Gibberellins

Question 1

Gibberellin

Answer 1

A substance secreted by parasitic fungi causes the foolish seedling disease, a rice disease in which plants grow extremely fast, look spindly and pale, and break off easily.

Question 2

Gibberellins were identified as..

Answer 2

Endogenous plant growth regulators promote stem elongation and seed germination and, in some plants, flowering and fruit development.

Question 3

Gibberellins are made via two pathways:

Answer 3

mevalonic acid-dependent and mevalonic acid-independent,

Question 4

3 different sites in the plant where gibberellin biosynthesis occurs.

Answer 4

1. Developing seeds and fruits
2. Young leaves
3. Root tips

Question 5

3 different regions of the cell where gibberellin biosynthesis occurs.

Answer 5

1. Early stages (cyclizations) in the proplastids, but not in the mature chloroplast.
2. Next stage (oxidation) is in the ER.
3. Final stage (formation of different GAs) in the cytosol.

Question 6

Gibberellins are made up of

Answer 6

Conjugated sugars are used either for storage or inactivation.

Question 7

Gibberellins vs auxin in cell elongation and division

Answer 7

Similar to auxin GA, it increases the extensibility and stress relaxation of the wall, but there is no change in cell wall acidification and a longer lag time.

Question 8

Transgenic experiments support that GA-induced cell elongation is partially mediated by

Answer 8

EXPANSIN 4, which also naturally increases in deepwater rice when flooded or when GA treatment is given.

Question 9

How do GAs promote growth

Answer 9

GAs induce the expression of cell cycle regulatory proteins called cyclins. GAs promote elongation by cell wall loosening and stabilizing the orientation of cortical microtubules, which help direct growth.

Question 10

GA promotes elongations and ..

Answer 10

1. promotes avoidance of submergence: keep plant above the water line.
2. During germination, nutrient-mobilizing enzymes are expressed: breakdown of stretch in the endosperm initiated by GA, produced by the embryo or added via the malting process.
3. GA is synthesized in the embryo and moves into aleurone to induce the production of alpha-amylase (enzyme that breakdown starch)

Question 11

What is seed germination and aleurone layer

Answer 11

1. seed germination: mobilization of enzyme reserves through the
   activation of α-amylase
   expression. Barley seed
   germination as a model
   system for GA action.
   Scutellum: absorptive
   organ
2. aleurone layer: contains
   Protein bodies.

Question 12

The role of gibberellins in germination involves the activation of enzymes.

Answer 12

1. Following imbibition, the seed embryo begins to synthesize gibberellins.
2. The gibberellins diffuse to the aleurone layer of the seed where they
   induce the synthesis of a-amylases and proteases.
3. These enzymes break down the nutrient reserves in the seed to provide
   the embryo with the resources to maintain growth

Question 13

GID1

Answer 13

Gibberellin Insensitive Dwarf 1- encodes as a GA receptor. Unlike the biosynthesis mutant, the rice GID1 mutant is not rescued by GA; it is gibberellin insensitive.

Question 14

Semidominat GA insensitive dwarfs

Answer 14

These mutants do not respond to exogenous GA and accumulate very high levels of GA; they are not biosynthesis mutants.

Question 15

What mutants encode the DELLA repressor, and what is it?

Answer 15

Ga-insensitive1 and slender1. The enhanced DELLA respressor = loss of function.

Question 16

GA, GID, DELLA process

Answer 16

Active GA binds to soluble receptor GID1 in the nucleus, and the GA-GID1 complex binds to the DELLA protein repressor. The complex binding induces DELLA protein degradation from the GRAS domain, allowing gene transcription.

If there is No GA, the DELLA repressor blocks the transcription of GA-inducible genes.

Question 17

Is the DELLA domain necessary for GID1 binding?

Answer 17

Yes, deleting the DELLA domain confers a GA-insensitive, semi-dominant dwarf phenotype.

Question 18

Auxin signaling vs. GA signaling

Answer 18

For auxin, the F-box
protein TIR1 is the
auxin receptor and
auxin binds to the
receptor directly.

For GA, GID1 is the
receptor and GA binds
the receptor to the
DELLA protein, which
then associates with
the F-box protein.

Question 19

Reduced height 1 mutation

Answer 19

In wheat, encodes a mutant DELLA. Insertion in the regulatory domain reduces binding to GID receptor, stabilizing the DELLA repressor protein.