Physiological responses of antioxidant enzymes in the leaves of Derris trifoliata seedlings under varying tidal conditions
In recent years the rapid proliferation of Derris trifoliata populations in mangrove areas has resulted in extensive mortality of mangrove plants in certain regions,posing a serious threat to the mangrove wetland ecosystem.During field investigations it was observed that the impact of D.trifoliata on mangrove plants was more pronounced in areas with shorter flooding durations and lower salinity levels compared to those with longer flooding durations and higher salinity levels.To investigate the underlying causes of this phenomenon,an attempt was made to simulate 25 different tidal environments through controlled artificial experiments,under which D.trifoliata seedlings were raised to observe variations in antioxidant enzyme activity,osmotic regulation mechanisms,and membrane system damage levels in their leaves.The results demonstrated that under the individual influence of salinity and flood,the activities of superoxide dismutase(SOD)and catalase(CAT)in the leaves of D.trifoliata seedlings initially increased and then decreased at a salinity level of 0-40‰.The peak value was observed at a salinity level of 20‰.In D.trifoliata seedlings SOD and CAT activities in the leaves did not show significant changes during the 0 h/d-8 h/d flooding period.However,free proline(FPRO)and malondialdehyde(MDA)contents in the seedling leaves exhibited an increasing trend with salinity levels and flooding duration,and their maximum values were reached under treatment conditions of 40‰ salinity and 8 h/d flooding.When both salinity levels and flooding duration were put together,the SOD activity,CAT activity,FPRO content,and MDA content in the seedling leaves came to peak under the treatment of 20％o salt for 6 h/d,20‰ salt for 8 h/d,and 40‰ salt for 8 h/d,respectively.In summary,in an environment with short flooding durations and low salinity levels,D.trifoliata seedlings exhibited a heightened capacity for antioxidant enzymes to combat stress-induced damage,resulting in normal growth and consequently a relatively significant impact on mangrove plants.Conversely,in an environment with prolonged flooding duration and high salinity levels,the efficacy of antioxidant enzymes in mitigating stress damage was diminished,leading to inhibited growth and consequently a relatively less influence on the mangrove plants.
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