Physiological and proteomics responses of nitrogen assimilation and glutamine/glutamine family of amino acids metabolism in mulberry ( Morus alba L.) leaves to NaCl and NaHCO ₃ stress

In order to find out the response mechanism of nitrogen assimilation and glutamine/glutamine family of amino acids metabolism in mulberry (Morus alba L.) leaves under NaCl and NaHCO₃ stress, and to reveal its role in salt alkali adaptation. The effects of the nitrogen metabolism of mulberry leaves were studied under 100 mmol L^-1 NaCl and NaHCO₃ stress.The results showed that the activity of NR and the content of TN and SP did not change significantly, the expression of NiR, Fd-NiR, Fd-NiR gene and theactivity of NiR increased significantly under NaCl stress, but nitrogen assimilation was inhibited under NaHCO₃ stress. NaCl stress had no significant effect on the expression and activity of GS and GOGAT in mulberry leaves. Under NaHCO₃ stress, the expression of Fd-GOGAT, Fd-GOGAT2, Fd-GOGAT gene, and the activity of GS and GOGAT were significantly decreased. NaCl stress can promote the accumulation of Pro, Put and Spd in mulberry leaves. The accumulation of Pro under NaHCO₃ stress is greater than that under NaCl stress. NaCl stress also induced the up-regulation of GAD, GAD1 and GAD1 gene expression, so promoting the synthesis of GABA may be an adaptive mechanism for mulberry to cope with NaCl stress, but the expression of GAD did not change significantly and GAD gene expression lower than CK under NaHCO₃ stress. Although both NaCl and NaHCO₃ stress could promote the synthesis of GSH by up-regulation of GCLM expression, GSH under NaHCO₃ stress was significantly higher than that under NaCl stress, the content of H₂O₂ was still significantly higher than that of NaCl stress, that means GSH may not play a key role in alleviating the oxidative damage in mulberry leaves caused by salt and alkali.

Keywords: Mulberry; nitrogen metabolism; polyamines; proline; proteomics; salt and alkali.