Time-course biochemical analyses of soybean plants during waterlogging and reoxygenation

Soil waterlogging and subsequent reoxygenation can severely impair soybean (Glycine max) growth and productivity. Here we aimed at showing the main biochemical events that occur in soybean plants during waterlogging and reoxygenation conditions. Roots and leaves were analyzed from the first hour up to ten days of waterlogging and reoxygenation imposition. During the first hours of waterlogging, reactive oxygen species (ROS) and nitric oxide (NO) accumulated in roots and leaves. In roots, only NO levels were persistent, while ROS peaked and decreased over time. In leaves, both ROS and NO increased and remain at high levels during the entire experiment. Despite the increased activity of antioxidant enzymes, malondialdehyde (MDA) levels increased and photosynthetic pigment levels declined. The NO levels increased in response to the increment in nitrate reductase activity in the roots, while in the leaves additional biosynthetic pathways seemed to be involved. The activity of fermentative enzymes and the accumulation of lactate and ethanol occurred after a few hours of waterlogging. Regarding reoxygenation, the transient increase in ROS and NO levels were again observed in roots as well as the increase in MDA levels and antioxidant enzyme activities. In leaves, the levels of ROS and NO decreased as did the activity of the antioxidant enzymes and the MDA levels. In contrast, the levels of photosynthetic pigments increased to pre-waterlogging levels. Both the activity and products of fermentative metabolism decreased. Overall, the biochemical events in soybean plants under waterlogging and reoxygenation conditions are dynamic and change during the time course of stress.