Adaptations to abiotic stresses Flashcards
Different sensitivity to stress of plant tissues
Sensitive tissues:
Young/growing tissues (seedlings, meristems, primordia)
Reproductive organs
Tolerant tissues:
Seeds
Acclimated tissue (already experienced or expecting stress)
Dry and/or hot biomes
Tropical woodland/savanna
Tropical forests
Hot desert
Drought avoidance adaptations: get more water
Maximize water uptake through adapted root systems
Phreatophytes (e.g. alfalfa, willow) have long tap roots that can reach the water table.
Some xerophytes (e.g. cacti) have an extensive shallow root system to capture moisture from light rain and dew in the upper soil layer.
Drought avoidance adaptations: get more water
Collect water from the atmosphere
Use specially structured spines and trichomes
Use grooves on leaves to direct drops to plant base
Collect water from the atmosphere
Absorb fog water through the leaves (e.g. Drimys brasiliensis)
Contribution of leaf water uptake to plant water status
Drought avoidance adaptations: lose less water
Reduce water loss at the stomatal level
CAM metabolism (savanna, grassland, deserts): stomata closed during the day
Sunken stomata
A boundary is a thin layer of air (a form of insulation)
Reduce transpiration by increasing the leaf boundary layer / Increase heat dissipation by decreasing the leaf boundary layer. Leaf pubescence (high density of hairs) significantly thickens the boundary layer.
A thick boundary layer decreases air convection between the leaf and the atmosphere, resulting in:
Less water evaporation
Less heat transfer
The thickness of the boundary layer increases with:
Leaf size
Leaf border smoothness (absence of lobes and serration)
Reduce water loss from cuticular transpiration
Thick cuticle
Epicuticular waxes
Leaf surface properties can also protect against solar radiation and heat
Epicuticular waxes
Pubescence
Sage
Rosemary
Broccoli glaucous leaves
Drought and heat adaptations
More vertical leaf orientation limits interception of solar radiation.
Agave deserti (CAM/glaucus/succulence and vertical growth)
Aloe africana
Drought avoidance adaptations: store water
Succulence has evolved many times as a strategy to survive seasonal drought
They store water in living tissues
The have Stem and leaf succulence
Stem succulence
Resurrection plants: extreme tolerance to cellular desiccation
Accumulation of high concentrations of sugars allows resurrection plants to avoid damages due to desiccation
Craterostigma plantagineum (arid environments)
Saline biomes
Sea shores
Mangrove
Tidal zones
Salt marshes
Salt deserts
Halophytic adaptations: salt compartmentation
Accumulation of inorganic ions into a big vacuole is an important aspect of osmotic adjustment in halophytes.
Na+ is actively imported into the vacuole by tonoplast transporters while Cl- entry is probably passive.
Accumulation of compatible solutes in the cytoplasm balances the osmotic potential.
This strategy maintains water influx into the plant.
Halophytic adaptations
In addition to salt compartmentation, two main adaptations of halophytes are salt excretion and salt exclusion.
Salt crystals on Avicennia marina var resinifera
Adaptations of halophytes are often similar to drought adaptations: succulence, long tap roots, reduction of water loss.
Adaptations of halophytes are often similar to drought adaptations: succulence, long tap roots, reduction of water loss.
Cold biomes
Tundra
Alpine grassland/shrubland (high altitudes)
Cold deserts (Arctic, Antarctic)
Taiga coniferous forest
Cold adaptations
Harvest heat
Dark leaves
Sun tracking solar furnace flowers (focus sunlight on reproductive organs)
Dryas octopetala (Svalbard, coastal tundra)
Ranunculus glacialis (Arctic, alpine)
Papaver radicatum (Greenland, coastal tundra)
Limit cold exposure
Adapted life forms:
Crytophytes and geophytes: buds below ground (5 and 6)
Hemycrytophytes and chamaephytes: buds close to ground (2, 3 and 4)
Deschampsia antarctica Antarctic hairgrass
Colobanthus quitensis Antarctic pearlwort
Cushion growth habit
under ice creates insulation layer
Why is it more advantageous for the plant to set up a more effective acclimation under medium/long days?
plants in summer need to acclimate for warm days then cold nights however in winter under snow they are insulated and less fluctuation in temperature.
The regulation of seed dormancy
Seed dormancy prevents germination in future unfavorable conditions.
The level of seed dormancy varies with time and temperature. soil moisture and light.
The regulation of seed dormancy
The thermal regulation of dormancy is often coordinated with seasonal conditions.
Seed dormancy underlies stress escape strategies
Germination: bet hedging strategy
In the case of dormancy, bet hedging consists in having a fraction of all seeds able to germinate under appropriate conditions.
Bet hedging allows some of the progeny to survive in environments with unpredictable conditions.
his favours survival over competition
Life strategy of trees to avoid cold damage to leaves in winter
SD = short days
LD = long days
LT = low temperature
WT = warm temperature
Bud formation in white spruce. Instead of seeds they can survive as buds
