Leaf anatomy

Leaves start as outgrowths from apical meristem: leaf primordia.

Leaf anatomy 3 primary meristems –protoderm: becomes __________ –procambium: becomes ___________ –ground meristem: becomes ____________.

Leaf anatomy Epidermis: note cuticle, stomata Veins with vascular tissues (__________ __________) Supply water & nutrients, remove sugars for transport elsewhere.

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

Monocot vs dicot anatomy Stem: Dicot with bundles __________. Pith and cortex present. Monocot: scattered vascular bundles. No _______________.

Monocot vs dicot anatomy Root: Dicot, < 6 phloem patches, no pith

Monocot vs dicot anatomy Root: Monocot, many _____________, pith present

Monocot vs dicot summary Note root system type: dicot often with single major root axis (taproot system), monocot lacking this (fibrous root system)

Plant Growth Phenomena Hormones: molecules produced in small amounts that change _________________ _________ Can inhibit or stimulate processes to occur 5 major types: –auxins –cytokinins –gibberellins –ethylene –abscisic acid

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

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

Auxins Can stimulate production of ______________ roots (roots produced on stem or leaf) Useful in rooting cuttings (asexual plant reproduction)

Cytokinins Stimulate cell division where auxin is also present Acts as ____________ hormone (keeps detached leaves green).

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

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

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

Other plant growth phenomena Gravitropism: response of stem/root to gravity Stems bend away from gravity (___________ gravitropism) Roots bend toward gravity (_________ gravitropism)

Other plant growth phenomena Mechanism unclear. May involve ________ ________ called statoliths (in root cap of root, in parenchyma cells of stem)

Other plant growth phenomena Thigmotropism: response of plant to __________ Examples: Many tendrils grow toward stimulus and wrap around object

Turgor movement Not growth: involves loss of water pressure (turgor pressure) in some cells Can be reversed May involve rapid movement (electrical signal) Ex, sensitive plant

Flowering Some plants use daylength as flowering cue Can measure length of night (photoperiod) by pigment called ______________

Flowering Long day plants: flower when night is ________ than some critical time Short day plants: flower when night is _______ than some critical time Day neutral plants: don’t use photoperiod as flowering cue

Flowering Use: Can make some plants bloom when we want them Ex, poinsettia. A short-day plant that growers make flower for Christmas holidays.

Plant transport Phloem: sugars and water (often from leaf to root) Xylem: water and minerals from root to shoot Movement driven by _____________: measure of tendency of water to move from one place to another

Plant transport Water potential is affected by: –solutes (high solutes = ______ tendency to move) –pressure (high pressure = ______ tendency to move) –tension (pull: high tension = ______ 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 _______ from leaves. Water under tension. Water potential high in soil and low in air.

Water transport 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 ________ but can close if plant lacks sufficient water. Stomata!

Sugar transport Phloem: sugars and water Flow from ______ to _____ Pressure flow mechanism

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

Sugar transport Result: sugar flows to wherever demand is high

Secondary Growth

Two types of growth Primary growth: up and down. Generated by apical meristems. Form _________ tissues Secondary growth: growth in girth. Generated by lateral (secondary meristems). Form __________ tissues. All plants do primary growth Woody plants do __________ growth

Secondary Growth Lateral meristems –1) ______________: makes new phloem and xylem –Called ________ phloem and xylem tissues (vs. primary phloem and xylem made directly from procambium) –Function: xylem takes water + minerals to leaves, phloem takes sugars to roots

Secondary Growth Lateral meristems –2) ___________: makes new cell type, cork cell. Cork cells with primary wall impregnated with waxy material (_______). Dead at maturity. Forms waterproof layer on outside of body to replace epidermis. –_________: Tissue composed of cork cells and made by cork cambium. Also is a secondary tissue.

Secondary Growth Stem cross section

Secondary Growth Vascular bundles contain __________________ Located between primary xylem and phloem Meristematic: can still do _______________

Secondary Growth Residual procambium cells start to divide Produce new cells ______________

Secondary Growth Parenchyma cells between bundles also start to divide Together form solid ring of cells, all dividing laterally This is __________________

Secondary Growth Vascular cambium makes secondary xylem on __________, secondary phloem on __________ Note how cambium moves outward over time

Secondary Growth Note arrangement of primary phloem and secondary phloem, primary xylem and secondary xylem

Secondary Growth Secondary xylem may contain: –1) Vessel elements –2) Tracheids –3) ____________ –4) Fibers Secondary phloem may contain: –1) Sieve tube elements –2) Companion cells –3) Parenchyma –4) ___________

Secondary Growth Two

Secondary Growth Later secondary growth

Secondary Growth First cork cambium: Forms under ___________

Secondary Growth Cork cambium: Makes files of cork cells to outside. Forms first __________. Epidermis cut off from rest of stem and dies.

Secondary Growth Problem: cork cells are dead at maturity. Cork layer cannot _________ as vascular cambium continues to grow. Solution: form new ______ ______ in cortex under old one After time, several __________ build up (yellow lines). Newest (inner) one cuts off water to layers beyond it and they _______.

Secondary Growth Periderm replaces epidermis. How get _______ into stem?

Secondary Growth Lenticels: Loosely packed __________. Allow oxygen to diffuse into stem to support living cells there.

Secondary Growth Note ____ made by vascular cambium: Form ________ transport system (often parenchyma cells) In phloem: phloem ray In xylem: xylem ray (wood ray)

Secondary Growth In temperate zone, cambium activity varies between _____ and ______ in growing season Spring: big cells (_______ wood). Summer: small cells (_______ wood). Form growth ring (tree ring): one season’s growth Ex, pine (mostly tracheids)

Secondary Growth Ex, oak (note vessels, thick-walled _________)

Secondary Growth Young tree section: Note rays here (phloem and xylem) Also note growth rings: early and late wood How old was this stem when cut?

Secondary Growth In older tree: wood is secondary xylem Heartwood: old non-functional xylem ________: younger often functional xylem

Secondary Growth Bark: From vascular cambium outward ___________: From current cork cambium outward (all is dead) __________: From vascular cambium to current cork cambium. Contains functional secondary phloem

Secondary Growth Removing inner bark is deadly: girdling tree often will kill it Why? Roots ______ Why? No ________ from leaves.

Secondary Growth Flow chart, showing how primary and secondary tissues develop in stem

Secondary Growth Note that roots of woody plants also do secondary growth Vascular cambium forms from __________ First cork cambium forms in _____________.

Secondary Growth So outer cortex and epidermis are sloughed off and lost

Uses of Growth Rings 1) Fire frequency Break in bark (_________) allows fire to burn through vascular cambium into wood Leaves burned layer If tree survives, can have record of fires in wood. Ponderosa pine, WY

Uses of Growth Rings 1) Fire frequency Helpful information when trying to determine “natural” frequency of fires for managing forests.

Uses of Growth Rings 2) Climate patterns (___________________) Width of rings can indicate growth conditions for tree (rainfall, etc.) Can reconstruct climate information Oldest reconstructions go back 8,000 yr B.C.

Uses of Growth Rings 2) Climate patterns Oldest reconstructions from bristlecone pine wood go back as far as ________ yr B.C.