Simulation · Biology · Class 11
ABA against GA
From the lesson Ethylene and abscisic acid in Plant Growth and Development. Change the values and watch what happens.
ABA against GABiology · Class 11
The idea behind it
NCERT §13.4.3.4–§13.4.3.5
- Ethylene is a simple gaseous PGR, made in large amounts by tissues undergoing senescence and by ripening fruits.
- On seedlings it causes horizontal growth, a swollen axis and, in dicots, the apical hook. It speeds senescence and abscission, especially of leaves and flowers.
- Ethylene is highly effective in fruit ripening and raises the rate of respiration during ripening; this rise is called the respiratory climacteric.
- It breaks seed and bud dormancy, starts germination in peanut seeds and sprouting of potato tubers. It promotes rapid internode and petiole elongation in deep-water rice, keeping the upper shoot above water. It promotes root growth and root hair formation, increasing the absorbing surface.
- Ethylene is used to start flowering and synchronise fruit-set in pineapple, and induces flowering in mango. Its most widely used source is ethephon, which is absorbed from aqueous solution, moves through the plant and releases ethylene slowly.
- Ethephon hastens ripening in tomato and apple, speeds abscission of flowers and fruits (thinning of cotton, cherry, walnut) and promotes female flowers in cucumber, raising the yield.
- Abscisic acid (ABA) was found for its role in abscission and dormancy. It acts as a general inhibitor of plant growth and metabolism and inhibits seed germination.
- ABA stimulates stomatal closure and raises tolerance to many kinds of stress, so it is called the stress hormone. It is important in seed development, maturation and dormancy; by inducing dormancy it helps seeds withstand desiccation. In most situations ABA is an antagonist of GAs.
- PGR roles can be complementary or antagonistic, individual or synergistic. Events such as seed and bud dormancy, abscission, senescence and apical dominance involve more than one PGR.
- PGRs are just one layer of internal control. Genes and outside factors act too, and many outside factors, such as light and temperature, work by changing PGR levels.