A Comparison of Two Soybean (Glycine max, L.) Lines for Flood Tolerance Mechanisms

Flooding can be defined as excess water in the root environment of land plants. This excess water can be injurious or lethal to plants due to blocking of oxygen transfer and other gases between root, soil, and atmosphere. Since waterlogging and flooding occur primarily at root-level, changes in environmental oxygen have effects on root biochemistry and metabolism that lead to physical changes in plant anatomy. Plants that can tolerate flooded soils demonstrate a myriad of responses. Physiological and molecular responses to flooding have been reported for soybean, a generally flood intolerant plant. Greenness (chlorophyll amounts) significantly decreased in flooded soybeans and total nitrogen content of flooded soybeans decreased significantly in roots and shoots. Photosynthesis rates reportedly are reduced significantly. Some soybean lines showed greater acclimation to flooding by avoidance of water loss by transcription (small leaf area) and increased transport of atmosphere O2 to roots via adventitious roots and aerenchyma tissue formation. A research project was developed to examine one flood tolerant and one flood intolerant soybean line for flood tolerance mechanisms. Specifically, whole-plant morphological changes, root tip DNA activity, and root nodule characteristics were observed under flooded and nonflooded conditions. Cytokinins, plant growth regulators produced mainly in root meristematic areas, were also examined as a possible key factor for flood tolerance. The results provided no absolute evidence for cytokinins and cytokinin production as the key to soybean flood tolerance. Rather, evidence indicated flood tolerant soybeans having the anatomical structure and metabolic pathways in place prior to flooding, resulting in vital resources being used for growth and development. Flood intolerant soybeans, responding to flood conditions, metabolically and morphologically changed, resulting in vital resources being diverted to flood survival