Physical barriers, chemical toxins, and even mutualistic animals are included in plant defenses.
The variety of ways flowering plants can respond to their environment is discussed in this chapter.
All organisms can respond to environmental stimuli.
Being able to respond to stimuli leads to organisms' longevity and ultimately to the survival of the species.
Plants respond to a variety of stimuli.
Light, gravity, carbon dioxide levels, and pathogen infections are examples.
When plants respond to gravity with the downward growth of the root and the upward growth of the stem, their responses can be short-term.
The mechanism that brings about a response at the cellular level is what we think of when we think of responses in terms of a plant structure.
Section 13.3 describes the concept of signal transducers.
The nucleus receives the hormone auxin from the cell.
The lightreceptor in the plasma is sensitive to blue light.
Gene expression changes are caused by stimulation of a transduction pathway.
When attacked by an animal, the flowering plant produces defense hormones.
A specific signal causes a specific set of genes to be activated.
The nucleus, the cytoplasm, and the endoplasmic reticulum are some of the places where the Receptors can be found.
A receptor that responds to light has a component.
There is a region that is sensitive to red light and a region that is sensitive to blue light.
A second messenger, such as Ca2+, can initiate the response in some instances.
The end product of an activated metabolic pathway is usually the response.
The visible change is brought about by the cellular response.
They are chemical signals that coordinate cell responses.
Page 476 is produced in very low concentrations and is active in another part of the organisms.
When hormones are stored in one part of the plant, they travel within phloem or from cell to cell to another part of the plant.
They said that plants bend toward light.
The young seedlings' coleoptile was specifically looked at by the Darwins.
A coleoptile is a protective sheath for young leaves.
The influence that causes curvature is transmitted from the coleoptile tip to the rest of the shoot.
Researchers tried and failed to find the chemical involved in phototropism by crushing and analyzing coleoptile tips.
Frits W. cut off the tips of coleoptiles and placed them on agar blocks.
He placed an agar block on one side of the tipless coleoptile and found that the shoot moved away from that side.
Even though the seedlings were not exposed to light, the bending occurred.
Indoleacetic acid is the most common naturally occurring form of auxin.
The coleoptile is a hollow sheath.
The curve in the agar can be caused by a block of the agar to one side of the cut coleoptile.
When exposed to a light source, auxin causes the coleoptile to bend.
When a stem is exposed to light, auxin moves to the shady side, where it enters the nucleus of shady cells.
The hydrogen ion pumped into the cell wall creates an acidic environment.
The weakened cell wall is a result of the acid triggering the enzymes.
Auxin binding to the receptors.
The hydrogen ion is pumped into the cell wall.
The cell wall is activated when the pH decreases.
The wall of the cell can be loosened by breaking the Cellulose fibers.
A new, longer wall is built after the cell expands as turgor pressure increases.
A weak and loose cell wall will result in a decrease in turgor pressure.
In Section 25.3 you learned that the water potential inside the cell is less than the water potential outside the cell.
Water is flowing into the cell from other parts of the plant.
The plant cell responds to the pressure of the water by building a longer wall, resulting in cell growth.
The cell would burst without the rebuilding.
The wall is weakened so that it can be stretched and rebuilt even longer.
The stem is getting longer because the cells on the shady side are bending the stem toward the light.
A plant's exposure to the sun is maximized by auxin.
The roots curve downward and the stems curve upward.
Section 26.2 contains more information about phototropism and gravitropism.
A phenomenon called apical dominance is caused by this versatile hormone.
In a plant that has not been altered, auxin produced in the apical meristem of the terminal bud is transported downward.
Pruning removes the shoot tip from apical dominance.
The plant takes on a full appearance when the axillary buds grow.
If auxin were applied to the broken terminal stem, apical dominance would be restored.
Page 478 causes adventitious roots to develop more quickly.
The growth of fruit is promoted by Auxin production.
If auxin is concentrated in leaves or fruits rather than in the stem, leaves and fruits do not fall off.
It is possible to keep mature fruit from falling to the ground by spraying trees with auxin.
The most common naturally occurring auxin, IAA, has a relatively simple chemical structure that can be easily copied and altered into synthetic forms.
Synthetic auxins are used in a number of applications.
These auxins are sprayed on tomatoes to create seedless varieties.
Broadleaf weeds, such as dandelions and other plants, can be controlled with synthetic auxins.
The substances have no effect on grasses.
During the Vietnam War, Agent Orange was used to defoliate the forests of Vietnam.
Individuals who were exposed to this powerful auxin have been harmed.
The plants were weakened by rapid stem elongation.
The isolated form of gibberellin, now known as gibberellic acid, was isolated from a flowering plant.
gibberellic acid, GA3 is the most common gibberellin, and it's a subscript designation.
There are places where natural gibberellins can be found.
Stem elongation is the most obvious effect when gibberellins are applied to plants.
Stem elongation is caused by gibberellins.
The plant on the right was treated with gibberellins while the plant on the left was not.
The grapes are larger on the right because gibberellins increased the space between them.
Apples, cherries, and sugarcane are some of the crops that are stimulated by gibberellins.
A notable example is their use on table grapes.
Commercial grapes can produce small fruit on very small bunches.
The source of gibberellins for fruit growth can be found in the presence of seeds.
The dormancy of buds and seeds can be broken by gibberellins.
One way to speed up the development of a flower bud is by applying gibberellins.
When gibberellins break the dormancy of barley seeds, a large endosperm is broken down into sugars to provide energy for the growing seedling.
This happens because amylase makes its appearance.
Adding gibberellins to the seeds breaks the dormancy and provides sugar for the fermentation process.
When coconut milk and yeast extract were added to the culture medium, cell division occurred.
Plant growth is influenced by the promotion of cell division.
Plant organ formation is influenced by the interaction between auxin and cytokinins.
There are different plant hormones that are required for embryo survival.
The root formation of nitrogen-fixingbacteria, as well as the formation of gall on wounded trees, are caused by the cytokin noduleins.
A gall is a growth caused by infections.
These organisms can cause a plant to grow uncontrollably in small areas.
Tissue culture experiments show that auxin and cytokinin interact.
Tobacco cells develop into a callus of undifferentiated tissue in tissue culture that has the usual amounts of these two hormones.
The callus produces roots if the ratio of auxin to cytokinin is right.
Another ratio causes flowers to grow.
The relative concentrations of both hormones produce an effect, and it is now clear that each plant hormone rarely acts alone.
The aging of plants is called senescent.
Large molecule within the leaf are broken down and transported to other parts of the plant.
Some plants lose their Page 480 lower leaves as they grow taller, butescence does not affect the entire plant at once.
In the autumn, low levels of cytokinin cause leaves to change color and eventually die.
It has been found that the application of cytokinins can prevent the senescence of leaves.
Some varieties of lettuce have been genetically modified to produce something called cytokinins.
The lettuce heads are modified to stay fresh.
When cytokinin levels are low, leaves change colors.
There is a drop in the production of cytokinin when there is a seasonal change.
Abscisic acid is a hormone that is produced in the chloroplast.
The stress hormone is Abscisic acid, which is used to initiate and maintain seed and bud dormancy.
This hormone is no longer believed to function naturally in this process despite the external application of ABA.
The hormone ethylene seems to bring about an erection.
dormancy is a period of low activity in the metabolism.
When a plant stops growing, it's called dormancy.
It is believed that the hormone ABA travels from leaves to buds in the fall, which are converted to buds in the winter.
A reduction in the level of ABA and an increase in gibberellins is believed to break seed and bud dormancy.
After seeds grow, buds send leaves.
If a plant becomes sensitive to ABA, Figure 26.7 shows what can happen.
In normal corn, a home gardener can leave a cob on the stalks to dry, then collect the dry kernels to plant the following year.
ABA will keep the dry kernels from germinating.
The arrows are red.
When a plant is under water stress, the closing of the stomata is brought about by the reception of abscisic acid.
ABA causes rapid depolymerization of actin filaments and formation of a new type of actin that is randomly oriented throughout the cell.
The change in actin organization may be related to the stomata closure.
Abscisic acid closes the stomata.
K+ exits the guard cells.
After K+ leaves, so does water.
Abscission involves dropping leaves and fruit, and the ripening of fruits.
Abscission probably begins with the absence of auxin and gibberellin.
When abssioncis has begun, ethylene stimulates certain enzymes, which causes leaf, fruit, or flower drop.
There is a ripe apple under the bell jar on the right, but not under the bell jar on the left.
Only the holly plant on the right has leaves.
When a holly twig is placed under a glass jar for a week, there is no problem.
Abscission of the holly leaves occurs when an apple is also under the jar.
In the early 1900s, it was a common practice to prepare fruit for market by placing them in a room with a stove.
Researchers realized that an incomplete combustion product of kerosene, ethylene, can cause fruit to rot.
It makes fruits softer by increasing the activity of enzymes.
In addition to stimulating the production of cellulase, it promotes the activity of enzymes that produce the flavor and smell of ripened fruits and breaks down chlorophyll, inducing the color changes associated with fruit ripening.
Because it is a gas, ethylene can move through the air and through the plant.
A bunch of bananas can be ripening some distance away from a basket of ripening apples.
One rotten apple spoils the whole crop because ene is released at the site of a plant wound.
In agriculture, the use of ethylene is extensive.
Tomatoes are usually ripe on the vine.
Tomatoes can be genetically modified to not produce ethylene.
Green tomatoes are not subject to as much damage as red tomatoes.
Tomatoes can be exposed to ethylene when they arrive at their destination.
There are many products on the market that can be purchased by consumers.
The product usually consists of a pouch filled with a liquid.
Fruits and vegetables can be kept in the refrigerator for longer with this chemical.
Plants are unable to escape from competing plants in the area because they are roots to the ground.
Plants have been able to overcome these constraints by producing a variety of chemical defenses.
Plants can attract mycorrhizal partners with various organic chemicals.
They are also good at repelling plants.
Chemical ecology studies the interaction between plants, animals, and the environment in which they live.
Chemical ecology brings together scientists from many different fields, such as entomology, chemistry, and plant biology, who work together to study the complex chemical communication systems that occur in nature.
Coevolution of plants and insect herbivores is the most common research focus.
Studying the constant battle between plants and insects helps us understand the interactions that have produced the diverse range of species in existence today.
Chemical ecology examines how the chemicals within plants are made, how these chemicals contribute to a plant's overall fitness, and how they evolve in response to environmental pressures.
Four examples of chemical interactions are highlighted in this feature.
Systemin is produced by wounded leaves and travels in phloem to all parts of the plant.
The production of jasmonic acid by these cells leads to the production of a molecule that limits insect feeding.
The defense compounds travel in phloem and become widely distributed throughout the plant.
When a predator eats the same plant, it will either be poisoned or repelled by the bad taste of the inhibitors.
Many of the defense compounds are volatile and can cause defenses in nearby plants.
The hawkmoth caterpillar is resistant to nicotine and decimates the weedy shrubs.
The plant is ridding itself of the hawkmoth caterpillar by using a new method.
The trichomes of some plants produce poison lollipops that are irresistible to hungry caterpillars.
The volatile substance in the sugar makes the caterpillar smell good to ants, who grab them and carry them off to their nest.
Scientists theorize that dodders could smell their preferred meal because they seemed to have a preference for certain plants.
A tomato and a wheat plant were placed in a pot to test this.
The dodder latched onto the tomato plant after vacillating for several hours.
The volatile chemical produced by the tomato was confirmed in a subsequent experiment.
The tomato was placed near the dodder.
The dodder "smelled" its prey and moved in that direction.
There are poison lollipops that contain sugar.
Other chemicals help the caterpillar.
Plants are protected from other plants by chemical toxins.
This strategy maximizes exposure to the sun.
The dodder will choose the best host for the parasites to live in.
The hormones are mostly used for the plant's response to abiotic stimuli, such as light, oxygen, water, and temperature.
Plants need an arsenal of chemicals to deal with biotic stimuli, such as herbivory and competition from other plants.
A plant's bark and skin do a good job of discouraging attackers.
herbivores have ways around a plant's first line of defense.
A fungus can enter a leaf through the stomata and set up shop inside the leaf, where it feeds on the plant's nutrition.
The mouth parts of underground Nematodes break through the skin of a root to form a relationship.
Aphids have mouths that allow them to open the phloem of a nonwoody stem.
Plants need a variety of defenses that are not dependent on the outer surface.
The normal workings of a cell are dependent on the primary metabolites of plants.
Plants produce defense or survival mechanism.
Secondary metabolites are part of a plant's arsenal and used to be thought of as waste products.