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 PlantsAll Plants…• multicellular, eukaryotic, autotrophic, alternation of generations

Alternation of GenerationsSporophyte (diploid)• produces haploid spores via meiosis

Gametophyte (haploid)• produce haploidgametes via mitosis

Fertilization• joins two gametes toform a zygote

Angiosperms

Monocots vs. Dicots• named for the numberof cotyledons present on the embryo of the plant + monocots

- orchids, palms, lilies, grasses

+ dicots- roses, beans, sunflowers, oaks

Plant MorphologyMorphology (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)

ParenchymaSt: “typical” plant cellsFu: perform most metabolic functions

Ex: fleshy tissue of most fruit

CollenchymaSt: unevenly thickened primary wallsFu: provide support but allow growthin young parts of plantsEx: celery

SclerenchymaSt: hardened secondary wallsFu: specialized for support; deadEx: fibers (hemp/flax); slereids (nut shells/seed coats)

Water- and Food-conducting CellsXylem (water)

• dead at functional maturity• tracheids- tapered with pits• vessel elements- regular tubes

Phloem (food)• alive at functional maturity• sieve-tube members- arranged end to end with sieve plates

Plant TissuesThree 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 GrowthMeristems• 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 RootsPrimary 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 ShootsPrimary 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 AnatomyEpidermal 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 CambiumPeriderm• protective coat of secondary plant body + cork cambium and dead cork cells

- bark• cork cambium producescork cells + cork cells deposit suberin and die• secondary growthcommences farther downthe shoot + transforms older regions first

Plant NutritionWhat 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 DeficiencyMineral 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!

SoilTexture 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

NitrogenSoil Bacteria• decompose humus to release nitrogen in soil + plants absorb ammonium (NH4

+), nitrate (NO3-)

- nitrogen-fixing bacteria- ammonifying bacteria- nitrifying bacteria

Nutritional AdaptationsSymbiotic 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 PlantsTransport• 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 SolutionSymplastic Route• continuum of cytosol basedon plasmodesmata

Apoplastic Route• continuum of cell walls andextracellular spaces

Lateral transport of soilsolution alternates betweenapoplastic and symplastic routes until it reaches theCasparian strip

Mycorrhizae

Casparian StripThe Casparian strip is a beltof suberin (purple) thatblocks the passage of water and dissolved minerals.Only minerals that are alreadyin the symplast or enter thatpathway by crossing the plasma membrane can detouraround the Casparian strip andpass into the stele.

Summary of uptakeof soil animation

Transport of Xylem SapTranspiration• the loss of water vapor from leaves and other aerial parts of the plant + transpirational pull

- transpiration-cohesion-tension mechanismWater vapor diffuses from the moistair spaces of the leaf to the drier airoutside via stomata.

Tension is created by the evaporation of water and pulls water from locations where hydrostatic pressureis greater (xylem).

Transpirational pull draws water outof xylem and through mesophyll tissue to the surfaces near stomata.

Cohesion and Adhesion of WaterHydrogen Bonding• cohesion + water molecules tug on to each other• adhesion + water molecules adhering to the hydrophillic walls of xylem cells

Control of TranspirationPhotosynthesis-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 SapSource 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 ReproductionSporophyte (diploid)• produces haploid spores via meiosis

Gametophyte (haploid)• produce haploidgametes via mitosis

Fertilization• joins two gametes toform a zygote

Angiosperm Life CycleSporophyte (diploid)• actual plant with flowers

Gametophyte (haploid)• male: germinatedpollen grain• female: embryo sac

Fertilization• joins two gametes toform a zygote

Moss Life CycleGametophyte• 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 CycleSporophyte• produce spores viameiosis + spores develop into young gametophyte

Gametophyte• has both sexes and produces gametes

- archegonia (eggs)- antheridia (sperm)

Fertilization• similar to mosses

Gymnosperm Life CycleSporophyte• produce gametophytes insideof cones + Pollen cone (male)

- produces microsporesvia meiosis

+ Ovulate cone (female)- produces megasporesvia meiosis

Fertilization• pollen grains discharge sperminto egg

Male and Female Gametophyte of Flowering Plant

Male Gametophyte• pollen grain + microspores produced within the anther + divide once to produce two sperm cellsFemale Gametophyte• embryo sac + megaspore produced within the ovule + divide to produce three egg cells

- 2 polar nuclei

Double FertilizationDouble 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