Ethylene Induce Abscission Induce Abscission Fruit ripening Radial growth Yellowing of leaf Closure of stomata ABA ABA . Occurrence This hormone is found abundantly inside the chloroplast of green cells. . Precursors The hormone is formed from mevalonic acid pathway or xanthophylls.
. Transport in plants Abscisic acid is transported to all parts of the plant through diffusion as well as through phloem and xylem. . Chemical structure It has carotenoid structure.
. Bioassay (Rice Coleoptile) The inhibition of IAA induces straight growth of rice seedling coleoptiles. . Physiological effects • It helps in reducing transpiration rate by closing stomata.
• ABA is a powerful growth inhibitor. It causes % inhibition of growth in Oat coleoptile. • It induces bud and seed dormancy. • It promotes the abscission of leaves, flowers and fruits by forming abscission layers.
• ABA plays an important role in plants during water stress and during drought conditions. It results in loss of turgor and closure of stomata. • In Cannabis sativa, induces male flower formation on female plants. • It promotes sprouting in storage organs like Potato.
• It inhibits the shoot growth and promotes growth of root system. This character protect the plants from water stress. Hence, ABA is called as stress hormone. .
Photoperiodism Trees take several years for initiation of flowering whereas an annual herb flowers within few months. Each plant requires a specific time period to complete their vegetative phase which will be followed by reproductive phase as per their internal control points through Biological Clock. . Occurrence Maximum synthesis occurs during climacteric ripening of fruits ( see Box info) and tissues undergoing senescence.
It is formed in almost all plant parts like roots, leaves, flowers, fruits and seeds. . Transport in plants Ethylene can easily diffuse inside the plant through intercellular spaces. .
Precursor It is a derivative of amino acid methionine, linolenic acid and fumaric acid. . Bioassay (Gas Chromatography) Ethylene can be measured by gas chromatography. This technique helps in the detection of exact amount of ethylene from different plant tissues like