*2.2.2.4 Regulation of dormancy/germination by GA and ABA*

The two main plant growth regulators that regulate dormancy-germination cycling are ABA and GA3. A model for the regulation of dormancy by ABA and GA in response to the environment has been proposed [37]. This model suggests that, the sensitivity of embryo to ABA and GA ratios within the seed is influenced by environmental factors like temperature. If the ABA synthesis and signaling (GA catabolism) dominates then dormant state is induced and maintained while the opposite event promotes transition to germination. Variations in the level of dormancy alter the requirements for germination when these overlap with varying environmental factors. Throughout the process of seed development, dormancy can be induced and maintained depending on GA/ABA balance. During imbibition, GA levels increases while ABA levels decline, suggesting that GA and ABA have antagonistic roles in seed dormancy and germination processes [53]. GA counteracts the effect of ABA by promoting the embryo growth potential and the weakening of tissues covering the embryo [54].
