Changes in photosynthesis, chloroplast ultrastructure, and antioxidant metabolism in leaves of sorghum under waterlogging stress

Waterlogging limits plant growth and yield. We investigated the effects of waterlogging stress on leaf photosynthesis, chlorophyll fluorescence, antioxidant capacity, chloroplast ultrastructure, and yield of sorghum (Sorghum bicolor L.). Two sorghum cultivars, Jinuoliang01 (JN01, waterlogging-tolerant cultivar) and Jinza31 (JZ31, waterlogging-sensitive cultivar) were subjected to a 12-d waterlogging treatment; the plants of the two cultivars which were not subjected to waterlogging were used as control (CK), respectively. After waterlogging treatment, the yield of JZ31 and JN01 decreased by 72.3 and 52.9%, the net photosynthetic rate of JZ31 and JN01 decreased by 61.8 and 39.0%, respectively, compared with CK. The chlorophyll content was higher, PSII was more stable, and chloroplast structure remained more intact in JN01 than that in JZ31 under waterlogging. This was due to the higher peroxidase and catalase activities and nonphotochemical quenching in JN01 compared to JZ31. Therefore, greater antioxidant capacity and nonphotochemical quenching could alleviate damage to PSII and chloroplast ultrastructure to maintain higher net photosynthetic rate under waterlogging. This may be an important waterlogging-tolerance mechanism of sorghum.