45. The role of ethylene and abscissic acid 1s both positive and negative Justify the statement.



Positive affects

Negative effects







Abscissic Acid

Promotes horizontal/transverse growth

Makes stem positively geotropic.

Promotes apical dominance.

Breaks seed and bud dormancy.

Enhances fruits ripening and root initiation.


ABA is used as anti transpirant, by reducesing water requirement and during irrigation (by partial closure of stomata).

Also, induces flowering and root initiation in some plants.

Used in prolonging dormancy of buds and seeds.

Increases resistance of plants, to cold and other types of stresses thus also known as stress hormone.

Inhibits longitudinal grown

Decreases sensitivity to gravity i.e. root become apogeotropic.

Enhances senescence of leaves and flowers, fruits.

Prolongs dormancy of lateral buds

Mediates formation of ABA under water stressed conditions

Promotes abscission of flower and fruits.

Stimulates senescence of leaves by stopping protein and RNA synthesis.

Promotes bud and seed dormancy. Retards cambial activity by stopping mitosis in vascular strands and cambium.

Act as antagonist to gibberellin and counteracts the effect of other growth hormones (IAA and cytokinin).

Inhibits seed germination and growth of embryos in them