Abstract: The effects of D1 protein turnover and xanthophylls cycle on photosystem Ⅱ functions of Morus alba leaves under NaCl stress were studied by using their inhibitors. The results showed that there were sound mechanisms of photoprotection in M. alba leaves and PSⅡ reaction center remained high activity under 100 mmol·L^-1 NaCl stress. PSⅡfunctions in SM or DTT treated leaves were damaged under NaCl stress. More severe damage occurred in SM treated leaves than that in DTT treated ones, which indicated D1 protein turnover and xanthophylls cycle played an important role in protecting PSⅡ functions in leaves of M. alba under NaCl stress, and D1 protein turnover might play more important role than xanthophylls cycle. DTT treatment limited protection ability of the xanthophlly cycle in leaves of M. alba under NaCl stress, but was able to reduce the damage of the excessive excitation energy to PSⅡ reaction center by increasing dissipation of ineffective fluorescence and heat. SM not only damaged the xanthophylls cycle but also fluorescence and heat dissipation functions, leading to (1-q_P)/NPQ large accumulation and PSⅡ reaction center deactivation. SM not only suppressed the D1 protein turnover, but also aggravated the Q_B reduction degree, which reduced the electronic transfer and the capacity of PQ. The decrease of PQ capacity ievitably depressed the thylakoid membrane functions establishing protons gradient (△pH) and limited the xanthophylls cycle that is dependent on △pH. In summary, inhibition of D1 protein turnover damaged xanthophylls cycle, which could interpret the reason why D1 protein turnover played more important role than xanthophylls cycle in protecting PS Ⅱ functions in leaves of M. alba under NaCl stress.

Key words: Morus alba, NaCl stress, D1 protein turnover, xanthophylls cycle, photosystem Ⅱ