Chapter 35: Vascular Plant Structure, Growth, and Development - PDF

Chapter 35 Vascular Plant Structure, Growth, and Development Vascular Plants - multicellular and photosynthetic - possess xylem and phloem - adapted to land existence (ex: protection from desiccation, vertical growth) - share a common ancestor with green algae (charophytes) Plant evolution...

Chapter 35 Vascular Plant Structure, Growth, and Development Vascular Plants - multicellular and photosynthetic - possess xylem and phloem - adapted to land existence (ex: protection from desiccation, vertical growth) - share a common ancestor with green algae (charophytes) Plant evolution Liverworts (bryophytes) plants Nonvascular Plants Origin of plants (470 mya) ANCESTRAL 1 Mosses GREEN ALGA Hornworts Lycophytes (club mosses, Vascular plants plants vascular Seedless spikemosses, quillworts) Origin of vascular plants (425 mya) 2 Monilophytes (ferns, horsetails, whisk ferns) Gymnosperms Seed plants Origin of seed plants (360 mya) 3 Angiosperms 500 450 400 350 300 50 0 Millions of years ago (mya) Vascular Plants (cont.) Plant groups Mosses and other Ferns and other Seed plants (gymnosperms and angiosperms) nonvascular plants seedless vascular plants Reduced, independent Reduced (usually microscopic), dependent on Gametophyte Dominant (photosynthetic and surrounding sporophyte tissue for nutrition free-living) Reduced, dependent Sporophyte on gametophyte Dominant Dominant for nutrition Gymnosperm Angiosperm Sporophyte Microscopic female (2n) gametophytes (n) inside Sporophyte ovulate cone Microscopic (2n) female gametophytes (n) inside these parts of flowers Example Microscopic male gametophytes Microscopic male (n) inside gametophytes (n) these parts inside pollen of flowers cone Gametophyte Sporophyte (n) Sporophyte (2n) Gametophyte (2n) (n) Vascular Plants (cont.) In this Unit we will focus on vascular plants, particularly the angiosperms and their two major groups: monocots and eudicots. Embryos Leaf venation Stems Roots Pollen Flowers Monocot Characteristics Root system Floral One Veins Vascular usually Pollen organs cotyledon usually tissue fibrous grain with usually in parallel scattered (no main one opening multiples root) of three Eudicot Characteristics Vascular Floral Two Veins Taproot Pollen tissue organs cotyledons usually (main root) grain with usually usually netlike arranged usually three present openings in multiples in ring of four or five 35.1 Plants Are Organized into Organs, Tissues, and Cells cell = fundamental unit of life tissue = group of cells that perform a specialized function organ = several types of tissues that perform a specialized function At the cellular level Photosynthetic cells contain chloroplasts. At the organ level At the tissue level Leaves provide Dermal Vascular surface area. tissue tissue protects supports and organs. transports. Chloroplasts Stems support and elevate. Tube-shaped cells transport resources. Leaf cross section Ground tissue Cells with carries out root hairs photosynthesis. increase surface area. Roots anchor and absorb. 35.1 Plants Are Organized into Organs, Tissues, and Cells (cont.) ORGANS: Roots, Stems, and Leaves The roots, stems, and leaves are organized into two systems: - root system - shoot system Reproductive shoot (flower) Apical bud Node Internode Apical bud Shoot Vegetative system shoot Leaf Blade Petiole Axillary bud Stem Taproot Root Lateral system (branch) roots 35.1 Plants Are Organized into Organs, Tissues, and Cells (cont.) ORGANS: Roots, Stems, and Leaves (cont.) Roots Functions: anchor plant, absorb water and minerals, store sugars primary root = the first root to emerge lateral roots = branch from primary roots to improve anchorage and water absorption Tall plants have a taproot system. - taproot prevents the plant from toppling - lateral roots are responsible for absorption Fibrous root Small plants have a fibrous root system. Taproot - adventitious roots arise from the stem and give rise to many branching lateral roots Most absorption occurs near the tips of roots. Root hairs increase the surface area of the roots, along with mycorrhizae. 35.1 Plants Are Organized into Organs, Tissues, and Cells (cont.) ORGANS: Roots, Stems, and Leaves (cont.) Roots (cont.) Root specializations: 1. Prop roots. Support tall, top-heavy plants 2. Storage roots. 3. Pneumatophores. Prop roots Gas exchange for plants that grow in Storage water roots 4. Aerial roots. Climbing, capturing moisture in air or photosynthesis 5. Buttress roots. For plants with shallow root systems Pneumatophores “Strangling” aerial roots Buttress roots 35.1 Plants Are Organized into Organs, Tissues, and Cells (cont.) ORGANS: Roots, Stems, and Leaves (cont.) Stems Functions: elongate and orient shoot to maximize sunlight absorption for photosynthesis - alternating system of nodes, the points at which leaves are attached - internodes, the stem segments between nodes The growing shoot tip, or __________ bud, causes elongation of a young shoot. An __________ bud is a structure that has the potential to form a lateral branch, thorn, or flower. 35.1 Plants Are Organized into Organs, Tissues, and Cells (cont.) ORGANS: Roots, Stems, and Leaves (cont.) Stems (cont.) Stem specializations: Rhizome 1. Rhizomes. Underground, horizontal stems 2. Stolons. Aboveground, Root horizontal stems Rhizomes Stolon 3. Tubers. Storage stems Stolons Tubers 35.1 Plants Are Organized into Organs, Tissues, and Cells (cont.) ORGANS: Roots, Stems, and Leaves (cont.) Leaves Functions: capture sunlight, exchange gases, dissipate heat, defend against herbivores and pathogens Leaves generally consist of: 1. blade = flat to capture sunlight Simple leaf 2. petiole = stalk which joins the leaf to a node of the stem A simple leaf has a single, undivided blade. Some Monocots and eudicots differ in the simple leaves are deeply lobed, as shown here. arrangement of leaf vascular tissue (veins): Axillary - most monocots have parallel veins bud Petiole - most eudicots have branching veins Compound leaf Leaflet In a compound leaf, the In classifying angiosperms, taxonomists blade consists of multiple may use leaf morphology as a criterion: leaflets. A leaflet has no axillary bud at its base. In some plants, - simple leaves: single undivided blade each leaflet is further divided - compound leaves: multiple leaflets into smaller leaflets. Axillary Petiole bud 35.1 Plants Are Organized into Organs, Tissues, and Cells (cont.) ORGANS: Roots, Stems, and Leaves (cont.) Leaves (cont.) Leaf specializations: 1. Spines. Perform photosynthesis 2. Tendrils. Support 3. Reproductive leaves. 4. Storage. Tendrils Spines Storage leaves Plantlet Stem Storage leaves Reproductive leaves 35.1 Plants Are Organized into Organs, Tissues, and Cells (cont.) TISSUES: Dermal, Vascular, and Ground Each tissue system is continuous throughout the plant. Dermal tissue Ground tissue Vascular tissue 35.1 Plants Are Organized into Organs, Tissues, and Cells (cont.) TISSUES: Dermal, Vascular, and Ground (cont.) Dermal Tissue Function: forms the outer protective covering of a plant cabbage seedling Modifications include: 1. Epidermis (nonwoody). Contains closely root hairs packed epidermal cells that are exposed to elongating air and covered with waxy cuticle. trichomes tip of root 2. Periderm (woody). Replace the epidermis Root hairs in older regions of stems and roots. 3. Root hairs. Increase surface area of root chloroplasts for water absorption. 4. Trichomes. Protect from sun and moisture loss, and discourage herbivory. Trichomes stoma guard cell 5. Guard cells. Control leaf stomata. epidermal periderm cells lenticel cork cambium cork Stoma of leaf Cork of older stem 35.1 Plants Are Organized into Organs, Tissues, and Cells (cont.) TISSUES: Dermal, Vascular, and Ground (cont.) Vascular Tissue Function: transports materials through the plant xylem = conducts water and dissolved minerals upward from roots into the shoots phloem = transports sugars from where they are made to where they are needed vascular bundle = a bundle of vascular tissue in roots, stems and leaves Ground Tissue Function: forms the bulk of the plant pith = ground tissue internal to the vascular tissue cortex = ground tissue external to the vascular tissue Ground tissue includes cells specialized for storage, photosynthesis, support, and transport. 35.1 Plants Are Organized into Organs, Tissues, and Cells (cont.) CELLS: Xylem and Phloem Xylem Two types of water-conducting cells are dead at maturity. 1. Tracheids are long, thin, tapered Vessel Tracheids cells found in the xylem of all 100 µm vascular plants. Water moves between tracheids through pits. 2. Vessel elements are wider, shorter, and thinner than tracheids, and align end to end to form long pipes called vessels. Pits Tracheids and vessels Perforation plate Vessel element Pits Vessel elements, with perforated end walls Tracheids 35.1 Plants Are Organized into Organs, Tissues, and Cells (cont.) CELLS: Xylem and Phloem Phloem Two types of sugar-conducting cells are alive at maturity. 1. Sieve-tube elements consist of Sieve-tube elements: 3 µm longitudinal view chains of cells which they lack organelles. Sieve plates are porous end walls between sieve-tube elements that Sieve plate allow fluid to flow between cells. Sieve-tube element Companion and companion cell cells 2. A companion cell connects with Sieve-tube each sieve-tube element by elements numerous plasmodesmata. The Plasmodesma companion cell’s nucleus and ribosomes serve both cells. Sieve 30 µm plate Nucleus of companion cell 15 µm Sieve-tube elements: Sieve plate with pores longitudinal view 35.2 Meristems Generate New Cells for 1o and 2o Growth The ability of a plant to grow throughout its life is known as indeterminate growth, which is due to meristems. Some plant organs cease to grow at a certain size; this is called determinate growth. Two types of meristems: 1. ____________: tips of roots and shoots; involved in… Meristem cell Cell division 2. ____________: vascular cambium and cork cambium; involved in… Vascular cambium: adds layers of vascular tissue Meristem cell Differentiated cell called 2o xylem (wood) and 2o phloem. Cell division Cork cambium replaces the epidermis with periderm, which is thicker and tougher. Apical Meristem Meristem cell Differentiated cell Cell division Epidermal tissue Ground tissue Vascular tissue forms the outer fills the interior transports water protective covering of the plant. and nutrients of the plant. within the plant and provides support. Meristem cell Differentiated cell 35.2 Meristems Generate New Cells for 1o and 2o Growth (cont.) 1o Growth Primary Growth (growth in length) Apical meristem cells are undifferentiated. When they divide, Primary growth is made possible by apical some daughter cells remain in the apical meristem, ensuring meristems at the tips of shoots and roots. Shoot apical a continuing population of undifferentiated cells. Other Leaf primordia daughter cells become partly differentiated as primary meristem meristem cells. After dividing and growing in length, they become fully differentiated cells in the mature tissues. Cell division in Youngest Primary apical meristem differentiated meristems cells Growth Daughter cell in Time primary meristem Older differentiated Mature Cell division in cells tissues primary meristem Growing cells in Dermal Ground Vascular primary meristem The addition of elongated, differentiated cells Differentiated cells lengthens a stem (as shown here) or root. Root apical Cutaway view of primary (for example, meristem growth in a shoot tip vessel elements) 35.2 Meristems Generate New Cells for 1o and 2o Growth (cont.) 2o Growth Secondary Growth (growth in thickness) Addition of secondary xylem Direction of secondary growth Secondary growth is made possible by two lateral and phloem cells: When a Vascular cambium cell meristems extending along the length of a shoot or vascular cambium cell divides, root where primary growth has ceased. sometimes one daughter cell X1 Vascular cambium becomes a secondary xylem cell Time X1 P1 (X) to the inside of the cambium The lateral meristems, or a secondary phloem cell (P) to called the vascular X1 X2 P1 the outside. Although xylem and cambium and cork phloem cells are shown being X1 X2 P2P1 cambium, are cylinders added equally here, usually many of dividing cells that are more xylem cells are produced. Direction of secondary growth one cell thick. Addition of cork cells: Cork cambium cell Increased circumference: Cork cambium When a cork cambium cell Time When a cambium cell divides, sometimes one daughter C1 divides, sometimes both cell becomes a cork cell (C) to daughter cells remain in the outside of the cambium. C2C1 the cambium and grow, Cell Cell increasing the cambium division growth circumference. Completed primary growthWhen the vascular cambium and cork cambium become active in a stem (or root), primary growth Vascular cambium cell has ceased in that area. Cork cambium cell Direction of secondary growth Lateral A stem (or root) thickens as meristems secondary xylem, secondary phloem, and cork cells are Youngest Youngest Cork added. Most of the cells are xylem cell phloem cellcells secondary xylem (wood). Oldest Oldest xylem cell phloem cell 35.2 Meristems Generate New Cells for 1o and 2o Growth (cont.) Three years’ growth in a winter twig Apical bud Bud scale Axillary buds This year’s growth (one year old) Leaf scar Bud Node scar One-year-old branch formed Internode from axillary bud near shoot tip Last year’s growth (two years old) Leaf scar Stem Bud scar Growth of two years ago (three years old) Leaf scar 35.3 1o Growth Lengthens Roots and Shoots Primary Growth of ROOTS The root tip is covered by a root cap, which protects the apical meristem as the root pushes through soil. Cortex Vascular cylinder Growth occurs just behind the root tip, Epidermis in three zones of cells: Key 3. Zone of to labels 1. Zone of cell division Root hair differentiation via mitosis Dermal Ground Vascular 2. Zone of elongation via 1o meristems Primary meristems 70 µm (elongating, partly differentiated cells) 2. Zone of 3. Zone of differentiation elongation ex: root hairs Protoderm Mitotic Ground cells meristem Procambium 1. Zone of cell division (including Root apical meristem apical (undifferentiated cells) meristem) Root cap 35.3 1o Growth Lengthens Roots and Shoots (cont.) Primary Growth of ROOTS (cont.) Primary growth of roots produces the epidermis, ground tissue, and vascular tissue. Eudicots: the xylem is starlike in appearance with phloem between the “arms.” Epidermis Endodermis Cortex Pericycle Endodermis Xylem Vascular cylinder Pericycle Phloem Xylem Ground Phloem 70 μm Vascular 100 μm Eudicot root with xylem Dermal and phloem in the center Ground Vascular 35.3 1o Growth Lengthens Roots and Shoots (cont.) Primary Growth of ROOTS (cont.) Monocots: a core of parenchyma cells is surrounded by rings of xylem then phloem. Epidermis Cortex Endodermis Vascular cylinder Pericycle Core of parenchyma cells Xylem Phloem 100 μm Dermal Monocot root with parenchyma in Ground the center Vascular 35.3 1o Growth Lengthens Roots and Shoots (cont.) Primary Growth of SHOOTS At the shoot tip, leaves develop from leaf primordia along the sides of the apical meristem. Axillary buds develop from meristematic cells left at the bases of leaf primordia. The closer an axillary bud is to the active apical bud, the more inhibited it is. This is known as __________________. Leaf primordia Axillary buds may grow if the shoot tip is removed or shaded. Young leaf Shoot apical meristem Protoderm Procambium Ground meristem Axillary bud meristems 0.25 mm 35.3 1o Growth Lengthens Roots and Shoots (cont.) Primary Growth of SHOOTS (cont.) Lateral shoots develop from axillary buds on the stem’s surface. Eudicots: the vascular tissue consists of vascular bundles arranged in a ring. Monocots: the vascular bundles are scattered throughout the ground tissue. Phloem Sclerenchyma Xylem Ground tissue Ground (fiber cells) connecting tissue pith to cortex Pith Epidermis Epidermis Cortex Vascular Vascular bundles bundle 1 mm 1 mm Dermal Eudicot stem with vascular Monocot stem with scattered Ground bundles forming a ring Vascular vascular bundles 35.3 1o Growth Lengthens Roots and Shoots (cont.) Primary Growth of SHOOTS (cont.) Leaves Stomata - pores that allow gas exchange between the air and the photosynthetic cells - a major means by which water is lost by evaporation Each stoma is flanked by two ____________, which regulate its opening and closing. Mesophyll - the ground tissue in a leaf - sandwiched between the upper and lower epidermis The mesophyll of eudicots has two layers: - ________________ mesophyll in the upper part of the leaf - ________________ mesophyll in the lower part of the leaf; the loose arrangement allows for gas exchange The vascular tissue of each leaf is continuous with the vascular tissue of the stem. Veins are the leaf’s vascular bundles and function as the leaf’s skeleton. Each vein in a leaf is enclosed by a protective bundle sheath. 35.3 1o Growth Lengthens Roots and Shoots (cont.) Primary Growth of SHOOTS (cont.) Leaves (cont.) Guard cells Stomatal pore 50 μm Epidermal cell Cuticle Sclerenchyma fibers Stoma Surface view of a spiderwort leaf Upper epidermis Palisade mesophyll Spongy mesophyll 100 μm Lower epidermis Bundle- Cuticle sheath Vein cell Xylem Vein Air spaces Guard cells Guard Dermal Phloem cells Cross section of a lilac leaf Ground Cutaway drawing of leaf tissues Vascular 35.4 2o Growth Increases the Diameter of Stems and Roots The Vascular Cambium and Secondary Vascular Tissue The vascular cambium, a cylinder of meristematic cells one cell layer thick, is wholly responsible for the production of secondary vascular tissue. In cross section, the vascular cambium appears as a ring of meristematic cells. Division of these cells increases the vascular cambium’s circumference and adds secondary xylem to the inside and secondary phloem to the outside. Vascular cambium Growth X X C P P Vascular cambium Secondary Secondary X X C P phloem xylem X C P X C C After one year After two years of growth of growth 35.5 Growth, Morphogenesis, and Cell Differentiation Cell Expansion Plant cells grow rapidly and “cheaply” by intake and storage of water in vacuoles. Plant cells expand primarily along the plant’s main axis (ie, vertically). Cellulose microfibrils in the cell wall restrict the direction of cell elongation. Cellulose microfibrils Expansion Nucleus Vacuoles Microfibrils Cross-links 5 µm 35.5 Growth, Morphogenesis, and Cell Differentiation (cont.) Genetic Control of Flowering (cont.) Stigma Flower formation involves a phase change Stamen Anther Single carpel from vegetative growth to reproductive Style Filament Ovary growth, which is due to a combination of environmental cues and internal signals. In a developing flower, the order of each primordium’s emergence determines its fate: sepal → petal → stamen → carpel Petal Sepal Ovule Receptacle Organ identity genes (A, B, and C) regulate the development of the floral pattern. A mutation in a plant organ identity gene can cause abnormal floral development. The ABC hypothesis of flower formation identifies how floral organ identity genes direct the formation of the four types of floral organs. An understanding of mutants of the organ identity genes depicts how this model accounts for floral phenotypes. 35.5 Growth, Morphogenesis, and Cell Differentiation (cont.) Genetic Control of Flowering (cont.) Note: A inhibits C, and C inhibits A. Also, if either A or C is missing, the Sepals A schematic diagram of the other gene takes its place (see Petals ABC hypothesis Mutant lacking A below). Stamens A Carpels B C C gene activity Carpel B+C gene Petal activity A+B gene activity Stamen A gene activity Sepal Active BB BB BB BB AA AA genes: A A C CC C A A C C C C CC C C A A C CC C A A AB BA A B BA Whorls: Stamen Carpel Petal Sepal Wild type Mutant lacking A Mutant lacking B Mutant lacking C Side view of flowers with organ identity mutations