Chapter 35 Plant Structure, Growth and Development

Plants Are very plastic in their body forms. They can’t move, so they adapt the growth and structure of their bodies instead.

Case in Point

Chapter focus Plant structure and growth Warning – many terms or vocabulary words Warning – many diagrams Focus – structure, function, located next to ….

Question ? What heading can be given to the following groups of words?

--------- Lettuce Peas Beans ---------- Rhubarb Apples Oranges

Question ? What is a vegetable? What is a fruit?

Vegetables Lettuce Rhubarb Fruits Peas Beans Apples Oranges

Point Plants have tissues and organs too, just like animals. Asexual organs (vegetables) Sexual organs (fruits)

Asexual Organs 1. Stem 2. Leaf 3. Root

Stem The main body of the portion above ground of a tree, shrub or herb. The ascending plant axis. Have buds.

Stem Functions Support of other plant organs. Ps. Storage (water and food).

Modified Stems 1. Rhizomes 2. Stolons 3. Tubers 4. Tendrils

Rhizome An elongated underground horizontal stem. Ex: Iris, many grasses

Stolon An elongated above-ground horizontal stem. Ex: Strawberries Airplane Plant

Tuber A much-enlarged, short, fleshy underground stem tip. Ex: Dahlia, Potato

Leaf Lateral outgrowths of the stem axis. Primary photosynthetic organs. Function: Photosynthesis Storage

Leaf Modifications 1. Tendrils: for support 2. Bulbs: for food storage Ex: Peas 2. Bulbs: for food storage Ex: Onion 3. Insect Catching Ex: Carnivorous Plants 4. Flowers: thought to be modified leaves.

Other Modifications of Leaves Tendrils Spines Succulent Leaves Bracts

Root The descending axis of a plant, normally below ground. Functions: Anchorage. Absorption of water and minerals. Storage.

Root Types Taproot - one main root. Ex: carrot Fibrous Roots - many small roots of equal size. Ex: grass roots

Other Root Types

Sexual Organs 1. Flowers 2. Fruits 3. Seeds

Flowers Modified leaves grouped together on a stem. Sexual reproductive organs. Function: Sexual Reproduction

Fruit A mature ovary, sometimes including other floral parts. Function: Seed dispersal Seed protection

Fruits

Seed Mature ovule containing the embryo and nutrient tissues. Function: Dispersal unit in sexual reproduction.

Plant Cell Types Differentiated by the type and thickness of the cell wall. 1. Parenchyma (soft tissue) 2. Collenchyma (glue tissue) 3. Sclerenchyma (hard tissue)

Parenchyma Cells Primary wall only. Thin cell wall. Alive when mature, “typical" plant cell.

Functions Ps Storage "Filler" cells Cell division (mitosis)

Collenchyma Primary wall only. Wall is thickened, especially in the corners. Alive when mature.

Function Support of non-woody plant parts. Ex: veins, stems.

Sclerenchyma Secondary wall present. Wall strengthened with lignin. Dead when mature.

Sclerenchyma Types 1. Fibers 2. Sclereids 3. Tracheids 4. Vessel Elements

Fibers Elongated thin cells used for support. Ex: Hemp fibers

Sclereids Used for hard dense areas and support. Ex: Nut shells, seed coats

Tracheids Spindle - shaped cells with pits in the cell walls. Used for water transportation. Vessel Fiber

Vessel Elements Wide stocky cells with pits in the side walls; lack end walls. Used for water transportation.

Plant Tissues Can be named by several methods: Ex: Cell Location Cell Origin Cell Function

Point The same cell can have several tissue names depending on the criteria for naming.

Main Tissue Systems 1. Dermal 2. Vascular 3. Ground

Dermal Tissue Epidermis or "skin" of the plant. Often has a cuticle, a waxy coating to prevent water loss. Functions: Prevent water loss. Water absorption (root hairs).

Vascular Tissue Made of Xylem and Phloem. Functions: Transport and support Xylem - Water Phloem - Food

Xylem

Phloem

Phloem Sieve Cell – alive when functioning, but lacks a nucleus. Companion Cell – alive, controls itself and the sieve cell.

Ground Tissue Tissue between the dermal and the vascular tissues. Functions: "Filler" tissue Ps storage support

Question ? How does plant growth and animal growth differ ?

Animals Whole organism increases in size. Determinant Growth: grow to a certain size, then stop.

Plants Growth in specialized areas only. Indeterminant Growth: grow as long as they live because the specialized areas remain embryonic.

Plant Meristems Perpetual embryonic regions. Zones for cell division.

Meristem Types 1. Apical growth in length. Primary growth. 2. Lateral/Cambiums growth in diameter. Secondary growth.

Comment Some tissues like Xylem may be Primary or Secondary depending on which meristem produced the cell. Ex: Primary xylem Secondary xylem

Apical Meristem Types 1. RAM – Root Apical Meristem: primary growth of roots. 2. SAM – Shoot Apical Meristem: primary growth of shoots.

RAM Located at the tip of each growing root. Protected from the soil by the Root Cap. RAM

Root Cap Protects RAM. Secrets a polysaccharide lubricant for root growth.

Primary Root Zones 1. Cell Division - cells small and embryonic. 2. Cell Elongation - cells elongate and start to mature. 3. Cell Differentiation - cells mature into final cell types.

Root Hairs Extensions of the epidermis to increase surface area for water absorption. Not a true tissue. Comment - root hairs are very delicate and must be continually replaced.

Root Hairs

RAM - Primary Tissues 1. Protoderm 2. Procambium 3. Ground Meristem

Protoderm Will mature into the epidermis and root hairs.

Procambium Stele Matures into the vascular tissues of the stele: Xylem Phloem Pericycle – site of branch roots

Ground Meristem Matures into the ground tissues: Cortex – storage tissue Endodermis – second skin around the stele that controls the movement of materials into the stele.

Epidermis Cortex Stele

Endodermis Pericycle Xylem Phloem

Branch Roots Originate from the pericycle. Burst their way to the outside.

SAM Produces 1. Protoderm 2. Procambium 3. Ground Meristem Comment – these tissues mature into the same things as seen in RAM.

SAM Differences No "root" cap. Produces leaves as stem out-growths at the nodes. Has buds.

Buds Apical Meristems protected by modified leaves or bud scales. Axillary Buds

Branch Stems Develop from axillary meristems or axillary buds. "External" development.

Leaves Stem outgrowths for Ps. Leaf Morphology: 1. Gross 2. Fine

Gross Morphology Blade - the flattened portion of a leaf. Petiole - stalk of a leaf.

Axillary Buds Blade Petiole

Blade/Leaf Types Simple - 1 blade. Compound - Several blades.

Nodes and Internodes Node - stem area where a leaf and bud are attached. Internode - stem area between nodes.

Nodes } Internode

Fine Morphology The tissues within a leaf. 1. Upper Epidermis 2. Mesophyll 3. Lower Epidermis 4. Veins

Upper Epidermis Cuticle present. Usually 1 cell layer thick. Cells w/o chloroplasts . Function: protects the mesophyll.

Mesophyll 1. Palisade upright cells. 2. Spongy loosely organized cells with air spaces. Function: major sites for Ps. Epidermis Epidermis

Lower Epidermis Cuticle present. Usually 1 cell layer. Cells w/o chloroplasts. Stomata present for gas exchange.

Stomata (mouth) Regulated by Guard Cells which have chloroplasts.

Vein Structure Xylem: dorsal Phloem: ventral Often surrounded by bundle sheath cells for support.

Xylem Phloem Bundle Sheath Cells Collenchyma

Stem Vascular Tissue Eudicots – vascular bundles join together to make a ring. Often have secondary growth. Monocots – vascular bundles are scattered. No true secondary growth.

Secondary Growth Growth in diameter. Growth from lateral meristems or cambiums.

Cambium Types 1. Vascular – produces xylem and phloem. 2. Cork – produces “cork”.

Vascular Cambium Location: between primary xylem and phloem. Produces: secondary xylem and phloem.

Fibers Phloem Vascular Cambium Xylem Fibers

Vascular Cambium: Cell Maturation Internal  xylem External  phloem The VC pushes the xylem and phloem apart from each other.

Result Newest xylem is next to the cambium. Oldest xylem is in the center of stem.

Result Newest phloem is next to cambium. Oldest phloem is under the epidermis.

Result Xylem accumulates over time. Phloem is destroyed by the outward growth and must be replaced yearly.

Cork Cambium Location: Cortex (external to the VC). Produces: Cork Comment – commercial cork is harvested from a Cork Oak.

Cork Cells Produced "outwardly" only. Covered with suberin and are dead when mature. Function – insulation and protection.

Epidermis Cork Cambium Fibers Cortex Phloem Vascular Cambium Xylem

Bark All tissues external to the VC. Includes: Phloem (1 degree and 2 degree) Cork Cortex Epidermis Fiber cells

Wood Xylem tissue of a dicot stem. Comment – monocots don’t have VC and technically don’t produce true “wood”.

Xylem Growth Springwood - Large cells Rapid growth Summerwood - Small cells Slow growth

Annual Rings Formed by the growth difference between springwood and summerwood. Usually one produced per year.

Comment Ring size varies by climate and growing conditions. Rings can be used to date wooden structures.

Summer Wood Spring Wood One Year’s Growth

Angiosperms Divided into two main types: 1. Eudicotyledons or Eudicots 2. Monocotyledons or Monocots Cotyledons = seed leaves

Monocots vs. Eudicots 1. Seeds and embryos 2. Leaves 3. Stems 4. Roots 5. Pollen 6. Flowers

Seeds and Embryos Eudicots - no endosperm. - 2 cotyledons. Monocots - endosperm - 1 cotyledon

Leaves Eudicots – netted veins. Monocots - parallel veins.

Stems Eudicots - ring pattern - vascular cambium Monocots - scattered pattern - no vascular cambium

Roots Eudicots - taproot. - xylem centermost tissue. Monocots - fibrous roots. - pith centermost tissue.

Pollen Eudicots – 3 openings Monocots – 1 opening

Flowers Eudicots – parts in 4's or 5's. Monocots – parts in 3's.

How do plants make their bodies different? By changes in growth, morphogenesis and differentiation.

Growth Meristems give information to new cells on how they should develop. Plane and symmetry of cell division Orientation of cell elongation

Plane of Cell Division

Cell Expansion

Mophogenesis How cells organize into tissues and organs. Determined by: Positional information Homeotic genes

Cell Differentiation Regulation of transcription and translation to make specific proteins. Often “keyed” by positional information.

Cell Differentiation

Example - Flowering Flowering is a phase change from indeterminate growth to determinate growth. Triggered by environmental or internal signals. ABC model of organ identity genes.

ABC Model The 4 flower parts are controlled by interaction of genes A, B and C in 4 layers of cells.

Model Sepals – Gene A only in the outermost or 4th layer Petals – Genes A and B in the 3rd layer. Stamens – Genes B and C in the 2nd layer. Carpels – Gene C only in the centermost layer.

Model

Mutants – ABC model

African Violet Mutants ABC active in 2nd layer A only mutant

Summary Know the main organs of plants and their functions. Know the main cell types or tissues in plants and their functions.

Summary Know the structural organization of stems, roots, and leaves. Know the differences between eudicots and monocots.

Summary Know about meristems and how plants grow. Know about growth, morphogenesis and differentiation in plant bodies.