Next Tuesday Bring Blue Scan sheet Bring 2

Next Tuesday • Bring Blue Scan sheet • Bring #2 pencils • Bring erasers if you want to change your mind

Plant Development and Anatomy

Plant Development • Seed: baby plant (embryo) in box (seed coat) with its lunch (endosperm) • Some babies finish lunch early • All that’s left in box (seed coat) is baby (embryo)! • Example, bean seed. Fig. 40. 2

Plant Development • Embryo parts: – Cotyledons: seed leaves. Bean is dicot (2 cotyledons). These contain stored food. – Epicotyl: Located above cotyledons. Will develop into shoot system (stem and leaves) of plant – Radicle: Will develop into root system of plant – Hypocotyl: Below cotyledons. Stem that connects cotyledons to radicle.

Plant Development • Epicotyl and radicle each have apical meristem • Meristem: tissue (collection of cells) capable of rapid cell division • Epicotyl: shoot apical meristem (SAM) • Radicle: root apical meristem (RAM).

Plant Development • Bean seed germination • Hypocotyl pulls cotyledons/epicotyl from soil • Root and shoot systems start to grow. Fig. 40 -15 a

Plant Development • Primary growth occurs due to activity of meristems (SAM and RAM) • These produce specialized dividing cells called primary meristems • Primary meristems develop into primary tissues.

Plant Cells • Focus on cell walls: form plant skeleton (supports body) • Primary wall: cellulose, penetrated by plasmodesmata • Middle lamella: “cement” between adjacent walls.

Plant Cells • Secondary cell wall: laid down inside primary wall • Thick, contains lignin (strong, rot resistant) • Note: In our lab slides, secondary wall will stain __RED_____ whereas primary wall will stain __GREEN______. primary secondary

Plant Cells • Secondary cell wall: laid down inside primary wall • Thick, contains lignin (strong, rot resistant) • Opening in secondary wall called pit • Note pits still have primary wall present (pit membrane: pit not a completely open space between cells).

Tissues and cell types • Tissue: Group of cells organized as a functional unit • Tissues made of cell types • Simple tissues contain 1 cell type • Complex tissues contain >1 cell type.

Tissues and cell types • 3 main types of tissues: – 1) ground (yellow) – 2) dermal (white) – 3) vascular (purple).

Ground Tissues • Usually simple tissues; – Parenchyma – Collenchyma – Sclerenchyma.

Ground Tissues: Parenchyma • Usually rounded cells, primary wall • May have chloroplasts, large storage vacuoles • May be used as “packing tissue” to fill space. Purple structures are chloroplasts single cell

Ground Tissues: Collenchyma • Contains collenchyma cells • Elongate cell, thick primary walls, especially thick at corners, alive at maturity • Used as strengthening tissue in young plant parts.

Ground Tissues: Sclerenchyma • Simple tissue: contains 1 cell type • But two types of cells possible: • 1) fiber: elongate, thick secondary wall, often dead at maturity • Strengthening cell/tissue.

Ground Tissues: Sclerenchyma • Simple tissue: contains 1 cell type • But two types of cells possible: • 2) sclereid: Not elongated (mostly branched or rounded), thick secondary wall, often dead at maturity • Used to strengthen tissues, protect areas (hard endocarp of drupe is sclereids). 1 cell

Ground Tissues: Sclerenchyma • An astrosclereid alone and others in leaf section. 1 cell

Dermal Tissues • Epidermis: Surface covering of all plant body • Typical epidermal cells: flattened, no chloroplasts, primary wall, thick outer walls • In shoot/stem, outer walls have cuticle (waxy layer) on outside. Thick cuticle (orange layer)

Epidermis • Special cell types: guard cell • In pairs on stems/leaves • Have chloroplasts, primary wall, open and close pore of stoma (plural: stomata) • Control water loss, CO 2 uptake.

Epidermis • Special cell types: guard cell • In pairs on stems/leaves • Have chloroplasts, primary wall, open and close pore of stoma (plural: stomata) • Control water loss, CO 2 uptake.

Epidermis • Special cell types: trichome cells • On stems/leaves • Have primary wall, elongate.

Epidermis • Special cell types: trichome cells • Function to slow water loss • Function to reflect light to keep leaf cool

Epidermis • Special cell types: trichome cells • Function: defense against herbivores. sticky trichomes stinging nettle trichome

Epidermis • Special cell types: root hairs • On roots • No chloroplasts, little/no cuticle, hair is extension of epidermal cell wall • Increases root surface to take up water/minerals • Ephemeral, hair withers after few days.

Vascular Tissues • Complex tissues (<1 cell type) • Phloem (conducts sugars) • Xylem (conducts water and minerals).

Vascular Tissues • Phloem (conducts sugars) • 4 cell types possible: • 1) Sieve tube elements: conducting cells • Elongate, primary wall, no nucleus • Ends connect by sieve plate (large plasmodesmata). sieve plates face view sieve plates side view

Vascular Tissues • 2) Companion cell: smaller cells with nuclei, direct action of sieve tube element.

Vascular Tissues • Phloem (conducts sugars) • 3) parenchyma cells • 4) fibers.

Vascular Tissues • Xylem (conducts water and minerals) • 4 cell types possible: • 1) vessel element: elongate, wide, thick secondary wall, holes (perforations) at ends of cell, dead at maturity • Functions as sections of “pipe” to form vessel, which conducts water and minerals • Found almost exclusively in flowering plant xylem.

Vascular Tissues • Xylem (conducts water and minerals) • 4 cell types possible: • 2) tracheid: elongate, wide, thick secondary wall, many pits in wall • Functions to conduct water and minerals also. These must pass through pits to reach next cell (pits have primary wall in center and are not open holes) • Found in xylem of both flowering plants and gymnosperms.

Vascular Tissues • Comparison of tracheids and vessel.

Vascular Tissues • Comparison of tracheids and vessel.

Vascular Tissues • Xylem (conducts water and minerals) • 4 cell types possible: • 3) fibers: covered earlier. Note they have secondary wall and are usually dead at maturity • 4) parenchyma: covered earlier. Note they have primary walls and are alive.

Plant Organs • 1) Flower (covered previously) • 2) Stem • 3) Leaf • 4) Root.

Plant Organs • 2) Stem: aboveground portion of shoot, bearing leaves • Divided into nodes (where leaves attach) and internodes (where no leaves attached) • Note also: bundle scar, leaf scar, terminal bud scale scar. Fig. 38. 23

Plant Organs • 2) Special stem modifications – Photosynthesis (cactus) – Climbing (some tendrils).

Plant Organs • 2) Special stem modifications – Protection (thorn). Honey locust (Gleditsia)

Plant Organs • 2) Special stem modifications – Storage (tuber). Also asexual reproduction – Explore world (runner). Also asexual reproduction.

Plant Organs • 2) Special stem modifications – Underground stems (bulb, rhizome). Bulb (A) and corm (B)

Plant Organs • 3) leaf – major site of photosynthesis – stalk is petiole, flattened part is blade – axillary bud: small meristem (contains a SAM) at base of leaf: can grow to make branch.

Plant Organs • 3) leaf – note stipules: pairs of appendages at base of petiole of some leaves.

Plant Organs • 3) leaf – Venation: netted for dicots, parallel for monocots.

Plant Organs • 3) leaf – Simple – Compound (pinnate and palmate, doubly compound).

Plant Organs • 3) leaf – Arrangement.

Plant Organs • 3) Special leaf modifications – Carnivory! (obtain nutrients) – Venus flytrap: leaf like steel trap (leg-hold trap).

Plant Organs • 3) Special leaf modifications – Carnivory! (obtain nutrients). Help me! From movie: The Fly

Plant Organs • 3) Special leaf modifications – Carnivory! (obtain nutrients) – Pitcher plants (leaf acts as pitfall trap). white-top pitcher plant

Plant Organs • 3) Special leaf modifications – Carnivory! (obtain nutrients) – Sundew: uses sticky hairs to catch prey on leaf.

Plant Organs • 3) Special leaf modifications – Asexual reproduction (ex, plantlets). Plantlets on Kalanchoe leaves

Plant Organs • 3) Special leaf modifications – Pollinator attraction (bracts).

Plant Organs • 3) Special leaf modifications – water storage: succulent leaf. Lithops: stone plant

Plant Organs • 4) Root – anchors plant – absorbs water/nutrients.

Plant Organs • 4) Special root modifications – Pneumatophores. Section showing air spaces Mangrove tree pneumatophores

Plant Organs • 4) Special root modifications – Pneumatophores – Cypress knees. cypress knees Plant Ecology class in cypress swamp

Plant Organs • 4) Special root modifications – Contractile roots

Plant Organs • 4) Special root modifications – Parasitic roots (haustoria) Leafy mistletoe (parasite on trees) tree branch

Plant Organs • 4) Special root modifications – Storage roots – Ex, carrot

Plant Organs • 4) Special root modifications – Climbing (aerial roots)

Root anatomy

Root anatomy • At tip: apical meristem covered by root cap • Protects RAM from abrasion by soil particles.

Root anatomy • Next: primary meristems – protoderm: becomes epidermis – procambium: becomes vascular tissue – ground meristem: becomes rest of tissue (region called cortex).

Root anatomy • Mature root tissues – Epidermis: root hairs – Cortex (region): parenchyma tissue (storage) • endodermis

Root anatomy • Mature root tissues – Cortex (region): parenchyma tissue (storage) • endodermis: cells with Casparian strips (waxy material called suberin: blocks water from going thru walls).

Root anatomy • Mature root tissues – Vascular cylinder • pericycle • phloem and xylem

Root anatomy • Lateral roots – develop from pericycle.

Stem anatomy

Stem anatomy • SAM at tip • Protected by developing leaves called primordia ( -ium).

• SAM at tip • 3 primary meristems Stem anatomy – protoderm: becomes epidermis tissue – procambium: becomes vascular tissues – ground meristem: becomes rest of stem (cortex and pith).

Stem anatomy • Epidermis on outside • Vascular tissue in bundles • Note regions: – cortex – pith (parenchyma).

Stem anatomy • Epidermis • Cortex • Vascular bundle. Helianthus stem

Stem anatomy • Cortex closeup: note collenchyma here. Also parenchyma deeper. Helianthus stem

Stem anatomy • Vascular bundle close • Note phloem on outside, xylem on inside.

Leaf anatomy • Leaves start as outgrowths from apical meristem: leaf primordia.

Leaf anatomy • 3 primary meristems – protoderm: becomes epidermis tissue – procambium: becomes vascular tissues – ground meristem: becomes rest of leaf.

• Epidermis: note cuticle, stomata • Veins with vascular tissues (xylem on top, phloem on bottom) • Supply water & nutrients, remove sugars for transport elsewhere. Leaf anatomy

Leaf anatomy • Mesophyll – Parenchyma tissue layers (palisade and spongy: do photosynthesis.

Plant Growth Phenomena • Hormones: molecules produced in small amounts that change plant physiology or growth • Can inhibit or stimulate processes to occur • 5 major types: auxins, cytokinins, gibberellins, ethylene, abscisic acid

Auxins • Promote stem elongation and growth • Example, phototropism. Bending of stem toward light

Auxins • Also involved in apical dominance: suppression of lateral meristems by apical meristem

Cytokinins • Stimulate cell division where auxin is also present • Acts as anti-aging hormone (keeps detached leaves green).

Gibberellins • Promote stem elongation • Mutant plants with low amounts are dwarfs (internode lengths short)

Ethylene • Promotes fruit ripening • Stimulates abscission (dropping) of leaves, flowers

Abscisic acid • Induces formation of winter buds (bud scales, dormant meristem) • Involved in opening and closing of stomata • Can cause seed dormancy

Plant transport • Phloem: sugars and water (often from leaf to root) • Xylem: water and minerals from root to shoot • Movement driven by water potential: measure of tendency of water to move from one place to another • Affected by solutes (high solutes low tendency to move), pressure (high pressure high tendency to move), tension (pull: high tension high tendency to move).

Water transport • Xylem: water and minerals from root to shoot • How much of water remains in plant?

Water transport • Transpiration: evaporation of water from leaves • Driven by pull from leaves. Water under tension. Water potential high in soil and low in air.

Water transport • Transpiration greatly controlled by stomata • Stomata open in light but can close if plant lacks sufficient water. Stomata!

Sugar transport • Phloem: sugars and water • Flow from source to sink • Pressure flow mechanism

Sugar transport • Source: lots of sugar dissolved in water. Generates pressure as water flows in to dilute sugar • Sink: little sugar dissolved in water. Low pressure as water flows out • Creates pressure gradient that moves fluid thru sieve tubes.

Sugar transport • Result: sugar flows to wherever demand is high