Flooding is one of the serious problems for soybean plants because it inhibits growth. Proteomic and metabolomic
techniques were used to determine whether proteins and metabolites are altered in the root tips of soybeans under
flooding stress. Two-day-old soybean plants were flooded for 2 days, and proteins and metabolites were extracted
from root tips. Flooding-responsive proteins were identified using two-dimensional- or SDS-polyacrylamide gel electrophoresis-
based proteomics techniques. Using both techniques, 172 proteins increased and 105 proteins decreased in abundance
in the root tips of flood-stressed soybean. The abundance of methionine synthase, heat shock cognate protein,
urease, and phosphoenol pyruvate carboxylase was significantly increased by flooding stress. Furthermore, 73 floodingresponsive
metabolites were identified using capillary electrophoresis-mass spectrometry. The levels of gammaaminobutyric
acid, glycine, NADH2, and phosphoenol pyruvate were increased by flooding stress. Taken together, these
results suggest that synthesis of phosphoenol pyruvate by way of oxaloacetate produced in the tricarboxylic acid cycle is
activated in soybean root tips in response to flooding stress, and that flooding stress also leads to modulation of the urea
cycle in the root tips.
Flooding, metabolomics, proteomics, root tip, soybean.
National Institute of Crop Science, NARO, Kannondai 2-1-18, Tsukuba 305-8518, Japan.