| To investigate changes in the osmoregulatory capacity of different rice varieties under the combined effects of partial root-zone drying (PRD) and nitrogen forms, the conventional indica rice ‘Meixiangzhan No. 2’ (Variety A), the two-line hybrid indica rice ‘Shentaiyou 7278’ (Variety B), and the three-line hybrid indica rice ‘Taifengyou 208’ (Variety C) were selected for experiments. Three water treatments were set: non-water-stressed condition (CK), partial root-zone drying (PRD), and whole-root water stress induced by polyethylene glycol (PEG), in combination with three ammonium-to-nitrate nitrogen ratios: 100/0 (A100/N0), 50/50 (A50/N50), and 0/100 (A0/N100). The results showed that under the combined treatment of PRD and A50/N50 nitrogen form, the leaf free amino acid contents of Varieties A, B, and C increased by 90.00%, 14.78%, and 25.43%, respectively. Under the same treatment, root proline contents increased by 13.25%, 12.51%, and 7.08%, respectively. Under PRD combined with A100/N0 nitrogen, root Δ1-pyrroline-5-carboxylate synthetase (P5CS) activity increased by 75.10% in Variety A and by 20.47% in Variety B. In addition, PRD combined with A50/N50 nitrogen increased P5CS activity by 63.64% and 28.58% in Varieties A and B, respectively. Under PRD combined with A0/N100 nitrogen, proline dehydrogenase (ProDH) activity in the root system increased by 16.93%, 29.30%, and 28.24% in Varieties A, B, and C, respectively. Overall, the coupling of PRD and nitrogen forms can generally enhance the osmoregulatory capacity of rice by regulating free amino acid and proline metabolism. |
