber cells5 m Water-conducting cells of the xylem and sugar-conducting cells of the phloemFigure. 35.9WATER-CONDUCTING CELLS OF THE XYLEMVesselTracheids100 m Tracheids and vesselsVesselelementVessel elements withpartially perforated end wallsPitsTracheidsSUGAR-CONDUCTING CELLS OF THE PHLOEMCompanion cellSieve-tubememberSieve-tube members:longitudinal viewSieveplateNucleusCytoplasmCompanioncell30 m 15 m Concept 35.2: Meristems generate cells for new organsApical meristemsAre located at the tips of roots and in the buds of shootsElongate shoots and roots through primary growthLateral meristemsAdd thickness to woody plants through secondary growthAn overview of primary and secondary growthFigure. 35.10In woody plants, there are lateral meristems that add secondary growth, increasing the girth of roots and stems.Apical meristemsadd primary growth,or growth in length.VascularcambiumCorkcambiumLateralmeristemsRoot apicalmeristemsPrimary growth in stemsEpidermisCortexPrimary phloemPrimary xylemPithSecondary growth in stemsPeridermCorkcambiumCortexPrimary phloemSecondaryphloemVascular cambiumSecondaryxylemPrimaryxylemPithShoot apicalmeristems(in buds)The corkcambium addssecondarydermal tissue.The vascularcambium addssecondaryxylem andphloem.In woody plantsPrimary and secondary growth occur simultaneously but in different locationsFigure 35.11This year’s growth(one year old)Last year’s growth(two years old)Growth of twoyears ago (threeyears old)One-year-old sidebranch formedfrom axillary budnear shoot apexScars left by terminalbud scales of previouswintersLeaf scarLeaf scarStemLeaf scarBud scaleAxillary budsInternodeNodeTerminal budConcept 35.3: Primary growth lengthens roots and shootsPrimary growth produces the primary plant body, the parts of the root and shoot systems produced by apical meristemsPrimary Growth of RootsThe root tip is covered by a root cap, which protects the delicate apical meristem as the root pushes through soil during primary growthFigure 35.12DermalGroundVascularKeyCortexVascular cylinderEpidermisRoot hairZone ofmaturationZone ofelongationZone of celldivisionApicalmeristemRoot cap100 mThe primary growth of rootsProduces the epidermis, ground tissue, and vascular tissueOrganization of primary tissues in young rootsFigure 35.13a, bCortexVascularcylinderEndodermisPericycleCore ofparenchymacellsXylem50 mEndodermisPericycleXylemPhloemKey100 mVascularGroundDermalPhloemTransverse section of a root with parenchymain the center. The stele of many monocot roots is a vascular cylinder with a core of parenchymasurrounded by a ring of alternating xylem and phloem.(b)Transverse section of a typical root. In theroots of typical gymnosperms and eudicots, aswell as some monocots, the stele is a vascularcylinder consisting of a lobed core of xylemwith phloem between the lobes.(a)100 mEpidermisLateral rootsArise from within the pericycle, the outermost cell layer in the vascular cylinderFigure 35.14CortexVascularcylinderEpidermisLateral root100 m1234EmerginglateralrootPrimary Growth of ShootsA shoot apical meristemIs a dome-shaped mass of dividing cells at the tip of the terminal budGives rise to a repetition of internodes and leaf-bearing nodesFigure. 35.15Apical meristemLeaf primordiaDevelopingvascularstrandAxillary budmeristems0.25 mmTissue Organization of StemsIn gymnosperms and most eudicotsThe vascular tissue consists of vascular bundles arranged in a ringFigure 35.16aXylemPhloemSclerenchyma(fiber cells)Ground tissueconnecting pith to cortexPithEpidermisVascularbundleCortexKeyDermal GroundVascular1 mm(a) A eudicot stem. A eudicot stem (sunflower), withvascular bundles forming a ring. Ground tissue towardthe inside is called pith, and ground tissue toward theoutside is called cortex. (LM of transverse section) GroundtissueEpidermisVascularbundles1 mm(b) A monocot stem. A monocot stem (maize) with vascularbundles scattered throughout the ground tissue. In such anarrangement, ground tissue is not partitioned into pith andcortex. (LM of transverse section) Figure 35.16bIn most monocot stemsThe vascular bundles are scattered throughout the ground tissue, rather than forming a ringTissue Organization of LeavesThe epidermal barrier in leavesIs interrupted by stomata, which allow CO2 exchange between the surrounding air and the photosynthetic cells within a leafThe ground tissue in a leafIs sandwiched between the upper and lower epidermisThe vascular tissue of each leafIs continuous with the vascular tissue of the stemKeyto labelsDermalGroundVascularGuardcellsStomatal poreEpidermalcell50 µmSurface view of a spiderwort(Tradescantia) leaf (LM)(b)CuticleSclerenchymafibersStomaUpperepidermisPalisademesophyllSpongymesophyllLowerepidermisCuticleVeinGuard cellsXylemPhloemGuard cellsBundle-sheathcellCutaway drawing of leaf tissues(a)VeinAir spacesGuard cells100 µmTransverse section of a lilac(Syringa) leaf (LM)(c)Figure 35.17a–cLeaf anatomyConcept 35.4: Secondary growth adds girth to stems and roots in woody plantsSecondary growthOccurs in stems and roots of woody plants but rarely in leavesThe secondary plant bodyConsists of the tissues produced by the vascular cambium and cork cambiumThe Vascular Cambium and Secondary Vascular TissueThe vascular cambiumIs a cylinder of meristematic cells one cell thickDevelops from parenchyma cellsVascular cambiumPithPrimary xylemSecondary xylemVascular cambiumSecondary phloemPrimary phloemPeriderm(mainly cork cambiaand cork)PithPrimary xylemVascular cambiumPrimary phloemCortexEpidermisVascular cambium4First cork cambium Secondary xylem (twoyears ofproduction)PithPrimary xylemVascular cambiumPrimary phloem216GrowthPrimary xylemSecondary xylemSecondary phloemPrimary phloemCorkPhloem ray3Xylem rayGrowthBark8Layers of periderm7Cork5Most recentcork cambiumCortexEpidermis9In the youngest part of the stem, you can see the primary plant body, as formed by the apical meristem during primary growth. The vascular cambium is beginning to develop.As primary growth continues to elongate the stem, the portion of the stem formed earlier the same year has already started its secondary growth. This portion increases in girth as fusiform initials of the vascular cambium form secondary xylem to theinside and secondary phloem to the outside.The ray initials of the vascular cambium give rise to the xylem and phloem rays.As the diameter of the vascular cambium increases, the secondary phloem and other tissues external to the cambium cannot keep pace with the expansion because the cells no longer divide. As a result, these tissues, including the epidermis, rupture. A second lateral meristem, the cork cambium, develops from parenchyma cells in the cortex. The cork cambium produces cork cells, which replace the epidermis.In year 2 of secondary growth, the vascular cambium adds to the secondary xylem and phloem, and the cork cambium produces cork.As the diameter of the stem continues to increase, the outermost tissues exterior to the cork cambium rupture and slough off from the stem. Cork cambium re-forms in progressively deeper layers of thecortex. When none of the original cortex is left, the cork cambium develops from parenchyma cells in the secondary phloem.Each cork cambium and the tissues it produces form a layer of periderm.Bark consists of all tissues exterior to the vascular cambium.123456789Secondary phloem(a) Primary and secondary growthin a two-year-old stemPrimary and secondary growth of a stemFigure 35.18aSecondary phloemVascular cambiumLate woodEarly woodSecondaryxylemCorkcambiumCorkPeriderm(b) Transverse sectionof a three-year-old stem (LM)Xylem rayBark0.5 mm0.5 mmFigure 35.18bViewed in transverse section, the vascular cambiumAppears as a ring, with interspersed regions of dividing cells called fusiform initials and ray initialsFigure 35.19a, bVascularcambiumCXCPCXCXCPPPCXXPCXXCCTypes of cell division. An initial can divide transversely to form two cambial initials (C) or radially to form an initial and either a xylem (X) or phloem (P) cell.(a)Accumulation of secondary growth. Although shown here as alternately adding xylem and phloem, a cambial initial usuallyproduces much more xylem.(b)As a tree or woody shrub agesThe older layers of secondary xylem, the heartwood, no longer transport water and mineralsThe outer layers, known as sapwoodStill transport materials through the xylemGrowth ringVascularrayHeartwoodSapwoodVascular cambiumSecondary phloemLayers of peridermSecondaryxylemBarkFigure 35.20Cork Cambia and the Production of PeridermThe cork cambiumGives rise to the secondary plant body’s protective covering, or peridermPeridermConsists of the cork cambium plus the layers of cork cells it producesBarkConsists of all the tissues external to the vascular cambium, including secondary phloem and peridermConcept 35.5: Growth, morphogenesis, and differentiation produce the plant bodyThe three developmental processes of growth, morphogenesis, and cellular differentiationAct in concert to transform the fertilized egg into a plantMolecular Biology: Revolutionizing the Study of PlantsNew techniques and model systemsAre catalyzing explosive progress in our understanding of plantsArabidopsisIs the first plant to have its entire genome sequencedCell organization and biogenesis (1.7%)DNA metabolism (1.8%)Carbohydrate metabolism (2.4%)Signal transduction (2.6%)Protein biosynthesis (2.7%)Electron transport(3%)Proteinmodification (3.7%)Proteinmetabolism (5.7%)Transcription (6.1%)Other metabolism (6.6%)Transport (8.5%)Other biologicalprocesses (18.6%)Unknown(36.6%)Figure 35.21Growth: Cell Division and Cell ExpansionBy increasing cell numberCell division in meristems increases the potential for growthCell expansionAccounts for the actual increase in plant sizeThe Plane and Symmetry of Cell Division The plane (direction) and symmetry of cell divisionAre immensely important in determining plant formIf the planes of division of cells are parallel to the plane of the first divisionA single file of cells will be producedFigure 35.22aDivision insame planePlane ofcell divisionSingle file of cells formsCube formsNucleusCell divisions in the same plane produce a single file of cells, whereas cell divisions in three planes give rise to a cube.(a)Division inthree planesIf the planes of division vary randomlyAsymmetrical cell division occursFigure 35.22bUnspecializedepidermal cellcell divisionAsymmetricalUnspecializedepidermal cellGuard cell“mother cell”Unspecializedepidermal cellDevelopingguard cells(b) An asymmetrical cell division precedes the development of epidermal guard cells, the cells that borderstomata (see Figure 35.17).The plane in which a cell dividesIs determined during late interphaseMicrotubules in the cytoplasmBecome concentrated into a ring called the preprophase bandPreprophase bandsof microtubulesNucleiCell plates10 µmFigure 35.23Orientation of Cell ExpansionPlant cellsRarely expand equally in all directionsThe orientation of the cytoskeletonAffects the direction of cell elongation by controlling the orientation of cellulose microfibrils within the cell wallFigure 35.24CellulosemicrofibrilsVacuolesNucleus5 µmMicrotubules and Plant GrowthStudies of fass mutants of ArabidopsisHave confirmed the importance of cytoplasmic microtubules in cell division and expansionFigure 35.25a–cWild-type seedlingfass seedlingMature fass mutant(a)(b)(c)Morphogenesis and Pattern FormationPattern formationIs the development of specific structures in specific locationsIs determined by positional information in the form of signals that indicate to each cell its locationPolarityIs one type of positional informationIn the gnom mutant of ArabidopsisThe establishment of polarity is defectiveFigure 35.26Morphogenesis in plants, as in other multicellular organismsIs often under the control of homeotic genesFigure 35.27Gene Expression and Control of Cellular DifferentiationIn cellular differentiationCells of a developing organism synthesize different proteins and diverge in structure and function even though they have a common genomeCellular differentiationTo a large extent depends on positional informationIs affected by homeotic genesFigure 35.28When epidermal cells border a single corticalcell, the homeotic gene GLABRA-2 is selectivelyexpressed, and these cells will remain hairless.(The blue color in this light micrograph indi-cates cells in which GLABRA-2 is expressed.)Here an epidermal cell borders twocortical cells. GLABRA-2 is not expressed,and the cell will develop a root hair.The ring of cells external to the epi-dermal layer is composed of rootcap cells that will be sloughed off asthe root hairs start to differentiate.Corticalcells20 µmLocation and a Cell’s Developmental FateA cell’s position in a developing organDetermines its pathway of differentiationShifts in Development: Phase ChangesPlants pass through developmental phases, called phase changesDeveloping from a juvenile phase to an adult vegetative phase to an adult reproductive phaseThe most obvious morphological changesTypically occur in leaf size and shapeLeaves produced by adult phaseof apical meristemLeaves produced by juvenile phaseof apical meristemFigure 35.29Genetic Control of FloweringFlower formationInvolves a phase change from vegetative growth to reproductive growthIs triggered by a combination of environmental cues and internal signalsThe transition from vegetative growth to floweringIs associated with the switching-on of floral meristem identity genesPlant biologists have identified several organ identity genesThat regulate the development of floral patternFigure 35.30a, b(a) Normal Arabidopsis flower. Arabidopsisnormally has four whorls of flower parts: sepals(Se), petals (Pe), stamens (St), and carpels (Ca).(b) Abnormal Arabidopsis flower. Reseachers haveidentified several mutations of organ identity genes that cause abnormal flowers to develop.This flower has an extra set of petals in place of stamens and an internal flower where normal plants have carpels.CaStPeSePePeSePeSeThe ABC model of flower formationIdentifies how floral organ identity genes direct the formation of the four types of floral organsPetalsStamensCarpelsABSepalsCC geneactivityB + CgeneactivityA + BgeneactivityA geneactivity(a) A schematic diagram of the ABChypothesis. Studies of plant mutationsreveal that three classes of organ identitygenes are responsible for the spatial patternof floral parts. These genes are designated A,B, and C in this schematic diagram of a floralmeristem in transverse view. These genesregulate expression of other genesresponsible for development of sepals,petals, stamens, and carpels. Sepals developfrom the meristematic region where only Agenes are active. Petals develop where bothA and B genes are expressed. Stamens arisewhere B and C genes are active. Carpels arisewhere only C genes are expressed.Figure 35.31aAn understanding of mutants of the organ identity genesDepicts how this model accounts for floral phenotypesFigure 35.31bStamenCarpelPetalSepalWild typeMutant lacking AMutant lacking BMutant lacking C(b) Side view of organ identity mutant flowers. Combining the modelshown in part (a) with the rule that if A gene or C gene activity ismissing, the other activity spreads through all four whorls, we can explain thephenotypes of mutants lacking a functional A, B, or C organ identity gene.Activegenes:Whorls:AACCCCAACCCCCCCCAACCCCABBBBBBBBAABBAABBAAAAA