Lecture 11 Flashcards
What is foolish seedling?
A rice disease caused by toxins in fungus that causes plant to grow and grow then fall over
Origin of gibberellin (GA)
What pathway synthesizes it?
Immature/germinating seeds Elongating stems Growing fruits (plastids, ER, cytosol)
Synthesized by the terpenoid pathway
GA promotes stem elongation 2 ways (2) (3 methods inside one)
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)
Economic uses of GA (2)
The Green Revolution (favours short plants for mass growth)
Enhancing cell size (increasing sugar cane yield)
What is the aleurone layer? How does GA work here?
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
GA promoting seed germination growth
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
GA induced Ca+2-independent pathway
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
GA induced Ca+2-dependent pathway
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
What is the role of calcium and calmodulin with exocytosis, respectively
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
What is ethylene? Where does it originate? How was it synthesized? How is it regulated?
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
Categories of fruit (2)
Climacteric (ripening associated w sharp rise in respiration and ethylene)
Non-climactic (little to no response to ethylene)
How is ethylene autocatalytic?
Applying exogenous ethylene showed that the plant ultimately produced ethylene as well
What is the abscission zone composed of? (2)
Separation layer (cells divide, Golgi-vesicles secrete enzymes into the apoplast, cells “round out”)
Protective layer (cells become suberized (“scab”))
What is the function of removing leaves (abscission)?
To remove leaves/fruits/flowers during times of drought/seasonally as a method of restricting resources p
What are the rice forms that have risen in response to flooding? (2)
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)
How does GA promote cell elongation in snorkel rice? (2)
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)
What synergistic interactions bw GA and Ethylene occur to promote elongation? (2)
Biosynthesis + entrapment of ethylene
What does ethylene to GA that aids in elongation?
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)
Deep water rice flooding strategy (how does snorkel rice try to survive during flooding?) (explain the pathway and outcomes)
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
Submergence tolerant rice flooding strategy (how does scuba rice try to survive during flooding?) (explain the pathway and outcomes)
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
What are SixSub1 “mega varieties”?
A backcrossed plant variety containing SUB1 so they can survive floods
What is aerenchyma? What is their function?
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
Explain the two processes leading to aerechyma cell formation
What initiates these processes?
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
Problem with aerenchyma and the global climate change
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
