Lecture 7 Flashcards
abiotic stressors
light, high temperature, water deficit, salt stress, cold, anaerobic stress, oxidative stress,
adaptations for life is stressful environments
constitutive mechanists to tolerate or resist stress
acclimation to stress
induced mechanisms to tolerate or resist stress
example of stress adaptation
saguaro cactus is tolerant of water deficits due to morphology: barrel shaped photosynthetic stem, reduced surface area, stores water in barrel
example of stress acclimation
spinach is tolerant to drought by accumulation of osmoprotective compounds which when produced reduce the water potential inside the plant cells reducing water loss down the gradient
water deficit
caused by saline soils, cold or freezing temperatures, drought; low available water potential in soil
response to water deficit
close stomata
regulate of stress response gene expression
accumulation of osmolytes and LEA proteins
ABA and adaptation to stress
aba is involved in regulation of stomata opening and regulation of ABA-dependent stress response gene expression
ABA stomata signalling pathway
1 Roots perceive low water potential 2 ABA is synthesized in roots and shoots 3 ABA travels in xylem to leaves 4 ABA is perceived by guard cells 5 Signaling 6 Stomata close
ABA independent stomata opening process
phototropic receptors recognize blue light at sunrise and signal stomata to open
LEA proteins (dehydrins)
late embryogenesis abundant proteins; hydrophilic, coat intracellular macromolecules to prevent aggregation of macromolecules as water level drops in cell, abundant during embryogenesis and seed maturation because seed maturation requires desiccation, mitigate low water levels by binding to water in water stressed plants;
LEA proteins rice example
transgenic LEA rice grew well under water stress conditions compared to wt
osmolyte accumulation in response to water stress
accumulation of compatible solutes to maintain water content even if water potential in soil drops; lowers water potential in cells allowing increased water uptake; some drought plants use this response very effectively
compatible solutes
don’t interfere with cellular structure and function; inert
osmolyte protective function
compatible solutes protect proteins, membranes, from build-up of physiologically damaging and denaturing ions during water deficit
mechanism of desiccation resistance in resurrection plants
LEA proteins; osmoprotective sugars: 50% of hydrated plant weight is octulose which can quickly be turned into sucrose during dessication
ROS
reactive oxygen species; produced during respiratory and photosynthetic electron transport, produced in response to stress, toxic, produced by reduction of molecular oxygen, reactive, strips electrons from biological molecules
causes for ROS production
high light, extreme temperatures, ozone pollution, pathogen infection, drought, salinity,
Ascorbate
vitamin C is a major antioxidant in plants; high concentrations in chloroplast, present in leaf apoplast
RT-PCR
Reverse Transcriptase Polymerase Chain Reaction;
1 obtain mRNA from plant tissue
2 add RT to make cDNA of mRNA
3 add Taq polymerase to make second strand of cDNA
4 add gene specific primers and let Taq amplify specific cDNA
5 run gel electrophoresis and observe bands of specified cDNA
SOD and APX
superoxide dismzutase and ascorbate peroxidase; antioxidant enzymes which when over expressed can increase tolerance to heat or cold induced oxidative stress
Freezing damage:
ice crystals damage and kill cells–frozen water is unavailable causing drought conditions–freezing and thawing cycles block/interrupt xylem with air bubbles
conifers conical or scale like leaves
conical or scale like leaves; shed snow, reduce surface area, thick waxy cuticle, retain leaves through winter allowing photosynthesis to begin immediately in spring
conifers dehydrin LEA proteins
accumulate in leaves and trucks in winter, prevent aggregation and denaturation of macromolecules in cells
conifers tracheids
adapted for efficient conduction of water even in dry/cold conditions– torus prevents air bubbles from flowing to next tracheid–water can still flow through other tracheas even in winter
3 evolutionary solutions for angiosperms to fight cold
1 drop leaves seasonally, shut down water transport
2 thinner water conducting vessels and tracheas to reduce air bubble formation
3 overwinter as seeds or storage organs
cork bark
reduces water loss in hot dry climates; full of Suberin (wax)
xerophytes
likes dry conditions; needs little water; 2 types: succulents and non succulents
succulent
stores water in various organs in cells with large vacuoles
non succulents
various morphological features including small leaves, deep roots, thick cuticles, sunken stomata, many trichomes
sunken stomata
trichomes line stomatal cavity and trap damp air creating microclimate limiting transpirational water loss in open stomata
atmospheric bromeliads
tillandsia species; obtain water from atmosphere through modified trichomes
torrey pine
pine species in sandy soil of San Diego desert; extensive long root system and obtain water from summer fogs that role in off coast through grooves in needles which condense water vapour and directs it down groove onto soil around trunk. produces its own rain
flooding
too much water around roots results in oxygen deprivation or anaerobic stress
aerenchyma
internal long distance gas transport pathways made up of cortical tissues that form gas filled spaces; constitutively formed in wetland species; formed by cell expansion and separation; surrounded by water-impermeable endodermis
corn aerenchyma
acclimation; develops as a result of programmed cell death in root cortical cells in response to flooding
adventitious roots
grow in response to flooding (O2 deprivation); grow at soil surface where oxygen levels are higher
what stress tolerating traits would be beneficial to Ontario’s major crops for example soybeans?
drought tolerance due to the hotter and dryer summers
over-expressed SOD and APX antioxidant genes to cope with increasing air pollution especially near cities
lithops
living stones; 2 succulent xerophyte leaves
CAM plants
take in CO2 at night and store it until day time for photosynthesis reducing water loss because stomata are closed during the day,
prickly pear cactus
shallow roots to collect water from fog
air plants
live on other plants for support, they don’t have roots, they have
blue agave
tequila plant; sunken stomata
ponytail palm
succulent roots, water storage root above the surface, ponytail shaped
spanish moss
tillandsia air plant grows on trees
