Leaf anatomy Leaf anatomy Leaves start as outgrowths

Leaf anatomy

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

Leaf anatomy • 3 primary meristems – protoderm: becomes _____ – procambium: becomes ______ – ground meristem: becomes ______.

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

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 _______

• 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

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

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.