**2. Seed Respiration**

To fulfill the higher energy requirement during the transition period (from quiescent to active state) of the seed, cellular respiration is rapid, high, and synchronized with the mitochondrial activity [13]. According to Law et al., proteins required for the biogenesis of mitochondria were already present in the dried seeds and this process is activated upon imbibition. Although the import of mitochondrial proteins is highly required for the biogenesis, amount of ATP consumption by mitochondria is limited as compared with other processes. On the other hand, amount of ATP required by the mitochondria for the protein import is lesser than the energy required for protein synthesis [14]. In the transition period, oxygen (O2) released by the respiration governs the internal communications between the cell organelles and the rapid cell division and expansion [15]. The excessive generation of ROS is extremely harmful to the cells. Although the O2 − has very limited half-life (2 μs), the reduction in O2 − (superoxide dismutation) results in the production of hydrogen peroxide (H2O2). Hydrogen peroxide can travel long distance and reaches the target as its half-life was determined to be about 1 ms. Other free radicals formed during the enzymatic reduction of O2 − and H2O2 is •OH [16]. The formation of •OH radical is mediated by iron in the Haber-Weiss and Fenton reactions. The uncoupled electrons present in the ROS cross-react with other essential metabolites or cellular compo‐ nents, affecting the normal cell physiology. However, a proper antioxidant system detoxifies the excessively generated free radicals and leads to the nondormant phenotype [16]. Detailed mechanisms on the involvement of ROS in seed germination are discussed below.
