Presentation on theme: "Plant Structure, Growth, and Development"— Presentation transcript:
1Plant Structure, Growth, and Development Chapter 35Plant Structure, Growth, and DevelopmentKristin Spitz, Amanda Munoz, Caity Graham,Michelle Lamberta, and Sam Noto
2Plant StructureThe plant body has a hierarchy of organs, tissues, and cells.tissue: an integrated group of cells with a common structure, function, or bothorgan: a specialized center of body function composed of several different types of tissues
3Plant Structure: Organs Plants have three basic organs: roots, shoots, and leaves.
4Plant Structure: Organs Root System: all of a plant′s roots that anchor it in the soil, absorb and transport minerals and water, and store foodRoots anchor vascular plants to the ground, absorb minerals and nutrients, and store organic nutrients.Some plants have a taproot system that consists of one main vertical root that has many smaller lateral root branching off from it.Seedless vascular plants and most monocots have a fibrous root system: a mat of generally thin roots spread out below the surface of the soil, with no root standing out as the main one.
5Plant Structure: Organs Absorption of water and minerals is greatly enhanced by root hairs: tiny extensions of a root epidermal cell, growing just behind the root tip and increasing surface area for absorption of water and mineralsEnvironmental conditions may result in roots being modified for a variety of functions. Many modified roots are aerial roots that are above the ground during normal development.
6Plant Structure: Organs Stem: a vascular plant organ consisting of an alternating system of nodes and internodes that support the leaves and reproductive structuresNode: a point along the stem of a plant at which leaves are attachedInternode:a segment of a plant stem between the points where leaves are attached
7Plant Structure: Organs Axiallary bud: a structure that has the potential to form a lateral shoot, or branch. The bud appears in the angle formed between a leaf and a stemTerminal bud: embryonic tissue at the tip of a shoot, made up of developing leaves and a compact series of nodes and internodesApical dominance: concentration of growth at the tip of a plant shoot, where a terminal bud partially inhibits axillary bud growthModified stems, including stolons, rhizomes, tubers, and bulbs, have evolved in many plants as environmental adaptations.
8Plant Structure: Organs The leaf is the main photosynthetic organ of plants.Leaves consist of a blade and a stalk.Blade: the flattened portion of a typical leafStalk or Petiole: joins the leaf to a node of the stem
9Plant Structure: Organs Vein: a vascular bundle in a leafMonocots have parallel major veins that run the length of the leaf blade.Eudicots have a multibranched network of major veins.Some modified leaves have evolved to function in support, protection, storage, and reproduction, not only in photosynthesis.
11Plant Structure: Tissues Plants have three main tissue systems: dermal, vascular, and groundTissue System: one or more tissues organized into a functional unit connecting the organs of a plant
12Plant Structure: Tissues Dermal Tissue System: the outer protective covering of plantsEpidermis: the dermal tissue system of nonwoody plants, usually consisting of a single layer of tightly packed cellsPeriderm: the protective coat that replaces the epidermis in plants during secondary growth, formed of the cork and cork cambiumCuticle: a waxy covering on the surface of stems and leaves that acts as an adaptation to prevent desiccation in terrestrial plants
13Plant Structure: Tissues Vascular Tissue System: a system formed by xylem and phloem throughout a vascular plant, serving as a transport system for water and nutrients, respectivelyXylem: vascular plant tissue consisting mainly of tubular dead cells that conduct most of the water and minerals upward from roots to the rest of the plantPhloem: vascular plant tissue consisting of living cells arranged into elongated tubes that transport sugar and other organic nutrients throughout the plant
14Plant Structure: Tissues The vascular tissue of a root or stem is collectively called the stele.The stele of the root is in the form of a vascular cylinder: the central cylinder of the vascular tissue in a root.The stele of stems and leaves is divided into vascular bundles: a strand of vascular tissues (both xylem and phloem) in a stem or leaf
15Plant Structure: Tissues Ground Tissue System: plant tissues that are neither vascular nor dermal, fulfilling a variety of functions, such as storage, photosynthesis, and supportPith: ground tissue that is internal to the vascular tissue in a stem; in many monocot roots, parenchyma cells that form the central core of the vascular cylinderCortex: ground tissue that is between the vascular tissue and dermal tissue in a root or dicot stem
16Plant Structure: Cells Plants, like any multicellular organism, are characterized by cellular differentiation.Parenchyma cells: a relatively unspecialized plant cell type that carries out most of the metabolism, synthesizes and stores organic products, and develops into a more differentiated cell typeCollenchyma cells: a flexible plant cell type that occurs in strands or cylinders that support young parts of the plant without restraining growthSclerenchyma cells: a rigid, supportive plant cell type usually lacking protoplasts and possessing thick secondary walls strengthened by lignin at maturity
17Plant Structure: Cells Plants have special water-conducting cells of the xylem.Tracheid: a long, tapered water-conducting cell that is dead at maturity and is found in the xylem of all vascular plantsVessel Element: a short, wide, water-conducting cell found in the xylem of most angiosperms and a few nonflowering vascular plants. Dead at maturity, vessel elements are aligned end to end to form micropipes called vessels
18Plant Structure: Cells Plants also have special sugar-conducting cells of the phloem.Sieve-Tube Member: a living cell that conducts sugars and other organic nutrients in the phloem of angiosperms. They form chains called sieve tubesSieve Plate: an end wall in a sieve-tube member, which facilitates the flow of phloem sap in angiosperm sieve tubesCompanion Cell: a type of plant cell that is connected to a sieve-tube member by many plasmodesmata and whose nucleus and ribosomes may serve one or more adjacent sieve-tube members
19Plant GrowthPlants continue to grow throughout their whole life. This condition is known as indeterminate growth. At any given time, a typical plant consists of embryonic, developing, and mature organs.The length of a plant’s life cycle classifies it as an annual, biennial, or perennial.Annual: a flowering plant that completes its entire life cycle in a single year or growing seasonBiennial: a flowering plant that requires two years to complete its life cyclePerennial: a flowering plant that lives for many years
20Plant GrowthPlants are capable of indeterminate growth because they have meristems: plant tissue that remains embryonic as long as the plant lives
21Plant GrowthApical Meristem: embryonic plant tissue in the tips of roots and in the buds of shoots that supplies cells for the plant to grow in lengthThe process of growth in length due to apical meristems is called primary growth. Primary growth allows roots to extend throughout the soil and shoots to increase exposure to light and CO2Lateral Meristem: a meristem that thickens the roots and shoots of woody plants. The vascular cambium and cork cambium are lateral meristemsThe process of growth in thickness due to lateral meristems is called secondary growth.
22Plant GrowthThe cells within meristems divide relatively frequently. Some of the cells remain in the meristem and produce more cells while others differentiate and are incorporated into tissues and organs.Cells that remain within an apical meristem as sources of new cells are called initials.New cells that are displaced from an apical meristem and continue to divide until the cells they produce become specialized are called derivatives.
23Plant GrowthPrimary growth produces the primary plant body: the tissues produced by apical meristems, which lengthen stems and roots.Herbaceous plants: primary plant body is the entire plantWoody plants: primary plant body is only the youngest parts
24Plant GrowthThe root tip is covered by a root cap: a cone of cells at the tip of a plant root that protects the apical meristemThe root cap protects the delicate apical meristem as the root pushes through the abrasive soil during primary growth.Growth occurs just behind the root tip, in three zones of cells at successive stages of primary growth. Moving away from the root tip, they are the zones of cell division, elongation, and maturation.
25Plant GrowthZone of Cell Division: the zone of primary growth in roots consisting of the root apical meristem and its derivatives. New root cells are produced in this region.Zone of Elongation: the zone of primary growth in roots where new cells elongate, sometimes up to ten times their original lengthCell elongation is mainly responsible for pushing the root tip farther into the soilZone of Maturation: the zone of primary growth in roots where cells complete their differentiation and become functionally mature
27Plant GrowthPrimary growth produces the epidermis, ground tissue, and vascular tissue.The ground tissue of roots, consisting mostly of parenchyma cells, fills the cortex, the region between the vascular cylinder and epidermis.Endodermis: the innermost layer of the cortex in plant roots; a cylinder one cell thick that forms the boundary between the cortex and the vascular cylinderPericycle: the outermost layer of the vascular cylinder of a root, where lateral roots originate
28Plant Growth Leaf Primordia: finger-like projections along the flanks of a shoot apical meristem,from which leaves ariseThe apical meristemof a shoot is located in theterminal bud, where it gives riseto a repetition of internodesand leaf–bearing nodes.
29Plant GrowthThe epidermis covers stems as part of the continuous dermal tissue system. Vascular tissue runs the length of a stem in vascular bundles.
30Plant GrowthStoma: a microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior of the plantGuard Cells: the two cells that flank the stomatal pore and regulate the opening and closing of the poreMesophyll: the ground tissue of a leaf, sandwiched between the upper and lower epidermis and specialized for photosynthesisPalisade Mesophyll: one or more layers of elongated photosynthetic cells on the upper part of a leaf; also called palisade parenchymaSpongy Mesophyll: loosely arranged photosynthetic cells located below the palisade mesophyll cells in a leaf
31Plant GrowthThe vascular tissue of each leaf is continuous with the vascular tissue of the stem.Leaf Trace: a small vascular bundle that extends from the vascular tissue of the stem through the petiole and into a leafThe vascular structure also functions as a skeleton that reinforces the shape of the leaf.Bundle Sheath: a protective covering around a leaf vein, consisting of one or more cell layers, usually parenchyma
32Plant GrowthThe secondary plant body consists of the tissues produced by the vascular cambium and cork cambium, or secondary growth.A secondary xylem is added by the vascular cambium.A thick, tough covering that consists mainly of cork cells is produced by the cork cambium.The vascular cambium increases in circumference and also lays down successive layers of secondary xylem to its interior and secondary phloem to its exterior.The vascular cambium is developed from undifferentiated cells that regain the capacity to divide.The meristematic bands combine to become a continuous cylinder of dividing cells. This eventually becomes a cylinder.
33Plant GrowthThe vascular cambium appears as a ring, with interspersed regions of cells called fusiform initials and ray initials. When these initials divide, they increase the circumference of the cambium itself and add secondary xylem to the inside of the cambium and secondary phloem to the outside.Fusiform Initials: cells within the vascular cambrium that produce elongated cells such as tracheids, vessel elements, fibers, and sieve–tube membersRay Initials: cells within the vascular cambrium that produce xylem and phloem rays, radial files that consist mostly of parenchyma cells
34Plant GrowthAs secondary growth continues over the years, layers of secondary xylem (wood) accumulate, consisting mainly of tracheids, vessel elements, and fibers.Heartwood: older layers of secondary xylem, closer to the center of a stem or root, that no longer transport xylem sapHeartwoods are closer to the center of the sten or root.Sapwood: outer layers of secondary xylem that still transport xylem sap
35Plant GrowthThe cork cambium gives rise to the secondary plant body′s protective covering, or periderm, which consists of the cork cambium plus the layers of cork cells it produces (phelloderm and suberin).Most of the periderm is impermeable to water and gases.Lenticels: small raised areas that dot the periderm in the bark of stems and roots that enable gas exchange between living cells and the outside air
36Plant GrowthCells of the cork cambium do not continue to divide so the thickening of the stem or roots splits the first cork cambium, which loses its meristematic activity and differentiates into cork cells. A new cork cambium forms to the inside, resulting in another layer of periderm. Older layers of periderm are aloughed off, as is evident in the cracked, peeling barks of many tree trunks.Bark: all tissues external to the vascular cambium, consisting mainly of the secondary phloem and layers of periderm
37Plant DevelopmentMorphogenesis: the development of body shape and organizationThree developmental processes act to transform the fertilized egg into a plant: growth, morphogenesis, and cellular differentiation
38Plant DevelopmentModern molecular techniques are helping plant biologists explore how growth, morphogenesis, and cellular differentiation give rise to a plant.Arabidopsis thaliana was the first plant to have its entire genome sequenced.A quest has been launched to determine the function of every one of the plant’s genes.Systems Biology: an approach to studying biology that aims to model the dynamic behavior of whole biological systemsA goal of systems biology is the establish a blueprint for how plants are built.
39Plant DevelopmentThe plane (direction) and symmetry of cell division are immensely important in determining plant form.Asymmetrical cell division is when one daughter cell receives more cytoplasm than the other during mitosis.Plane is determined during interphase.The plane in which a cell divides is determined during late interphase. The first sign of this spatial orientation is a rearrangement of the cytoskeleton. Microtubules in the cytoplasm become concentrated into a ring called the preprophase band: microtubules in the cortex (outer cytoplasm) of a cell that are concentrated into a ring
40Plant DevelopmentAnimal cells grow mainly by synthesizing protein–rich cytoplasm, a metabolically expensive process. Growing plant cells also produce additional protein–rich material in their cytoplasm, but water uptake typically accounts for about 90% of expansion.Plant cells rarely expand equally in all directions. Their greatest expansion is usually oriented along the plant′s main axis.Mutants have abnormal microtubule arrangements.
41Plant DevelopmentMorphogenesis must occur for development to proceed properly.Pattern Formation: the ordering of cells into specific three–dimensional structures, an essential part of shaping an organism and its individual parts during development.Positional Information: signals to which genes regulating development respond, indicating a cell′s location relative to other cells in an embryonic structure.
42Plant DevelopmentOne type of positional information is associated with polarity, the condition of having structural differences at opposite ends of an organism.Morphogenesis in plants is often under the control of master regulatory genes called homeotic genes.Homeotic genes regulate major events, such as the formation of an organ.
43Plant DevelopmentCellular differentiation depends to a large extent on gene expression and positional information.The challenge of understanding cellular differentiation is explaining how cells with matching genomes diverge into various cell types.A cell′s position in a developing organ determines its pathway of differentiation.
44Plant DevelopmentPlants pass through phases, developing from a juvenile phase to an adult vegetative phase to an adult reproductive phase. In plants the phases occur within a single region, the shoot apical meristem.Phase Change: a shift from one developmental phase to another.During the transition from a juvenile phase to an adult phase, the most obvious morphological changes typically occur in leaf size and shape.Any new leaves that develop on branches that emerge from axillary buds at juvenile nodes will also be juvenile.Phase changes are examples of plasticity in plant development.
45Plant DevelopmentThe transition from vegetative growth to flowering is associated with the switching-on of floral meristem identity genes.Meristem Identity Gene: a plant gene that promotes the switch from vegetative growth to flowering.The protein products of these genes are transcription factors that regulate the genes required for the conversion of the indeterminate vegetative meristems into determinate floral meristems.
46Plant DevelopmentOrgan Identity Genes: regulate the characteristic floral pattern: -floral organs – stamen, carpal, sepal, and petal – develop into whorls based on position.Organ identity genes, also called plant homeotic genes, code for transcription factors.ABC Model: a model of flower formation identifying three classes of organ identity genes that direct formation of the four types of floral organs.
47Plant DevelopmentA genes are switched on in the two outer whorls (sepals and petals); B genes are switched on in the two middle whorls (petals and stamens); and C genes are switched on in the two inner whorls (stamens and carpels).Sepals arise from those parts of the floral meristems in which only A genes are active; petals arise where A and B genes are active; stamens where B and C genes are active; and carpels where only C genes are active.The ABC model can account for the phenotypes of mutants lacking A, B, or C gene activity.