Improving Soybean (Glycine max L.) N sub(2) Fixation under Stress

Soybean is a major leguminous plant that has the ability to establish a symbiotic association with the N-fixing bacteria, Bradyrhizobium japonicum. Soils are usually subjected to stress including salinity, drought, acidity, and suboptimal root zone temperature, adversely affecting the symbiotic process between soybean and the bacteria. One of the important processes affecting the performance of soybean under stress is the inhibited exchange of symbiosis-related signaling molecules, specifically genistein, between the host legume and B. japonicum during the initiation of symbiosis. Interestingly, inoculation of B. japonicum with the signal molecule genistein can partially or completely alleviate the stress. Understanding the techniques and the precise molecular pathways, which may be influenced by the signaling molecules during the stress, can be useful to determine parameters that enhance the plant's ability to cope with stress. For example, the use of proteomic techniques to identify proteins expressed under stress can help characterize those proteins and their involvement in stress. Biotechnological-genetic techniques, either breeding or transformation, are also among the effective methods of improving soybean's ability to fix N sub(2) under stress. This can be achieved by identifying the genes, which may be expressed under stress in tolerant bacterial and plant species, and inserting them into the non-tolerant species. This article highlights some important advances in soybean N sub(2) fixation under different stress conditions, and reviews some of the techniques used to improve the ability of plants and bacteria to efficiently fix N sub(2) under stress.