Plant Physiology: Coleoptile and Stomatal Movements

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Questions and Answers

What is the purpose of the coleoptile in grass seedlings?

To protect the growing shoot (correct)

To store energy for the plant

To facilitate water uptake

To absorb nutrients from the soil

What results from unequal light perception in the coleoptile?

Balanced growth on all sides

Uniform bending of the coleoptile

Unequal concentrations of auxin (correct)

Complete cessation of growth

What causes phototropic bending in coleoptiles?

Growing organs perceiving unilateral light (correct)

Temperature fluctuations

Presence of nutrients

Exposure to soil moisture

When does a coleoptile stop growing?

Once the shoot has emerged from the soil Signup and view all the answers

Which statement about the growth of coleoptiles is true?

Bending does not occur in non-growing organs Signup and view all the answers

What triggers unequal growth in the coleoptile?

Differing concentrations of auxin Signup and view all the answers

How do coleoptiles respond to sunlight?

They may bend towards the light source Signup and view all the answers

What happens to coleoptiles and shoots that have stopped elongating when exposed to unilateral light?

They do not bend Signup and view all the answers

What factor most closely regulates stomatal opening in Vicia faba according to the data provided?

Photosynthetically active radiation Signup and view all the answers

At what time of day is stomatal aperture most likely to be affected by blue light?

Midday Signup and view all the answers

Which type of light is related to stomatal movements in the provided data?

Blue light Signup and view all the answers

What happens to protoplasts when exposed to blue light?

They swell. Signup and view all the answers

What element of light was indicated as a dominant response for stomatal opening?

Blue light Signup and view all the answers

In which experimental condition is the stomatal pore measured?

Under a blue-light background Signup and view all the answers

What is the unit of measurement for stomatal aperture provided in the data?

Micrometers (µm) Signup and view all the answers

Which statement is correct regarding stomatal pore changes over the day?

They fluctuate with light intensity. Signup and view all the answers

What is the role of cryptochromes in plants?

Inhibit stem elongation. Signup and view all the answers

What is characteristic of the hy4 mutant of Arabidopsis?

It has elongated hypocotyl when exposed to blue light. Signup and view all the answers

Which light condition is associated with the hy4 mutant's phenotypic expression?

Blue light. Signup and view all the answers

What effect do cryptochromes have on hypocotyl elongation in normal plants?

They inhibit elongation. Signup and view all the answers

In which plant species is the hy4 mutant observed?

Arabidopsis thaliana. Signup and view all the answers

What is one of the metabolic pathways that supply osmotically active solutes to guard cells?

Production of sucrose from starch hydrolysis Signup and view all the answers

Which compound has been proposed as the chromophore of a blue-light photoreceptor in stomatal guard cells?

Carotenoid zeaxanthin Signup and view all the answers

What is the outcome of the identification of mutants for key blue-light responses?

Isolation of the relevant gene Signup and view all the answers

What role do K+ and Cl– play in the metabolic pathways for guard cells?

They are coupled to the biosynthesis of malate2–. Signup and view all the answers

Which process occurs during the production of sucrose in guard cells?

Starch hydrolysis Signup and view all the answers

What remains to be established regarding the blue-light photoreceptor in guard cells?

The identity of the apoprotein Signup and view all the answers

What process in guard cell chloroplasts is responsible for producing sucrose?

Photosynthetic carbon fixation Signup and view all the answers

Which of the following is NOT a source of osmotically active solutes in guard cells?

Respiration of carbohydrates Signup and view all the answers

What is the main cell type responsible for blue light-dependent stomatal movements?

Guard cells Signup and view all the answers

How does the stomatal response to blue light differ from phototropism?

It is rapid and localized in a single cell type. Signup and view all the answers

What characteristic of blue light–dependent stomatal movements makes it suitable for experimental studies?

It is rapid and reversible. Signup and view all the answers

Which physiological process is NOT mentioned as being functionally important at early stages of plant development?

Stomatal response to blue light Signup and view all the answers

What does the signal transduction cascade associated with blue light regulation involve?

The perception of blue light linked to stomatal opening. Signup and view all the answers

What does the rapidity of the stomatal response to blue light indicate?

It happens almost instantaneously. Signup and view all the answers

Which statement is true regarding the regulation of stomatal movements by blue light?

It is reversible and can be influenced by other light colors. Signup and view all the answers

The characteristic of blue light response in stomata enables what specific feature?

Maintaining water loss regulation. Signup and view all the answers

Study Notes

Coleoptile Growth and Phototropism

Grass shoots are protected by a coleoptile, a modified leaf.
Unequal light perception in the coleoptile leads to uneven auxin distribution, causing it to bend (phototropism).
Phototropic bending only occurs in actively growing organs; it ceases once the shoot emerges from the soil.

Stomatal Movements and Blue Light

Stomatal movements are a valuable model for studying blue light responses.
The stomatal response to blue light is rapid, reversible, and localized to guard cells.
This response regulates stomatal movements throughout the plant's life, unlike phototropism or hypocotyl elongation which are primarily important in early development.
Stomatal opening in Vicia faba closely follows photosynthetically active radiation (400-700 nm).
Four metabolic pathways supply osmotically active solutes to guard cells: K+ and Cl- uptake coupled with malate2- biosynthesis; sucrose production from starch hydrolysis; sucrose production via photosynthetic carbon fixation in guard cell chloroplasts.

Blue Light, Stomatal Aperture, and Time of Day

Figure 18.10 shows the response of stomata to blue light under a red-light background.
Stomatal aperture increases significantly with blue light exposure.

Blue Light Responses and Gene Identification

Research on blue-light responses, such as phototropism and stem elongation inhibition, involved identifying mutants and isolating relevant genes.
Gene cloning led to identifying and characterizing encoded proteins, important for elucidating mechanisms.

Cryptochromes and Hypocotyl Elongation

The hy4 mutant of Arabidopsis lacks blue-light stimulated inhibition of hypocotyl elongation.
hy4 plants exhibit elongated hypocotyls under blue light due to the genetic defect.
Zeaxanthin is a proposed chromophore for a blue-light photoreceptor in stomatal guard cells, but the apoprotein remains unidentified.

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Description

Explore the fascinating mechanisms of coleoptile growth and phototropism, as well as the role of blue light in regulating stomatal movements. Understand how auxiliary factors like auxin distribution and metabolic pathways influence plant development. This quiz will challenge your knowledge of plant physiological responses to light.