Lecture 11

Question 1

What is foolish seedling?

Answer 1

A rice disease caused by toxins in fungus that causes plant to grow and grow then fall over

Question 2

Origin of gibberellin (GA)

What pathway synthesizes it?

Answer 2

Immature/germinating seeds
Elongating stems
Growing fruits (plastids, ER, cytosol)

Synthesized by the terpenoid pathway

Question 3

GA promotes stem elongation 2 ways (2) (3 methods inside one)

Answer 3

Increasing cell wall extensibility (GA stimulates XET to cleave hemicellulose to allow microtubules to move for elongation/enhances expansion synthesis/promotes transverse arrangement of microtubules)

Stimulate proliferation (increase cell division in SAM)

Question 4

Economic uses of GA (2)

Answer 4

The Green Revolution (favours short plants for mass growth)

Enhancing cell size (increasing sugar cane yield)

Question 5

What is the aleurone layer? How does GA work here?

Answer 5

The layer sitting bw the seed coat and embryo (important for GA stimulated pathways)

GA binds to the GA Receptor on the plasma membrane -> initiates 2 separate signalling events

Question 6

GA promoting seed germination growth

Answer 6

Gibberellins released into endosperm -> diffuse into aleurone layer -> layer secretes alpha-amylase/hydrolases into the endosperm -> starch/other macromolecules breakdown -> endosperm solutes are absorbed by the scutellum + transported to growing embryo

Question 7

GA induced Ca+2-independent pathway

Answer 7

GA binds to plasma membrane -> activated G-protein to make cGMP -> activated signalling molecules that bind to DELLA repressors -> DELLA inactivates -> MYB activates and binds to an amylase promoter -> transcription/translation occur

Question 8

GA induced Ca+2-dependent pathway

Answer 8

Rough ER releases vesicles containing alpha-amylase -> travels to Golgi body to get processed -> vesicles released w secretory proteins to plasma membrane -> Enzyme released into endosperm to degrade starch

Question 9

What is the role of calcium and calmodulin with exocytosis, respectively

Answer 9

Ca + exocytosis: Ca imp for proper fusion of amylase containing vesicles with the plasma membrane of aleurone cells

Calmodulin + exocytosis: Ca-CaM upregulates an ER Ca-ATPase that fns in proper processing of amylase in the ER

Question 10

What is ethylene? Where does it originate? How was it synthesized? How is it regulated?

Answer 10

An unstable hormone that freely diffuses in air

Origin: in all plants (especially in ripening fruit and senescing leaves)

Synthesis: O2 concerts ACC oxidase into ethylene

Regulation: conjugations of ethylene with ACC to form n-malonyl ACC

Question 11

Categories of fruit (2)

Answer 11

Climacteric (ripening associated w sharp rise in respiration and ethylene)

Non-climactic (little to no response to ethylene)

Question 12

How is ethylene autocatalytic?

Answer 12

Applying exogenous ethylene showed that the plant ultimately produced ethylene as well

Question 13

What is the abscission zone composed of? (2)

Answer 13

Separation layer (cells divide, Golgi-vesicles secrete enzymes into the apoplast, cells “round out”)

Protective layer (cells become suberized (“scab”))

Question 14

What is the function of removing leaves (abscission)?

Answer 14

To remove leaves/fruits/flowers during times of drought/seasonally as a method of restricting resources p

Question 15

What are the rice forms that have risen in response to flooding? (2)

Answer 15

Deep water/Snorkel Rice (adapted to long periods of flooding by elongating very rapidly so part of its foliage is above water)

Submergence Tolerant/Scuba Rice (adapted to short periods of flooding where it doesn’t grow until flooding is over)

Question 16

How does GA promote cell elongation in snorkel rice? (2)

Answer 16

Elongation (increased synthesis of expansion, promote transverse arrangement of microtubules)

Division (increased synthesis of CDKs at G1-S/2-M check points, increased synthesis of cyclins)

Question 17

What synergistic interactions bw GA and Ethylene occur to promote elongation? (2)

Answer 17

Biosynthesis + entrapment of ethylene

Question 18

What does ethylene to GA that aids in elongation?

Answer 18

ACC synthase increases its presence in the cell elongation zones

Ethylene increases GA production and tissue sensitivity to GA (by upregulating transcription of necessary enzymes)

Question 19

Deep water rice flooding strategy (how does snorkel rice try to survive during flooding?) (explain the pathway and outcomes)

Answer 19

Submergence of plant into water -> ethylene activated -> SK1, SK2 (regulate ethylene response) -> -> GA biosynthesis or GA signal transduction -> promote stem elongation

Outcomes:
Water level far above plant = plant exhausts its carb reserves before growing above the water -> dies
Water level just below plant = plant grows above surface before E deficiency -> SUBMERGENCE-ESCAPE

Question 20

Submergence tolerant rice flooding strategy (how does scuba rice try to survive during flooding?) (explain the pathway and outcomes)

Answer 20

Submergence of plant in water -> ethylene activated -> SUB1A (ethylene response factor) -> SLR1, SLR2 (GA repressor signal) -> inhibition of elongation

Outcomes:
Carbs are exhausted before flood subdues = plant becomes E deficient -> SUBMERGENCE-INTOLERANT
Carbs are economized until flood subdues = new leaves can grow -> SUBMERGENCE-TOLERANT

Question 21

What are SixSub1 “mega varieties”?

Answer 21

A backcrossed plant variety containing SUB1 so they can survive floods

Question 22

What is aerenchyma? What is their function?

Answer 22

A parenchyma cell w very large intercellular (air) spaces

Act as an oxygen reserve in anoxic environments (ex. After flooding); allow oxygen to enter the root from the shoot

Question 23

Explain the two processes leading to aerechyma cell formation

What initiates these processes?

Answer 23

1) tissue development -> differential cell growth -> cell separation (move away from one another) -> Schizogeous aerenchyma
2) tissue development -> uniform cell growth -> cell death (die to make air space) -> Lysigenous aerenchyma

Initiated by ethylene

Question 24

Problem with aerenchyma and the global climate change

Answer 24

Aerenchyma release methane into the atmosphere and with more flooding, more plants have turned to aerenchyma formation to survive resulting in an increase in aerenchyma release, adding to global warming