Pbl Plant Adaptation
Transcript of Pbl Plant Adaptation
How the plant respond and adapt to the environment changes???
Learning Issues:
Group Members:
Lee Yian Ping D20091034823
Wong Li Hun D20091034877
Yee Chin Tien D20091034824
Wang Chiao Ching D20091034838
Plant Stress• Physical• temperature
• Chemical• Salt Abiotic
• Biological insult• Insect• dieseaseBiotic
CONDITION
AVERAGE• Mesophyte
ARID• Xerophyte
AQUATIC• Hydrophyte
SALTY• Halophyte
MESOPHYTES
• Mesophytes make up the largest ecological group of terrestrial plants which inhabit regions of average water conditions, neither a particularly dry nor particularly wet environment.
• This group of plants is intermediate between Xerophytes and Hydrophytes, which includes the majority of wild and cultivated plants.
• Mesophytes generally require a more or less continuous water supply.
ADAPTATION
TO
ENVIRONMENT
CHANGES
• The leaves are green, well developed and of variable shape and measurement.
• They are provided with cuticle. • The leaves have a greater number
of stomata on the lower surface. • Mesophyll layer in leaves is well
differentiated with many inter cellular spaces.
Leaves
Cross-sections Comparing Monocot and Dicot Leaves
Mag. 40xMidrib (largest vein)
Which is the monocot?Which is the dicot?
Mag. 100x
Phloem-lower layer of cells in the veins
Monocot leaf xsEpidermis Stomata
Xylem- top layerof cells in the vein
Mag. 400x
Cuticle
Upper epidermis
Palisade mesophylllayer
Spongy mesophylllayer
Lowerepidermis
Dicot leaf xs Mag. 40x
Mag. 100x
Vascular tissue:(Vein) made ofXylem
Phloem
Stomata
Stem • The stem is solid, aerial and profusely branched.
Root• The root system is well developed and provided with a
root cap with the taproot in dicotyledons and fibrous roots in monocotyledons.
• Because of their lack of particular xeromorphic adaptations, when they are exposed to extreme conditions they lose water rapidly, and are not tolerant of drought.
• For example, in hot weather they may overheat and suffer from temperature stress.
• They have no specific adaptations to overcome this, but, if there is enough water in the soil to allow this, they can increase their rate of transpiration by opening their stomata, thus meaning some heat is removed by the evaporating water.
• In dry weather they may suffer from water stress (losing more water via transpiration than can be gained from the soil).
• Again they have no specific adaptations to overcome this, and can only respond by closing their stomata to prevent further transpiration.
• This does actually have some benefits as it reduces the surface area of the leaf exposed to the atmosphere, which reduces transpiration.
• Prolonged periods of dehydration, however, can lead to permanent wilting, cell plasmolysis, and subsequent death.
Xerophytes
• “Xero” means dry and “phyte” means plant
• Plants that can survive in dry conditions where the habitat is with little available water or moisture.
• Specialized mechanisms or structures mainly on:- Minimize the loss of water - Increase the water uptake efficiency-Develop efficient storage system that can withhold available water for long time
• Water stress habitats : - Desert - High Altitude & High Latitude
(low precipitation or water locked up as snow or ice)
- Rapid drainage (sand dunes)
Adaptation To
Environment Changes
1. Fold especially during the day to decrease the number of the stomata exposed
2. Shed during dry seasons to avoid water loss
3. Well developed sclerenchyma4. No leaves or small seasonal leaves that
only grow after the rains. 5. Hairs allow water vapor to be retained
which reduces water loss through the pores.
6. Groove formed by the rolled leaf acts as a channel for rain water to drain directly to the specific root of the grass stem
LEAVES
7. Thick waxy upper epidermis extends around the rolled up leafe.g. Leaves of Mesquite (Prosopis)
- have cuticles ten times thicker than mesquite plants which are growing in damp areas.
- adapted by having smaller leaves, grow compactly and close to the ground, and a non-porous covering on their leaves such as wax.
8. Stomata • Fewer stomata & often only present on the bottom leaf surface to decrease transpiration
• Reversed stomatal rhythm
• Sunken stomata in pits - creates a relatively high humidity chamber & decreases exposure to air currents.
STEM
1. Thick, leaflike pads covered by sharp spines(modified leaves) to reduce the surface area for transpiration
2. Succulents and have a thick waxy cuticle and epidermis e.g. - Sedum
- Large desert cacti (Carnegiea gigantia) literally store ten tonnes of water in their parenchymatous tissue.
Sedum Carnegiea gigantia
3. Hairs to trap a layer of still & moist air
4. Main photosynthetic tissue where chlorophyll in the outer tissue of their skin and stems to conduct photosynthesis for the manufacture of food
5. Numerous cushion or pit-like structures known as areoles on their surface, from which usually emerge clusters of spines
ROOT
1. Extensive deep root systems2. Thin cortex provides a small distance between soil, water and xylem 3. Well developed xylem which allows rapid transport & absorption of
water4. Hydrophilic colloids accumulate in root cortex to accelerate water
absorption- reduce the water potential of the root's tissue, accelerating water uptake by osmosis
Crassulacean-acid metabolism (CAM)- Allows stomata to be kept tightly closed during the day is an efficient way of conserving water in dry environments
C4 cycle - e.g. bunchgrass - More efficient in maximizing energy gain than normal photosynthesis although it is not used by many plants
Slower growing requires less energy
Dormancy- Seeds of Xerophytes lay dormant in the sand until sufficient rain has fallen-The seeds are coated in a chemical that prevents germination until rain has washed the chemical away.- May remain dormant several years.
Abscisic Acid• Occur in mature, green leaves• Synthesized in cytoplasm of leaf mesophyll cell and
accumulated in chloroplast• Regulating stomatal closure during water stress• Regulating abscission and bud dormancy
Stomatal closure• In drought, leaves will synthesize high level of ABA to allow
stomata closure• Water will be stored during drought/water stress
Hydrophytes
Plants growing in water or on a substrate that is at least periodically deficient in oxygen as a result
of excessive water content.
These conditions create anaerobic environments that require plants to develop specialized adaptations for growth and reproduction.
Definition:
Classification of Hydrophytes
Free floating hydrophytes
Floating but rooted hydrophytes
Submerged but not rooted
Submerged but rooted
Amphibious and rooted
Emergent but rooted
1. Free floating hydrophytes
These plant float freely on the water surface and are not rooted.
Eg: Eichhornia
Clas
sific
ation
of H
ydro
phyt
es
2. Floating but rooted hydrophytes
These plants float on the surface of water but remain attached to the bottom of
water reservoir by their roots.
Eg: JussiaeaEg: Trapa
Clas
sific
ation
of H
ydro
phyt
es
These plants occur below the water surface and remain free being not rooted.
Eg: Ceratophyllum
3. Submerged but not rootedCl
assi
ficati
on o
f Hyd
roph
ytes
Eg: Vallisneria
These plants remain below
water surface but are attached to the reservoir bottom
by their roots.
4. Submerged but rootedCl
assi
ficati
on o
f Hyd
roph
ytes
Eg: Marsilea
These plants grow near the water reservoirs in shallow and muddy places.
5. Amphibious and rootedCl
assi
ficati
on o
f Hyd
roph
ytes
Eg: CyperusEg: Ranunculus
These plants are found in shallow water. They grow half below the water and the half above it.
6. Emergent but rootedCl
assi
ficati
on o
f Hyd
roph
ytes
Effect of prolonged flooding or soil saturation: 1. Causes the leaves of most plants to turn yellow and
drop off.2. Cause the roots to die from oxygen starvation.
Plant Adaptations for Life in Water or Wetlands
A. Roots:
1. Shallow root systemi. Poorly developed. ii. May even be absent
2. Prolonged wetness causes a change in root directioni. Grow upward to the surface to obtain
oxygen.ii. Grow horizontally to enable the plant to get
air near the ground surface.
3. Two types of water roots:
i. Thin, many-branched roots growing at the ground surface
ii. Thick, white, weakly branched roots that penetrated the saturated soil
4. Develop other roots, to compensate for the dieback of primary roots:
i. In free floating plants, adventitious roots are developed for buoyancy.
ii. Sheath-like root pockets are developed to help the plants to float.
iii. Spongy roots which are negatively geotropic develop for floating.
5. Some root system well developed mainly for the purpose of attachment
B. Stem and leaf:
1. Many marsh plants rapidly increase their stem and leaf growth.
2. The stems are spongy, delicate and flexible.
3. A complex set of biochemical reactions stimulates shoot elongation, allowing the plants to move their leaves and stems out of the water to photosynthesize and to move oxygen down to their roots.
4. Petiole • Very long and delicate in plants with roots attached
and leaves floating• Bulbous petiole helps the plant to float on water
surface
5. Woody plants have lenticels on their bark • To facilitate gas exchange between the inner
tissues and the environment.
• Lenticels permit a plant to take in air and carbon dioxide and to release gases like oxygen, a by-product of photosynthesis.
• When flooded, the lenticels of many trees and shrubs become fleshy and enlarged, or “hypertrophied,” to increase gas exchange
C. Flowers:
Most wetland plants reproduce through flowers, an adaptation required for life on land.
Most live in ponds, lake and rivers
Since flowers must be pollinated by insects or by wind, how do plants living underwater
become pollinated?
Many aquatic plants, like water lilies, spatterdock, and pondweeds, produce flowers at the water’s surface.
1. This plant produces separate male and female flowers.
2. The female flower is attached to a stalk that elongates until the flower reaches the surface.
3. At the surface, the flower opens and is ready to be pollinated.
4. Meanwhile, the male flower breaks off from the plant below and floats up.
5. Reaching the surface, it opens and develops into a sort of “love boat” that is carried by the currents to a waiting female flower.
6. Eventually the male flower unites with the female flower and pollination takes place
Upper epidermis
Note: Large air spaces in spongy mesophyll why might this be helpful?
Stomata: why would the stomata be on the top?
Lower epidermis: are there any Stomata?
Ecology:
Halophyte
• Plants that can inhabit areas of HIGH SALINITY such as those in salt marches and mudflats where the salinity is constantly changing and may exceed that of sea water.
• Salt stress• Example:–api-api (Avicennia), – red
mangrove(Rhizophora)
Types •grow only in
salty habitats•plant species
may maintain a 'normal' internal salt concentration by excreting excess salts through its leaves or by concentrating salts in leaves that later die and drop off.
Obligatory halophytes
(true halophyte)
•are able to settle on salty soils, but their optimum lies in a salt-free or at least low-salt condition.
•the salt is tolerated
•avoid growing during the high salt climates
Facultative halophytes
Classification • have glandular cells capable of
secreting excess salts from plant organsExcretives
• use increase in water content within large vacuoles to minimize salt toxicitySucculents
Leaf
• Large central vacuole in thin-walled celled of watery leaves accumulate substantial quantities of salts.
• Salts are removed from the plant when the leaf is shed.
Stem
• Lenticels – facilitates gaseous exchange
Root
pneumatophores• To avoid suffocation
in the oxygen poor (anaerobic) mud
• stabilise the tree
adventitious roots• for anchorage and
purposes of water and ion uptake
extensive system of rhizomes• for propagation
SeedVivipary• the condition whereby the embryo (the young plant within the seed)
grows first to break through the seed coat then out of the fruit wall while still attached to the parent plant
Cryptovivipary• the seed does germinate on the mother tree, the growing shoot does
not penetrate the seed coat while the fruit is still on the tree• The shoot and roots only appear after the fruit falls off. And these
grow best in water of the right temperature and salinity
Dormancy• Induced by accumulation of high ion content• seeds only germinate when temperature and edaphic conditions are
favourable
Physiological adaptation
• The active concentration of salt in the vacuole and the storage of large volumes of water help to keep the salt concentration of the plasma low
Succulence
Trichomes (hairs) on the surface of leaf•has a stalk and a balloon-like tip, the bladder cell•accumulates sodium, potassium, and chloride ions in the bladder and release the salt back into the environment when leave are ruptured.
Secrete salts from leaves•crystalline salt can occur on the leaf of black mangrove•it appears whitish
Ultra filtration system•enabling only selective absorption of ions•Transpiration at the leaf surface creates negative pressure in the xylem.