Plant Responses To Abiotic Stress

Question 1

what are examples of abiotic stress?

Answer 1

• changes in day length
• cold and heat
• water availability
• wind
• changes in salinity.

Question 2

why do trees lose leaves?

Answer 2

the amount of glucose requireed for respiration to maintain the leaves and to produce chemicals that may protect them against freezing is greater than the amount of glucose produced by photosynthesis.

Question 3

what is photoperiodism?

Answer 3

plants are sensitive to a lack of light in their environment.

Question 4

what pigment results in photoperiodism?

Answer 4

phytochrome.

Question 5

how does abscission occur?

Answer 5

1. falling light levels result in less auxin.
2. ethene is produced when auxin concentrations fall.
3. ethene initiates gene switching in abscission zone resulting in the production of enzymes.
4. these enzymes digest and weaken cells in outer layer of abscission zone (seperation layer.)
5. vascular bundles carrying materials into and out of leaf are sealed off.
6. fatty material deposited in cells on stem side of seperation layer. forming a protective scar so pathogens cannot enter.
7. cells deep in seperation zone respond to hormonal cues by retaining water and swelling, putting more strain on already weakened layer.
8. Abiotic factors finish the process and leaf seperates from the plant.

Question 6

what happens if cells freeze?

Answer 6

membranes are distrupted and they will die.

Question 7

how do plants protect their cells from freezing?

Answer 7

• cytoplast of plant cells contain solutes which lower the freezing point.
• some plants produce sugars which ac as antifreeze to prevent cytoplasm from freezing.

Question 8

which hormone controls stomatal closure?

Answer 8

abscisic acid.

Question 9

how does abscisic acid control stomatal closure?

Answer 9

1. levels of soil water fall.
2. plant roots produce ABA
3. ABA is transported to the leaves where it binds to receptors on the plasma membrane of the stomatal guard cells.
4. ABA activates changes in ionic concentration of guard cells, reducing water potential and therefore turgor of the cells.
5. as a result of reduced turgor, guard cells close the stomata.