PGs were dissected at −72 h, 0 h and 72 h. Each sample includes at least 300 PGs. The collected samples were completely homogenized with a STD buffer(4% SDS, 1 mM DTT, 150 mM Tris-HCl pH 8.0), heated at 100°C for 5 min and then cooled to room temperature. The supernatants were transferred to new tubes and the corresponding protein concentration was determined using the Bicinchoninic acid (BCA) assay protocol (Bio-Rad, Berkeley, CA).