Energy dissipation and antioxidant enzyme system protect photosystem II of sweet sorghum under drought stress

The effect of drought stress on energy dissipation and antioxidant enzyme system in two sweet sorghum inbred lines (M-81E and Roma) was investigated. Results showed that the germination indicator increased more in M-81E than that in Roma under rehydration. Under drought stress, both the maximal photochemical efficiency of PSII (F-v/F-m) and oxidoreductive activity (Delta I/I-0) of Roma decreased more than those in M-81E. Relative to Fv/Fm, the Delta I/I0 decreased markedly, which indicated that PSI was more sensitive to drought stress than PSII. Increases in the reduction state of Q(A) (1-q(p)), nonphotochemical quenching (NPQ) and minimal fluorescence yield of the dark-adapted state (F-0) were greater in Roma than those in M-81E; meanwhile, the H2O2 content was lower in M-81E than that in Roma. Our results suggested that the photoinhibition might be related to the accumulation of reactive oxygen species (ROS). The antioxidant enzyme system and energy dissipation of M-81E could respectively increase drought tolerance by eliminating ROS and excess energy more efficiently than that of Roma.