Effects of graft with pumpkin rootstock on nitrogen metabolism and protein expression in the cucumber seedlings under iso-osmotic Ca(NO3)2 or NaCl stress
Abstract:Effects of grafting on the growth, nitrogen metabolism, osmoregulatory substances and soluble protein expression was conducted with pumpkin (Cucurbita maxima×Cucurbita moschata) as the rootstock and a cultivar cucumber ‘Jinyou No. 3’ as the scion under iso-osmotic Ca(NO3)2 or NaCl stress. Results showed that the rootstock-grafted seedlings significantly enhanced the growth, NR activity, NO3--N, soluble protein, soluble sugar, proline content and decreased NH4+-N content under iso-osmotic Ca(NO3)2 and NaCl stress. SDS-PAGE profiles show that there were twelve differentially-expressed proteins in leaves of rootstock-grafted seedlings in present of salt treatment. Of these twelve proteins, ten proteins were up-regulated including the proteins of relative molecular weight (×103) for 188.4, 156.1, 120.4, 54.0, 37.3, 32.1, 30.6, 18.9, 17.8 and 17.1 while one proteins of 81.0×103 were down-regulated and turned a novel protein of 63.4 ×103. And thus, we considered these twelve proteins were related to enhancement of salt-tolerance rootstock-grafting in cucumber seedlings. Results also showed the expressing of four proteins of relative molecular weight (×103) such as 86.1，23.4, 18.9 and 17.8 were stronger in both self-grafted and rootstock-grafted seedlings under NaCl stress than that under Ca(NO3)2 stress, whereas the expressing of proteins relative molecular weight (×103) such as 188.4, 156.1, 54.0 and 17.1 were lower under NaCl stress than that under Ca(NO3)2 stress. And three proteins of 39.1×103, 35.4×103 and 21.2×103 even disappeared in self-grafted seedlings under NaCl stress for 9 days. It was possible that these eleven proteins have relations with rootstock-grafted seedlings improving the Ca(NO3)2 stress tolerance of cucumber seedlings．In conclusion, the damages caused by NaCl stress were more serious than that by Ca(NO3)2 stress, and rootstock-grafting could effectively alleviated the injury via regulating nitrogen metabolism and osmoregulatory substances of cucumber seedlings under salt stress. It seems this catabatic fuction in rootstock-grafted plants was more expressing under Ca(NO3)2 stress.