what could happen if I expose a plant to a large amount of light?

*It would depend on the species*. Plants that grow on the tundra of the arctic circle and are exposed to 24 hours of daylight during the brief Summer are all species which evolved under those conditions. Some plant species such a _Poinsettia_, demand a certain number of hours in total darkness or they will never bloom. Those adapted to life on the tundra will thrive. Some plants such as the vegetables you mentioned could grow much larger because of constant photosynthesis. Plants do not _need nighttime to live_, only they use night for dark phases of photosynthesis, but it does not mean photosynthesis cannot proceed even during daylight. However, there are _other growth-related mechanisms_ in plants that depend on photoperiod (large cycles of growth and rest, flowering, disease and pest resistance, and others). Some plants can be given hormonal supplements to counteract these negatives (often this is the case with commercially sold cut flowers). But with most plants, if you grew under lights 24/7, without any special treatment, they might start to decline.

Does phototropism and photoperioddism happen in every plant?Why did Darwin and his son choose coleoptile?Was it because the result of experiment is more obvious?And why choose a young plant?Was it because phototropism changes by time of the plant(age)? How did Danish physiologist come up with the idea to cut off the tip of a coleoptile?

No, actually, it only happens in some plants. One plant that does phototropism is the sunflower. It will bend towards the sun as it moves around.

Did you know a flower of a plant is the reproductive organ of the plant? I did not understand why it has a really great aroma and beauty? Is it for attraction for bees and other animals?

Just to be clear, Pollination is not the same as fertilization. Just because the pollen is passed to the next plant doesn't mean it will fertilize the egg to make a seed. Fertilization is when the sperm in the microspores (pollen) reaches the megaspores (eggs) and then they combine into one. Pollination is just the movement of pollen from plant to plant.

I am curious, is negative phototropism a simple derivative of the positive phototropism as a mandatory part of the nomenclature, or is it actually a well-described phenomenon? And if so, which plants exhibit this behaviour and why?

I believe some forms of negative phototropism would involve things such as the roots of plants in order to ensure, along with other direction-of-growth determining factors, that the roots go into the ground and don't just grow out of the seed wherever.

Main content

Course: Biology library > Unit 34

Lesson 1: Plant responses to light

Phototropism & photoperiodism

Google Classroom

Phototropism, plant growth towards or away from light, and photoperiodism, regulation of flowering and other developmental transitions by day/night length.

Key points

Plants have a variety of developmental, physiological, and growth responses to light—sometimes only to particular wavelengths of light.
In phototropism a plant bends or grows directionally in response to light. Shoots usually move towards the light; roots usually move away from it.
In photoperiodism flowering and other developmental processes are regulated in response to the photoperiod, or day length.
Short-day plants flower when day length is below a certain threshold, while long-day plants flower when day length is above a certain threshold.
In many plants, photoperiodism is controlled by the overlap between the day length cue and the plant's internal circadian rhythms.

Introduction

Almost all plants can photosynthesize, and photosynthesis is key to these plants' survival: it lets them make sugar molecules that serve as fuel and building materials. But plants respond to light—sometimes, to specific wavelengths of light—in other ways as well. These non-photosynthesis-related responses allow plants to adjust to their environment and optimize growth.

For instance, some types of seeds will germinate only when they receive a sufficient amount of light—along with other cues. Other plants have ways to detect if they are in the shade of neighboring plants based on the quality of light they receive. They can increase their upward growth to outcompete their neighbors and get a bigger share of sunshine.

Plant responses to light depend, logically enough, on the plant’s ability to sense light. Light sensing in plants involves special molecules called photoreceptors, which are made up of a protein linked to a light-absorbing pigment called a chromophore. When the chromophore absorbs light, it causes a change in the shape of the protein, altering its activity and starting a signaling pathway. The signaling pathway results in a response to the light cue, such as a change in gene expression, growth, or hormone production.

In this article, we will focus on two examples of plant responses to light and explore how these responses allow plants to match their growth to their environments:

Phototropism is a directional response that allows plants to grow towards, or in some cases away from, a source of light.
Photoperiodism is the regulation of physiology or development in response to day length. Photoperiodism allows some plant species to flower—switch to reproductive mode—only at certain times of the year.

Let's take a look at how these light responses work!

Phototropism

One important light response in plants is phototropism, which involves growth toward—or away from—a light source. Positive phototropism is growth towards a light source; negative phototropism is growth away from light.

Shoots, or above-ground parts of plants, generally display positive phototropism—they bend toward the light. This response helps the green parts of the plant get closer to a source of light energy, which can then be used for photosynthesis. Roots, on the other hand, will tend to grow away from light.

^{1}

Phototropism involves a mobile signal

In 1880, Charles Darwin and his son Francis published a paper in which they described the bending of grass seedlings towards light. Specifically, they examined this response in very young plants that had just sprouted whose leaves and shoots were still covered by a sheath called the coleoptile.

The father-and-son team analyzed the bending response using experiments in which they covered either the tip or the lower part of the coleoptile.

^{1}

Through these experiments, they found that light was perceived at the coleoptile's tip. However, the response—bending, at a cellular level, unequal elongation of cells—took place well below the tip. They concluded that some kind of signal must be sent downwards from the coleoptile’s tip towards its base.

In 1913, Danish physiologist Peter Boysen-Jensen followed up on this work by showing that a chemical signal produced at the tip was indeed responsible for the bending response:

He first cut off the tip of a coleoptile, covered the cut section with a block of gelatin, and replaced the tip. The coleoptile was able to bend normally when it was exposed to light.
When he tried the experiment again using an impermeable flake of mica instead of gelatin, the coleoptile lost the ability to bend in response to light.

Only the gelatin—which allowed a chemical signal to travel through its pores—could allow the necessary communication between tip and base.

Through a variation on this experiment, Boysen-Jensen was also able to show that the mobile signal traveled on the shaded side of the seedling. When the mica plate was stuck in on the illuminated side, the plant could still bend towards the light, but when it was stuck in on the shaded side, the bending response no longer occurred. The results of this experiment also implied that the signal was a growth stimulant rather than a growth repressor since the phototropic response involved faster cell elongation on the shaded side than on the lit side.

Phototropins and auxin

Today, we know that proteins called phototropins are the main photoreceptors responsible for light detection during phototropism—the name is a handy reminder of their role! Like other plant photoreceptors, phototropins are made up of a protein bound to a light-absorbing organic molecule, called the chromophore. Phototropins absorb light in the blue range of the spectrum. When they absorb light, they change shape, become active, and can change the activity of other proteins in the cell.

When a coleoptile is exposed to a source of light, phototropin molecules on the illuminated side absorb lots of light, while molecules on the shady side absorb much less. Through mechanisms that are still not well understood, these different levels of phototropin activation cause a plant hormone called auxin to be transported unequally down the two sides of the coleoptile.

More auxin is transported down the shady side, and less auxin is transported down the illuminated side. Auxin promotes cell elongation, causing the plant to grow more on the shady side and bend in the direction of the light source.

Photoperiodism

Some types of plants require particular day or night lengths in order to flower—that is, to transition to the reproductive phase of their life cycle.

Plants that flower only when day length drops below a certain threshold are called short-day plants. Rice is an example of a short-day plant. $^{2}$ ‍
Plants that flower only when day length rises above a certain threshold are called long-day plants. Spinach and sugar beets are long-day plants. $^{2}$ ‍

By flowering only when day or night lengths reach a certain threshold, these plants are able to coordinate their flowering time with changes in the seasons.

No, not necessarily. Plants often use multiple types of cues to determine when to flower. For instance, temperature and moisture availability may also play into the decision.

Also, some plants have mechanisms to detect when the day lengths are getting shorter or longer—they compare the present day length against days recently experienced in the past—and flower only in response to the lengthening or shortening of the days.

These types of mechanisms can, for instance, cause a plant to flower only once a year rather than the two times a year that would be predicted by a mechanism based purely on absolute day length.

Not all plants are short-day or long-day. Some plants are day-neutral, meaning that flowering does not depend on day length. Also, flowering is not the only trait that can be regulated by photoperiod—day length—although it's the one that's gotten the most attention from researchers. Tuber formation in potatoes, for instance, is also under photoperiodic control, as is bud dormancy in preparation for winter in trees growing in cold areas.

^{3}

What is the plant actually measuring?

Although we classify plants as short-day or long-day, in some cases, plants may actually be measuring the length of the night. That is, it can be the length of the period of continuous darkness, not the length of the period of continuous light, that determines whether or not the plant flowers.

This is particularly true of short-day plants, whose photoperiodic response is often tightly linked to the length of the night. Typical short-day plants share the following characteristics:

^{2, 4, 5}

They flower when the day is short and the night is long.
They do not flower when the day is long and the night is short.
They do not flower when the long night is interrupted by a brief period of light.
They do not flower when the long day is interrupted by a brief period of dark.

What exactly does all that tell us? The pattern in the diagram above means that short-day plants measure the length of the night—the continuous period of darkness—and not the length of the day—the continuous period of light. That is, a short-day plant will only flower if it gets uninterrupted darkness for a length of time that meets or exceeds its flowering threshold. If there is an interruption to the darkness, such as a brief period of light, the plant will not flower, even though the continuous period of light—day—is still short.

The situation changes a bit when we consider long-day plants. Some long-day plants do measure the length of the night, like the short-day plants in the diagram above. However, unlike short-day plants, these long-day plants need the period of darkness to be shorter than or equal to a critical length! Long-day plants that measure the night length are said to be dark-dominant because it's the period of continuous darkness that's important for flowering.

Many other long-day plant species, however, seem to measure the length of the day, not the night, in determining when to flower. These plants are said to be light-dominant.

^{6}

Scientists think that the majority of long-day plant species are actually light-dominant, while the majority of short-day plant species are dark-dominant.

^{6}

How does the plant determine day or night length?

This is a question plant biologists have been wondering about for decades! Many models have been suggested over the years, but today, most biologists think photoperiodism—at least, in many species—is the result of interactions between a plant's "body clock" and light cues from its environment. Only when the light cues and the body clock line up in the right way will the plant flower.

This model is called the external coincidence model of photoperiodism. Its name highlights that an external cue—day length—has to coincide in a certain way with the plant's internal rhythms in order to trigger flowering. These rhythms are circadian rhythms, patterns in gene expression or physiology that repeat on a 24-hour cycle and are driven by the plant's internal body clock.

How the external coincidence model works is best understood for the long-day plant Arabidopsis, a relative of mustard. In this plant, levels of a specific m

RNA

that encodes a flowering induction protein rise and fall on a circadian cycle, with m

RNA

levels going up sharply in the evening.

^{2, 7}

RNA

stands for messenger

RNA

—messenger ribonucleic acid. A messenger

RNA

is an intermediate molecule that carries information from a gene. The messenger

RNA

is "read" during a process called translation in which the information it carries is used to build a specific protein—the one encoded by the gene.

The basic overview of this process is:

DNA

gene

\to

RNA

\to

protein

You can learn more about how this works in the tutorials on the central dogma of molecular biology.

When there is no light in the evening, the high levels of m

RNA

don't get the plant very far. That's because the flowering induction protein is usually broken down as soon as it's made. If, however, there's light in the evening—a long day—photoreceptors are activated by the light and jump in to save the protein from degradation. The protein can then build up and trigger flowering.

^{2, 7, 8}

Thanks to this molecular system, the plant flowers only when the days are long—when light extends late enough to overlap with the high m

RNA

expression.

In Arabidopsis, a gene named CONSTANS plays a key role in photoperiodism. In order for the plant to flower, high levels of the CONSTANS protein must build up, triggering the release of a signaling molecule that travels to the shoot tip and induces flowering.

^{2, 7}

The levels of messenger

RNA

for the CONSTANS gene are controlled by the circadian clock—rising in the evening, falling in the morning, and staying low throughout the day.

^{2, 7}

In the absence of evening light—that is, under short-day conditions—the CONSTANS protein made from the m

RNA

in the evening will be broken down right away. So, no flowering will take place on short days.

However, there is a way that the CONSTANS protein can be protected so that it can accumulate. If the plant gets light late in the evening, when there is lots of m

RNA

, photoreceptor proteins will be activated by the light. These photoreceptors intercede and protect the CONSTANS protein from destruction, allowing it to build up to high levels and trigger flowering.

^{2, 7, 8}

So, under long-day conditions, flowering will occur.

Great questions! This system is actually quite a bit more complex than the view we're taking of it here.

In the morning, a specific type of phytochrome—light-sensing protein—responds to red light by causing the CONSTANS protein to be broken down. This step ensures that flowering won't be triggered by morning light.

^{7, 8}

If you compare the short-day and long-day m

RNA

curves, you'll see that they are actually a little different. The long-day m

RNA

curve has a broader—lumpier—peak in the evening. This reflects that long days change the transcription pattern of CONSTANS a little through other pathways not discussed in this article.

^{7}

The plant circadian clock and its interaction with light actually involve a lot of different molecules that work together in complex ways—not just the ones that we're focusing on in this article. These molecules are like the many tiny parts of a machine or computer, each of which must do its job to keep the whole system running.

What exactly are these photoreceptors that step in to save the day? In the presence of light, the CONSTANS protein is stabilized by

Cryptochromes, which absorb blue light, and
Phytochromes, photoreceptors that absorb red and far-red light to switch between two forms.

Only certain phytochromes protect CONSTANS protein in the evening, and they do so in response to far-red light.

How is this regulatory system an example of external coincidence? There are two elements involved in triggering flowering: the plant's internal, circadian pattern of CONSTANS m

RNA

expression and the window of time during which it receives light, an external cue. When the window of light coincides with the peak of m

RNA

expression in the evening, the light protects the CONSTANS protein from destruction and allows flowering to proceed.

Other models of photoperiodism

Although it seems likely that many plant species use some type of external coincidence model to control flowering and other photoperiod-regulated processes, different plants have different genes and "wiring". It's possible that some plant species have fundamentally different ways of measuring photoperiod and linking this information to developmental changes.

For instance, an older model of photoperiodism, the phytochrome hourglass model, does not depend on overlap between circadian rhythms and photoperiod length. Instead, it suggests that phytochromes could act as a clock to measure the length of the night. Although this model is no longer widely accepted, it could potentially be valid for certain types of plants.

A phytochrome is a light-absorbing molecule that can exist in two forms with different shapes and activities:

The $P_{r}$ ‍ form absorbs red light—about 667 nm. When it absorbs red light, the $P_{r}$ ‍ form of the phytochrome is immediately converted to the alternative form, $P_{fr}$ ‍.
The $P_{fr}$ ‍ form absorbs far-red light—about 730 nm. When it absorbs far-red light, it’s quickly converted back to $P_{r}$ ‍. Additionally, $P_{fr}$ ‍ will slowly turn back into $P_{r}$ ‍ if left for an extended period in the dark.

In sunlight, there is more red than far-red light, so essentially all of the phytochrome molecules are in their

P_{fr}

form during daylight hours. After the sun goes down, however,

P_{fr}

starts converting back into

P_{r}

. In theory, the conversion of the phytochromes could act as an sort of hourglass, with the ratio of

P_{fr}

P_{r}

reflecting how much time has passed since the sun went down—that is, telling the plant how long the night has been.

This model is appealing because it is so simple and elegant, and it fits well with some pieces of evidence. For instance, a flash of red light in the middle of the night will prevent some types of short-day plants from flowering, but the effects of the red-light flash can be reversed by a second flash of far-red light.

^{2}

However, there seems to be more evidence suggesting this model is not correct, or not correct for the majority of plant species. For instance, a simple hourglass model does not explain why there's a circadian rhythm to most plants' ability to respond to a light flash—even when the plant is kept in extended darkness.

^{4}

In general, the kind of external coincidence model described above seems to be a more likely and/or common mechanism for photoperiodism than a phytochrome hourglass.

^{7}

Yes! Plants use the phytochrome system to detect light for many different purposes.

For instance, phytochromes can help a plant determine whether it’s being shaded by neighbors—and thus, whether it needs to grow upwards to get a larger share of the sunlight.

Phytochromes are also involved in light sensing during germination, helping a seed “decide” whether it’s in an environment that’s likely to provide sufficient sun to support growth of a seedling.

Attribution

This article is a modified derivative of "Plant sensory systems and responses" by OpenStax College, Biology, CC BY 4.0.

Download the original article for free at http://cnx.org/contents/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.53.

The modified article is licensed under a CC BY-NC-SA 4.0 license.

Works cited

John W. Kimball, "Tropisms," Kimball's Biology Pages, last modified May 18, 2011, http://www.biology-pages.info/T/Tropisms.html.
John W. Kimball, "Photoperiodism," Kimball's Biology Pages, last modified February 7, 2016, http://www.biology-pages.info/P/Photoperiodism.html.
Ulf Lagercrantz, "At the End of the Day: A Common Molecular Mechanism for Photoperiod Responses in Plants?" Journal of Experimental Botany 60, no. 9 (2009): 2507, http://dx.doi.org/10.1093/jxb/erp139.
William K. Purves, David Sadava, Gordon H. Orians, and H. Craig Heller, "Photoperiodic Control of Flowering," In Life: The Science of Biology, 7th ed. (Sunderland: Sinauer Associates, 2003), 758.
Brian Thomas and Daphne Vince-Prue, "What is perceived?" in Photoperiodism in Plants, 2nd ed. (Academic Press: San Diego, 1997), 13.
Ulf Lagercrantz, "At the End of the Day: A Common Molecular Mechanism for Photoperiod Responses in Plants?" Journal of Experimental Botany 60, no. 9 (2009): 2503, http://dx.doi.org/10.1093/jxb/erp139.
Ulf Lagercrantz, "At the End of the Day: A Common Molecular Mechanism for Photoperiod Responses in Plants?" Journal of Experimental Botany 60, no. 9 (2009): 2504, http://dx.doi.org/10.1093/jxb/erp139.
Federico Valverde, Aidyn Mouradov, Wim Soppe, Dean Ravenscroft, Alon Samach, and George Coupland, "Photoreceptor Regulation of CONSTANS Protein in Photoperiodic Flowering," Science 303 (2004): 1006, http://dx.doi.org/10.1126/science.1091761 .

References

Golembeski, Greg S., Hannah A. Kinmonth-Schultz, Young Hun Song, and Takato Imaizumi. "Photoperiodic Flowering Regulation in Arabidopsis thaliana." Adv. Bot. Res. 72 (2014): 1-28. http://dx.doi.org/10.1016/B978-0-12-417162-6.00001-8.

Gruber, Jennifer. "Photoperiodism and phytochrome." Introductory Biology I. Accessed July 5,2016. https://online.science.psu.edu/biol011_sandbox_7239/node/7272.

Hammack, Steve. "Photoperiodism." Hammack's Universe of Ideas. Accessed July 5, 2016. http://www.hammiverse.com/lectures/39/1.html.

Imaizumi, Takato. "Research." The Imaizumi Lab. Accessed July 5, 2016. http://faculty.washington.edu/takato/i.html.

Kimball, John W. "Etiolation." Kimball's Biology Pages. Last modified February 7, 2016. http://www.biology-pages.info/E/Etiolation.html.

Kimball, John W. "Photoperiodism." Kimball's Biology Pages. Last modified February 7, 2016. http://www.biology-pages.info/P/Photoperiodism.html.

Kimball, John W. "Tropisms." Kimball's Biology Pages. Last modified May 18, 2011. http://www.biology-pages.info/T/Tropisms.html.

Koning, Ross. "Photoperiodism." Plant Physiology Information Website. Accessed July 5, 2016. http://plantphys.info/plant_physiology/photoperiodism.shtml.

Lagercrantz, Ulf. "At the End of the Day: A Common Molecular Mechanism for Photoperiod Responses in Plants?" Journal of Experimental Botany 60, no. 9 (2009): 2501-2515. http://dx.doi.org/10.1093/jxb/erp139.

Mockler, Todd, Hongyun Yang, XuHong Yu, Dhavan Parikh, Ying-chia Cheng, Sarah Dolan, and Chentao Lin. "Regulation of Photoperiodic Flowering by Arabidopsis Photoreceptors." PNAS 100, no. 4 (2003): 2140-2145. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC149972/.

Nilsson, Ove. "Plant Evolution: Measuring the Length of the Day." Current Biology 19, no. 7 (2009): R302-R303. http://dx.doi.org/10.1016/j.cub.2009.02.012.

Pedmale, Ullas V., R. Brandon Celaya, and Emmanuel Liscuma. "Phototropism: Mechanism and Outcomes." Arabidopsis Book 8 (2010): e0125. http://dx.doi.org/10.1199/tab.0125.

"Photoperiodism." Wikipedia. Last modified June 5, 2016. https://en.wikipedia.org/wiki/Photoperiodism.

"Phototropism." Wikipedia. Last modified June 13, 2016. https://en.wikipedia.org/wiki/Phototropism.

Purves, William K., David Sadava, Gordon H. Orians, and H. Craig Heller. "Photoperiodic Control of Flowering." In Life: The Science of Biology, 756-761. 7th ed. Sunderland: Sinauer Associates, 2003.

Shim, Jae Sung and Takato Imaizumi. "Circadian Clock and Photoperiodic Response in Arabidopsis: From Seasonal Flowering to Redox Homeostasis." Biochemistry 54, no. 2 (2015): 157-170. http://dx.doi.org/10.1021/bi500922q.

Thomas, Brian and Daphne Vince-Prue. "What is perceived?" In Photoperiodism in Plants, 10-18. 2nd ed. Academic Press: San Diego, 1997.

Valverde, Federico, Aidyn Mouradov, Wim Soppe, Dean Ravenscroft, Alon Samach, and George Coupland. "Photoreceptor Regulation of CONSTANS Protein in Photoperiodic Flowering." Science 303 (2004): 1003-1006. http://dx.doi.org/10.1126/science.1091761.

Whippo, Craig W. "Phototropism: Bending Towards Enlightenment." The Plant Cell 18, no. 5 (2006): 1110-1119. http://dx.doi.org/10.1105/tpc.105.039669.

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Petra Yang
Posted 7 years ago. Direct link to Petra Yang's post “Does phototropism and pho...”
Does phototropism and photoperioddism happen in every plant?Why did Darwin and his son choose coleoptile?Was it because the result of experiment is more obvious?And why choose a young plant?Was it because phototropism changes by time of the plant(age)?
How did Danish physiologist come up with the idea to cut off the tip of a coleoptile?
Button navigates to signup pageComment on Petra Yang's post “Does phototropism and pho...”
(3 votes)
Answer
- Ruth S
  Posted 7 years ago. Direct link to Ruth S's post “No, actually, it only hap...”
  No, actually, it only happens in some plants. One plant that does phototropism is the sunflower. It will bend towards the sun as it moves around.
  Comment on Ruth S's post “No, actually, it only hap...”
  (7 votes)
Camila Ccama
Posted 5 years ago. Direct link to Camila Ccama's post “what could happen if I ex...”
what could happen if I expose a plant to a large amount of light?
Button navigates to signup pageButton navigates to signup page
(4 votes)
Answer
- Ivana - Science trainee
  Posted 4 years ago. Direct link to Ivana - Science trainee's post “*It would depend on the s...”
  It would depend on the species. Plants that grow on the tundra of the arctic circle and are exposed to 24 hours of daylight during the brief Summer are all species which evolved under those conditions.
  
  Some plant species such a Poinsettia, demand a certain number of hours in total darkness or they will never bloom. Those adapted to life on the tundra will thrive. Some plants such as the vegetables you mentioned could grow much larger because of constant photosynthesis.
  
  Plants do not need nighttime to live, only they use night for dark phases of photosynthesis, but it does not mean photosynthesis cannot proceed even during daylight.
  
  However, there are other growth-related mechanisms in plants that depend on photoperiod (large cycles of growth and rest, flowering, disease and pest resistance, and others). Some plants can be given hormonal supplements to counteract these negatives (often this is the case with commercially sold cut flowers). But with most plants, if you grew under lights 24/7, without any special treatment, they might start to decline.
  Button navigates to signup page
  (2 votes)
hannahcollins
Posted 7 years ago. Direct link to hannahcollins's post “on the short day and long...”
on the short day and long day plants would that mean that those either grow in the fall and winter.also in the summer and spring
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- SVlucero
  Posted 4 years ago. Direct link to SVlucero's post “the plant responds from w...”
  the plant responds from weather and what direction the sun is heading neer
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  (1 vote)
Kumail Korai
Posted 6 years ago. Direct link to Kumail Korai's post “Did you know a flower of ...”
Did you know a flower of a plant is the reproductive organ of the plant? I did not understand why it has a really great aroma and beauty? Is it for attraction for bees and other animals?
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(2 votes)
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- Kat
  Posted 6 years ago. Direct link to Kat's post “Just to be clear, Pollina...”
  Just to be clear, Pollination is not the same as fertilization. Just because the pollen is passed to the next plant doesn't mean it will fertilize the egg to make a seed. Fertilization is when the sperm in the microspores (pollen) reaches the megaspores (eggs) and then they combine into one. Pollination is just the movement of pollen from plant to plant.
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_yasss.14
Posted 7 years ago. Direct link to _yasss.14's post “what is RNA”
what is RNA
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- William Duan
  Posted a year ago. Direct link to William Duan's post “i dont know”
  i dont know
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Electricifiked Baguette
Posted 4 years ago. Direct link to Electricifiked Baguette's post “Does all of this mean tha...”
Does all of this mean that you can control when a plant flowers and fruits depending how much light it you give it?
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Ariel
Posted 3 years ago. Direct link to Ariel's post “If auxin goes to the shad...”
If auxin goes to the shady side of the plant, How does negative phototropism trigger? I mean, if say, light impacts a root, will auxin build up on the lighted side, of the root, and bend it against the light?
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Revan Rangotis
Posted 7 years ago. Direct link to Revan Rangotis's post “I am curious, is negative...”
I am curious, is negative phototropism a simple derivative of the positive phototropism as a mandatory part of the nomenclature, or is it actually a well-described phenomenon? And if so, which plants exhibit this behaviour and why?
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(1 vote)
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- Joshua Beaudin
  Posted 6 years ago. Direct link to Joshua Beaudin's post “I believe some forms of n...”
  I believe some forms of negative phototropism would involve things such as the roots of plants in order to ensure, along with other direction-of-growth determining factors, that the roots go into the ground and don't just grow out of the seed wherever.
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  (3 votes)
Christian Johnson
Posted 4 years ago. Direct link to Christian Johnson's post “why does the Auxin move a...”
why does the Auxin move away from the light? and make the cells in the shade elongate in comparison to the cells getting directly hit by the sun?
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- Justin Franswah
  Posted 4 years ago. Direct link to Justin Franswah's post “When light hits one side ...”
  When light hits one side of the coleoptile, the phototropins are more active on the side with light, causing the auxin to flow down the shady side. ... Auxin promotes cell elongation, causing the plant to grow more on the shady side and bend in the direction of the light source.
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  (1 vote)
seanwaag
Posted 7 years ago. Direct link to seanwaag's post “Could you limit the amoun...”
Could you limit the amount of red-spectrum light a plant receives to stimulate growth, as phytochromes help determine whether or not the plant is being shaded by its neighbors, or would that not work? Would that change how quickly the plant produces seeds or fruit?
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(2 votes)
Answer
- Ivana - Science trainee
  Posted 4 years ago. Direct link to Ivana - Science trainee's post “Yes, you can. Those exper...”
  Yes, you can. Those experiments are done with LED light indoors.
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  (1 vote)