lec 27- Abiotic stress Flashcards
what are the 7 types of abiotic stress on plants?
-high light: causes creation of reactive oxygen species
-high temperature: stress denatures proteins
-water deficit: interferes with metabolism
-soil sanity: caused by excess salts and decreases nutrient uptake
-air pollution: causes oxidative damage to tissues
-mechanical damage: triggers expression of defensive genes
-cold stress: interferes with metabolic pathways and frosting damages tissues
what is the most common and costly abiotic stress in the world?
water deficit/drought stress
what do droughts do to crop yield?
causes huge amounts of crop yield loss
what is increasing and decreasing in the world with respect to water use?
water use is increasing while water availability is decreasing
what is the definition of drought?
meteorological term for insufficient precipitation
what is the definition of water deficit?
insufficient water for plant cells to maintain cell turgor, growth etc.
what is water potential deficit values of plants?
-mild water potential of cell = -0.5 MPa (90% water content)
-moderate water potential of cell = -0.5 to -1.5 MPa (80-90% water content)
-severe water potential of cell = smaller than -1.5 MPa (<80% water content)
what water potential deficit can some drought tolerant plants endure?
survives water potential of cell = -11.5 MPa
photosynthesizes at -5 to -8 MPa
what are the two plant strategies to deal with water deficit?
-adaptation: evolve over time (cacti)
-acclimations: plant adjusting/acclimating (closing leaf stomata)
what are the three subcategories to drought resistance where a plant can practice any of these?
-avoidance: better water uptake and saving water (e.g. rooting depth, mycorrhizae, stomata closing)
-escape: shortening of the growing season so less use of water ( e.g. early maturity, developmental plasticity, assimilate remobilization)
-tolerance: survival mechanisms like osmotic adjustment, protective solutes, and dessication tolerant enzymes
what are examples of adaptations to deal with water deficit?
-the blades of grass lead water to the base of the plant
-water tanks in bromeliads
-deep roots for more water uptake
what are the examples of acclimations to deal with water deficit?
-leaf rolling which reduces transpiration and water loss, seen in stressed corn
-changing leaf orientation from sunlight and wind reduces water loss, seen in eucalypts
what are physiological adaptations to water deficit and heat?
C4 grass-sugarcane
CAM plant- pineapple
both have mechanisms to reduce transpiration while maintaining photosynthesis
what are resurrection plants?
-plants that are extremely tolerant to water deficit by enhanced adaptations and acclimation responses
-shrivel when dehydrated, but sprout out again with water
what occurs in the plant when water deficit is sensed and stomata must close?
- osmotic stress in root cells is sensed by histidine kinase
- abscisic acid (ABA) is produced
- ABA moves in transpiration stream
- root and leaf produced ABA triggers stomata closure, reducing water loss
water deficit can also be perceived in the leaf, leading to ABA production
what occurs when ABA is present and what reverses the effects?
-decrease in soil water potential
-decrease in cell water potential due to soil drying out
-increase in ABA content
-increase in stomatal resistance (gas flow through stomata as they close)
-watering/rain reverses the effects
what drops ABA content in plants?
the activation of gene encoding enzymes that degrade ABA and downregulation of genes in ABA biosynthesis
what does water deficit do to plant growth?
increases root growth to get more water and decreases shoot growth to reduce water loss
what are other common acclimations seen in plants?
smaller leaves and thicker cuticles
what is water loss effects on leaf expansion and photosynthesis?
-leaf expansion stops rapidly due to water being needed for expansion
-photosynthesis decreases gradually but is also sensitive to water stress
what can plants do to counteract the effects of water deficit?
-osmotic adjustment: plant cells accumulate solutes to create a gradient so root cells can take up remaining water by osmosis
what are the two places in which osmotic adjustment can take place?
-inside vacuoles
-in cytosol
how does signal transduction occur from abiotic stress?
- abiotic stress triggers receptors or sensors
- signal transduction occurs
- signal transduction triggers activation of genes to respond to abiotic stress
do root cells take up ions from the soil and store them in the roots?
yes
