Ozone stress-induced proteomic changes in leaf total soluble and chloroplast proteins of soybean reveal that carbon allocation is involved in adaptation in the early developmental stage

Considerable soybean yield losses caused by ozone (0 3 ) stress have been demonstrated by large-scale meta-analyses of free-gas concentration enrichment systems. In this study, comparative proteomic approach was employed to explore the differential changes of proteins in 0 3 target structures such as leaf and chloroplasts of soybean seedlings. Acute O 3 exposure (120 parts-per-billion) for 3 days did not cause any visible symptoms in developing leaves. However, higher amounts of ROS and lipid peroxidation indicated that severe oxidative burst occurred. Immunoblot analysis of O 3 -induced known proteins revealed that proteins were modulated before symptoms became visible. Proteomic analysis identified a total of 20 and 32 differentially expressed proteins from O 3 -treated leaf and chloroplast, respectively. Proteins associated with photosynthesis, including photosystem I/II and carbon assimilation decreased following exposure to O 3 . In contrast, proteins involved in antioxidant defense and carbon metabolism increased. The activity of enzymes involved in carbohydrate metabolism increased following exposure to O 3 , which is consistent with the decrease in starch and increase in sucrose concentrations. Taken together, these results suggest that carbon allocation is tightly programmed, and starch degradation probably feeds the tricarboxylic acid cycle while the photosynthesis pathway is severely affected during O 3 stress.