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UNIT III: PLANT FORM AND FUNCTION
•Plant structure and growth
•Plant nutrition
•Plant reproduction and development
Cardinal Flower
Arabidopsis thaliana
Red Maple
Purves et al 2000
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).
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
Purves et al 2000
Examples of Monocot angiosperms
Purves et al 2000
Cactus
Flowering Dogwood
Rose
Examples of Dicots (more specifically, Eudicots)
Source: Freeman (2002)
Phylogenetic relationships among Angiosperm lineages
Angiosperms
Oldest living
Non-Angiosperms angiosperm lineages
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
Several lineages
related to magnolias Monocots
Eudicots
Phylogenetic relationships
of the orders of flowering
plants (AGP, 1998)
•Monocots apparently
diverged from dicots early
in the history of the
phylum
http://www.csdl.tamu.edu/FLORA/newgate/cronang.htm
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.
Desert annuals (above) and a giant
redwood (below)
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)
Sources: Raven & Johnson 1999, Purves 2000)
PLANT STRUCTURE AND GROWTH
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)
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
Solomon et al 1999
Campbell et al 1999
Shoot
Root
Roots
Shoots
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.
Shoot
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.
Root
CELL SPECIALIZATION; STRUCTURAL ADAPTATION IN CELL WALLS AND
CELL PROTOPLAST*
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
Purves et. al. 2000
CELL SPECIALIZATION; STRUCTURAL ADAPTATION IN
CELL WALLS AND CELL PROTOPLAST
In addition to other
features of Eukaryotic
cells, plant cells have:
•cell wall
•chloroplasts
•central vacuole,
Raven & Johnson 1999
Cell plate formation between two nuclei, during plant cytokinesis
Raven and Johnson 1999
PLANT CELLS ARE ORGANIZED INTO TISSUE SYSTEMS
Plant 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
THE THREE TYPES OF CELLS AND GROUND TISSUES IN PLANTS
Parenchyma
Collenchyma
• Parenchyma cells are
relatively unspecialized; large
vacuoles, thin primary wall (no
secondary)
•Collenchyma cells provide
support to growing stems and
leaves; thickened primary cell
walls
• most common type of plant
cell; responsible for most of
plant metabolic functions primary sites of photosynthesis,
starch storage….
•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
•Fleshy tissue of most fruits
(Solomon et al 1999)
cross-section from grass
blade
cross-section of a young
elderberry branch
cluster of sclereids (stained
red) in pulp of pear
Raven and Johnson 1999
Vascular tissue functions in the movement of water, dissolved
inorganic materials and carbohydrates through a plant
Cell Types in Vascular Tissue System
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
Tracheids
Vessel Elements
•long, thin cells with
tapered ends
•usually wide, short,
oblique ends, thinwalled, compared to
tracheids
•water moves between
cells across pits
•function in support;
secondary walls
hardened with lignin
•perforated end walls
facilitates water flow
VESSEL ELEMENT
Photomicrograph
shows longitudinal
section of two
vessel elements
from an unknown
woody dicot
Solomon et al 1999
longitudinal section
transverse section
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
SELECTED CELL TYPES OF THE PLANT DERMAL TISSUE SYSTEM
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)
solomon et al 1999
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
Raven and Johnson 1999
Vascular tissue functions in the movement of water, dissolved
inorganic materials and carbohydrates through a plant