Physiological and proteomic responses of reactive oxygen species metabolism and antioxidant machinery in mulberry (Morus alba L.) seedling leaves to NaCl and NaHCO stress.

In this paper, the effects of 100 mM NaCl and NaHCO stress on reactive oxygen species (ROS) and physiological and proteomic aspects of ROS metabolism in mulberry seedling leaves were studied. The results showed that NaCl stress had little effect on photosynthesis and respiration of mulberry seedling leaves. Superoxide dismutase (SOD) activity and the expression of related proteins in leaves increased by varying degrees, and accumulation of superoxide anion (O·) not observed. Under NaHCO stress, photosynthesis and respiration were significantly inhibited, while the rate of O· production rate and HO content increased. The activity of catalase (CAT) and the expression of CAT (W9RJ43) increased under NaCl stress. In response to NaHCO stress, the activity and expression of CAT were significantly decreased, but the ability of HO scavenging of peroxidase (POD) was enhanced. The ascorbic acid-glutathione (AsA-GSH) cycle in mulberry seedling leaves was enhancement in both NaCl and NaHCO stress. The expression of 2-Cys peroxiredoxin BAS1 (2-Cys Prx BAS1), together with thioredoxin F (TrxF), thioredoxin O1 (TrxO1), thioredoxin-like protein CITRX (Trx CITRX), and thioredoxin-like protein CDSP32 (Trx CDSP32) were significantly increased under NaCl stress. Under NaHCO stress, the expression of the electron donor of ferredoxin-thioredoxin reductase (FTR), together with Trx-related proteins, such as thioredoxin M (TrxM), thioredoxin M4 (TrxM4), thioredoxin X (TrxX), TrxF, and Trx CSDP32 were significantly decreased, suggesting that the thioredoxin-peroxiredoxin (Trx-Prx) pathway's function of scavenging HO of in mulberry seedling leaves was inhibited. Taken together, under NaCl stress, excessive production of O· mulberry seedlings leaves was inhibited, and HO was effectively scavenged by CAT, AsA-GSH cycle and Trx-Prx pathway. Under NaHCO stress, despite the enhanced functions of POD and AsA-GSH cycle, the scavenging of O· by SOD was not effective, and that of HO by CAT and Trx-Prx pathway were inhibited; and in turn, the oxidative damage to mulberry seedling leaves could not be reduced.