SCIENCE AND AGRO STUDIES

Ethylene (C2H4):- > It is the only gaseous hormone. > It is found in ripening fruits. 1. Discovery of Ethylene:- -   Sarah Doubt (1917) discovered that ethylene stimulated abscission. - Gane (1934) established that ethylene was natural product of ripening fruits and possibly stimulated fruit ripening. - Crocker and Knight (1908, 1913) identified ethylene as the active constituent of both, illuminating gas and tobacco smoke. - With the discovery of gas chromatography, it became possible to estimate ethylene levels and soon after in 1969 ethylene came to be accepted as a plant hormone. 2. Chemical nature of Ethylene:-  Ethylene is a hydrocarbon. As the name suggests it has four atoms of hydrogen and two atoms of carbon connected with a double bond.  3. Biosynthesis of Ethylene:-  Ethylene is known to be synthesized in plant tissues from the amino acid methionine. A non-protein amino acid, 1-amino cyclopropane-l-carboxylic acid (ACC) is an important intermediate a...

Abscisic Acid (ABA):- > It is found in older leaves, apical buds and seeds. > Both GA and ABA hormones work opposite to each other. > ABA inhibits the biosynthesis of the hormone GA. 1. Discovery of Abscisic Acid:- - Torsten Hemberg (1940) reported that dormant potato tubers and buds of ash (Fraxinus excelsior) contained inhibitor (rather than stimulators) that blocked the effects of IAA. When the buds germinated, the amount of these inhibitors decreased.  - Eagles and Wareing (1963) isolated an inhibitor from the birch (Betula pubescens) leaves held under short day conditions. When this substance was reapplied to the leaves of birch seedlings, apical growth was completely arrested. As this substance induced dormancy, they named it as ‘dormin’.  - Cornus and Addicot (1963) isolated this compound from the shedding bolls of cotton plant. - Ohkum (1965) isolated an inhibitor from cotton fruits and named it ‘abscisin II’.  - Cornforth (1965) demonstrated that both Do...