March 28, 2005

Plant Tissues

Chapter 26

Jin Hoe Huh

Angiosperms – flowering plants • The angiosperms are seed-bearing vascular plants • In terms of distribution and diversity, they are the most successful plants on Earth • The structure and function of this plant group help explain its success

Flowering Plant Life Cycle Double fertilization Diploid Haploid Meiosis pollination microspores Meiosis Mitosis without cytoplasmic division Two sperms enter ovule Female gametophyte

Plant Life Histories •

Annuals

complete life cycle in one growing season •

Biennials

live for two seasons; flowers form in second season •

Perennials

grow and produce seeds year after year

Shoot and Root Systems

Shoot system

- produces sugars by photosynthesis - carries out reproduction

Root system

- anchors the plant - penetrates the soil and absorbs water and minerals - stores food Shoot System Root System

Shoot and root systems are interdependent water & minerals

SHOOT SYSTEM ROOT SYSTEM

sugar

Plant Tissue Systems • Ground tissue system • Vascular tissue system • Dermal tissue system

EPIDERMIS VASCULAR TISSUES GROUND TISSUES SHOOT SYSTEM ROOT SYSTEM

Meristems – Where Tissues Originate • Regions where cell divisions produce plant growth • Apical meristems – Lengthen stems and roots – Responsible for

primary

• Lateral meristems growth – Increase width of stems – Responsible for

secondary

growth

Apical Meristems Lengthen shoots and roots: SAM and RAM Cells that form at apical meristems: protoderm  epidermis ground meristem tissues  ground procambium  vascular tissues primary

activity at meristems new cells elongate and start to differentiate into primary tissues

Lateral Meristems Increases girth of older roots and stems Cylindrical arrays of cells

vascular cambium



secondary vascular tissues periderm



cork cambium

thickening

Simple Tissues Made up of only one type of cell Parenchyma Collenchyma Sclerenchyma

Morphology of three simple tissue types parenchyma collenchyma sclerenchyma

Parenchyma: A Simple Tissue • Comprises most of a plant’s soft primary growth • Cells are pliable, thin walled, many sided • Cells remain alive at maturity and retain capacity to divide • Mesophyll is a type of parenchyma that contains chloroplasts

Collenchyma: A Simple Tissue • Specialized for support for primary tissues • Cells are elongated, with walls (especially corners) thickened with pectin • Makes stems strong but pliable • Cells are alive at maturity

Sclerenchyma: A Simple Tissue • Supports mature plant parts • Protects many seeds • Cells have thick, lignified walls and are dead at maturity • Two types: – Fibers: Long, tapered cells – Sclereids: Stubbier cells

Complex Tissues Composed of a mix of cell types Xylem Phloem Epidermis

Xylem • Conducts water and dissolved minerals • Conducting cells are dead and hollow at maturity tracheids vessel member

Phloem: A Complex Vascular Tissue

sieve plate

• Transports sugars • Main conducting cells are sieve tube members • Companion cells assist in the loading of sugars

sieve-tube member companion cell

Epidermis: A Complex Plant Tissue - Covers and protects plant surfaces - Secretes a waxy, waterproof cuticle - In plants with secondary growth, periderm replaces epidermis

Monocots and Dicots – same tissues, different features 1 cotyledon 3 floral parts 2 cotyledons 4 or 5 floral parts Vascular bundles in ring Parallel veins 1 pore Netlike veins 3 pores Vascular bundles dispersed

shoot apical meristem

Shoot Development

protoderm procambrium ground meristem cortex procambrium pith primary xylem primary phloem

Bud = undeveloped shoot of meristematic tissue Leaves Internode Axillary bud at node Longitudinal section of terminal bud

Roots also have meristems

Internal Structure of a Dicot Stem - Outermost layer is epidermis - Cortex lies beneath epidermis - Ring of vascular bundles separates the cortex from the pith - The pith lies in the center of the stem

Internal Structure of a Monocot Stem • The vascular bundles are distributed throughout the ground tissue • No division of ground tissue into cortex and pith

Dicots Ground tissue system Monocots Dermal tissue system Vascular tissue system Dicots and Monocots have different stem and root anatomies

Leaf Gross Structure

DICOT petiole axillary bud MONOCOT blade node sheath blade node

Adapted for Photosynthesis • Leaves are usually thin – High surface area-to-volume ratio – Promotes diffusion of carbon dioxide in, oxygen out • Leaves are arranged to capture sunlight – Are held perpendicular to rays of sun – Arrange so they don’t shade one another

xylem phloem

Leaf Structure

cuticle UPPER EPIDERMIS PALISADE MESOPHYLL SPONGY MESOPHYLL LOWER EPIDERMIS O 2 CO 2 one stoma

Mesophyll: Photosynthetic Tissue • A type of parenchyma tissue • Cells have chloroplasts • Two layers in dicots – Palisade mesophyll – Spongy mesophyll

Collenchyma Parenchyma

Leaf Veins: Vascular Bundles • Xylem and phloem – often strengthened with fibers • In dicots, veins are netlike • In monocots, they are parallel

Root Systems

Root Structure • Root cap covers tip • Apical meristem produces the cap • Cell divisions at the apical meristem cause the root to lengthen • Farther up, cells differentiate and mature

root apical meristem root cap

Internal Structure of a Root • Outermost layer is epidermis • Root cortex is beneath the epidermis • Endodermis, then pericycle surround the vascular cylinder • In some plants, there is a central pith

endodermis pericycle phloem xylem epidermis cortex root hair

Root Hairs and Lateral Roots • Both increase the surface area of a root system • Root hairs are tiny extensions of epidermal cells • Lateral roots arise from the pericycle and must push through the cortex and epidermis to reach the soil

new lateral root

Secondary Growth • Occurs in perennials • A ring of vascular cambium produces secondary xylem and phloem • Wood is the accumulation of these secondary tissues, especially xylem

Secondary Growth

Woody Stem

periderm (consists of cork, cork cambium, and secondary cortex) secondary phloem HEARTWOOD SAPWOOD BARK vascular cambium

Annual Rings • Concentric rings of secondary xylem • Alternating bands of early and late wood • Early wood – Xylem cells with large diameter, thin walls • Late wood – Xylem cells with smaller diameter, thicker walls

Types of Wood • Hardwood (oak, hickory) – Dicot wood – Xylem composed of vessels, tracheids, and fibers • Softwood (pine, redwood) – Gymnosperm wood – Xylem composed mostly of tracheids – Grows more quickly