Responses Of Rice Seedlings To Water Deficiency And Its Relationship With Carbohydrate Partitioning

This study is consisted of three experiments. In the first experiment, two rice cultivars (Zhenshan97 and IRAT109) were employed to investigate the relationships between dry matter distribution and carbohydrate partitioning grown in soil-pot culture. In the second experiment, four rice cultivars (Zhenshan97, IRAT109, Apo and Shanyou63) were grown hydroponically to study the changes in the activities of sucrose metabolizing enzymes under control and water deficit condition. In the third experiment, three rice cultivars (Zhenshan97, IRAT109 and Apo) were grown on petri dishes to further explore the changes of sucrose metabolizing enzyme activities with the addition of calcium ions under water deficit condition.1. Under drought and drought-rewatering-drought condition, root shoot ratio and soluble sugar distribution in root were higher compared with thoes under well-watered condition. This demonstrated that the drought treatment could increase R: S ratio of rice seedlings in adaptation to drought stress by distributing more pre-stored carbohydrates into the root.2. Under water deficit condition, root shoot ratio and soluble sugar distributed in root were notably higher compared with those under normal condition. In addition, the water deficit condition increased the activities of sucrose metabolizing enzymes. Significantly positive correlations were also observed between soluble sugar distribution in root and the activities of SPS (Sucrose Phosphate Synthase) in leaf, acid and neutral INV (Invertase) in root, indicating that sucrose metabolizing enzymes promoted the distribution of carbohydrates to roots under water-stressed condition.3. Under PEG with Ca²⁺treatment, root shoot ratio, dry matter and fresh weight were higher compared with those without adding Ca²⁺ in PEG solution. Besides, the PEG with Ca²⁺ treatment increased the activities of SPS in leaf, SPS and SS (Sucrose Synthase) in stem and acid INV (Invertase) in root. The results indicated that the addition of calcium ions of moderate concentration under water deficit condition can effectively promote a higher root shoot ratio of rice seedlings in adaptation to stress by accelerating the distribution of pre-stored carbohydrates into the root of rice through regulating activities of certain sucrose metabolizing enzymes.