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?

    <p>Cell-cycle regulatory proteins called cyclins.</p> Signup and view all the answers

    Which of the following is true about GA transport?

    <p>GA transport is influenced by environmental factors.</p> Signup and view all the answers

    Which process is directly activated by GA during seed germination?

    <p>Amylase production.</p> Signup and view all the answers

    What effect does GA have on cortical microtubules?

    <p>It stabilizes their orientation.</p> Signup and view all the answers

    How does GA contribute to cell expansion?

    <p>Through the loosening of cell walls.</p> Signup and view all the answers

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

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

    What characteristic is unique to the gid1 rice mutant?

    <p>It exhibits gibberellin insensitivity.</p> Signup and view all the answers

    What effect does overexpression of GID1 have on plants?

    <p>It makes plants more responsive to gibberellin.</p> Signup and view all the answers

    How many GID1 genes does Arabidopsis contain?

    <p>Three</p> Signup and view all the answers

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

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

    What type of family do GA receptors belong to?

    <p>Serine hydrolases</p> Signup and view all the answers

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

    <p>Nature 437:693-698</p> Signup and view all the answers

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

    <p>They do not exhibit significant phenotypes.</p> Signup and view all the answers

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

    <p>Facilitating the degradation of DELLA proteins</p> Signup and view all the answers

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

    <p>DELLA levels remain stable</p> Signup and view all the answers

    How would you describe the phenotype of the gid2 mutant?

    <p>Short and dwarf due to inhibited GA responses</p> Signup and view all the answers

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

    <p>Encodes a mutated non-functional DELLA protein</p> Signup and view all the answers

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

    <p>DELLA proteins accumulate, inhibiting growth</p> Signup and view all the answers

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

    <p>Enhancement of dwarfism characteristics</p> Signup and view all the answers

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

    <p>DELLA protein</p> Signup and view all the answers

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

    <p>SLEEPY is required for the degradation of DELLA proteins.</p> Signup and view all the answers

    How many DELLA proteins does Arabidopsis have?

    <p>5</p> Signup and view all the answers

    Which DELLA protein is unique to rice?

    <p>SLR1</p> Signup and view all the answers

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

    <p>Repressing floral development</p> Signup and view all the answers

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

    <p>Proteasome-mediated degradation</p> Signup and view all the answers

    Which of the following is the DELLA protein in barley?

    <p>SLN1</p> Signup and view all the answers

    Which mutation leads to constitutive GA responses in Arabidopsis?

    <p>GAI deletion</p> Signup and view all the answers

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

    <p>Both are transcribed in most tissues</p> Signup and view all the answers

    Which DELLA protein is responsible for increased height in wheat?

    <p>RHT</p> Signup and view all the answers

    Which modification is NOT associated with DELLA protein regulation?

    <p>Methylation</p> Signup and view all the answers

    What is a common function of DELLA proteins in plants?

    <p>Repress stem elongation</p> Signup and view all the answers

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

    <p>They act as inhibitors of gibberellin responses.</p> Signup and view all the answers

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

    <p>They have a strong constitutive growth response.</p> Signup and view all the answers

    What is a characteristic of the gai mutation in Arabidopsis?

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

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

    <p>It breaks down target proteins and recycles ubiquitin.</p> Signup and view all the answers

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

    <p>No response to gibberellin signaling.</p> 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.

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