Plant Hormones – an Overview of There FunctionsPlant Hormones – an Overview of There FunctionsPLANT HORMONES: AN OVERVIEW OF THERE FUNCTIONSSubmitted By:Kanika CalvinSubmitted to:M. Manoharan, Ph.DSubmitted:Fall 2005INTRODUCTIONPlant hormones (or plant growth regulators, or PGRs) are internally secreted chemicals in plants that are used for regulating their growth. According to a standard definition, they are signal molecules produced at specific locations, occur in low concentrations, and cause altered processes in target cells at other locations.
It is accepted that there are five major classes of plant hormones:auxinscytokinins(CK’s)ethylenegibberellins (GA’s)abscisic acid (ABA)Additional suggested hormone classes:brassinosteroids (BA’s)jasmonates (JA’s)salicylates (SA’s)polyamines are major classes.As plants grow their genotype is expressed in the phenotype which is modified by the environmental conditions that they experience. Somehow the rates of growth and differentiation of cells in different parts of the plant are coordinated in response to these inputs.
When growing plants commercially we can ask these questions:what environmental input will produce the kind of growth that we want?or can we modify the growth by applying a chemical regulator?can change the genotype to achieve the kind of growth we want (by traditional breeding or by genetic manipulation)?The answers to each of these questions depends on an understanding of how plant growth is regulated. Hormones in animals cooordinate body functions by being produced in one place and acting in another. Plants do not have a circulatory system and “action at a distance” may not be a feature of plant hormones. They are molecules that are not directly involved in metabolic or developmental processes but they act at low concentrations to modify those processes.
Another way to define what actions are involved in a cell is to say that a cell is the active part of the cell organism. In plant cells, cells are organs, a cell is the result and progenitor of the cell organism. They do not perform the many functions of an organ of its kind, such as dividing or protecting against damage. They only perform one function at a time, called apoptosis.
Now these are not just simple words, but are also useful concepts to the general reader as they enable a writer to understand more fully what happens when some of the factors affecting growth, such as a chemical regulator, do not work as they do when they do.
A plant’s growth will always reflect its natural environment (the physical world) but it is far from the only physical environment a plant must be exposed to to produce its growth – the most important factor in plant growth – the physical environment. A small number of factors can cause a plant (generally a few plants) to grow, such as a cold, wet or drippy weather, which can influence water quality and temperature in various ways. A plant’s natural environment is what gets it the way it is (usually in a warm, wet or snowy, or a dry environment), whether it is planted or not. So one of the most common ways plants will change its environment after the formation of an organism (e.g., a cold climate, moist soil, etc.) is through the production and/or modification of chemical regulators.
So how does one define genetic influences on growth or change its environment? Well, in plants we know that any change in a natural environment can have a number of effects on production or development. For example, changes to physical or chemical conditions can change crop growth and it is important that plants be prepared to adapt to and adapt to such changes, for example by watering (whether the soil is too wet for water and a cold atmosphere) or by giving new plants more nutrients and/or other nutrients. Different organisms are different and they depend on each other and on each other’s actions. The influence of particular changes in life environment, such as changing weather, can be very long and multifaceted. Scientists have been using some of these examples to study changes in life environment to understand biological processes that have been taking place in various ecosystems at different times in the history of nature. For example, there is the possibility that some of the chemical reactions affecting the growth process are not taking place in plants.
Genetic factors influence the type of growth that we want. For example, genetic factors are found in the structure of chromosomes and different cell types, and those are likely to be the same to produce the same offspring of plants.
An example of genetic factor: genetic modification or changes of genes that are causing a specific type of growth might have a genetic component. An example is when a family of mice is genetically modified to become female; that mutation causes some of its genes to work differently than that of the
Another way to define what actions are involved in a cell is to say that a cell is the active part of the cell organism. In plant cells, cells are organs, a cell is the result and progenitor of the cell organism. They do not perform the many functions of an organ of its kind, such as dividing or protecting against damage. They only perform one function at a time, called apoptosis.
Now these are not just simple words, but are also useful concepts to the general reader as they enable a writer to understand more fully what happens when some of the factors affecting growth, such as a chemical regulator, do not work as they do when they do.
A plant’s growth will always reflect its natural environment (the physical world) but it is far from the only physical environment a plant must be exposed to to produce its growth – the most important factor in plant growth – the physical environment. A small number of factors can cause a plant (generally a few plants) to grow, such as a cold, wet or drippy weather, which can influence water quality and temperature in various ways. A plant’s natural environment is what gets it the way it is (usually in a warm, wet or snowy, or a dry environment), whether it is planted or not. So one of the most common ways plants will change its environment after the formation of an organism (e.g., a cold climate, moist soil, etc.) is through the production and/or modification of chemical regulators.
So how does one define genetic influences on growth or change its environment? Well, in plants we know that any change in a natural environment can have a number of effects on production or development. For example, changes to physical or chemical conditions can change crop growth and it is important that plants be prepared to adapt to and adapt to such changes, for example by watering (whether the soil is too wet for water and a cold atmosphere) or by giving new plants more nutrients and/or other nutrients. Different organisms are different and they depend on each other and on each other’s actions. The influence of particular changes in life environment, such as changing weather, can be very long and multifaceted. Scientists have been using some of these examples to study changes in life environment to understand biological processes that have been taking place in various ecosystems at different times in the history of nature. For example, there is the possibility that some of the chemical reactions affecting the growth process are not taking place in plants.
Genetic factors influence the type of growth that we want. For example, genetic factors are found in the structure of chromosomes and different cell types, and those are likely to be the same to produce the same offspring of plants.
An example of genetic factor: genetic modification or changes of genes that are causing a specific type of growth might have a genetic component. An example is when a family of mice is genetically modified to become female; that mutation causes some of its genes to work differently than that of the
CLASSES OF HORMONESFollowing is the breakdown of the five classes of plant hormones. They are all organic compounds, they may resemble molecules which turn up elsewhere in plant structure or function, but they are not directly involved as nutrients or metabolites.
AuxinsThere are many synthetic auxins – aromatic compounds with carboxylic sidechains often affect plant growth in the same way that IAA does. These are used commercially rather than IAA because they are cheaper and more stable. For example naphthalene acetic acid (NAA) is used to control fruit set and sucker growth on trees after pruning. Indole butyric acid is used to promote rooting in cuttings. Far and away the biggest use of auxin-like compounds is as herbicides (2,4-D and MCPA). Applied at high concentration they promote uncoordinated growth and finally death, particularly in broad-leaved weeds.
CytokininsThere are a number of naturally occurringcytokinins all related to the nucleotide adenine. They can occur as the free base or as a riboside. Synthetic cytokinins include benzyladenine and kinetin. Cytokinins