Physiological roles (Includes both positive and negative effects)

Physiological role

1. Fruit ripening :

Broadly fruits can be classified into two types on the basis of their respiratory pattern during ripening. In some fruits like apple and banana as the fruit matures and attains its maximum size, the rate of respiration decreases and becomes very low. After the fruit is harvested and stored for ripening, there is a great increase in the rate of respiration and the rise continues till it attains a sharp peak. This is called climacteric peak and the fruits are called climacteric fruits. In climacteric fruits ripening occurs even after harvesting. The climacteric rise is soon followed by a sharp decline.

The non-climacteric fruits like grapes and lemon, the respiratory rate gradually decrease after the fruit is harvested without showing any abrupt rise. The peak respiratory rate in climacteric fruits usually corresponds to peak ethylene production.

Application of ethylene hastens ripening of climacteric fruits such as banana, mango, apple and tomato. This is being commercially employed. In non-climacteric fruits such as lemon and orange ethylene application does not hasten ripening however rate of respiration increases greatly.

2. Abscission and senescence :

Ethylene promotes both abscission and senescence of flowers. The flowers of orchids and roses are most sensitive to externally applied ethylene. Ethylene also promotes leaf abscission. In general, older leaves are more sensitive to ethylene and abscise faster than younger ones. Older leaves produce more ethylene than younger ones. This is
probably responsible for abscission of older leaves.

3. Roots on stem cuttings :

Application of ethylene promotes callus formation and initiation of adventitious roots on the stem cuttings. Sometimes adventitious roots may arise on the stem of intact plant as well.

4. Root and shoot growth

Ethylene inhibits linear growth of the stem and root of dicots. The effect increases with increasing concentration.

5. Flowering and sex expression:

Application of ethylene causes flowering in pine apple and shift the sex ratio of flowers towards femaleness in several cucurbits and cannabis.

6. Epinasty :

Ethylene causes swelling of cells on the upper part of the petiole of the leaf resulting in drooping of leaves (down ward curvature). This is termed as epinasty. It is best exhibited in leaves of tomato, potato and pea etc.

7. Thinning in apple :

Thinning of fruits in apple eliminates biennial bearing and also improves fruit size and quality. Application of ethephon at 100 to 300 ppm reduces fruit set. In cotton also ethylene induces fruit thinning.

8. Exudation of sap and latex :

When ethereal is applied to rubber plants, flower of latex continues for a longer duration. Etherel probably prevents coagulation of latex and consequent blocking of laticiterious ducts.

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