Plant Structure, Growth, and Development

Introduction

The Angiosperm Body

Plant Growth

Introduction to Modern Plant Biology

• Molecular biology is identifying crucial genes (flower development); giving a better understanding of processes such as water flow, disease resistance, shoot and root control

• Structure and function is a key theme

The Angiosperm Body

• Problems to be solved: gravity, light, water transport, reproduction, and desiccation

• Root and shoot systems

The Root System

• Functions: anchor, store food, absorb and conduct water and minerals

• two types: taproot and fibrous root systems

• role of root hairs

• mycorrhizae

• adventitious roots: form above ground from stem or leaf

The Shoot System

• Stems, leaves and flowers

• growth occurs at apex

• apical dominance has evolutionary importance

• underground stems:bulbs and rhizomes(potatoes)-store food

• leaves: main photosynthetic organ

Types of Plant Cells

• Function determined by protoplast and cell wall adaptations

• five types of plant cells:

1. Parenchyma-synthesis and storage

2. Collenchyma-support in young plants

3. Sclernchyma-thick secondary walls, lack

protoplast in mature cells?, supportive

4. Xylem-water conduction, two types:

tracheids and vessel elements

5. Phloem-food conduction

Tissue Systems

• Three tissue systems: dermal, vascular and ground tissues

• Dermal-single outside layer

• Vascular-xylem and phloem, transport and support

• Ground-between dermal and vascular, storage, synthesis, and support

Plant Growth

• Meristems generate cells; two types: apical and lateral

• genetically determined life spans (most)

• annuals and perennials

• plants exhibit indeterminate growth

• two types of growth: primary and secondary

Root Growth

• Primary growth divided into three zones: 1. Cell division: apical meristem, this

differentiates into: protoderm, procambium, and ground meristem (primary tissues)2. Cell elongation: elongate at least 10X, pushes tip through the soil 3. Maturation: cells complete their differentiation

Primary Tissues in the Root

• Protoderm: outermost layer of primary meristem, give rise to epidermis, many with root hairs

• Procambium: forms stele (central cylinder) containing xylem and phloem,

• Ground meristem: cortex between stele and epidermis, parechyma cells, stores food, endodermis single cell layer boundary between cortex and stele, pericycle inside endodermis

Primary Growth of Stems

• Apical meristem forms primary meristems (protoderm, ground meristem, and procambium)

• Procambium forms vascular tissue in bundles

• Ground meristem forms pith and cortex

• Protoderm forms epidermal tissues

Leaf Growth

• Ground tissues form the mesophyll

• procambium forms the veins

• Protoderm forms the upper and lower epidermis, guard cells waxy cuticle

Secondary Growth

• Produced by growth in diameter

• results from vascular and cork cambium

• vascular produces xylem and phloem

• cork cambium produces covering of roots and stems that replace epidermis

• occurs in all gymnosperms and most angiosperms, rare in monocots

Stages of Differentiation

• Apical meristem• differentiates into: protoderm, ground meristem,

and procambium• protoderm differentiations into epidermal

structures• procambium differentiates into the vascular tissues• ground meristem produces tissues that fill in

between the epidermis and vascular tissues

Secondary Growth in Stems

• Vascular cambium produces secondary vascular tissues: xylem--forms wood; phloem--contributes to the formation of bark and sloughs off

• cork cambium produces the periderm (protective coat of plant, combination of cork cambium, layers of cork, and phelloderm,)

• bark-all tissues external to the vascular cambium

Secondary Growth in Roots

• Vascular cambium produces secondary xylem to the inside and secondary phloem to the outside

• cortex and epidermis split and are shed as the stele increases in diameter

• very similar to stems, produces annual rings