Abstract
Soybean is sensitive to flooding stress and exhibits reduced growth under flooding conditions. To better understand the flooding-responsive mechanisms of soybean, the effect of exogenous calcium on flooding-stressed soybeans was analyzed using proteomic technique. An increase in exogenous calcium levels enhanced soybean root elongation and suppressed the cell death of root tip under flooding stress. Proteins were extracted from the roots of 4-day-old soybean seedlings exposed to flooding stress without or with calcium for 2 days and analyzed using gel-free proteomic technique. Proteins involved in protein degradation/synthesis/posttranslational modification, hormone/cell wall metabolisms, and DNA synthesis were decreased by flooding stress; however, their reductions were recovered by calcium treatment. Development, lipid metabolism, and signaling-related proteins were increased in soybean roots when calcium was supplied under flooding stress. Fermentation and glycolysis-related proteins were increased in response to flooding; however, these proteins were not affected by calcium supplementation. Furthermore, urease and copper chaperone proteins exhibited similar profiles in 4-day-old untreated soybeans and 4-day-old soybeans exposed to flooding for 2 days in the presence of calcium. These results suggest that calcium might affect the cell wall/hormone metabolisms, protein degradation/synthesis, and DNA synthesis in soybean roots under flooding stress.
Highlights
Flooding events caused by heavy rainfall have increased globally over the past six decades as a consequence of climate change (Bailey-Serres et al, 2012)
To investigate the effects of calcium on morphological changes induced by flooding in soybean and evaluate the corresponding degree of root tip damage, 2-day-old soybeans were flooded for 2, 4, and 6 days without or with 1, 5, 10, and 50 mM CaCl2
Changes in calcium ion levels influenced the molecular size of xyloglucans by modifying the expression of VaXTHS4 in azuki bean (Soga et al, 2007). These results suggest that the regulation of cell wall-related proteins, such as xyloglucan endotransglucosylase/hydrolase (XTH), by exogenous calcium might promote the elongation of soybean roots under flooding stress
Summary
Flooding events caused by heavy rainfall have increased globally over the past six decades as a consequence of climate change (Bailey-Serres et al, 2012). Flooding severely affects the productivity of farmland, because most agriculturally important crops are intolerant to flooding stress (Setter and Waters, 2003). When plants are exposed to flooding conditions, the roots initially suffer from oxygen deficiency (Sauter, 2013), leading to the inhibition of root respiration and a marked decrease in the energy status of root cells (Ashraf, 2012). Plants activate an alternative fermentation metabolic pathway to produce ATP and regenerate NAD+ (Gibbs and Greenway, 2003), as evidenced by the drastic increase in alcohol dehydrogenase activity in soybean under flooding stress (Komatsu et al, 2011). The floodinginduced changes in energy metabolism are important processes in adaptation to flooding conditions, metabolism induced by flooding and adaption to flooding in soybean remain unclear
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