Plant Reproduction and Development 2 Lecture Notes PDF

PLANT REPRODUCTION AND DEVELOPMENT 2 Concepts 35.1-35.5 Campbell. Biology. 3rd ed Outline • 1. Plant Organs, Tissues, Cells • 2. Meristems and Growth • 3. Primary Growth and Apical Meristems • 4. Secondary Growth and Lateral Meristems 1. Plant Organs, Tissues, Cells • Tissues – groups of cells p...

PLANT REPRODUCTION AND DEVELOPMENT 2 Concepts 35.1-35.5 Campbell. Biology. 3rd ed Outline • 1. Plant Organs, Tissues, Cells • 2. Meristems and Growth • 3. Primary Growth and Apical Meristems • 4. Secondary Growth and Lateral Meristems 1. Plant Organs, Tissues, Cells • Tissues – groups of cells performing similar functions • Organs – groups of tissues that perform specialized functions • Plants organs are arranged into systems • Shoot system – leaves, stems, flowers (fruits) • Root system – taproot, lateral root • The two systems are connected by vascular tissues • Shoot system = photosynthate • Root system = water and minerals Roots • Anchors plant into soil and absorbs water and minerals • Primary root = derived from the radicle • Lateral roots = branch from primary root and increase root surface area and contact with soil • Taproot = Radicle may develop into thick taproot with thinner branch roots. • Common root structure in dicotyledonous plants (dicots) • Fibrous root system = Adventitious roots may arise that develop into a fibrous root system. • Adventitious roots do not develop from another root, but instead from a stem or leaf. • Fibrous roots - Large number of fine roots of similar diameter • Monocotyledonous plants (monocots) and some dicots • Root hairs- thin extensions of root epidermal cells that emerge from root and increase absorptive surface area Root hairs Specialized Roots • Prop roots = support tall, top heavy trees • Storage roots = roots that store food and water • Green roots = aerial roots that perform photosynthesis • Pneumatophores = modified for respiration. Air roots such as those found on mangroves in swamps, which rise above the water line and allow roots to obtain oxygen • Contractile roots = pull plants deeper into the soil such as lily bulbs or dandelions • Buttress roots = stability in shallow soils such as Ficus in tropical soils Buttress roots left Pneumatophores below Prop root Green roots Storage root Stems Cells produced by meristems in the stem become shoot system with branches and leaves. • Woody twig consists of an axis with attached leaves. • Node - Area of stem where leaves are attached • Internode - Stem region between nodes • Leaf has a flattened blade and is usually attached to the twig by petiole. Specialized Stems Rhizomes - Horizontal stems that grow below-ground and have long to short internodes ❖ • Irises, some grasses, ferns, ginger ❖ Runners - Horizontal stems that grow above ground and have long internodes. • ❖ Strawberry, wood sorrel (Oxalis), dog grass (Cynodon) Stolons - Produced beneath the surface of the ground and tend to grow in different directions. • Potato Specialized Stems ❖ Tubers - Swollen, fleshy, underground stem • Store food • Potatoes - Eyes of potato are nodes ❖ Bulbs - Large buds surrounded by numerous fleshy leaves, with a small stem at lower end • Store food • Onions, lilies, hyacinths, tulips Specialized Stems ❖ Corms - Resemble bulbs, but composed almost entirely of stem tissue, with papery leaves • Store food • Crocus and gladiolus, taro ❖ Cladophylls Flattened, leaf-life stems • Greenbriars, some orchids, prickly pear cactus Prickly pear cactus LEAVES ❖ Green leaves capture light energy by means of photosynthesis. • Photosynthesis - Trapping and storing of energy in sugar molecules that are constructed from water and carbon dioxide ❖ Stomata - Tiny pores on lower surfaces of leaves • Allow carbon dioxide to enter and oxygen to diffuse out • Water vapor also escapes via stomata. – Guard Cells control water loss by opening or closing pore of stomatal apparatus. Leves ❖ All leaves originate as primordia in buds. ❖ At maturity, most leaves have: • Stalk = petiole – Leaves sessile if lacking petiole • Flattened blade = lamina • Network of veins = vascular bundles • Stipules at base of petiole http://www.icoachmath.com/biology/definition-of-l eaf-lamina.html Simple & Compound Leaves Simple & Compound Leaves http://www.robinsonlibrary.com/science/botany/anatomy/leafparts.htm Leaf Arrangements and Types ❖ Leaves are attached to stems at nodes, with stem regions between known as internodes. • Phyllotaxy - Arrangement of leaves on stem – Alternate - One leaf per node – Opposite - Two leaves per node – Whorled- Three of more leaves at a node Alternate Opposite Whorled Leaf Arrangements and Types ❖ Venation - Arrangement of veins in a leaf or leaflet blade • Pinnately veined leaves - Main midvein included within enlarged midrib. – Secondary veins branch from midvein. • Palmately veined leaves - Several primary veins fan out from base of blade. Pinnate venation Palmate venation Leaf Arrangements and Types ❖ Monocots - Primary veins parallel = Parallel venation ❖ Eudicots - Primary veins divergent in various ways = netted or reticulate venation. ❖ Dichotomous venation - Veins fork evenly and progressively from base of blade. Parallel venation Reticulate venation Dichotomous venation (e.g.Ginkgo trees. ) Specialized Leaves ❖ Shade Leaves • Receive less total light than sun leaves • Compared to sun leaves, shade leaves: – – – – Tend to be larger Tend to be thinner Have fewer well-defined mesophyll layers and fewer chloroplasts Have fewer hairs Sun leaf Shade leaf Specialized Leaves ❖ Tendrils • Modified leaves that curl around more rigid objects, helping the plant to climb or to support weak stems – ❖ Garden peas Tendrils Spines • Modified leaves that reduce leaf surface and water loss, and protect from herbivory. – Cacti (prickly pear) o Leaf tissue replaced with sclerenchyma. o Photosynthesis occurs in stems. Spines of barbery (Berberis) (Berberidaceae) Specialized Leaves ❖ Storage leaves • Succulent leaves are modified for water storage. – Have parenchyma cells with large vacuoles – Many desert plants • Fleshy leaves store carbohydrates. – Onions, lily Specialized Leaves ❖ Reproductive Leaves • Walking fern - New plants at leaf tips • Air plant - Tiny plantlets along leaf margins Air Plant Specialized Leaves ❖ Floral Leaves (bracts) • At bases of flowers or flower stalks • Poinsettia - Flowers do not have petals, instead brightly colored bracts surround flowers. Poinsettia Clary’s sage Specialized Leaves ❖ Insect-Trapping Leaves • Grow in swampy areas and bogs – Nitrogen and other elements are deficient in soil. o Specialized leaves trap and digest insects. • Pitcher Plants – Insects trapped and digested inside cone-shaped leaves. Pitcher plant Tissues • Plants have 3 major tissue types found in all organs • Dermal, vascular and ground • Each tissue type forms a tissue system that connects all plant parts • Dermal Tissue • outer protective covering • Epidermis = in non woody plants = layer of tightly packed cells surrounding the plant body • Cuticle = waxy coating on the epidermal surface of leaves and stems • Periderm = in woody plants = replaces the epidermis in older regions of stems and roots • phellem, phellogen, and phelloderm cells • In shoots, specialized epidermal cells known as guard cells regulate gas exchange and transpiration through the stomata • Trichomes = specialized epidermal cells in shoots that reduce water loss and reflect light (found in desert plants). Some trichomes defend against pathogens and secrete toxic substances • Vascular Tissue • Long distance transports of sugars, water, minerals and other organic substances (eg hormones) • Links root and shoot systems • Xylem = water and mineral conduction upward from root to shoot • Phloem = sugar conduction down from shoot to root • Ground Tissue • Ground tissue is supportive tissue • Internal ground tissue (interior of the vascular tissue) is called pith • Ground tissue that is external to vascular tissue is called cortex Figure 35.8 The three tissue systems Cells • Parenchyma • Thin, flexible cell wall. Lack secondary cell wall • Alive at maturity • Function in storage and photosynthesis (potato tuber parenchyma cells with starch in plastids) • Collenchyma • Unevenly thickened cell wall • Alive at maturity • Provide flexible support without restraining growth (strings of celery) • Sclerenchyma • • • • Thick, tough, secondary walls, normally impregnated with lignin Dead at maturity Function in support Two types: sclereid and fibre cells • Sclereid – stone cell of peach pit; very thick lignified walls; boxier than fibre cells • Fibre – hemp fibre for rope; flax fibre for linen; grouped into strands; long and tapered Figure 35.10 Exploring examples of differentiated cell types Xylem - Chief conducting tissue for water and minerals that are absorbed by the roots • Composed of parenchyma cells, fibers, vessels, tracheids and ray cells (ray cells = xylem cells which are extended radially) • Vessels – cylindrical tubes whose cells have lost their cytoplasm • Made of vessel elements (single cell) which are: • Open at each end, but may have perforation plate • Dead at maturity • Thick secondary cell walls • Many have spiral thickenings (secondary wall pattern) on cell walls • Tracheids - xylem cell, tapered at the ends with pairs of pits (areas without secondary cell) that allow water to pass from cell to cell • Dead at maturity • Thick secondary cell walls • May have spiral thickenings on cell walls Phloem - Conducts dissolved food materials produced by photosynthesis throughout plant • Composed of sieve tube members, companion cells, fibers, parenchyma cells and ray cells • Sieve Tube Members: • Lack secondary cell walls and nuclei • Lay end to end to form sieve tubes • Walls have sieve plates with small pores • Callose forms callus plug - Prevents leaking of sieve tube contents when cell injured • Companion cells - Aid in conduction of food • Rays - Function in lateral conduction and food storage • Composed of long-lived parenchyma cells Figure 35.10 Exploring examples of differentiated cell types •2. Meristems and Growth • Unlike animals, plants continue to grow throughout their lives • Indeterminate growth vs determinate growth • Occurs due to meristems = regions of permanent, active cell division • Three types of meristems • Apical = found at the tips of roots and shoots and axillary buds. Responsible for growth in length/primary growth • Lateral = meristems found inside roots and shoots and are responsible for growth in width • Vascular cambium – adds layers of vascular tissue called secondary xylem (wood) and secondary phloem • Cork cambium – replaces the epidermis with thicker, tougher periderm • Intercalary= meristems found in the vicinity of nodes (leaf attachment area) and add to stem length Meristematic Tissues Apical Meristems Meristematic Tissues Intercalary Meristems http://www2.puc.edu/F aculty/Gilbert_Muth/bo tglosi.htm •3. Primary Growth and Apical Meristems • In herbaceous plants there is only primary growth • Woody plants have both primary and secondary growth • Primary growth leads to lengthening of roots and shoots from cells derived from apical meristems, however, the primary growth of roots differ from that in shoots Primary Growth of Roots • 4 regions of roots: • 1. Root cap • 2. Region of cell division • 3. Region of cell elongation • 4. Region of maturation • Root Cap - Thimble-shaped mass of parenchyma cells covering each root tip • Protects tissues from damage as root grows • Secretes mucilage that acts as lubricant • Functions in gravitropism • Region of Cell Division - Composed of apical meristem in the center of root tip • Region of Elongation – root cells elongate • Cells become several times their original length. • Region of Maturation – cells complete differentiation and become distinct, specialized cell types • Root hairs form Root Structure Region of Maturation • Cortex - Parenchyma cells between epidermis and vascular cylinder • Mostly stores food Cross section of eudicot root Root Structure Region of Maturation • Endodermis - Inner boundary of cortex, consisting of a single-layered cylinder of compact cells • Cell walls with suberin bands (fatty substance) called Casparian strips on radial and tangential walls • Forces water and dissolved substances entering and leaving the central core to pass through endodermis • Regulates types of minerals absorbed – Eventually inner cell walls become thickened with suberin, (except for some endodermal cells, called passage cells). Root Structure Region of Maturation • Vascular cylinder - Core of tissues inside endodermis • Pericycle - Outer boundary of vascular cylinder – Continues to divide, even after mature – Forms lateral (branch) roots and part of the vascular cambium Root Structure Region of Maturation • Most of cells of vascular cylinder are primary xylem or primary phloem. • In eudicot or conifer roots - Solid core of xylem, with “arms” in cross section • Phloem in patches between xylem arms • In monocots, xylem surrounds pith. • Vascular cambium forms secondary phloem to the outside and secondary xylem to the inside. Vascular cylinder of dicot root Primary Growth of Shoots • Apical meristem at stem tip • Contributes to increase in stem length • Dormant before growing season begins • Protected by bud scales and by leaf primordia • Leaf primordia - Tiny embryonic leaves that develop into mature leaves • Branching, part of primary growth, arises from the activation of auxiliary buds • Auxiliary buds close to the apical bud are inhibited by production of auxin from the apical bud leading to apical dominance • Clipping the apical bud leads to "bushing" in a plant because the hormonal control is severed. Gardeners use this technique in pruning Stem Growth and Anatomy • Stem is covered by epidermis (one cell thick) with a waxy cuticle • also guard cells and trichomes • Ground tissue of stems is mostly parenchyma cells • Some collenchyma cells add support • Sclerenchyma cells are found in stems that are no longer elongating • Vascular tissue runs the length of the stem • Arranged in vascular bundles in a ring in most eudicots (dicots) with xylem adjacent to the pith and phloem adjacent to the cortex • Vascular bundles are scattered in monocots Leaf Growth and Anatomy • Leaf epidermis is covered by waxy cuticle • Stomata with guard cells and trichomes also present • Leaf ground tissue called the mesophyll is between upper and lower epidermis • Mesophyll contains mostly parenchyma cells specialized for photosynthesis • Parenchyma cells are loosely arranged with air spaces that allow CO2 and O2 to circulate. Many air spaces in vicinity of stomata • Veins make up the vascular tissue (bundles) of the leaf and connect to the vascular tissue of the stem • Transport sugars and, water, minerals (ie phloem and xylem) • Also reinforce the shape of the leaf and each vein is surrounded by bundle sheath of parenchyma cells Figure 35.18 Leaf anatomy •4. Secondary Growth and Lateral Meristems • Growth in thickness (width) is due to lateral meristems • Not typically found in monocots • Occurs in stems and roots of woody plants • Consists of tissues produced by vascular cambium and cork cambium (lateral meristems) • Vascular cambium add secondary xylem and phloem • Cork cambium produces tough, thick, waxy covered cells that protect the plant from water loss and invasion by pathogens • Process is similar in roots and shoots Figure 35.19 Primary and secondary growth of a woody stem The Vascular Cambium • Located in between primary xylem and primary phloem in woody stems • In a woody root, vascular cambium forms to the exterior of primary xylem and interior of primary phloem and pericycle • Vascular cambium is a ring of meristematic cells that increase the width of the stem or root as these cells divide • Add secondary xylem to the inside of cambium • Rings on a tree are rings of secondary xylem (used to indicate age) • Produce same cell types as primary xylem (tracheids, vessels, etc) • Cell walls of secondary xylem are heavily lignified, giving wood its hardness and strength • A thick ring indicates wet, warm year because more growth would occur • As a tree ages, the oldest rings of secondary xylem stop conducting water and minerals = heartwood. Closer to the center • Hollow core of the tree • Newest, outer layers of secondary xylem that are still conducting = sapwood https://climate.nasa.gov/news/2540/tree-rings-provide-snapshots-of-earths-past-climate/ Figure 35.22 Anatomy of a tree trunk The Cork Cambium • Epidermis replaced by tissues of the cork cambium during early secondary growth • Periderm is the protective coat that replaces the epidermis and is composed of cork and cork cambium • Cork cambium is a cylinder of meristematic cells that is found in the outer cortex of stems and the pericycle of roots • Cork cambium produces cork cells which contain in their cell walls a waxy, waterproof material called suberin • Periderm is protective coat usually impermeable to water and gases (unlike epidermis) • Cork functions as a barrier to protect stems and roots from water loss, pathogens • Bark = secondary phloem, periderm • Lenticels = raised areas along the periderm that allow for gas exchange https://open.lib.umn.edu/horticulture/chapter/7-1-meristem-morphology/ The End • Thank you • Question? • Have a great day!