Prepared by-A. Naga tharunResarch scholar M. Sc. (Pl. Physiology)BACA, AAU,Anand

ABSCISIC ACID(STRESS HORMONE) BIOSYTHESIS

. Addicot and his colleagues (1964) isolated this abscission causing compound from cotton bolls and named it as abscisin I & abscisin 11

PHYSIOLOGICAL ROLE

A) Seed dormancy: seed dormancy is controlled by GA-ABA balance at least in some species

eg appleb. Effect of stomataApplication of ABA causes rapid closure of stomata. c. senescence: It quite effective in promoting senescence of excised leaf discs of both monocots and dicots.d. Antagonism:ABA inhibits GA stimulated growth in various forms Therefore ABA is known as Anti gibberellin.

ETHYLENE

Neljubow (1901) a Russian plant physiologist was the first to show importance of ethylene

Role of ethylene:A. Fruit ripening In fruits like mango, apple and tomato ,it causes fruit ripening.b. Abscission and senescence Ethylene promotes both abscission and senescence of flowers C. Roots on stem cuttings Ethylene inhibits linear growth of the stem and root of

dicotyledons.

e. 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.

f.Epinasty Ethylene causes swelling of cells on the upper part of the petiole

of the leaf resulting in drooping of leaves (down ward curvature). It is best exhibited in leaves of tomato, potato and pea etc.

GROWTH RETARDANTS The term growth retardant refer to the chemicals that slow down cell

division and cell elongation of shoot tissue They do not occur naturally in plants. Examples: AMO 1618, CCC (Chloro choline chloride ) (2-Chloroethyl - trimethyl ammonium

chloride) Chlormequat chloride ( Cycocel) Alar or B9 paclobutrazol Mepiquat chloride,

SENESCENCE

‘A degenerative and Irreversible change in a plant which leads to death’ is called senescence.

CLASSIFICATION OF SENESCENCE

Eg a)riceb)Sugarbeatc)Tobaccod)Ficus,Delonix