(i) ABA stands for Abscisic Acid.
(ii) ABA promotes the process of separation of leaves, flowers and fruits (abscission).
(iii) During water stress and drought conditions ABA causes stomatal closure.
(iv) ABA promotes senescence in leaves by causing loss of chlorophyll.
(v) ABA induces bud dormancy towards the approach of winter in trees like birch.
(vi) ABA is a powerful inhibitor of lateral bud growth in tomato.

(i) Ethylene promotes the ripening of fruits.
Eg : Tomato, Apple, Mango,Banana, etc.
(ii) Ethylene inhibits the elongation of stem and root in dicots.
(ii) Ethylene hastens the senescence of leaves and flowers.
(iv) Ethylene stimulates formation of abscission zone in leaves, flowers and fruits. This leads to premature shedding.
(v) Ethylene breaks the dormancy of buds, seeds and storage organs.

The hormones secreted by the posterior lobe (Neurohypophysis) of the pituitary gland are:
Vasopressin or Antidiuretic hormone (ADH), Oxytocin
a. Vasopressin or Antidiuretic hormone (ADH) :
(i) In kidney tubules it increases reabsorption of water. It reduces loss of water through urine and hence the name antidiuretic hormone.
(ii) Deficiency of ADH reduces reabsorption of water and causes an increase in urine output (polyuria). This deficiency disorder is called Diabetes insipidus.
b. Oxytocin: It helps in the contraction of the smooth muscles of uterus at the time of child birth and milk ejection from the mammary gland after child birth.

(i) The parathyroid glands are four small oval bodies that are situated on the posterior surface of the thyroid lobes.
(ii) The chief cells of the gland are mainly concerned with secretion of parathormone.
(iii) The parathormone regulates calcium and phosphorus metabolism in the body. They act on bone, kidney and intestine to maintain blood calcium levels.
Parthyroid Dysfunction:
The secretion of parathyroid hormone can be altered due to following conditions.
(i) Removal of parathyroid glands during thyroidectomy (removal of thyroid) causes decreased secretion of parathormone. The conditions are
(ii) Muscle spasm known as Tetany (sustained contraction of muscles in face, larynx, hands and feet).
(iii) Painful cramps of the limb muscles.