UNIT III: PLANT FORM AND FUNCTION

•Plant structure and growth

•Plant nutrition

•Plant reproduction and development

Cardinal Flower Red Maple

http://www.csdl.tamu.edu/FLORA/hdwimages1/

Arabidopsis thaliana

Purves et al 2000

Evolutionary relationships among the Angiosperms. The monocots and eudicots are the largest monophyletic groups among the angiosperms. (The “other groups” remain to be placed accurately on the phylogenetic tree).

Purves et al 2000

Monocotylenous and Dicotyledonous Plants

•Monocots

• ~65,000 species

• Lilies, irises, orchids, cattails, all the grasses and grains…

•Monocot lineage, taxon, is monophyletic; evolved from dicot ancestor

•Dicots

•~175,000 species

• Most trees and shrubs

• Most annual plants – mints, sunflowers, peas, snapdragons

•Most dicots are in members of the Eudicot lineage – a monophyletic taxon

Palms

Grasses

Lilies

Examples of Monocot angiospermsPurves et al 2000

Examples of Dicots (more specifically, Eudicots)

Cactus

Flowering Dogwood

Rose

Purves et al 2000

EudicotsSeveral lineages related to magnolias Monocots

Oldest living angiosperm lineagesNon-Angiosperms

Angiosperms

Lineages in green are traditionally called dicots - the seeds of these lineages have two “seed leaves”.

“Dicots” don’t form a monophyletic group -- ie monocots are descended from a “dicot” lineage

“Eudicots” are a monophyletic group that includes much of the angiosperm diversity

Source: Freeman (2002)

Phylogenetic relationships among Angiosperm lineages

Phylogenetic relationships of the orders of flowering plants (AGP, 1998)

http://www.csdl.tamu.edu/FLORA/newgate/cronang.htm

•Monocots apparently diverged from dicots early in the history of the phylum

Sources: Raven & Johnson 1999, Purves 2000)

ANNUAL, BIENNIAL AND PERRENIAL PLANTS

Annual Plants Life cycle (vegetative growth and reproduction) occurs in the course of a single year; die after single year of growth.

Most are entirely herbaceous, ie, lack secondary growth, secondary tissue (wood); some (eg sunflowers) produce poorly developed secondary tissues. Many crop plants (incl. corn, wheat, soybeans) are annuals.

Biennial Plants Narrow definition; life cycle takes two years to complete. Generally, vegetative growth in the first year; flowering and senescence in the second year. Many “bienniels” flower in year 3 or later, but all flower only once before dying.

Much less common than annuals. Crop plants include carrots, cabbage. Wild plants include evening primrose, queen anne’s lace

Perennial Plants Life cycle extends for for multiple, often many years; flower repeatedly and live for many years. Most vascular plants are perennials.

Many are herbaceous plants (eg wildflowers of prairie, wetlands and woodlands) that usually lack secondary growth in stems; stems die back each year following food accumulation, often in substantial roots

Trees and shrubs have secondary growth and are perennial, they are either deciduous (shed leaves at particular time of year) or evergreen (leaves drop throughout year, plant never appears leafless)

Desert annuals (above) and a giant redwood (below)

The Angiosperm Body

•root and shoot systems; adaptations to terrestrial life

•structural adaptations of protoplasts and cell walls; specialized functions

•plant tissue systems; dermal, vascular and ground

Plant Growth

•meristems continuously generate cells for new organs

•Primary growth; apical meristems

•(Secondary growth: lateral meristems)

PLANT STRUCTURE AND GROWTH

BASIC ORGANIZATION OF PLANT BODY; ADAPTATION TO TERRESTRIAL LIFE

Root system; anchor; absorption & transport of water, ions, dissolved mineral nutrients; food storage

•Shoot system; stem is scaffold for photosynthetic leaves and reproductive structures; transport of sugars from photostynthetic to non-photosynthetic parts of plant

Roots Shoots

Solomon et al 1999 Campbell et al 1999Shoot

Root

Biological Organization in Plants

Cells Plant cells are eukaryotic, with some unique modifiations, including the cell wall. Cell types include Parenchyma, Collenchyma Schlerenchyma,

Tissues Tissues plant cells are organized into tissues; groups of cells that form a structural and functional unit. Simple plant tissues consist of single cell type. Complex plant tissues consist of two or more kinds of cells.

Tissue systems Groups of tissues that extend throughout plant body; Three main tissue sytems; ground, vascular, dermal

Organs Roots, stems. leaves, flower parts, and fruits are referred to as organs because each is composed of several different tissues. The tissue systems of different plant organs fornm an interconnected network througout the plant.

Shoot

Root

CELL SPECIALIZATION; STRUCTURAL ADAPTATION IN CELL WALLS AND CELL PROTOPLAST*

Purves et. al. 2000

In plant cell division, daughter cells secrete a “middle lamella” that will adhere the adjoining cells

Each the secretes a primary cell wall of cellulose and other polysaccharides, which grows with growing cell

Depending on cell specialization, after growth to final size, cell may lay down a secondary cell wall of polysaccarides and, depending on cell type, lignin (characteristic of wood) or suberin (characteristic of cork, bark)

Secondary cell walls typically function in structural support or waterproofing

*Protoplast: cell contents exclusive of cell wall

In addition to other features of Eukaryotic cells, plant cells have:

•cell wall

•chloroplasts

•central vacuole,

CELL SPECIALIZATION; STRUCTURAL ADAPTATION IN CELL WALLS AND CELL PROTOPLAST

Raven & Johnson 1999

Cell plate formation between two nuclei, during plant cytokinesis

Raven and Johnson 1999

PLANT CELLS ARE ORGANIZED INTO TISSUE SYSTEMSPlant organs have three tissue systems that are continuous throughout the plant body. The tissue systems derive from meristem tissue; localized regions of cell division

•Meristems; apical & lateral meristems give rise to all cells and tissues

•Ground tissue system; storage, secretion, photosynthesis; mostly parenchyma cells

•Vascular tissue system; conduct water & minerals (xylem), & carbohydrates, amino acids, hormones… (phloem)

•Dermal tissue system; outer protective covering

*We will discuss specialized reproductive tissue in a later lecture

Parenchyma

• Parenchyma cells are relatively unspecialized; large vacuoles, thin primary wall (no secondary)

• most common type of plant cell; responsible for most of plant metabolic functions - primary sites of photosynthesis, starch storage….

•Fleshy tissue of most fruits

Collenchyma

•Collenchyma cells provide support to growing stems and leaves; thickened primary cell walls

•Relatively flexible, allowing organs to bend without breaking

Sclerenchyma

•Sclerenchyma cells have tough, thick secondary walls, often impregnated with lignin

•Two types specialized for support; fibers and sclereids. Both function to strengthen tissue in which they occur

THE THREE TYPES OF CELLS AND GROUND TISSUES IN PLANTS

cross-section of a young elderberry branch

cross-section from grass blade

cluster of sclereids (stained red) in pulp of pear

(Solomon et al 1999)

Vascular tissue functions in the movement of water, dissolved inorganic materials and carbohydrates through a plant

Raven and Johnson 1999

Xylem cells

•Tracheids & vessel elements; both function in water transport; both modified sclerenchyma cells

•Both have secondary cell walls and are dead at functional maturity

•Dual function in gymnosperms; water transport, structural support (structural support in angiosperms provided mainly by fiber cells

Cell Types in Vascular Tissue System

Tracheids

•long, thin cells with tapered ends

•water moves between cells across pits

•function in support; secondary walls hardened with lignin

Vessel Elements

•usually wide, short, oblique ends, thin-walled, compared to tracheids

•perforated end walls facilitates water flow

Solomon et al 1999

VESSEL ELEMENT

Photomicrograph shows longitudinal section of two vessel elements from an unknown woody dicot

Phloem Cells

•Sieve-tube members: Food-conducting cells, arranged end to end with porous walls (sieve plates) between them; cells living at functional maturity, but lacking nuclei, ribosomes

•Companion cells: Nucleated companion cell lies along side each sieve-tube member

longitudinal section transverse section

solomon et al 1999

Epidermal Cell;

•living parenchyma cell with thin primary wall

•outer wall usually thickened and covered by an extra-cellular waxy cuticle

•reduces water loss & protects surface of plant body

•epidermis is usually one cell layer thick

Guard Cell

•specialized epidermal cells on leaves that function in pairs; stoma (pore) is a gap between two guard cells

•guard cells, stoma, regulate gas exchange and water loss (transpiration)

SELECTED CELL TYPES OF THE PLANT DERMAL TISSUE SYSTEM

PLANT GROWTH Meristems generate cells for new organs throughout the lifetime of a plant

•Primary plant growth;

-Apical meristems extend roots and shoots by giving rise to the primary plant body

•Secondary plant growth:

-Lateral meristems add girth by producing secondary vascular tissue and periderm

Apical and Lateral Meristems Apical meristems produces primary plant body; lateral meristems produce the secondary plant body

Vascular tissue functions in the movement of water, dissolved inorganic materials and carbohydrates through a plant

Raven and Johnson 1999