Physiological adversity resistance of sea rice to salinity stress

The sea rice varieties 'FL478' 'JX99' 'Pokkali' and salt-sensitive variety 'IR29' were used to determine malondialdehyde content, cell membrane permeability, soluble sugar and proline in rice leaf. We also investigated the activities of Δ1-pyrroline-5-carboxylic acid synthetase (P5CS), ornithine-δ-aminotransferase (δ-OAT) and superoxide dismutase (SOD) under 0 g·kg^-1, 1 g·kg^-1, 2 g·kg^-1, 3 g·kg^-1, 4 g·kg^-1 and 5 g·kg^-1 of soil salt treatments at booting stage of potted rice under rainproof greenhouse conditions. This aim of the study was to investigate the relationship between osmotic regulators, stress resistance enzymes and salt tolerance of sea rice under salinity stress. The study also provided theoretical basis for the exploration of salt tolerance genes and breeding sea rice varieties with salt tolerance. The results were as follows:1) salinity stress inhibited the synthesis and accumulation of chlorophyll in rice. Then chlorophyll content in rice leaf decreased with increasing salt stress concentration, and was significantly higher than that of salt-sensitive rice. 2) The response of soluble sugars of sea rice and salt-sensitive rice to salinity stress had significantly differences. The rise in soluble sugars of sea rice was less than that of salt-sensitive rice under 0-3 g·kg^-1 soil salt content, but the content of soluble sugars of sea rice was significantly higher than that of salt-sensitive rice under 4-5 g·kg^-1 soil salt content. 3) Malondialdehyde contents of sea rice and salt-sensitive varieties increased with increasing salt stress, resulting in increased cell membrane permeability. However, malondialdehyde content of sea rice was significantly lower than that of salt-sensitive rice. This implied that leaf membrane damage of sea rice was significantly less than that of salt-sensitive rice. 4) Proline content and P5CS, δ-OAT and SOD activities of rice leaf increased initially and then decreased with increasing salt stress. Proline content and P5CS, δ-OAT and SOD activities of sea rice and salt-sensitive rice were maximum under 3 g·kg^-1 and 2 g·kg^-1 salt content, respectively. However, proline content and P5CS, δ-OAT and SOD activities of sea rice were significantly higher than those of salt-sensitive rice. 5) Simple and partial correlations of soluble sugar, proline and P5CS were significantly positive under salinity stress. Salt tolerance characteristics of sea rice were considered as physiological salt tolerance. Proline synthetase P5CS and δ-OAT of sea rice were both activated by salinity stress. The activity of two pathways of proline synthesis (ornithine synthase and glutamate synthase pathways) were simultaneously increased, which promoted rapid and high accumulation of free proline in sea rice. Rapid accumulation of free proline also activated SOD activity, which effectively destroyed the accumulation of intracellular reactive oxygen species. Soluble sugar and proline synergistically alleviated osmotic stress and sea rice showed a strong salt tolerance.