Plant Growth and Development
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It helps to produce new leaves, chloroplasts in leaves, lateral shoot
growth and adventitious shoot formation.
Cytokinins help overcome the apical dominance.
They promote nutrient mobilisation which helps in the delay of leaf
senescence .
4 Ethylene (C2H2)
H. H. Cousins confirmed that ripened oranges released a volatile
substance that hastened the ripening of stored bananas. Later this
substance was identified as ethylene.
Ethylene is a simple gaseous PGR.
It is synthesised in large amounts by tissues undergoing senescence
and ripening fruits.
FÜÑÇTÏØÑS
Influences horizontal growth of seedlings, swelling of
the axis and apical hook formation in dicot seedlings.
Promotes senescence and abscission of plant
organs especially of leaves and flowers.
Promotes fruit ripening. It enhances respiration
rate during fruit ripening. This is called respiratory
climactic.
Breaks seed and bud dormancy, initiates germination in peanut seeds,
sprouting of potato tubers.
Promotes rapid internode/petiole elongation in deep water rice plants. It
helps leaves/upper parts of the shoot to remain above water.
Promotes root growth and root hair formation. It increases absorption
surface.
Used to initiate flowering and for synchronizing fruit set in pineapples. It
also induces flowering in mango.
(NEET 2019)
It is widely used in agriculture.
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 & apples and accelerates abscission in flowers
and fruits (thinning of cotton, cherry, walnut). It promotes female flowers
in cucumbers thereby increasing the yield.