lec 27- Abiotic stress

Question 1

what are the 7 types of abiotic stress on plants?

Answer 1

-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

Question 2

what is the most common and costly abiotic stress in the world?

Answer 2

water deficit/drought stress

Question 3

what do droughts do to crop yield?

Answer 3

causes huge amounts of crop yield loss

Question 4

what is increasing and decreasing in the world with respect to water use?

Answer 4

water use is increasing while water availability is decreasing

Question 5

what is the definition of drought?

Answer 5

meteorological term for insufficient precipitation

Question 6

what is the definition of water deficit?

Answer 6

insufficient water for plant cells to maintain cell turgor, growth etc.

Question 7

what is water potential deficit values of plants?

Answer 7

-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)

Question 8

what water potential deficit can some drought tolerant plants endure?

Answer 8

survives water potential of cell = -11.5 MPa

photosynthesizes at -5 to -8 MPa

Question 9

what are the two plant strategies to deal with water deficit?

Answer 9

-adaptation: evolve over time (cacti)
-acclimations: plant adjusting/acclimating (closing leaf stomata)

Question 10

what are the three subcategories to drought resistance where a plant can practice any of these?

Answer 10

-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

Question 11

what are examples of adaptations to deal with water deficit?

Answer 11

-the blades of grass lead water to the base of the plant
-water tanks in bromeliads
-deep roots for more water uptake

Question 12

what are the examples of acclimations to deal with water deficit?

Answer 12

-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

Question 13

what are physiological adaptations to water deficit and heat?

Answer 13

C4 grass-sugarcane
CAM plant- pineapple

both have mechanisms to reduce transpiration while maintaining photosynthesis

Question 14

what are resurrection plants?

Answer 14

-plants that are extremely tolerant to water deficit by enhanced adaptations and acclimation responses
-shrivel when dehydrated, but sprout out again with water

Question 15

what occurs in the plant when water deficit is sensed and stomata must close?

Answer 15

1. osmotic stress in root cells is sensed by histidine kinase
2. abscisic acid (ABA) is produced
3. ABA moves in transpiration stream
4. root and leaf produced ABA triggers stomata closure, reducing water loss

water deficit can also be perceived in the leaf, leading to ABA production

Question 16

what occurs when ABA is present and what reverses the effects?

Answer 16

-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

Question 17

what drops ABA content in plants?

Answer 17

the activation of gene encoding enzymes that degrade ABA and downregulation of genes in ABA biosynthesis

Question 18

what does water deficit do to plant growth?

Answer 18

increases root growth to get more water and decreases shoot growth to reduce water loss

Question 19

what are other common acclimations seen in plants?

Answer 19

smaller leaves and thicker cuticles

Question 20

what is water loss effects on leaf expansion and photosynthesis?

Answer 20

-leaf expansion stops rapidly due to water being needed for expansion
-photosynthesis decreases gradually but is also sensitive to water stress

Question 21

what can plants do to counteract the effects of water deficit?

Answer 21

-osmotic adjustment: plant cells accumulate solutes to create a gradient so root cells can take up remaining water by osmosis

Question 22

what are the two places in which osmotic adjustment can take place?

Answer 22

-inside vacuoles
-in cytosol

Question 23

how does signal transduction occur from abiotic stress?

Answer 23

1. abiotic stress triggers receptors or sensors
2. signal transduction occurs
3. signal transduction triggers activation of genes to respond to abiotic stress

Question 24

do root cells take up ions from the soil and store them in the roots?

Answer 24

yes

Question 25

at high concentrations, the ions are harmful, where are they pumped to in the cell?

Answer 25

-into the vacuole where they do not affect cell metabolism
-however other solutes must accumulate in cytosol to maintain water potential equilibrium

Question 26

what is the two main functions of taking up solutes into the cytosol?

Answer 26

1. increasing solute concentrations in the cell
2. to decrease solute potential (decrease in water potential) to increase water uptake

Question 27

what are the compatible solutes and what do they protect in plants?

Answer 27

-sugars
-sugar alcohols
-amino acids
-protect plasma membrane and proteins from damage

Question 28

what do sugar alcohols and prolines do to the plasma membrane?

Answer 28

-in low water: generate a hydration shell over plasma membrane
-in no water: form hydrogen bonds with plasma membrane to stabilize it

Question 29

what is produced to provide tolerance to water deficit?

Answer 29

proteins that act as:
molecular shields- suppress aggregation of proteins in dehydrated cells
molecular chaperones- aid folding, reduce misfolding

Question 30

what is the major class of molecular shield proteins in plants?

Answer 30

-LEA (late-embryogenesis-abundant) proteins
-have random structure then coil in dehydration

Question 31

what is the major class of chaperones in plants?

Answer 31

-heat shock proteins
-induced from water deficit and help fold and reduce misfolding

Question 32

what are ROS antioxidants?

Answer 32

antioxidants that reduce reactive oxygen species (ROS) from defective photosynthesis