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AIIMS / NEET 2019 - Plant Physiology : Plant Growth & Development Lecture - 5

Seller Inventory Perhaps the most celebrated compounds from plants are those with pharmacological activity, such as salicylic acid from which aspirin is made, morphine , and digoxin. Drug companies spend billions of dollars each year researching plant compounds for potential medicinal benefits. Plants require some nutrients , such as carbon and nitrogen , in large quantities to survive. Some nutrients are termed macronutrients , where the prefix macro- large refers to the quantity needed, not the size of the nutrient particles themselves.

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Other nutrients, called micronutrients , are required only in trace amounts for plants to remain healthy. Such micronutrients are usually absorbed as ions dissolved in water taken from the soil, though carnivorous plants acquire some of their micronutrients from captured prey. The following tables list element nutrients essential to plants. Uses within plants are generalized. Among the most important molecules for plant function are the pigments. Plant pigments include a variety of different kinds of molecules, including porphyrins , carotenoids , and anthocyanins.

All biological pigments selectively absorb certain wavelengths of light while reflecting others. The light that is absorbed may be used by the plant to power chemical reactions , while the reflected wavelengths of light determine the color the pigment appears to the eye. Chlorophyll is the primary pigment in plants; it is a porphyrin that absorbs red and blue wavelengths of light while reflecting green.

It is the presence and relative abundance of chlorophyll that gives plants their green color. All land plants and green algae possess two forms of this pigment: chlorophyll a and chlorophyll b. Kelps , diatoms , and other photosynthetic heterokonts contain chlorophyll c instead of b , red algae possess chlorophyll a. All chlorophylls serve as the primary means plants use to intercept light to fuel photosynthesis. Carotenoids are red, orange, or yellow tetraterpenoids.

They function as accessory pigments in plants, helping to fuel photosynthesis by gathering wavelengths of light not readily absorbed by chlorophyll. The most familiar carotenoids are carotene an orange pigment found in carrots , lutein a yellow pigment found in fruits and vegetables , and lycopene the red pigment responsible for the color of tomatoes. Carotenoids have been shown to act as antioxidants and to promote healthy eyesight in humans. Anthocyanins literally "flower blue" are water-soluble flavonoid pigments that appear red to blue, according to pH.

They occur in all tissues of higher plants, providing color in leaves , stems , roots , flowers , and fruits , though not always in sufficient quantities to be noticeable.

In these plants, the anthocyanin catches light that has passed through the leaf and reflects it back towards regions bearing chlorophyll, in order to maximize the use of available light. Betalains are red or yellow pigments. Like anthocyanins they are water-soluble, but unlike anthocyanins they are indole -derived compounds synthesized from tyrosine. This class of pigments is found only in the Caryophyllales including cactus and amaranth , and never co-occur in plants with anthocyanins.

Betalains are responsible for the deep red color of beets , and are used commercially as food-coloring agents. Plant physiologists are uncertain of the function that betalains have in plants which possess them, but there is some preliminary evidence that they may have fungicidal properties.

Plant physiology - Wikipedia

Plants produce hormones and other growth regulators which act to signal a physiological response in their tissues. They also produce compounds such as phytochrome that are sensitive to light and which serve to trigger growth or development in response to environmental signals. Plant hormones , known as plant growth regulators PGRs or phytohormones, are chemicals that regulate a plant's growth.

According to a standard animal definition, hormones are signal molecules produced at specific locations, that occur in very low concentrations, and cause altered processes in target cells at other locations. Unlike animals, plants lack specific hormone-producing tissues or organs. Plant hormones are often not transported to other parts of the plant and production is not limited to specific locations. Plant hormones are chemicals that in small amounts promote and influence the growth , development and differentiation of cells and tissues.

Hormones are vital to plant growth; affecting processes in plants from flowering to seed development, dormancy , and germination. They regulate which tissues grow upwards and which grow downwards, leaf formation and stem growth, fruit development and ripening, as well as leaf abscission and even plant death. The most important plant hormones are abscissic acid ABA , auxins , ethylene , gibberellins , and cytokinins , though there are many other substances that serve to regulate plant physiology.

While most people know that light is important for photosynthesis in plants, few realize that plant sensitivity to light plays a role in the control of plant structural development morphogenesis. The use of light to control structural development is called photomorphogenesis , and is dependent upon the presence of specialized photoreceptors , which are chemical pigments capable of absorbing specific wavelengths of light. Plants use four kinds of photoreceptors: [1] phytochrome , cryptochrome , a UV-B photoreceptor, and protochlorophyllide a. The first two of these, phytochrome and cryptochrome, are photoreceptor proteins , complex molecular structures formed by joining a protein with a light-sensitive pigment.

Cryptochrome is also known as the UV-A photoreceptor, because it absorbs ultraviolet light in the long wave "A" region. The UV-B receptor is one or more compounds not yet identified with certainty, though some evidence suggests carotene or riboflavin as candidates. The most studied of the photoreceptors in plants is phytochrome. It is sensitive to light in the red and far-red region of the visible spectrum. Many flowering plants use it to regulate the time of flowering based on the length of day and night photoperiodism and to set circadian rhythms.

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It also regulates other responses including the germination of seeds, elongation of seedlings, the size, shape and number of leaves, the synthesis of chlorophyll, and the straightening of the epicotyl or hypocotyl hook of dicot seedlings. Many flowering plants use the pigment phytochrome to sense seasonal changes in day length, which they take as signals to flower. This sensitivity to day length is termed photoperiodism. Broadly speaking, flowering plants can be classified as long day plants, short day plants, or day neutral plants, depending on their particular response to changes in day length.

Long day plants require a certain minimum length of daylight to starts flowering, so these plants flower in the spring or summer. Conversely, short day plants flower when the length of daylight falls below a certain critical level. Day neutral plants do not initiate flowering based on photoperiodism, though some may use temperature sensitivity vernalization instead. Although a short day plant cannot flower during the long days of summer, it is not actually the period of light exposure that limits flowering.

Rather, a short day plant requires a minimal length of uninterrupted darkness in each hour period a short daylength before floral development can begin. It has been determined experimentally that a short day plant long night does not flower if a flash of phytochrome activating light is used on the plant during the night.

Plants make use of the phytochrome system to sense day length or photoperiod. This fact is utilized by florists and greenhouse gardeners to control and even induce flowering out of season, such as the Poinsettia. Paradoxically, the subdiscipline of environmental physiology is on the one hand a recent field of study in plant ecology and on the other hand one of the oldest.

It is roughly synonymous with ecophysiology , crop ecology, horticulture and agronomy.

The particular name applied to the subdiscipline is specific to the viewpoint and goals of research. Whatever name is applied, it deals with the ways in which plants respond to their environment and so overlaps with the field of ecology. Environmental physiologists examine plant response to physical factors such as radiation including light and ultraviolet radiation , temperature , fire , and wind. Of particular importance are water relations which can be measured with the Pressure bomb and the stress of drought or inundation , exchange of gases with the atmosphere , as well as the cycling of nutrients such as nitrogen and carbon.

Environmental physiologists also examine plant response to biological factors. This includes not only negative interactions, such as competition , herbivory , disease and parasitism , but also positive interactions, such as mutualism and pollination. Plants may respond both to directional and non-directional stimuli. A response to a directional stimulus, such as gravity or sun light , is called a tropism.