Plant Hormones are chemical messengers that are made in one place in the plant body and deliver their message in a totally different place in the plant body. There are many hormones such as Auxin, Gibberellin, Cytokinin, Ethylene and Abscisic Acid by which each hormone is responsible for each function in plants. The drought signaling in plants is done by Abscisic acid during the time when there is stress on water availability. These hormones found only in small concentration but plays a vital role in plant growth, metabolism, aging etc. and study of these hormones are necessary to know well about plants.Modified crops have been developed to resist abiotic stresses, such as extreme temperature, drought or salinity, and biotic stresses, such as pathogens, insects etc. and to increase the crop yield.