PGR-2 Flashcards
describe ethylene
Ethylene is a simple gaseous PGR. It is synthesised in large amounts by
tissues undergoing senescence and ripening fruits. Influences of ethylene
on plants include horizontal growth of seedlings, swelling of the axis and
apical hook formation in dicot seedlings. Ethylene promotes senescence
and abscission of plant organs especially of leaves and flowers. Ethylene
is highly effective in fruit ripening.
what is respiratory climactic
ethylene enhances the respiration rate during
ripening of the fruits. This rise in rate of respiration is called respiratory
climactic.
explain effects of ethylene on plants
Ethylene breaks seed and bud dormancy, initiates germination in
peanut seeds, sprouting of potato tubers. Ethylene promotes rapid
internode/petiole elongation in deep water rice plants. It helps leaves/
upper parts of the shoot to remain above water. Ethylene also promotes
root growth and root hair formation, thus helping the plants to increase
their absorption surface.
Ethylene is used to initiate flowering and for synchronising fruit-set
in pineapples. It also induces flowering in mango. Since ethylene regulates
so many physiological processes, it is one of the most widely used PGR in
agriculture.
what is ethephon
The most widely used compound as source of ethylene is
ethephon. Ethephon in an aqueous solution is readily absorbed and
transported within the plant and releases ethylene slowly. Ethephon
hastens fruit ripening in tomatoes and apples and accelerates abscission
in flowers and fruits (thinning of cotton, cherry, walnut). It promotes female
flowers in cucumbers thereby increasing the yield.
describe ABA
abscisic acid (ABA) was discovered for its role in
regulating abscission and dormancy. But like other PGRs, it also has
other wide ranging effects on plant growth and development. It acts as a
general plant growth inhibitor and an inhibitor of plant metabolism. ABA
inhibits seed germination. ABA stimulates the closure of stomata in the
epidermis and increases the tolerance of plants to various kinds of stresses.
Therefore, it is also called the stress hormone. ABA plays an important
role in seed development, maturation and dormancy. By inducing
dormancy, ABA helps seeds to withstand desiccation and other factors
unfavourable for growth. In most situations, ABA acts as an antagonist
to GAs.
Describe the interaction between the different plant growth regulators
For the regulation of every phase of growth, i.e., for
differentiation and developmental processes in plants two
or more phytohormones are intimately related to each
other. These can either act synergistically or
antagonistically.
Thus, every PGR has one or the other role to play. Likevis
there are also number of events in the life of a plant whet
more than one PGR is also involved to affect that particular
event to take place, For example,
(i) Dormancy of seeds and buds is mostly due to abscit
acid, while it is broken down by gibberellins.
(li) Auxins and cytokinins act antagonistically in
controlling apical dominance, i.e., auxins cause apia
dominance, while cytokinins help to overcome cher
(it) Senescence is prevented by both auxins and
cytokinins, while its stimulation is done by abscis
acid.
(iv) Auxins and cytokinins act synergistically in
promoting cell division.
