Drought Tolerance in Rice Seedlings: Difference between Indica-type IR64 and Japonica-type TNG67 Varieties and Roles of Proline and Abscisic Acid

The mechanism of drought tolerance in rice was studied using an Indica-type IR64 and a Japonica-type TNG67 varieties. An increase of Δ1-pyrroline-5-carboxylate synthetase (P5CS) activity and a decrease of proline dehydrogenase activity as well as an accumulation of proline were observed in tolerant IR64 rice under drought stress. The effects of both exogenously applied abscisic acid (ABA) and an inhibitor of ABA biosynthesis confirmed the role of proline-mediated osmoregulation via an induction of P5CS activity controlled by the plant hormone ABA in the drought tolerance of this staple crop.