BSC 314 Lecture Notes - Lecture 32: Plant Hormone, Plant System, Abscission
27 Jun 2018
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Regulating Growth: Plant Hormones
Plant cells are in constant chemical communication with one another and with their
environment. They recognize and respond to stimuli of many kinds, using a system of
chemical messengers that receive and transmit the stimuli via ordinary body cells
(unlike the highly specialized cells of animal nervous systems). Control of the plant
system apparently resides in the genes of each cell, which are turned on and off by the
chemical messages they receive. The response may be stimulatory (initiating cellular
division and enlargement, for example) or inhibitory (such as stopping a metabolic
process).
The chemical messengers are hormones, organic substances manufactured in small
amounts in one tissue and usually transported to another where they initiate a
response. (A few act in the tissues where they are produced.) The hormone molecule
itself carries little information and produces a reaction only when it binds to appropriate
receptor molecules at the response site.
Plants, in comparison to animals, have both fewer hormones and fewer kinds of
responses. Plant hormones, however, usually act in combination, thus producing more
varied responses than if acting individually. The same hormone also can produce
different effects when acting in different tissues or in different concentrations in the
same tissue. The developmental stage of the plant additionally determines what effects
the hormone activates. Growth and development depend upon a successful
coordination of the activities of hormones, not just the presence or absence of individual
ones.
Senescence
Senescence is the orderly, age induced breakdown of cells and their components, ‐
leading to the decline and ultimate death of a plant or plant part. The timing of
senescence is species specific and varies among the organs of individual plants. Some ‐
species of plants produce short lived flowers whose petals last for only a few hours ‐
before shriveling and dropping off, while the leaves of deciduous plants last through
long growing seasons before senescing.
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Document Summary
Plant cells are in constant chemical communication with one another and with their environment. They recognize and respond to stimuli of many kinds, using a system of chemical messengers that receive and transmit the stimuli via ordinary body cells (unlike the highly specialized cells of animal nervous systems). Control of the plant system apparently resides in the genes of each cell, which are turned on and off by the chemical messages they receive. The response may be stimulatory (initiating cellular division and enlargement, for example) or inhibitory (such as stopping a metabolic process). The chemical messengers are hormones, organic substances manufactured in small amounts in one tissue and usually transported to another where they initiate a response. (a few act in the tissues where they are produced. ) The hormone molecule itself carries little information and produces a reaction only when it binds to appropriate receptor molecules at the response site.
