Calcium affecting protein expression in longan under simulated acid rain stress

Longan (Dimocarpus longana Lour. cv. Wulongling) of uniform one-aged seedlings grown in pots were selected to study specific proteins expressed in leaves under simulated acid rain (SiAR) stress and exogenous Ca2+ regulation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) results showed that there was a protein band specifically expressed under SiAR of pH 2.5 stress for 15 days with its molecular weight of about 23 kD. A 17 kD protein band specifically expressed after SiAR stress 5 days. Compared with pH 2.5, the pH 3.5 of SiAR made a less influence to protein expression. Two-dimensional electrophoresis (2-DE) results showed that six new specific proteins including C-4 (20.2 kD pI 6.0), F (24 kD pI 6.35), B-3 (22.3 kD pI 6.35), B-4 (23.5 kD pI 6.5), C-5 (21.8 kD pI 5.6), and C-6 (20.2 kD pI 5.6) specifically expressed. C-4 always expressed during SiAR stress. F expressed under the stress of pH 2.5 for 15 days and expressed in all pH SiAR stress for 20 days. The expression of proteins including B-3, C-5, and C-6 was related to pH value and stress intensity of SiAR. The expression of B-4 resulted from synergistic effects of SiAR and Ca. The expression of G(1) (Mr 19.3 kD, pI 4.5), G(2) (Mr 17.8 kD, pI 4.65), G(3) (Mr 16.6 kD, pI 4.6), and G(4) (Mr 14.7 kD, pI 4.4) enhanced under the treatment of 5 mM ethylene glycol tetraacetic acid (EGTA) and 2 mM chlorpromazine (CPZ). These proteins showed antagonistic effects and might be relative to the Ca-calmodulin (Ca-CaM) system of longan in response to SiAR stress.