Plant physiology
Plant physiology is a subdiscipline of botany concerned with the functioning, or physiology, of plants.[1]
Plant physiologists study fundamental processes of plants, such as
Aims
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The field of plant physiology includes the study of all the internal activities of plants—those chemical and physical processes associated with
First, the study of phytochemistry (plant chemistry) is included within the domain of plant physiology. To function and survive, plants produce a wide array of chemical compounds not found in other organisms. Photosynthesis requires a large array of pigments, enzymes, and other compounds to function. Because they cannot move, plants must also defend themselves chemically from herbivores, pathogens and competition from other plants. They do this by producing toxins and foul-tasting or smelling chemicals. Other compounds defend plants against disease, permit survival during drought, and prepare plants for dormancy, while other compounds are used to attract pollinators or herbivores to spread ripe seeds.
Secondly, plant physiology includes the study of biological and chemical processes of individual plant cells. Plant cells have a number of features that distinguish them from cells of animals, and which lead to major differences in the way that plant life behaves and responds differently from animal life. For example, plant cells have a cell wall which restricts the shape of plant cells and thereby limits the flexibility and mobility of plants. Plant cells also contain chlorophyll, a chemical compound that interacts with light in a way that enables plants to manufacture their own nutrients rather than consuming other living things as animals do.
Thirdly, plant physiology deals with interactions between cells, tissues, and organs within a plant. Different cells and tissues are physically and chemically specialized to perform different functions. Roots and rhizoids function to anchor the plant and acquire minerals in the soil. Leaves catch light in order to manufacture nutrients. For both of these organs to remain living, minerals that the roots acquire must be transported to the leaves, and the nutrients manufactured in the leaves must be transported to the roots. Plants have developed a number of ways to achieve this transport, such as vascular tissue, and the functioning of the various modes of transport is studied by plant physiologists.
Fourthly, plant physiologists study the ways that plants control or regulate internal functions. Like animals, plants produce chemicals called
Finally, plant physiology includes the study of plant response to environmental conditions and their variation, a field known as environmental physiology. Stress from water loss, changes in air chemistry, or crowding by other plants can lead to changes in the way a plant functions. These changes may be affected by genetic, chemical, and physical factors.
Biochemistry of plants
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The chemical elements of which plants are constructed—principally carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, etc.—are the same as for all other life forms: animals, fungi, bacteria and even viruses. Only the details of their individual molecular structures vary.
Despite this underlying similarity, plants produce a vast array of chemical compounds with unique properties which they use to cope with their environment.
Constituent elements
Plants require some
The following tables list element nutrients essential to plants. Uses within plants are generalized.
Element | Form of uptake | Notes |
Nitrogen | NO3−, NH4+ | Nucleic acids, proteins, hormones, etc. |
Oxygen | O2, H2O | Cellulose, starch, other organic compounds |
Carbon | CO2 | Cellulose, starch, other organic compounds |
Hydrogen | H2O | Cellulose, starch, other organic compounds |
Potassium | K+ | Cofactor in protein synthesis, water balance, etc. |
Calcium | Ca2+ | Membrane synthesis and stabilization |
Magnesium | Mg2+ | Element essential for chlorophyll |
Phosphorus | H2PO4− | Nucleic acids, phospholipids, ATP |
Sulphur | SO42− | Constituent of proteins |
Element | Form of uptake | Notes |
Chlorine | Cl− | Photosystem II and stomata function |
Iron | Fe2+, Fe3+ | Chlorophyll formation and nitrogen fixation |
Boron | HBO3 | Crosslinking pectin |
Manganese | Mn2+ | Activity of some enzymes and photosystem II |
Zinc | Zn2+ | Involved in the synthesis of enzymes and chlorophyll |
Copper | Cu+ | Enzymes for lignin synthesis |
Molybdenum | MoO42− | Nitrogen fixation, reduction of nitrates |
Nickel | Ni2+ | Enzymatic cofactor in the metabolism of nitrogen compounds |
Pigments
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.
Signals and regulators
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
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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
The most important plant hormones are
, though there are many other substances that serve to regulate plant physiology.Photomorphogenesis
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:
The most studied of the photoreceptors in plants is
Photoperiodism
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 start 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 24-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
Environmental physiology
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.[1] Environmental physiology is the preferred name of the subdiscipline among plant physiologists, but it goes by a number of other names in the applied sciences. 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
Environmental physiologists also examine plant response to biological factors. This includes not only negative interactions, such as
While plants, as living beings, can perceive and communicate physical stimuli and damage, they do not feel
Tropisms and nastic movements
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. A response to a nondirectional stimulus, such as temperature or humidity, is a nastic movement.
Plant disease
Economically, one of the most important areas of research in environmental physiology is that of
Because the biology of plants differs with animals, their symptoms and responses are quite different. In some cases, a plant can simply shed infected leaves or flowers to prevent the spread of disease, in a process called abscission. Most animals do not have this option as a means of controlling disease. Plant diseases organisms themselves also differ from those causing disease in animals because plants cannot usually spread infection through casual physical contact. Plant
One of the most important advances in the control of plant disease was the discovery of
History
Early history
Francis Bacon published one of the first plant physiology experiments in 1627 in the book, Sylva Sylvarum. Bacon grew several terrestrial plants, including a rose, in water and concluded that soil was only needed to keep the plant upright. Jan Baptist van Helmont published what is considered the first quantitative experiment in plant physiology in 1648. He grew a willow tree for five years in a pot containing 200 pounds of oven-dry soil. The soil lost just two ounces of dry weight and van Helmont concluded that plants get all their weight from water, not soil. In 1699, John Woodward published experiments on growth of spearmint in different sources of water. He found that plants grew much better in water with soil added than in distilled water.
Stephen Hales is considered the Father of Plant Physiology for the many experiments in the 1727 book, Vegetable Staticks;[10] though Julius von Sachs unified the pieces of plant physiology and put them together as a discipline. His Lehrbuch der Botanik was the plant physiology bible of its time.[11]
Researchers discovered in the 1800s that plants absorb essential mineral nutrients as inorganic ions in water. In natural conditions, soil acts as a mineral nutrient reservoir but the soil itself is not essential to plant growth. When the mineral nutrients in the soil are dissolved in water, plant roots absorb nutrients readily, soil is no longer required for the plant to thrive. This observation is the basis for hydroponics, the growing of plants in a water solution rather than soil, which has become a standard technique in biological research, teaching lab exercises, crop production and as a hobby.
Economic applications
Food production
In horticulture and agriculture along with food science, plant physiology is an important topic relating to fruits, vegetables, and other consumable parts of plants. Topics studied include: climatic requirements, fruit drop, nutrition, ripening, fruit set. The production of food crops also hinges on the study of plant physiology covering such topics as optimal planting and harvesting times and post harvest storage of plant products for human consumption and the production of secondary products like drugs and cosmetics.
Crop physiology steps back and looks at a field of plants as a whole, rather than looking at each plant individually. Crop physiology looks at how plants respond to each other and how to maximize results like food production through determining things like optimal planting density.
See also
- Biomechanics
- Hyperaccumulator
- Phytochemistry
- Plant anatomy
- Plant morphology
- Plant secondary metabolism
- Branches of botany
References
- ^ ISBN 0-534-15162-0.
- ^ Trevor Robinson (1963). The organic constituents of higher plants: their chemistry and interrelationships. Cordus Press. p. 183.
- ^ Kimler, L. M. (1975). "Betanin, the red beet pigment, as an antifungal agent". Botanical Society of America, Abstracts of Papers. 36.
- ISBN 0-12-262430-0.
- ^ "plantphys.net". Archived from the original on 2006-05-12. Retrieved 2007-09-22.
- ^ a b c Petruzzello, Melissa (2016). "Do Plants Feel Pain?". Encyclopedia Britannica. Retrieved 8 January 2023.
Given that plants do not have pain receptors, nerves, or a brain, they do not feel pain as we members of the animal kingdom understand it. Uprooting a carrot or trimming a hedge is not a form of botanical torture, and you can bite into that apple without worry.
- PMID 32880005. 32880005.
- ISBN 978-0-262-19186-9.
- ISBN 978-0-697-09948-8.
- ^ Hales, Stephen. 1727. Vegetable Staticks http://www.illustratedgarden.org/mobot/rarebooks/title.asp?relation=QK711H341727
- ISBN 978-0-8138-2498-7.
Further reading
- Lambers, H. (1998). Plant physiological ecology. New York: Springer-Verlag. ISBN 0-387-98326-0.
- Larcher, W. (2001). Physiological plant ecology (4th ed.). Springer. ISBN 3-540-43516-6.
- Frank B. Salisbury; Cleon W. Ross (1992). Plant physiology. Brooks/Cole Pub Co. ISBN 0-534-15162-0.
- Lincoln Taiz, Eduardo Zeiger, Ian Max Møller, Angus Murphy: Fundamentals of Plant Physiology. Sinauer, 2018.