Abstract
The threshold range of reactive oxygen species (ROS) concentration remains a critical challenge and focal point in future research concerning its influence on the growth and development of both beneficial and harmful plants. This study demonstrates that as the concentration of hydrogen peroxide (H(2)O(2)) increases from 0.0% to 0.6%, the seed germination rate gradually rises. At 0.6% H(2)O(2), the germination rate peaks at 94.67%, accompanied by the maximum activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). However, with further increases in H(2)O(2) concentration (0.7% - 1.3%), the seed germination rate and antioxidant enzyme activity gradually decline, while the levels of superoxide anion (O(2) (-)) and H(2)O(2) accumulate progressively. This suggests that higher H(2)O(2) concentrations impair the ROS scavenging capacity in cabbage-type rapeseed, leading to increased ROS production and subsequent inhibition of growth and development. At half-lethal H(2)O(2) concentrations (1.4%-1.5%), the seed germination rate before rehydration is significantly reduced to 10.97% and 9.03%, respectively, but can recover to approximately 50% after rehydration. H(2)O(2) concentrations exceeding 2.2% are lethal, resulting in a 0% seed germination rate both before and after rehydration; notably, the post-rehydration germination rate remains below 10%. At these concentrations, the levels of O(2) (-), SOD, POD, and CAT decrease to their minimum values, indicating that high exogenous H(2)O(2) concentrations induce cell death, which in turn suppresses ROS production and inactivates ROS-scavenging enzyme activity. Consequently, cellular osmotic potential increases, leading to the accumulation of high concentrations of exogenous H(2)O(2) within cells.