PJB-2020-293
MELATONIN ENHANCED SHORT-TERM SALT TOLERANCE BY IMPROVING THE WATER STATUS OF MAIZE SEEDLINGS
NINGNING ZHANG
Abstract
To determine the underlying mechanisms by which exogenous melatonin (MT) application enhances plant resistance to salt, the effects of melatonin (1 μM) on maize (Zea mays L.) seedling growth under short-term salt stress (2 h, 100 mM sodium chloride (NaCl)) were investigated. The results showed that exogenous MT increased the endogenous MT content in maize roots. Under normal conditions, seedling growth was not significantly affected by exogenous MT application, whereas under salt stress conditions, compared with no MT application, MT application resulted in 99% greater root biomass and 20.2% greater plant biomass. Salt stress significantly decreased the photosynthesis rate, stomatal conductance, transpiration rate, whole-plant hydraulic conductance (Kplant) and root hydraulic conductance (Lp), but MT application reduced these stress-induced decreases. Furthermore, compared with untreated seedlings, seedlings treated with MT had a greater photosynthesis rate (24.3%), stomatal conductance (39.4%), and transpiration rate (40.7%) under salt stress. Compared with normal conditions, salt stress conditions decreased the Lp by only 61% in MT-treated seedlings but decreased it by 97% in untreated seedlings. The contribution of aquaporins to Lp was characterized via RT-PCR and HgCl2, an aquaporin inhibitor. Under salt stress, MT increased the expression of specific aquaporin genes (ZmPIP1;6, ZmPIP2;3 and ZmPIP2;7), and exogenous application of HgCl2 reduced the transpiration rates of seedlings treated with and without MT to the same level. Taken together, the results of this study indicate that exogenous MT pre-treatment enhances maize resistance to short-term salt stress by regulating Lp via increased expression and activity of root aquaporins.
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