Osmotic adjustment, toxic ion exclusion and oxidative protection as key traits for the tolerance to NaCl stress in forage sorghum

The physiological and biochemical responses to 120 mmol L ^-1 NaCl in CSF20 genotype and Catissorgo variety of forage sorghum were studied. The salinity did decrease the plant growth, but it was stronger in CSF20 than in Catissorgo. Under salinity, K ⁺ content was not changed in CSF20 and it was solely reduced in the stems and roots of Catissorgo. Na  ⁺  and Cl ^– accumulation in young leaves and stems was lower in Catissorgo than in CSF20. Roots of Catissorgo did retain more toxic ions than those of CSF20. Alterations in water status and oxidative damage were observed in CSF20 leaves. The chlorophyll content increased in CSF20, but it was unchanged in Catissorgo. Such responses were associated with carotenoid and glucose contents. Salinity promoted osmotic adjustment of leaves and roots. The reduction of leaf osmotic potential was due to the increase of Cland Na  ⁺  in Catissorgo, and Na  ⁺  in CSF20. The contribution of organic solutes was similar among the control and salt-treated plants; glucose was the major organic osmolyte. The activity of guaiacol peroxidase and catalase was consistently higher in Catissorgo leaves than in CSF20 leaves. Salt stress induced the superoxide dismutase activity only in Catissorgo leaves, but it was weakly correlated with the low malondialdehyde accumulation. Isoforms of catalase and superoxide dismutase were increased in Catissorgo leaves. In summary, the systemic osmotic adjustment, the antioxidative protection by carotenoids and superoxide dismutase isoforms, and the toxic ion exclusion by roots are crucial to tolerate salt stress in forage sorghum.