Question
Blue-Light Photoreceptors
Blue light initiates a variety of responses in plants, including
phototropism, the light-induced opening of stomata (see
Figure 36.14), and the light-induced slowing of hypocotyl
elongation that occurs when a seedling breaks ground. The
biochemical identity of the blue-light photoreceptor was so
elusive that in the 1970s, plant physiologists began to call
this receptor “cryptochrome” (from the Greek kryptos, hidden,
and chrom, pigment). In the 1990s, molecular biologists
analyzing Arabidopsis mutants found that plants use as many
as three different types of pigments to detect blue light.
Cryptochromes, molecular relatives of DNA repair enzymes,
are involved in the blue-light-induced inhibition of stem
elongation that occurs, for example, when a seedling first
emerges from the soil. Phototropin is a protein kinase involved
in mediating phototropic curvatures, such as those studied in
grass seedlings by the Darwins, and in chloroplast movements
in response to light. There is currently much debate
about whether phototropin or a carotenoid-based photoreceptor
called zeaxanthin is the major blue-light photoreceptor
involved in blue-light-mediated stomatal opening.
Phytochromes as Photoreceptors
When introducing signal transduction in plants earlier in the
chapter, we discussed the role of the plant pigments called
phytochromes in the de-etiolation process. Phytochromes
regulate many plant responses to light. Let’s look at two more
examples: seed germination and shade avoidance.
Phytochromes and Seed Germination
Studies of seed germination led to the discovery of phytochromes.
Because of limited nutrient reserves, many types
of seeds, especially small ones, germinate only when the light
environment and other conditions are near optimal. Such
seeds often remain dormant for years until light conditions
change. For example, the death of a shading tree or the plowing
of a field may create a favorable light environment.
In the 1930s, scientists at the U.S. Department of Agriculture
determined the action spectrum for light-induced
germination of lettuce seeds. They exposed water-swollen
seeds to a few minutes of monochromatic (single-colored)
light of various wavelengths and then stored the seeds
in the dark. After two days, the researchers counted the
note: summarize
Blue light initiates a variety of responses in plants, including
phototropism, the light-induced opening of stomata (see
Figure 36.14), and the light-induced slowing of hypocotyl
elongation that occurs when a seedling breaks ground. The
biochemical identity of the blue-light photoreceptor was so
elusive that in the 1970s, plant physiologists began to call
this receptor “cryptochrome” (from the Greek kryptos, hidden,
and chrom, pigment). In the 1990s, molecular biologists
analyzing Arabidopsis mutants found that plants use as many
as three different types of pigments to detect blue light.
Cryptochromes, molecular relatives of DNA repair enzymes,
are involved in the blue-light-induced inhibition of stem
elongation that occurs, for example, when a seedling first
emerges from the soil. Phototropin is a protein kinase involved
in mediating phototropic curvatures, such as those studied in
grass seedlings by the Darwins, and in chloroplast movements
in response to light. There is currently much debate
about whether phototropin or a carotenoid-based photoreceptor
called zeaxanthin is the major blue-light photoreceptor
involved in blue-light-mediated stomatal opening.
Phytochromes as Photoreceptors
When introducing signal transduction in plants earlier in the
chapter, we discussed the role of the plant pigments called
phytochromes in the de-etiolation process. Phytochromes
regulate many plant responses to light. Let’s look at two more
examples: seed germination and shade avoidance.
Phytochromes and Seed Germination
Studies of seed germination led to the discovery of phytochromes.
Because of limited nutrient reserves, many types
of seeds, especially small ones, germinate only when the light
environment and other conditions are near optimal. Such
seeds often remain dormant for years until light conditions
change. For example, the death of a shading tree or the plowing
of a field may create a favorable light environment.
In the 1930s, scientists at the U.S. Department of Agriculture
determined the action spectrum for light-induced
germination of lettuce seeds. They exposed water-swollen
seeds to a few minutes of monochromatic (single-colored)
light of various wavelengths and then stored the seeds
in the dark. After two days, the researchers counted the
note: summarize
Answers
GPT-4o mini
Blue-light photoreceptors in plants play a crucial role in various physiological responses, such as phototropism, stomatal opening, and the inhibition of hypocotyl elongation during seedling emergence. The main blue-light photoreceptors are cryptochromes and phototropins. Cryptochromes, which are related to DNA repair enzymes, help inhibit stem elongation when seedlings emerge. Phototropins are involved in mediating phototropic responses and regulating chloroplast movement in response to light. There is ongoing debate about the primary photoreceptor for stomatal opening, with some evidence suggesting a carotenoid-based receptor called zeaxanthin may play a key role.
Phytochromes are another class of photoreceptors that regulate various plant responses, including seed germination and shade avoidance. Many seeds, particularly small ones, remain dormant until they detect optimal light conditions, which could occur due to changes in the surrounding environment, such as the death of a shading tree. Research in the 1930s established that light exposure is essential for the germination of seeds like lettuce, further confirming the important role of phytochromes in plant growth and development.
Phytochromes are another class of photoreceptors that regulate various plant responses, including seed germination and shade avoidance. Many seeds, particularly small ones, remain dormant until they detect optimal light conditions, which could occur due to changes in the surrounding environment, such as the death of a shading tree. Research in the 1930s established that light exposure is essential for the germination of seeds like lettuce, further confirming the important role of phytochromes in plant growth and development.