Transcript Unit XI: Plant Structure and Function

Unit XI: Plant Structure and
Function
Plant biology, perhaps the oldest branch of
science, is driven by a combination of curiosity
and need- curiosity about how plants work and a
need to apply this knowledge judiciously to feed,
clothe, and house a burgeoning human population.
Plant Biology- Why?
Molecular Biology and Plant Biology
• Arabidopsis thaliana
+ weed that belongs to the mustard family
- organism of choice for molecular study
• About Arabidopsis on the Internet
Genomic Sequence of 5 Chromosomes of Arabidopsis
Evolution of Plants
All Plants…
• multicellular, eukaryotic, autotrophic, alternation of generations
Alternation of Generations
Sporophyte (diploid)
• produces haploid
spores via meiosis
Gametophyte (haploid)
• produce haploid
gametes via mitosis
Fertilization
• joins two gametes to
form a zygote
Angiosperms
Monocots vs. Dicots
• named for the number
of cotyledons present on
the embryo of the plant
+ monocots
- orchids, palms,
lilies, grasses
+ dicots
- roses, beans,
sunflowers, oaks
Plant Morphology
Morphology (body form)
• shoot and root systems
+ inhabit two environments
- shoot (aerial)
+ stems, leaves, flowers
- root (subterranean)
+ taproot, lateral roots
• vascular tissues
+ transport materials between
roots and shoots
- xylem/phloem
Plant Anatomy
Anatomy (internal structure)
• division of labor
+ cells differing in structure and function
- parenchyma, collenchyma, sclerenchyma (below)
- water- and food-conducting cells (next slide)
Parenchyma
St: “typical” plant cells
Fu: perform most metabolic functions
Ex: fleshy tissue of most fruit
Collenchyma
St: unevenly thickened primary walls
Fu: provide support but allow growth
in young parts of plants
Ex: celery
Sclerenchyma
St: hardened secondary walls
Fu: specialized for support; dead
Ex: fibers (hemp/flax); slereids
(nut shells/seed coats)
Water- and Food-conducting
Cells
Xylem (water)
Phloem (food)
• dead at functional maturity
• tracheids- tapered with pits
• vessel elements- regular tubes
• alive at functional maturity
• sieve-tube members- arranged
end to end with sieve plates
Plant Tissues
Three Tissue Systems
• dermal tissue
+ epidermis (skin)
- single layer of cells that
covers entire body
- waxy cuticle/root hairs
• vascular tissue
+ xylem and phloem
- transport and support
• ground tissue
+ mostly parenchyma
- occupies the space b/n
dermal/vascular tissue
- photosynthesis, storage,
support
Plant Growth
Meristems
• perpetually embryonic tissues located at regions of growth
+ divide to generate additional cells (initials and derivatives)
- apical meristems (primary growth- length)
+ located at tips of roots and shoots
- lateral meristems (secondary growth- girth)
Primary Growth of Roots
Primary Growth of Roots
• apical meristem produces
all 3 tissue systems
+ primary meristems
- protoderm
- ground meristem
- procambium
+ root cap
+ three overlapping zones
- cell division
- elongation
- maturation
Primary Growth in Shoots
Primary Growth in Shoots
• apical meristem (1, 7)
+ cell division occurs
+ produces primary meristems
- protoderm (4, 8)
- procambium (3, 10)
- ground meristem (5, 9)
• axillary bud meristems
+ located at base of
leaf primordia
• leaf primordium (2, 6)
+ gives rise to leaves
Leaf Anatomy
Epidermal Tissue
• upper/lower epidermis
• guard cells (stomata)
Ground Tissue
• mesophyll
+palisade/spongy
parenchyma
Vascular Tissue
• veins
+ xylem and phloem
Secondary Growth
Lateral Meristems
• vascular cambium
+ produces secondary xylem/phloem (vascular tissue)
• cork cambium
+ produces tough, thick covering (replaces epidermis)
• secondary growth
+ occurs in all gymnosperms; most dicot angiosperms
Vascular Cambium
Production of Secondary Vascular Tissue
• Vascular Cambium cells give rise to xylem (X) and phloem (P)
+ Cambium cell (C) gives rise to initial and derivative (D)
- Derivative differentiates into xylem (X) or phloem (P) cell
Cork Cambium
Periderm
• protective coat of
secondary plant body
+ cork cambium and
dead cork cells
- bark
• cork cambium produces
cork cells
+ cork cells deposit
suberin and die
• secondary growth
commences farther down
the shoot
+ transforms older
regions first
Plant Nutrition
What does a plant need to
survive?
• 9 macronutrients, 8 micronutrients
+ macro- required in large quantities
- C, H, N, O, P, S, K, Ca, Mg
+ micro- required in small quantities
- Fe, Cl, Cu, Mn, Zn, Mo, B, Ni
+ usually serve as cofactors
of enzymatic reactions
Mineral Deficiency
Mineral deficiency
• symptoms related to function of element
+ Mg- causes chlorosis
- ingredient of chlorophyll
+ Fe- causes chlorosis
- required as cofactor in photosynthesis
• symptoms also related to mobility of element
+ Mg- chlorosis of older leaves
- relatively mobile
+ Fe- chlorosis of younger leaves
- relatively immobile
+ young, growing tissues have more
“drawing power”
• hydroponic culture
+ growing plants by bathing roots- no soil!
Soil
Texture and Composition
• texture depends on size of particles
+ sand-silt-clay
- loams: equal amounts of sand,
silt, clay
• composition
+ horizons
- living organic matter
- A horizon: topsoil, living
organisms, humus
- B horizon: less organic, less
weathering than A horizon
- C Horizon: “parent” material
for upper layers
• soil conservation issues
+ fertilizers, irrigation, erosion
Soil Bacteria
Nitrogen
• decompose humus to release nitrogen in soil
+ plants absorb ammonium (NH4+), nitrate (NO3-)
- nitrogen-fixing bacteria
- ammonifying bacteria
- nitrifying bacteria
Nutritional Adaptations
Symbiotic Relationships
• symbiotic nitrogen fixation
+ root nodules contain bacteroids (Rhizobium bacteria)
- mutualistic relationship
• mycorrhizae
+ symbiotic associations of fungi and roots
- mutualistic relationship
+ ectomycorrhizae
- mycelium forms mantle over root
+ endomycorrhizae
- does not form mantle; hyphae extend inward
• parasitic plants
+ plants that supplement their nutrition from host
- mistletoe, dodder plant, Indian pipe
• carnivorous plants
+ supplement nutrition by digesting animals
Transport in Plants
Transport
• occurs on three levels
+ cellular level
- absorption of water/minerals
from soil by root cells
+ short-distance transport
- cell to cell at tissue/organ level
+ loading of sugar from
photosynthetic cells to phloem
+ long-distance transport
- sap within xylem and phloem
throughout plant
Absorption of Water and
Minerals by Roots
soil --> epidermis --> root cortex --> xylem
Uptake of Soil Solution
Symplastic Route
• continuum of cytosol based
on plasmodesmata
Apoplastic Route
• continuum of cell walls and
extracellular spaces
Lateral transport of soil
solution alternates between
apoplastic and symplastic
routes until it reaches the
Casparian strip
Mycorrhizae
Casparian Strip
The Casparian strip is a belt
of suberin (purple) that
blocks the passage of water
and dissolved minerals.
Only minerals that are already
in the symplast or enter that
pathway by crossing the
plasma membrane can detour
around the Casparian strip and
pass into the stele.
Summary of uptake
of soil animation
Transport of Xylem Sap
Transpiration
• the loss of water vapor from leaves and other aerial parts of the plant
+ transpirational pull
- transpiration-cohesion-tension mechanism
Water vapor diffuses from the moist
air spaces of the leaf to the drier air
outside via stomata.
Tension is created by the evaporation
of water and pulls water from
locations where hydrostatic pressure
is greater (xylem).
Transpirational pull draws water out
of xylem and through mesophyll
tissue to the surfaces near stomata.
Cohesion and Adhesion of Water
Hydrogen Bonding
• cohesion
+ water molecules tug on to each other
• adhesion
+ water molecules adhering to the
hydrophillic walls of xylem cells
Control of Transpiration
Photosynthesis-Transpiration
Compromise
• guard cells help balance plant’s
need to conserve water with its
requirement for photosynthesis
+ stomata open (widen) and
close (narrow)
- guard cells change their
shape (turgid/flaccid)
- reversible uptake/loss of
potassium (K+) ions
Translocation of Phloem Sap
Source to Sink
• sugar source
+ organ that produces sugar
• sugar sink
+ organ that consumes/stores sugar
• phloem loading and unloading
+ chemiosmotic mechanism
actively transports sucrose
- sucrose is co-transported with
H+ back into cell
Plant Reproduction
Sporophyte (diploid)
• produces haploid
spores via meiosis
Gametophyte (haploid)
• produce haploid
gametes via mitosis
Fertilization
• joins two gametes to
form a zygote
Angiosperm Life Cycle
Sporophyte (diploid)
• actual plant with
flowers
Gametophyte (haploid)
• male: germinated
pollen grain
• female: embryo sac
Fertilization
• joins two gametes to
form a zygote
Moss Life Cycle
Gametophyte
• dominant generation
+ has both sexes and
produces gametes
- archegonia (eggs)
- antheridia (sperm)
Fertilization
• sperm move along moss to
find archegonia
Sporophyte
• grows on top of gametophyte
+ sporangia is where spores
are produced by meiosis
Fern Life Cycle
Sporophyte
• produce spores via
meiosis
+ spores develop
into young
gametophyte
Gametophyte
• has both sexes and
produces gametes
- archegonia
(eggs)
- antheridia
(sperm)
Fertilization
• similar to mosses
Gymnosperm Life Cycle
Sporophyte
• produce gametophytes inside
of cones
+ Pollen cone (male)
- produces microspores
via meiosis
+ Ovulate cone (female)
- produces megaspores
via meiosis
Fertilization
• pollen grains discharge sperm
into egg
Male and Female Gametophyte
of Flowering Plant
Male Gametophyte
• pollen grain
+ microspores produced
within the anther
+ divide once to
produce two
sperm cells
Female Gametophyte
• embryo sac
+ megaspore produced
within the ovule
+ divide to produce
three egg cells
- 2 polar nuclei
Double Fertilization
Double Fertilization
• pollen grain lands on stigma
+ pollen tube toward ovule
+ both sperm discharged down the tube
- egg and one of the sperm
produce zygote
- 2 polar nuclei and sperm
cell produce endosperm
+ ovule becomes the seed coat
+ ovary becomes the fruit
Seed Structure and Development