Plant Hormones and GA Movement

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Questions and Answers

What role does GA play in plant growth?

It restricts seed germination.

It eliminates the need for cyclins.

It promotes elongation by stabilizing microtubules. (correct)

It inhibits cell expansion.

In pea plants, how can a mutant na shoot be rescued?

By applying gibberellins directly.

By grafting onto a Na root. (correct)

By growing in isolation.

By treating with auxins.

During the germination of monocot seeds, where does GA move after the embryo?

To the stigma.

To the root.

To the aleurone. (correct)

To the cotyledon.

What does GA induce to promote cell division?

Cell-cycle regulatory proteins called cyclins. Signup and view all the answers

Which of the following is true about GA transport?

GA transport is influenced by environmental factors. Signup and view all the answers

Which process is directly activated by GA during seed germination?

Amylase production. Signup and view all the answers

What effect does GA have on cortical microtubules?

It stabilizes their orientation. Signup and view all the answers

How does GA contribute to cell expansion?

Through the loosening of cell walls. Signup and view all the answers

What is the primary function of GA receptors as described in the content?

They serve as soluble receptors without any detected enzymatic function. Signup and view all the answers

What characteristic is unique to the gid1 rice mutant?

It exhibits gibberellin insensitivity. Signup and view all the answers

What effect does overexpression of GID1 have on plants?

It makes plants more responsive to gibberellin. Signup and view all the answers

How many GID1 genes does Arabidopsis contain?

Three Signup and view all the answers

What is the phenotype of gid1a gid1b gid1c triple mutants in terms of growth and response to GA?

They show severe dwarfed characteristics with no GA responses. Signup and view all the answers

What type of family do GA receptors belong to?

Serine hydrolases Signup and view all the answers

What was the original publication that identified GID1 and its role?

Nature 437:693-698 Signup and view all the answers

What is a common feature of single GID1 receptor mutants in Arabidopsis?

They do not exhibit significant phenotypes. Signup and view all the answers

What is the primary role of F-box proteins SLEEPY (SLY) and GID2 in plant growth?

Facilitating the degradation of DELLA proteins Signup and view all the answers

What effect do sleepy and gid2 mutants have on DELLA protein levels in response to gibberellins (GA)?

DELLA levels remain stable Signup and view all the answers

How would you describe the phenotype of the gid2 mutant?

Short and dwarf due to inhibited GA responses Signup and view all the answers

What is the function of the slr1 gene in rice plants?

Encodes a mutated non-functional DELLA protein Signup and view all the answers

What happens to plant growth when both SLEEPY and GID2 are inactive in a plant?

DELLA proteins accumulate, inhibiting growth Signup and view all the answers

What does the phenotype of a slr1gid2 double mutant most likely exhibit?

Enhancement of dwarfism characteristics Signup and view all the answers

The accumulation of which protein is primarily affected in sleepy1-10 and gid2-1 mutants under GA treatment?

DELLA protein Signup and view all the answers

Which of the following statements is true regarding the function of SLEEPY in Arabidopsis?

SLEEPY is required for the degradation of DELLA proteins. Signup and view all the answers

How many DELLA proteins does Arabidopsis have?

5 Signup and view all the answers

Which DELLA protein is unique to rice?

SLR1 Signup and view all the answers

What type of function do RGA, RGL2, and RGL3 have in Arabidopsis?

Repressing floral development Signup and view all the answers

Which process affects the post-translational regulation of DELLA proteins?

Proteasome-mediated degradation Signup and view all the answers

Which of the following is the DELLA protein in barley?

SLN1 Signup and view all the answers

Which mutation leads to constitutive GA responses in Arabidopsis?

GAI deletion Signup and view all the answers

What do RGA and GAI have in common regarding their transcription?

Both are transcribed in most tissues Signup and view all the answers

Which DELLA protein is responsible for increased height in wheat?

RHT Signup and view all the answers

Which modification is NOT associated with DELLA protein regulation?

Methylation Signup and view all the answers

What is a common function of DELLA proteins in plants?

Repress stem elongation Signup and view all the answers

What is the role of DELLA proteins in the gibberellin signaling pathway?

They act as inhibitors of gibberellin responses. Signup and view all the answers

What happens in plants with a loss of DELLA repressors when exposed to gibberellin?

They have a strong constitutive growth response. Signup and view all the answers

What is a characteristic of the gai mutation in Arabidopsis?

It results in a wild-type phenotype under gibberellin treatment. Signup and view all the answers

What function does the 26S proteasome serve in relation to ubiquitinated proteins?

It breaks down target proteins and recycles ubiquitin. Signup and view all the answers

What is the consequence of enhanced DELLA repressor activity in the presence of gibberellin?

No response to gibberellin signaling. Signup and view all the answers

Study Notes

GA Biosynthesis and Regulation

Gibberellins (GAs) are regulated by various hormones and environmental factors.
GAs can move over long distances and are graft-transmissible, influencing nearby plants.
In peas, a dwarf mutant can be rescued through grafting onto a wild-type rootstock.
In maize, GA or a precursor transfers from wild-type plants to dwarf mutants, promoting their growth.

GA Transport and Action in Seed Germination

During seed germination in monocots, GAs move from the embryo to the aleurone layer to activate amylase, converting starch to sugars.
GA promotes plant growth primarily through cell expansion and division.

Mechanism of GA-Induced Growth

GAs induce cell division via cyclins, important regulatory proteins of the cell cycle.
Cell elongation is facilitated by GA's effects on cell wall loosening and stabilization of cortical microtubules.

DELLA Proteins and Their Functions

Different plants exhibit varying numbers of DELLA proteins; Arabidopsis has five.
In Arabidopsis, DELLA proteins (GAI, RGA, RGL1, RGL2, RGL3) play distinct roles in regulating seed germination, stem elongation, and floral development.
DELLA protein regulation occurs transcriptionally and post-translationally, with GA signaling leading to their degradation.

GA Receptors and Their Role

GA receptors, part of the serine hydrolase family, do not have enzymatic activity.
GID1, first identified in rice, acts as a GA receptor; its mutants are gibberellin-insensitive.
Overexpression of GID1 enhances plant sensitivity to GAs, increasing growth responses.

Functional Redundancy of GID1 in Arabidopsis

Arabidopsis possesses three GID1 genes; these show redundancy, with single mutants revealing minimal phenotypic changes.
Triple mutants of GID1 display severe dwarfism and lack GA responses.

SLEEPY/GID2 and DELLA Interaction

F-box proteins SLEEPY (SLY) in Arabidopsis and GID2 in rice bind to DELLA proteins for proteolytic degradation.
Mutants lacking SLEEPY or GID2 demonstrate reduced growth due to the stabilization of DELLA proteins, inhibiting GA-induced elongation.

Dominant and Recessive Mutations in GID and DELLA Proteins

Mutations in slr1 result in elongated and slender plants due to enhanced GA responses.
Mutations in gid2 lead to dwarfism as they fail to degrade DELLA proteins, resulting in restricted growth.
The double mutant of slr1 and gid2 combines traits from both, amplifying the GA response due to loss of DELLA repression.

Proteolytic Pathway Involving Ubiquitin

Ubiquitin ligase complexes target proteins for degradation, essential for regulating protein levels in response to GA.
The 26S proteasome is responsible for breaking down the ubiquitinated proteins, recycling ubiquitin for future use.

Summary of GA's Role

GAs interact with a complex regulatory network involving DELLA proteins and GID1 receptors to promote growth.
Understanding the balance of these factors is critical for manipulating plant growth and development in agricultural practices.

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Description

Explore the complex regulatory control of gibberellins (GAs) in plant biosynthesis and metabolism. This quiz examines the movement of GAs, their graft-transmissibility, and the physiological effects of grafting on mutant plants like peas and maize seedlings.