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What is the role of auxin in root bending?
What is the role of auxin in root bending?
Root gravitropism was absent in early plant evolution.
Root gravitropism was absent in early plant evolution.
False
What effect does encountering an obstacle have on root tips?
What effect does encountering an obstacle have on root tips?
Roots rapidly respond and adjust their growth direction.
The elimination of asymmetric auxin response and root bending is observed in _______ mutant.
The elimination of asymmetric auxin response and root bending is observed in _______ mutant.
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Match the following terms with their descriptions:
Match the following terms with their descriptions:
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What is the role of statoliths in seed plants?
What is the role of statoliths in seed plants?
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Thigmotropism involves the differential growth of plants in response to gravity.
Thigmotropism involves the differential growth of plants in response to gravity.
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What is the significance of PIN proteins in plant gravitropism?
What is the significance of PIN proteins in plant gravitropism?
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Statoliths first appear in the ______ of seed plants.
Statoliths first appear in the ______ of seed plants.
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Match the plant type with its statolith characteristics:
Match the plant type with its statolith characteristics:
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Which of the following is true regarding the evolution of gravitropism?
Which of the following is true regarding the evolution of gravitropism?
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The process of cell elongation in shoots is inhibited by more auxin on the basal side.
The process of cell elongation in shoots is inhibited by more auxin on the basal side.
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How does thigmotropism affect roots when they encounter obstacles?
How does thigmotropism affect roots when they encounter obstacles?
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Asymmetric growth in shoots involves changes to ______.
Asymmetric growth in shoots involves changes to ______.
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Which PIN proteins are specialized for gravitropism in plants?
Which PIN proteins are specialized for gravitropism in plants?
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Which photoreceptors are primarily responsive to red and far-red light?
Which photoreceptors are primarily responsive to red and far-red light?
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Blue light is primarily detected by phytochromes.
Blue light is primarily detected by phytochromes.
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What is the significance of the experiments performed by Darwin and his son regarding phototropism?
What is the significance of the experiments performed by Darwin and his son regarding phototropism?
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The photoreceptors known as __________ respond to blue and UVA light.
The photoreceptors known as __________ respond to blue and UVA light.
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Match the following photoreceptors with their light responsiveness:
Match the following photoreceptors with their light responsiveness:
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What happens to a coleoptile when its tip is covered?
What happens to a coleoptile when its tip is covered?
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Phototropism is the movement of plant shoots away from light.
Phototropism is the movement of plant shoots away from light.
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Identify the term for the proteins that have a photosensory domain interacting with chromophores.
Identify the term for the proteins that have a photosensory domain interacting with chromophores.
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What substance did Frits Went isolate that caused coleoptiles to bend towards light?
What substance did Frits Went isolate that caused coleoptiles to bend towards light?
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Briggs found that more auxin accumulates on the illuminated side of a maize seedling.
Briggs found that more auxin accumulates on the illuminated side of a maize seedling.
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What is the term used to describe the movement of auxin from the lighted side to the shaded side of a plant?
What is the term used to describe the movement of auxin from the lighted side to the shaded side of a plant?
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In phototropism, auxin causes cell elongation on the _____ side of the plant.
In phototropism, auxin causes cell elongation on the _____ side of the plant.
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In the Cholodny-Went hypothesis, auxin redistribution occurs leading to _____ in the shaded side.
In the Cholodny-Went hypothesis, auxin redistribution occurs leading to _____ in the shaded side.
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What analysis method shows higher auxin responses on the unilluminated side of the plant?
What analysis method shows higher auxin responses on the unilluminated side of the plant?
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Match the researchers with their contributions regarding auxin.
Match the researchers with their contributions regarding auxin.
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Frits Went's experiments involved removing tips from oat coleoptiles and placing them on _____ for 1 hour.
Frits Went's experiments involved removing tips from oat coleoptiles and placing them on _____ for 1 hour.
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Which of the following functions do phytochromes NOT control?
Which of the following functions do phytochromes NOT control?
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Phytochrome is involved in the greening of plants during photomorphogenesis.
Phytochrome is involved in the greening of plants during photomorphogenesis.
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What factor interacts with phytochrome to activate transcription?
What factor interacts with phytochrome to activate transcription?
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Phytochrome is important for _________ avoidance, which involves vertical leaves and stem elongation.
Phytochrome is important for _________ avoidance, which involves vertical leaves and stem elongation.
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Match the following phytochrome functions with their descriptions:
Match the following phytochrome functions with their descriptions:
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What wavelengths of light are enriched in light transmitted through plants?
What wavelengths of light are enriched in light transmitted through plants?
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The interaction between phytochrome and cryptochrome has no impact on flowering time.
The interaction between phytochrome and cryptochrome has no impact on flowering time.
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Which two genes increase their activity at dawn due to the action of phytochrome?
Which two genes increase their activity at dawn due to the action of phytochrome?
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What effect do short days (SD) have on tuber formation in potatoes?
What effect do short days (SD) have on tuber formation in potatoes?
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Long days induce tuber formation in potatoes.
Long days induce tuber formation in potatoes.
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What is the role of phytochrome (PHYB) in tuber formation?
What is the role of phytochrome (PHYB) in tuber formation?
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Grafting a wild type shoot onto a phyB mutant root __________ tuber formation.
Grafting a wild type shoot onto a phyB mutant root __________ tuber formation.
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What happens to phyB mutants when grown under long days?
What happens to phyB mutants when grown under long days?
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The signal of phytochrome (PHYB) is transmissible through grafting.
The signal of phytochrome (PHYB) is transmissible through grafting.
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What induces bud dormancy in plants?
What induces bud dormancy in plants?
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Study Notes
External Factors and Plant Growth
- Tropisms are movements of plant parts in response to external stimuli. Examples include gravitropism (gravity), phototropism (light), hydrotropism (water), and thigmotropism (touch).
- Positive tropisms are movements toward the stimulus, while negative tropisms are movements away from the stimulus.
- Gravitropism is the response of plants to gravity. Shoots display negative gravitropism, and roots display positive gravitropism.
- Changes in the direction of gravity in roots result in a change of auxin response on the side of the root toward gravity. This results in decreased cell elongation on the lower side, which causes the root to curve towards gravity.
- PIN1 is apically positioned in stele cells, PIN4 is positioned basally in the quiescent center, PIN3 is laterally positioned in the columella cells, and PIN2 is basally positioned in the lateral root cap, cortex, and epidermis.
- PIN3 is important for root and shoot gravitropism; pin3 mutants responding to gravity in both roots and hypocotyls.
- PIN3 is expressed in the starch sheath of stems and the root columella, which are the gravity sensing cells.
- Statoliths, which are amyloplasts, sediment to the bottom of statocytes in the root cap when the direction of gravity changes. This relocation of statoliths causes a shift in actin filaments, which targets vesicles containing PIN3 towards the basal side, resulting in increased auxin on that side and inhibition of the cell elongation in the root and promotion of cell elongation in the shoot.
- Starch biosynthetic mutants (pgm-1) show reduced responses to gravity. Auxin maximum shift (DR5:GFP) was not observed toward the lateral root cap in these mutants.
- Distribution of auxin depends on actin-dependent localization of vesicles carrying auxin efflux carriers. Sedimentation of amyloplasts causes a shift in actin filaments, which targets vesicles to the basal side.
- The evolution of "fast" gravitropic response occurred in seed plants. Statoliths first appeared in the root cap of seed plants.
- Thigmotropism is the differential growth of plants in response to touch. Asymmetric growth in shoots involves changes to calcium, though the molecular mechanisms are unclear. Roots growing around obstacles such as compacted soil or rock resume their positive gravitropism response.
- Roots rapidly respond to obstacles (e.g., scalpel blades) encountered by the root tip. Asymmetric auxin response correlates with root bending.
- Root bending depends on asymmetric auxin response, which is affected by the presence of eir1 and pin2 mutants.
- Plant responses to light vary via phytochromes (red/far-red), cryptochromes (blue), and phototropins (blue).
- Shoots display positive phototropism (movement towards light), with leaf-type structures moving along the light gradient.
- Photoreceptors are proteins with photosensory domains that interact with chromophores (light-absorbing pigments).
- Phytochromes are also needed for responses to red and far-red light wavelengths, and are relevant for germination and flowering responses.
- Phototropism is the movement of shoots toward light, while coleoptiles bend towards the light if the tip is not covered.
Circadian Rhythms
- Circadian rhythms are approximately daily rhythmic phenomena that control many plant responses to light.
- Examples of processes that are regulated by circadian rhythms are leaf folding and unfolding, and photosynthetic activity.
Vernalization
- Some plants require a cold treatment (vernalization) to flower.
- This cold treatment causes changes to plant morphology that result in flowering.
- Vernalization is a mechanism that allows plants to respond to seasonal cues.
- The cold treatment can be mimicked, which suggests various effects on plant morphology and gene expression.
- Vernalization response varies based on the ecotype of relevant plants.
- Some ecotypes require vernalization (winter annuals) while other do not (summer annuals)
Photoperiodism
- Photoperiodism is the response of plants to seasonal changes in the day/night cycle.
- Short-day plants flower when the light period is shorter than a certain critical length (e.g., Chrysanthemums, poinsettias, and strawberries).
- Long-day plants flower when the light period is longer than a certain critical length (e.g., some potatoes, wheat, spinach, lettuce).
- Day-neutral plants flower regardless of day length (e.g., cucumber, sunflower, rice, and pea).
- Different regions of the world result in different photoperiodic experiences of a given species, depending on latitude.
- Phytochrome (and cryptochrome) act as the main component in the long-day pathway.
- Plants use photoreceptors, like phytochrome and cryptochrome, to measure the photoperiod.
- A short-day plant's flowers are controlled by the plant's internal clock and the length of the light period.
Other
- Tuber formation in potato plants occurs primarily in response to short days.
- Phytochrome is needed to regulate tuber formation and is transmissible, between species.
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Explore the intricate role of auxin in root bending and gravitropism through this quiz. From the significance of PIN proteins to the effects of encountering obstacles, test your knowledge on plant responses to gravity and touch. Ideal for students studying plant biology.
