Proline and carbohydrate metabolism in rice varieties (Oryza sativa L.) under various drought and recovery conditions

Drought stress is a main limitation of rice production in many regions worldwide, as most improved rice varieties are not drought tolerant. This study analyzed the effects of various drought stresses and subsequent recovery on dry weight accumulation and biochemical characteristics of different rice varieties (the drought-tolerant variety DA8, the drought-sensitive variety Malagkit Pirurutong, and the fast-recovering variety Kinandang Patong). The water treatments were irrigated (control), drought stress, and subsequent re-watering. The results showed that under the same drought stress level, DA8 retained higher water content than the other varieties. In addition, water content in sheaths was higher than that in leaves. DA8 obtained a higher dry weight accumulation than the other varieties under both the control and drought conditions. Proline content in all varieties increased significantly after drought stress. In addition, it accumulated more in leaves than in sheaths. DA8 expressed a higher ability to accumulate proline than Malagkit Pirurutong or Kinandang Patong. Total soluble sugar and starch contents of the three varieties decreased under drought stress compared to control. However, the change in total soluble sugar and starch levels depended not only on the drought stress condition but also on the environment and variety. Proline-accumulating ability under drought stress may be a useful indicator of the drought tolerance of rice.