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 ____________.

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

QuickTime™ and aCinepak decompressorare needed to see this picture.

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

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.