1
Q
three ecological types of plants
A
mesophytes
xerophytes
hydrophytes
2
Q
mesophytes
A
require moderate amounts of water
3
Q
xerophytes
A
adapted to low levels of water
4
Q
hydrophytes
A
adapted to high levels of water
5
Q
eudicots leaves in sun vs shade
A
- in sun leaves have denser palisade
-shade have thinner less dense palisade
ex of phenotypic plasticity
6
Q
major veins
A
- may have a bundle sheath of parenchyma (largest do not)
- these veins have less exit/entry from the mesophyll
- serve more as a transport function in/out of leaf
- sometimes may undergo limited amount of secondary growth
- also may have bundle extensions of collenchyma for support
- some species move water to the epidermis by bundle extensions
7
Q
minor veins
A
- often lack bundle extensions
- always have a bundle sheath with few chloroplasts
- little space between bundle sheath cells
- helps control exit/entry to veins
- large degree of control because of large number of minor veins
8
Q
netted (reticulate) venation
A
in a typical eudicot leaf
-mesophyll divided into subregions called areoles
9
Q
a paradermal secttion
A
- dense packing of the palisade mesophyll
- vein network
- more air spaces in spongy mesophyll
- stomatal density of adaxial and abaxial differs
10
Q
vascular tissue
A
- bundle sheath is part of vascular tissue
- xylem and phloem similar in c3 and c4 grass leaves
- larger veins resemble stem bundles - have vessel elements, tracheids, parenchyma and a protoxylem lacuna
- minor veins generally have few tracheids, and no vessels
- sieve tube members and companion cells phloem
11
Q
evergreen angiosperm leaves
A
- some woody eudicots retain leaves year round
- called broad-leaved evergreens
- grow in low nutrient status habitats
- slow growers and stress tolerators
- plants conserve organs as some nutrients not salvageable but must be frost hardy and xerophytic (cold causes xerophytic things )
- tolerant of ice crystal formation within tissues, not cells (a tolerance of all temperate woody species)
- particularly found in ericaceae
- ericoid describes general leaf morphology
- example of convergent evolution
12
Q
different leaf habitat
A
stays on plant of the winter
- leaf said to be wintergreen = not true evergreen
- turns red/purple in late fall
- leaves senesce in spring
13
Q
leaf abscission
A
- controlled shedding of leaves
- important in woody species ie. perennials
- occurs yearly in deciduous species
- or at longer intervals for evergreens
- regulated by hormones
- leaves drop in response to environmental cues
14
Q
steps of leaf abscission
A
- environmental signal
- retrieval
- abscission layer formation
- protective layer formation
- vascular disconnection
15
Q
environmental signal
A
Photoperiod more reliable
Temperature can also influence
Warm temperatures in fall can inhibit onset, especially in non-native species
16
Q
retrieval
A
Plant recovers as many soluble nutrients as possible eg. Mg+2, sugars, amino acids
Stores in parenchyma in stem
Some minerals not mobile
ie. not retrievable eg. Ca+2
17
Q
abscission layer formation
A
New thin-walled parenchyma cells form at base of petiole
From dedifferentiating parenchyma
Cell walls of pre-existing cells also begin breaking down here
Forms an even break line
18
Q
protective layer formation
A
Another layer forms to the inside of the abscission layer
Is suberized to prevent or minimize water loss and pathogen entry
Creates a leaf scar on the stem
19
Q
vascular disconnection
A
Vessels in midrib of petiole still open Leaf may hang on for a time Nearby xylem parenchyma produce outgrowths that enter pits of vessel Is to seal off vessels Outgrowths called tyloses Can see bundle scars within leaf scars
20
Q
fall colors in deciduous leaves
A
A shorter photoperiod and cooler temperatures initiate leaf fall
Chlorophyll broken down by light all summer, but is not replenished in fall
Fat soluble carotenoids more resistant
In some species, water soluble anthocyanins are produced de novo in vacuole
Other plants always contain anthocyanins
Anthocyanins are increased with cold nights and sunny days
21
Q
morphology
A
- major ps organ
- important for other metabolic functions like synthesis of amino acids and secondary metabolites
- most variable organ in form and anatomy
- different environments have differing selection pressures
22
Q
blade/lamina
A
-flattened portion
23
Q
petiole
A
leaf stalk
24
Q
sessile
A
no petiole
25
stipules
base of leaf
26
exstipulate
if no stipule
27
in most monocots the base of blade is
enlarges and forms a sheath around the stem
28
axillary bud
in axil
29
simple leaf
blade on surface
30
compound leaf
blade subdivided into leaflets
31
pinnately compound
leaflets off a rachis
32
palmately compound
leaflets off the tip of petiole
| -may also have petiolules
33
margins
page 38
34
leaf base in grasses
- grass leave have sheathing base
- extends down stem
- has meristematic regions at base of leaf
- ligule is membrane or hairy fringe at collar
- ligule can have extensions called auricles
35
leafs and branches
both can have a central axis bearing leaf like structures
36
reliable criteia
- is there a SAM
- presence of axillary buds (or stipules for some)
- plane of leaves
37
is there a SAM
- branch has SAM, but not leaf
| - reflects indeterminate status of branch versus determinate leaf dimensions
38
presence of axillary buds
-in the axil of all simple leaves but not of leaflets
39
plane of leaves
- leaflets lie in same plane
| - different leaves on branch are usually in different planes
40
phyllotaxy
patterns of leaf arrangment
1. alternate is 1 leaf per node
2. opposite is 2 leaves per node
3. whorled is 3 or more leaves per node
41
alternate
most common subtype of alternate is spiral/helical
42
opposite
if each successive pair is at right angles to the next them it is termed decussate
43
whorled
a rosette is a dense cluster of leaves, really a spiral arrangement without internodal elongation
44
which leaf pattern most common
helical
45
the smaller the angle
the more files of leaves possible but still minimizing overlap
- rosette has small angle
- selected for light limiting habitats
46
distichous pattern allows much
overlap
- feasible in a hight light habitat
- allows for the increased packing of shoots in a crowded area
47
leaf limitations
Must access CO2 but H2O exits as C02 enters
Compromises in form therefore essential
Flat, 2-D shape facilitates light capture, gas exchange
But, this shape also exacerbates desiccation risk
So, leaf success in differing habitats involves a combination of anatomy and morphology in concert with physiology and stomatal opening/closing
48
why leaf morphology
| Page 48)
Leaf features used greatly in plant identification (also floral morphology)
Shape and size of leaves varies with habitat
Water availability especially influences leaf morphology
Smaller leaves tend to be found in hotter and drier habitats
Usually less divided in shape
Larger leaves tend to be found in moister habitats
Also more divided in shape
Submerged plants often have highly divided leaves
A greater surface area is beneficial because the entire leaf surface takes up gases from the water
49
heterophylly
- leaves on one plant can differ in form and function
- eg. submerged versus floating leaves of some aquatic angiosperms
- reflects phenotypic plasticity
- responding to greatly differing microhabitats
50
leaf development
Patterns of leaf development observed by analyzing genetic mosaics called chimeras
Causes layers of cells of differing genetic composition
Leaves arise from peripheral meristem as leaf primordia
First apparent as a bulge on side of SAM
Bulge called a leaf buttress
Flanking bulges produce opposite leaves eg. Coleus
Primary meristems later visible in the primordium
Cells differentiate as primordia are displaced by continued growth
Bud primordia develop in the axils of leaf primordia
51
when buttresses get larger they are called
bud primordium
52
grass leaf development
Exhibit basal growth
SAM remains basal in vegetative phase
Leaf primordia appear as hood-like structures
These enfold the SAM and alternate sides
These leaves retain a meristematic zone at the base of leaf
Cell elongation after cell divisions causes leaves to increase in size
53
vascular differentiaion
#1 priority, as it is critical for leaf development
Need to establish long distance source of energy
eg. From starch stored in cortex of stem or root
Major leaf veins differentiate from stem bundles into the leaf (still primordial)
But, minor veins differentiate from tip back towards the base of leaf
Also, major veins differentiate from mid-regions towards leaf margins
But, minor veins begin at leaf margins and develop inwards
Means a completed network of veins is first present towards the tip of a leaf, and not the base
Oldest part of a leaf is the tip
54
differentiation in eudicot leaves
- three leaf traces per leaf
- each from a different stem bundle
- leaves die from tip back
55
grass leaves differentiation
Because grass leaves retain meristematic zone at base
Vascular differentiation originates in mid-portion of blade
Major veins (parallel) differentiate back to base AND up to tip
Minor veins (cross) differentiate back from tip
flowering
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