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Leaves (Morphology and Anatomy of other leaf types (Bud scales image (one…
Leaves
Morphology and Anatomy of other leaf types
Bud scales
one of the most common modification of leaves is evolutionary conversion into bud scales
protect dormant shoot apical meristem in perennial plants from low temperatures and drying action of wind in winter
primary role is protection not photosynthesis
are small and rarely compound, not at risk from mechanical wind damage
petiole short or absent, must remain close to stem and folded over
frequently produce thin layer of corky bark, on exposed portions. provides greater protection :champagne:
have tougher and thicker wax than regular leaves :angry:
Spines
cacti have two types of leaves
green cactus body has microscopic green leaves
clusters of spines are on their axillary buds
are modified leaves of axillary buds
used for protection :dark_sunglasses:
no blade and mutated to have no lamina :red_cross:
needle shaped
no mesophyll or parenchyma present
after spines mature, they deposit legnin in their walls making them hard and resistant to decay
then dry and die out, not disadvantageous as cactus has other photosynthetic tissues
Leaves of conifers
almost all species' leaves are
epidermis and hypodermis cells have thick walls
contain unpalatable chemicals :warning:
have thick cuticle
always simple, never compound and have only a few forms
scerophylls
needles of varying sizes occur in all pines and spruces
small, flat, scale-like leaves form shield around stems of junipers and cypresses
in conifers of the southern hemisphere, leaves are large and broad held away from stem
leaves are perennial and remain on stem for many years
are evergreens
vascular bundles can produce new phloem each year but not xylem
only three conifers shed their leaves each autumn
Larix, Taxodium, Metaseuoia
and are all deciduous
Tendrils
can grow indefinitely and capable of sensing contact with objects :hourglass_flowing_sand:
when leave touches something, stops growing in contact spot and grows opposite way
will then coil around object and use it for support
includes peas and squash
no lamina forms, would be detrimental
foliage leaves can sense light direction and reorient themselves while tendrils sense solid object and grow around them :wavy_dash:
Scerophyllous Foliage leaves
must produce more sugar by photosynthesis than are used in their own construction and metabolism
this liimits the amount of sclerenchyma in foliage leaves
include barberry, holly,
Agave
and
Yucca
evolved perennial, existing on plant more than two years
makes sclerenchymatous leaves possible
hardness makes then more resistant to animals and the elements :check:
scelerenchyma is often present a layer below the epidermis and in bundle sheaths :star:
cuticle is very thick and waxy
Insect traps
obtain nitrogen from insects amino acids
classified into two types
active traps (move during capture)
largely metabolic rather than structural
trichomes and lamina must be able to sense and respond to insect
entire leaf blade curls around insect so many trichomes come into contact dropping digestive liquid on insect :skull_and_crossbones:
Venus fly trap contains motor cells on midrib that are extremely turgid and swollen
creates hair trigger when stimulated
stimulated when motor cells lose water quickly and trap closes two halves of lamina upward
after digestion is complete, midrib motor neurons fill up with H2O, swell and open again
once one trichome is stimulated by an insect, all adjacent trichomes bend towards victim :warning:
share features with foliage but upper surface covered in glandular trichomes that secrete sticky digestive liquid :red_flag:
passive traps (incapable of movement)
usually evolved in habitats that lack nitrates and ammonia :lock:
leaves appear highly modified but are similar to foliage leaves
thin, parenchymatous, and capable of photosynthesis
numerous stomata and vascular bundles
mesophyll containing arenchyma and chlorenchyma
lamina is tubular rather than flat, secretes watery digestive fluid :skull_and_crossbones:
epidermis in digestive region is absorptive rather than impermeable
throat of pitcher contain numerous trichomes that point toward liquid, easy for insects to walk on, lead to their death :red_cross:
insect traps have occurred in many families
succulent leaves
thick and fleshy leaves, which reduces surface to volume ratio for H20 conservation :potable_water:
can be spherical (optimal surface to volume shape), or cylindrical :black_circle_for_record:
characteristic of families Crassulaceae, Portulacaceae, and Aizoaceae
reduced surface area has consequence of reduced capacity for CO2 uptake
inside the leaf
lack of air spaces makes mesophyll more transparent, allowing light to penetrate farther in leaf
photosynthesis occurs more deeply than in foliage leaves
Mesophyll has very few air spaces, reducing internal evaporation and H2O loss through stomata
Lithops
and
Frithia
are so translucent they act as optical fibers
leaves located almost completely underground
exposed leaf allow sufficient light in and conducts energy underground
leaves with Kranz Anatomy
lack palisade parenchyma and spongy mesophyll
have prominent bundle sheaths composed of large chlorophyllous cells
have special metabolism called C4 photosynthesis
surrounding each sheath is a ring of mesophyll cells that appear to radiate form vascular bundle
possess a mechanism of CO2 transportation that requires Kranz anatomy and adapts C4 plants to arid environments
External structure of foliage leaves
parts of the leaf related to photosynthesis
leaf blade/lamina
large, flat, light harvesting side of leaf :sunny:
smooth, also called ventral surface/ adaxial
dorsal surface
not must photosynthesis/light occurs here :dark_sunglasses:
has large veins protruding on this side
arranged in a netted pattern called reticular venation
in monocots with long, strap-shaped leaves, veins run side by side with few interconnections
called parallel pattern
called abaxial side as well
petiole/stalk
holds leaf into the light
helps leaf receive adequate sunlight against leaves above them
long thin shape allows the leaf to flutter in wind
great when wind is blowing, not efficient when there is no wind :check: :red_cross:
fluttering helps prevent insects from landing on leaf
small or very small leaves are called sessile leaves
monocots such as grasses, lilies, and agaves lack petiole
this is due to adequate amounts of sunlight reaching majority of plant
form sheathing leaf base that wraps around stem
lack of sunlight in these plants occur at base
they do not require petiole as self-shading is not a problem
are not called petiolate :star:
called petiolate
other than photosynthesis, leaves have important functions
must not allow entry of fungi, bacteria, or epifoliar algae
must not be nutritious and delicious to animals :warning:
must not lose excessive amounts of water :potable_water:
must not be effective sails so wind could blow plant over
must be cheap to make and replace :moneybag:
leaf shape
simple leaf(one part)
can be disadvantageous compared to compound leafs
compound leaf(multiple parts)
small blades (leaflets)
always arranged in 2 rows, never spiral, whorled, or decussate
point of attachment for leaflet (petiolule)
Two types of compound leaves
palmately compound (attached at same point) :silhouettes:
pinnately compund (attached individually along rachis) :silhouette:
easily recognized as leaves but can be mistaken as simple leaf with stem
rachis (extension of petiole)
advantages
more disruption when wind blows= more CO2 and removal of wastes
less surface for insects and bacteria to be on
small leaves can flex more without tearing
no real agreement on how different leaf shapes may be adaptive
plants can have multiple types of leaves
can be based on location and age of plant
some produce two types of leaves simultaneously
some can be different sizes on the same stem
at base of leaf (petiole) is abscission zone perpendicular to petiole
involved on cutting of leaf when usefulness is up
swelled cells will cause leaf scar
internal structure of foliage leaves
Mesophyll
palisade parenchyma/palisade mesophyll contains most of leaf's photosynthetic tissue
has a large surface with cells slightly separated
can be on both surfaces of the leaf
horizontal leaves absorb sunlight from overhead :sun_with_face:
vertical leaves can absorb sunlight from both sides equally :sunrise:
allows for CO2 dissolution
lower portion of the leaf contains spongy mesophyll
rapid CO2 diffusion occurs here
appears in the center of leaf or is lacking
ground tissue interior to epidermis is called mesophyll
vascular tissue
eudicot leaf usually has one large midrib/midvein
these emerge into lateral veins and minor veins
minor veins important for releasing water in xylem and sugar loading in phloem
minor veins important for exchange of material
minor veins must have large surface in contact with palisade and spongy mesophyll
do not contain fibers or nonconducting cells
lateral vein and midrib contain both
primary xylem on upper side of leaf
primary phloem on lower side of leaf
both veins conduct and support leaf and may contain arranged fibers in a sheath called a bundle sheath
sheath makes it difficult for insects to chew vascular tissue
nonconducting cells such as mucilage, tannin, or starch present here
larger veins can contain mass of fibers below, above, or both called bundle sheath extension
this gives blade rigidity and may help transport H2O :potable_water:
occur between palisade parenchyma and spongy mesophyll
epidermis
epidermis must be somewhat waterproof, simultaneously translucent and allow CO2 entry
leaf and stem epidermises basically similar, contain
ordinary epidermal cells
contain coating of cutin and wax on outer wall
helps retain water, difficult for fungi digestion :warning:
guard cells
Large % of flat, tubular ( shaped like paving stones)
trichomes (either glandular or nonglandular)
makes the leaf epidermis hairy, affect leaf biology in many ways (especially notable for lower epidermis)
prevent rapid air movement and water loss :<3:
make walking and consumption difficult for insects :no_entry:
provide excellent foothold for appropriately sized insects
can be poisonous, preventing consumption :skull_and_crossbones:
in fog, water droplets form here instead for stomatal pores which would inhibit CO2 &O2 movement
water lost through epidermis is called transpiration
dorsivental nature of leaves causes upper and lower epidermis to exist in significantly lower micro climates :star:
number of stomata is greater in lower epidermis than upper epidermis, aids in water retention
some plants do not have stomata on upper epidermis
helps prevent disease caused insects landing on leaf :forbidden:
Leaves contain an upper and lower epidermis
lower epidermis contains crypts that created pocket of nonmoving air
trichomes are abundant in lower epidermis
helps reabsorb water molecules that leave stomata :recycle:
petiole
considered part of the leaf and transition between stem and lamina
petiole mesophyll is like cortex
compact and not especially arenchymatous
contain considerable amount of collenchyma when supporting heavy lamina
can be tiny or large depending on the plant
leaf traces are 1-5 bundles of vascular tissue connecting to the petiole
can be arranged in many shapes such as rings or plates
can even form a midvein with smaller bundles entering lamina as lateral veins
they can be distinct or fuse together in numerous bundles
significance of bundle patterns is unknown
could be proper distribution of sugars
patterns are not always disadvantageous
can contain two small flaps of tissue called stipules
can protect apical meristem
can contribute to photosynthesis
concepts
numerous types of leaves and functions
support
storage
protection
nitrogen procurement
shoot system
shows division of labor and integration
present in all leaf/ stem combos
leaves have to be cost effective for energy uptake
do not grow new cells every year like wooded plants
almost all contain primary wall, rarely secondary wall
Initiation and development of leaves
basal Angiosperms and eudicots
leaves are only produced through activity of a shoot apical meristem
at base of meristem, cells interior to protoderm grow outward
form protrusion called a leaf primordium
extands as narrow cone as surpasses apical meristem
increases thickness higher it grows, establishes midrib
row of cells extend outward on either side of primordium
initiate lamina
new leaf has midrib and two small wings
2 more items...
consists of leaf protoderm and leaf ground meristem.
all are meristematic
contain dense cytoplasm and small vacuoles
strand of cells is center differentiates into provascular tissue and primary xylem& phloem
Monocots
leaves are initiated by expansion of shoot apical meristem cells to form leaf primordium
adjacent apical meristem cells grow upwards with primordium
become part of primordium
give primordium a hood-like shape :umbrella:
more apical meristems join until primordium is a cylinder or surrounds shoot apical meristem
grows forward and becomes a sheathing leaf base
as shoot apex enlarges, new stem tissue is formed and new leaf primordium is initiated
new primordium will develop into tube in previous leaf's sheathing base :recycle:
original conical leaf primordium gives rise to lamina
outer surface of tube is abaxial epidermis and inner surface is adaxial epidermis
in some moncots, lamina becomes broad and expanded like eudicot :leaves:
however they have strap-shaped leaves and no predetermined size
lamina grows by meristem located at base where it is attached to top of sheathing leaf base
remains active mitotically, producing new cells to extend leaf
lamina can be regenerated despite many types of destruction to leaf
this also means protoxyleam and protophloem are constantly being stretched and disrupted :explode:
new vessel elements and sieve tube member differentiate rapidly & conducting is never interrupted :zap:
above basal meristem is where stomata and other features are differentiated
also includes initiation of primary xylem and phloem
higher above basal meristem tissues mature and differentiate similar to stems but upside down :upside_down_face:
