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What's the survival benefit of blue plants?

What's the survival benefit of blue plants?


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I'm working on a science-fiction worldbuilding setting and have been trying to find out what the survival benefits are of blue in plants, like this or this.

I have researched this but most of the answers that a Google search brings up are more to do with blue flowers, blue structural colouration in animals, and garden centre blogs and online stores selling conifers. The best I've been able to find has been a page about encouraging spruce plants to become as blue as possible by making sure they're fed planty of iron-rich fertilizer (but not fertilizing in the first year, so early impoverishment of nutrients seems to be a factor, but I don't see how that makes blue needles beneficial).

All I really want to know is what environmental conditions would cause a plant, any plant, to evolve blue leaves or needles.

Thank you in advance.


According to at least one gardening tutorial I found, the blue color of the Colorado Blue Spruce is not actually related to the color of the pigments in the leaves.

"… the intensity of the blue of a Colorado blue spruce (selections of Picea pungens 'Glauca') depends on the concentration of its “bloom,” a powdery white wax that coats its needles."

I can't say if this is the case for all "blue" conifers, but given that this tree is especially tolerant of cold and drought, it seems likely that the waxy "bloom" is related to retention of water vapor and possibly exclusion of external water from the needles. Since there are lots of other plants with waxy coatings that don't have such a powdery blue appearance, I'd speculate that it may also contribute some protection from UV radiation for these high-altitude trees.


Survival of the fittest

"Survival of the fittest" [1] is a phrase that originated from Darwinian evolutionary theory as a way of describing the mechanism of natural selection. The biological concept of fitness is defined as reproductive success. In Darwinian terms the phrase is best understood as "Survival of the form that will leave the most copies of itself in successive generations."

Herbert Spencer first used the phrase, after reading Charles Darwin's On the Origin of Species, in his Principles of Biology (1864), in which he drew parallels between his own economic theories and Darwin's biological ones: "This survival of the fittest, which I have here sought to express in mechanical terms, is that which Mr. Darwin has called 'natural selection', or the preservation of favoured races in the struggle for life." [2]

Darwin responded positively to Alfred Russel Wallace's suggestion of using Spencer's new phrase "survival of the fittest" as an alternative to "natural selection", and adopted the phrase in The Variation of Animals and Plants Under Domestication published in 1868. [2] [3] In On the Origin of Species, he introduced the phrase in the fifth edition published in 1869, [4] [5] intending it to mean "better designed for an immediate, local environment". [6] [7]


Scientists Discover Evolutionary Advantage For Homosexuality

It’s an evolutionary paradox that’s frustratingly difficult for biologists to explain, but researchers may have just found a benefit conferred by homosexual sex that could offer an explanation as to why this behavior has persevered, at least in one species. According to a new study in fruit flies, not only does same-sex sexual behavior seem to be heritable, but females with a genetic makeup associated with this trait actually display higher reproductive rates, which is an evolutionary advantage. These fascinating findings have been published in Proceedings of the Royal Society B.

If a certain trait or behavior is detrimental to the reproductive success, or fitness, of an organism, you wouldn’t expect it to persist in the population as natural selection should get rid of it. After all, the aim of the reproductive game is to keep your genes going. Why, then, do members of the same sex cop off with each other in so many species? And we’re not just talking about homosexual behaviors (observed in more than 1,500 species, since you asked) we mean the whole shebang.

Scientists have long pondered this and have struggled to come to any consensus. Although there are a few different ideas, two prevailing hypotheses that resulted from theoretical work suggest that same-sex sexual behaviors (SSB) could persist for two reasons: overdominance and sexual antagonism. The former proposes that SSB could persist in the population if genes for this behavior confer a harmonizing reproductive advantage in individuals only possessing one copy of the gene, or heterozygotes, as opposed to those in possession of two (homozygotes). The latter suggests that a gene that is detrimental to fitness in one sex could be maintained so long as it is beneficial to the other sex.

So how do researchers work out which hypothesis seems to better explain this behavior that is seemingly harmful to reproduction? The method chosen by scientists behind the latest study, based at the University of St. Andrews, involved a combination of genetic and behavioral tests. First, they screened inbred fruit fly lines in search of gene variations that could account for SSB.

They did this by both examining the genomes of male fruit flies and observing how they behaved with other males. This involved quantifying the amount of courtship behaviors males would display towards other males—such as licking, singing or attempted mounting𠅊nd then looking for genetic differences present in males displaying high levels of these behaviors. This information was then used to identify genetic lines of flies that either consistently showed high levels of SSB, or low levels of SSB.

The final stage of the investigation involved performing experimental crosses of flies from both of these identified lines and examining the resulting offspring. More specifically, they wanted to see whether coming from a genetic background associated with high levels of SSB affected reproductive rates in female offspring.

The researchers found that while their data lent more weight to the overdominance hypothesis, their results did not exclusively support one over the other. In fact, they think that both could be contributing to the maintenance of SSB in the gene pool. But that wasn’t the most interesting find of the study: Males with a genetic makeup associated with high levels of SSB produced female offspring with higher rates of reproduction, or fecundity. This suggests that genes associated with SSB could be persisting in the population because they actually confer a fitness advantage in females, despite being reproductively harmful to males.  


Isoprenoids: Structure, Distribution and Role

These terpenes contain 10-C atoms and are built up of two iso- preneitnits. There structure may be (i) acyclic, (ii) cyclohexanoid (mono, bi or tricyclic) and (iii) cyclopentanoid.

Monoterpenes are chiefly found in resin ducts in leaves, twigs and trunks of conifers such as pines.

Important monoterpene components of conifer resins are α -pinene, β -pinene, limonene and myrcene which are toxic to large number of insects.

Monoterpenes also occur as important components of essential oils in special secretory glands in many flowering plants, (e.g., mint) and give a characteristic odour to their foliage which has insects repelling properties.

Menthol is chief monoterpene component of peppermint oil. Essential oils are obtained from plants by steam distillation and find their use in flavouring foods and in perfumery. Structures of some common monoterpenes are given in Fig. 24.4.

Monoterpene esters pyrethroids occurring in leaves and flowers of Chrysanthemum possess strong insecticidal properties and are used on commercial scale in making insecticides.

2. Sesquiterpenes (C15):

These are largest group of isoprenoids which have great structural variations. Many sesquiterpenes co-exist with monoterpenes in essential oils in higher plants. Some sesquiterpene lactones such as costunolide found in the glandular hairs of sage brush and sunflower are feeding deterrents to herbivores. An aromatic sesquiterpene dimer gossypol found in cotton is known to provide resistance to insect, fungal and bacterial pathogens. The structures of above mentioned sesquiterpenes are given in Fig. 24.5.

3. Diterpenes (C20):

Plant resins produced by conifers such as pines and certain leguminous trees such as Hymenaea courbrail contain appreciable amount of diterpene abietic acid (Fig. 24.6). These diterpenes function as chemical deterrents to predators and also help in healing the wounds caused by insect bites.

4. Triterpenes (C30):

Triterpenes and their derivatives such as steroids represent another vast group of isoprenoids or terpenoid compounds. The steroids usually have a tetracyclic or pentacyclic molecular structure and many of them are modified to contain fewer than 30 – C atoms.

Some steroids such as plant sterols (e.g., sitosterol) have primary function in plant cells being part of their cell-membranes while others are defensive secondary products. Examples of the latter category are various phytoecdysones, limonoids, cardenolides, sapogenins, sterol alkaloids and steroid hormones.

A brief account of all these is as follows:

(i) Phytoecdysones (Ecdysteroids):

These have highly polar structure. Ponasterone A iso­lated from Podocarpus (a conifer) has the same basic structure as insect moulting hormones such as a-ecdysone and is therefore, a strong insect deterrent.

(ii) Limnoids (Bitter principles from citrus fruit):

These substances have highly com­plex structure. Azadirachtin from neem tree is a strong deterrent to insect feeding and other herbivores.

(iii) Cardenolides:

These are steroid glycosides highly toxic to higher animals and have important pharmacological effects on heart muscles. These substances are found in more than 10 families of higher plants. The glycoside parts of these steroids are complex and contain unique sugars such as digitoxose and acetyl digitoxose. Digitoxigenin is aglycone of dipitoxin that is obtained from Digitalis and is prescribed for heart ailments.

(iv) Sapogenins (Saponins):

These are also steroid glycosides found in many plants. They have detergent properties and ability to disrupt membranes and cause haemolysis of red blood cells. A saponin called yamogenin is obtained from Dioscorea and is used in making oral contraceptives.

(v) Sterol alkaloids (Terpenoid alkaloids):

These alkaloids occur in many plants as gly­cosides. For example, the aglycone of tomatin is tomatidine and of solanine is solanidine.

(vi) Steroid hormones:

Many steroids which occur in animals as hormones are also wide­spread in plants, but their role in plants is not yet clear. For example, the hormone progester­one (from placenta and corpus in animals) is also present in Holarrhena floribunda. Similarly, deoxycorticosterone (from adrenal cortex in animals) is also found in Digitalis lanata.

Structures of some steroids in plants are given in Fig. 24.7.

5. Polyterpenes [C5]n:

Many high molecular weight polyterpenes are found in plants as natu­ral products. Of these, rubber is best known. Other examples are gutta and chicle. Their func­tion in plants is to provide defense against herbivores and to help in wound healing.

It is high molecular weight polyisoprene or polyterpene compound produced in latex of over 300 genera of angiospcrms. However, the most important commercial source of rubber is Hevea brasiliensis. Rubber is found as particles suspended in milky latex in long vessels called laticifers or laticiferous ducts in plants.

Rubber consists of a large number (1500 – 60,000) isopentenyl units in which carbon- carbon double bonds have cis (Z) configuration, (Fig. 24.8). Accordingly, the molecular weight of rubber ranges from

It is a polymer of isoprene residues with a low molecular weight than rubber and in which carbon-carbon double bonds have trans (E) configuration (Fig. 24.9). It is obtained from various trees of the genus Palaquium (Family Sapotaceae). It is also obtained commer­cially on a small scale from desert shrub guayule (Parthenium argenatum) of the family Asteraceae.

It consists of a mixture of comparatively low molecular weight cis and trans polyisopentenyl units along with resins that are soluble in acetone. It is obtained from Sapodilla (Manilkara zapota) of family Sapotaceae and is used commercially as original chewing gum base.

Many terpenoids are well known to have a primary role in growth and development of plants and are therefore considered as primary metabolites rather than secondary plant products.

i. Phytohormones gibberellins are diterpenes.

ii. Absisic acid (ABA) is a sesquiterpene and degradation product of carotenoid precursor.

iii. Sterols are derivatives of triterpenes and are essential components of cell membranes.

iv. Carotenoids (red, orange and yellow) are tetraterpenes. Their roles as accessory pigment in pho­tosynthesis and to protect photosynthetic tissues from photo-oxidation are well known.

v. Phytol side chains of chlorophylls are diterpene derivatives. Bacteriochlorophylls also have terpe­noid side chains.


Importance of Wildlife Elsewhere

Besides basic survival and global health, wildlife plays an important role in other facets of life like economics and recreation.

A lot of cultures sustain themselves on the buying and selling of animal products or the animals themselves. Leather and fur are hot commodities, but so are goats and cows. In some communities these animals can be bartered in exchange for goods and services. Unfortunately, some wildlife dependent economics revolve around illegal industries like poaching. Poaching involves the unethical and highly illegal slaughtering of endangered or regulated animals – like elephants for their ivory tusks. Additionally, gardeners and farmers world-wide enjoy running businesses based on their ability to grow plants, flowers, food and market them to the public. Get started in your own gardening venture by taking this course on Organic Soil Growing.

On the flip side of illegal hunting (poaching) there is the legal kind of hunt. Game hunting is a widely enjoyed past time for many people around the world. Often the animals are used for their meat and hides, or their heads for trophies. While this sounds a bit sinister, hunting is actually a really resourceful way of population control. We discussed above about how out of control wildlife populations can wreak havoc on ecosystems and hunting is a well-organized solution to this problem. In many states hunters must register and receive tags for the animals they are hoping to shoot. This system provides a way for conservationists and biologists to monitor the current populations of certain animals while attaining population goals through legal hunting. In Bucks County, Pennsylvania the deer population is soaring. There are 8 bucks (male deer) to every doe (female deer) and the population is beginning to cause issues for the habitat (plant life is being destroyed) and for civilization (higher frequency of deer related car accidents).

Additional benefits to wildlife include bird watching, photography, fishing, hiking and the general aesthetics of living in a natural world. Want to be a wildlife photographer? Learn how to get close to these animals in Wildlife Photography.


What is a Gene Pool and Why is it Important?

Apart from a healthy habitat, the survival of a species depends on the genetic diversity among its members. BiologyWise defines the concept of a 'gene pool', and gives its examples to shed more light on this concept.

Apart from a healthy habitat, the survival of a species depends on the genetic diversity among its members. BiologyWise defines the concept of a ‘gene pool’, and gives its examples to shed more light on this concept.

Did You Know?

As far as humans are concerned, women have contributed more DNA to the gene pool than men, because women have outnumbered men throughout our history.

Would you like to write for us? Well, we're looking for good writers who want to spread the word. Get in touch with us and we'll talk.

A species is a way of describing organisms of the same kind who can breed among themselves. Therefore, dogs, humans, and horses belong to different species. However, all individuals of a species do not occur in a single region they live as groups in different geographical areas. These groups are called populations. Thus, every species is made up of a number of populations. For example, a group of deer living in a forest forms one population, while a group of the same species living on a wildlife reserve forms another.

The bodies of plants, animals, insects, and several other organisms are made of small units called cells. Each cell contains hereditary information passed down from parents to their offspring in the form of genes. Animals that reproduce sexually have two sets of every gene, called alleles one from each parent. For example, a gene that produces eye color can have two alleles – one produces brown color while the other imparts blue color. The characteristics produced by a gene depends on which allele of that gene is active in an individual. Let us now understand the concept of a gene pool.

What is a Gene Pool?

The combination of all the genes present in a given population is called the gene pool of that population. It represents the complete genetic diversity found within a population or species.

What are its Characteristics?

♦ The concept of a gene pool is only used for sexually-reproducing organisms (because asexual reproduction produces clones).

♦ It includes all the variants or alleles of every gene.

♦ It includes all the genes present in the population.

♦ In most cases, the population includes individuals of the same species only.

♦ A gene pool includes even those genes whose effects are not visible in an individual.

Why is it Important?

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Since a gene pool represents the total number of genes found within a population, those populations with larger gene pools tend to have more genes, and hence, more genetic diversity. Each gene has a specific purpose, such as giving the plant/animal a particular characteristic, resistance to a disease, tolerance to harsh climate, and so on. Therefore, a population with a larger genetic diversity will be better prepared to deal with disease outbreaks or extreme environmental changes, because they will, most likely, have those genes that protect them from such adverse changes.

On the other hand, populations with a lesser number of genes in their gene pool will be susceptible to such problems, which may cause them to become endangered or even perish altogether, i.e., become extinct. Therefore, populations with a large gene pool will have more chances of survival, while those with small gene pools are in danger of acquiring genetic diseases, deformities, and infertility.

How Does a Gene Pool Change?

1. By Mutations
Mutations are changes in the genes of an individual. These variations may be as minute as a change of a single nucleotide (an organic molecule) in the DNA, to changes in entire sets of chromosomes. Depending on whether the mutation is passed down to offspring, it may be permanent or temporary. They are beneficial to the population if they add valuable genes, but some may cause diseases.

2. By Natural Selection
Natural selection is one of the most important factors affecting a gene pool. Individuals from a population which carry beneficial genes are more likely to survive and produce offspring, than those that don’t. Therefore, the next generation will, most probably, carry genes from such individuals, which may even become fixed, i.e., occur in every individual.

3. By Genetic Drift
Sometimes, the type of genes in a population changes due to random events (such as the death of a few individuals), and not always because the change is beneficial. This is called ‘genetic drift’, and affects a smaller population more than a larger one, because, in the former, such genes are likely to occur in every individual.

Examples

❒ About 60,000 to 70,000 years ago, our early ancestors migrated out of Africa into Europe and the Middle East. Since the climate here was colder, genetic modifications produced lighter skin to help them absorb more ultraviolet light. Ultimately, these changes became a part of their gene pool, helping them evolve.

❒ The potato originated in the western part of South America, from where it spread to Europe and Ireland, where it eventually became a staple food for the population. Since all potatoes grown in Ireland descended from a small number of plants, the small gene pool made the entire crop susceptible to blight (a fungal plant disease). Potato crops all over the country were ruined in the mid-19th century, causing a million deaths due to starvation.

❒ A number of animal species, such as mountain lions in the Americas, and leopards in South Africa, are threatened by human activities. Their habitat has been divided into fragments, surrounded by towns and farmlands. This results in interbreeding among smaller populations, and the small gene pool makes them susceptible to diseases.

As can be seen, a gene pool represents the future of a species. This is the reason why wilderness areas should be protected – they contain the gene pools of a number of crops and domestic animals, which ensures our own survival.

Related Posts

The following article presents some points that are related to the subject of DNA studies, and which specifically describe the importance of DNA.

Meiosis is a phase in sexually reproductive organisms, wherein cell-division takes place. It is of great importance, because it creates genetic diversity in the population.

Meiosis is a phase in sexually reproductive organisms, wherein cell-division takes place. It is of great importance, because it creates genetic diversity in the population.


How much fertilizer actually goes to the plant?

Did you know that only 40 to 60% of the fertilizer we apply actually goes to the plant, the remaining is lost to run off into our waterways, volatilization to the air or is tied up in the soil. This is why soil health is such an imperative piece of plant health. Functional soil is a soil embedded with organic matter and soil microbes that work together to hold onto nutrients in the soil and convert nutrients locked in the soil.

Beneficial soil microbes form symbiotic relationships with the plant. In fact, the plant will exert as much as 30% of its energy to the root zone to make food for microbes. In return those microbes not only protect the plant from stress, but also feed the plant by converting and holding nutrients in the soil.

What are the different types of soil microbes?

There are five different types of soil microbes: bacteria, actinomycetes, fungi, protozoa and nematodes. Each of these microbe types has a different job to boost soil and plant health.

Bacteria

Bacteria is the crucial workforce of soils. They are the final stage of breaking down nutrients and releasing them to the root zone for the plant. In fact, the Food and Agriculture Organization once said “Bacteria may well be the most valuable of life forms in the soil.”

Actinomycetes

Actinomycetes were once classified as fungi, and act similarly in the soil. However, some actinomycetes are predators and will harm the plant while others living in the soil can act as antibiotics for the plant.

Fungi

Like bacteria, fungi also lives in the rootzone and helps make nutrients available to plants. For example, Mycorrhizae is a fungi that facilitate water and nutrient uptake by the roots and plants to provide sugars, amino acids and other nutrients.

Protozoa

Protozoa are larger microbes that love to consume and be surrounded by bacteria. In fact, nutrients that are eaten by bacteria are released when protozoa in turn eat the bacteria.

Nematodes

Nematodes are microscopic worms that live around or inside the plant. Some nematodes are predators while others are beneficial, eating pathogenic nematodes and secreting nutrients to the plant.

Want to keep digging into soil science?

Within the natural world there exists a complex balance among soil microbes known as the soil food web. Plants, animals and microbes are all instruments in an orchestra each plays a crucial part in the natural symphony of life. If even one of the players is out of tune, the whole soil food web suffers. However, when everything is in order, the results are beautiful.

Download our Digging into Soil Science ebook to explore:

1. How the soil food web supports healthy plants
2. The power behind soil microbes
3. Soil types and how to improve the health of your soil


How Did Early Scientists Explain Phototropism?

Early opinions on the cause of phototropism varied among scientists. Theophrastus (371 B.C.-287 B.C.) believed that phototropism was caused by the removal of fluid from the illuminated side of the plant's stem, and Francis Bacon (1561-1626) later postulated that phototropism was due to wilting. Robert Sharrock (1630-1684) believed plants curved in response to "fresh air," and John Ray (1628-1705) thought plants leaned toward the cooler temperatures nearer to the window.

It was up to Charles Darwin (1809-1882) to conduct the first relevant experiments regarding phototropism. He hypothesized that a substance produced in the tip induced the curvature of the plant. Using test plants, Darwin experimented by covering the tips of some plants and leaving others uncovered. The plants with covered tips did not bend toward light. When he covered a lower part of the plant stems but left the tips exposed to the light, those plants moved toward the light.

Darwin did not know what the "substance" produced in the tip was or how it caused the plant stem to bend. However, Nikolai Cholodny and Frits Went found in 1926 that when high levels of this substance moved to the shaded side of a plant stem, that stem would bend and curve so that the tip would move toward the light. The exact chemical composition of the substance, found to be the first identified plant hormone, was not elucidated until Kenneth Thimann (1904-1977) isolated and identified it as indole-3-acetic acid, or auxin.


Definition of Phototropism

Photo means “Light” and tropism means “Turning”. Therefore, phototropism purely refers to the bending of the plant towards the light. Tropism can be defined as the growth of a plant towards any of the environmental stimuli like heat, light, air, water, chemicals and many other sources. The shoot system’s growth relative to the direction of the light stimuli is called phototropism or positive phototropic reaction. Oppositely, the root system’s growth is opposite to the path of the light stimuli is known as negative phototropism or geotropism.

Phototropism is a mechanism that is necessary for the survival of the plant. Thus, it is the “Survival mechanism” where the plant absorbs as much light. The more plant leaves will open towards the light, more will be the efficiency of the photosynthesis, which in turn allow more energy to generate.

History of Phototropism

Many scientists contributed to introduce different experiments, approaches, and opinions that have led to the discovery of the phototropism mechanism.

YearDiscovererDiscovery
371-287 BCTheophrastusDiscovered that the phototropism was due to removal of fluid from the illuminated site of the plants stem
1561-1626Franscis BaconHe discovered that phototropism was due to wilting
1630-1684Robert SharrockAccording to him, plants get bends, due to fresh air
1628-1705John RayAccording to him, plants bends towards the cool temperature when placed near the window
1809-1882Charles DarwinHypothesized that one substance is produced at the tip of the plant which is responsible for the curvature of plant
1926Nikolai Cholodny and Frit’s WentThey found high level of that substance that moved to the shaded side of the plant stem
1904-1977Kenneth ThimannIsolated and identified substance like “Auxin”

Mechanism of Phototropism in Plants

The phototropism works on the principle of the light reaction. In phototropism, the photoreceptors in plants accept a light wavelength of around 450 nm and trigger a response. Blue light photoreceptor protein forms a complex, called phototropins. In the presence of light, auxin moves to the darker side of the stem.

Auxin releases hydrogen ions in the plant cell and shifts towards the darker portion of the stem, leading to a decrease in the plant cell’s pH. The decrease in pH activates the release of an enzyme (expansins). The enzyme expansins will cause swelling in the cell and finally result in the plant’s bending towards the light.

Types of Phototropism

There are two types of phototropism that occurs in the plant, namely positive and negative phototropism.

  1. Positive Phototropism: The movement or bending of plant parts (shoot system) in response to light, is the phenomena termed positive phototropism.
  2. Negative Phototropism: The movement or bending of plant part (root system) in response to light, is the phenomena termed negative phototropism.

Overview of Phototropism in Plants

Let us take a quick overview of the phototropism process by taking an example. We must have seen the bending of plantlets placed near a window towards the light. It is because plants need the exposure of sunlight to produce energy and food. The roots under the pot grow upward, and once they break through the surface, the shoot system starts bending towards the light.

The whole phenomena of bending of the plant can be understood by the signalling pathway concept that is explained below. Plant senses light, by the specific molecules called “Photoreceptors”. The photoreceptors are the protein molecules, which link with the chromophore pigment. Chromophore absorbs light and distorts the configuration and activity of the protein.

These alternations bring a signal in response to light, and the plants respond to promote gene expression, growth and hormone production. The pathway of the response production is called “Signalling pathway”. Therefore, phototropism is a directional response where a plant bends towards the stimulus (light).

Role of Phototropins and Auxins in Phototropism

The Phototropins are the photoreceptors, which detect the light and absorb the blue range of the spectrum. The plant’s tip (coleoptile) possesses a high concentration of auxin (plant growth hormone). An exposure of coleoptile to the sunlight causes an unequal distribution of phototropins.

Pht 1 and 2 are the two common types of phototropins in the higher plants, which respond differently towards the blue light. Under the influence of low-intensity blue light, phot-1 comes into action. In contrast, under the influence of high-intensity blue light, both phot 1 and 2 act redundantly.

The primary functions of phototropins include stomatal opening, photosynthetic exchange, chloroplast movement, leaf-blade and cotyledon expansion. The phototropins will be more active or absorb more light in the lighter regions. Oppositely, the phototropins will be less active on the darker side or absorb less light.

Thus, an unequal transport of a plant hormone (auxin) towards the darker side of the coleoptile is due to the different level of phototropins. Auxin will shift more towards the darker side than the illuminated side. The auxin on the darker side of the stem will promote cell elongation and more growth, which results in bending of the plant in response to a light source.


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