Unit XI Plant Structure and Function Plant biology

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 (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 (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 Phloem (food) Xylem (water) • 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 • 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 • 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 (NH 4+), nitrate (NO 3 -) - 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 • 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