20 Questions
Plant hormones include only auxin, cytokinin, and gibberellins
False
The concept of plant hormones originated from an experiment on phototropism conducted by Charles Darwin and his son Francis in 1880
True
Plant hormones are structurally similar to their animal counterparts
False
Ethylene gas and indole-3-acetic acid (IAA) are examples of relatively simple, small molecules that act as plant hormones
True
The bending of plants toward light, known as phototropism, is regulated by the hormone abscisic acid (ABA)
False
BR-induced genes are also up-regulated by auxin
True
The absence of a BR signal leads to the accumulation of BES1 and BZR1 in the nucleus
False
Elevating endogenous auxin levels makes plants less sensitive to BR application in hypocotyl elongation assays
False
The convergence of auxin and BR pathways occurs at an early point in hormone signaling
False
The majority of the phytohormones have identified receptors and other upstream signaling components
False
Ethylene receptors ETR1 and ERS1 have intact HK domains, while ETR2, ERS2, and EIN4 have degenerate HK domains and lack catalytic activity
True
Mutations in ethylene receptors confer dominant ethylene insensitivity, suggesting they function as negative regulators upstream of CTR1
True
Ethylene signal transduction involves a MAP kinase cascade and positive regulators EIN2, EIN3, and EIL1
True
Ethylene binds to receptors inactivating them, leading to down-regulation of CTR1 activity
False
Auxin and brassinosteroid (BR) signaling pathways converge and regulate each other in some developmental processes
True
Ethylene promotes leaf expansion and vascular differentiation in plants.
False
The green revolution in the 20th century utilized genetically modified tall varieties of wheat and rice.
False
Cytokinins were initially discovered for their ability to inhibit cell division during cytokinesis.
False
ABA promotes seed dormancy and inhibits stress signaling pathways in plants.
False
Aux/IAA proteins prevent the activity of ARF transcription factors in the presence of auxin stimulus.
True
Study Notes
- Plants use hormones for various aspects of growth and development, with each hormone eliciting specific responses.
- Ethylene promotes fruit ripening, senescence, and responses to pathogens and abiotic stresses.
- IAA (auxin) regulates cell division, expansion, vascular differentiation, lateral root development, and apical dominance.
- Cytokinins were first identified for their ability to promote cell division during cytokinesis.
- JA is a volatile signal that modulates pollen development and responses to pathogen infection.
- BRs regulate cell expansion and light-regulated development.
- GAs promote germination, stem elongation, and induction of flowering.
- ABA promotes seed dormancy and involves several stress signaling pathways.
- Historically, hormonal effects have been defined by the application of exogenous hormones, but recent research has used hormone biosynthetic and response mutants to gain a clearer understanding of their roles.
- The green revolution in the 20th century used genetically modified dwarf varieties of wheat and rice, which had shorter stems and were less susceptible to damage from weather, leading to the isolation of GA biosynthesis and response pathways.
- Arabidopsis thaliana, a genetically facile model plant, has been used to isolate mutations that confer altered response to applied hormones.
- Several hormone pathways have been reviewed for further information.
- Regulation by proteolysis has emerged as a major theme in plant hormone signaling, with key regulatory proteins being ubiquitinated and degraded.
- Auxin response is regulated by the Aux/IAA proteins, which form heterodimers with ARF transcription factors and prevent their activity.
- Upon auxin stimulus, the Aux/IAA proteins are targeted to the SCFTIR1 complex, resulting in their ubiquitination and degradation by the 26S proteasome, thereby de-repressing the ARF transcription factors.
- The auxin stimulus promotes the Aux/IAA–TIR1 interaction.
- Most yeast and animal SCF substrates are post-translationally modified, usually by phosphorylation, before they are recognized by their cognate F-box protein, but no such modification has been identified for auxin-induced modification of Aux/IAA proteins.
- The mechanism by which auxin regulates SCF–substrate interactions is unknown.
Test your knowledge of plant signaling pathways with this quiz. Explore topics such as ARF targets, Aux/IAA genes, ethylene, cytokinin, and eukaryotic modular signaling systems.
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