Submitted to: Plant Cell and Environment
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/28/2009
Publication Date: 2/1/2010
Publication URL: www3.interscience.wiley.com/journal/122681569/pdfstart
Citation: Yamaguchi, M., Valliyodan, B., Zhang, J., Lenoble, M.E., Yu, O., Rogers, E.E., Nguyen, H.T., Sharp, R.E. 2010. Regulation of Growth Response to Water Stress in the Soybean Primary Root. I. Proteomic Analysis Reveals Region-Specific Regulation of Phenylpropanoid Metabolism and Control of Free Iron in the Elongation Zone. Plant Cell and Environment. 33:223-243. Interpretive Summary: Drought, or water stress, is a leading cause of yield reduction in agriculture. When a plant root first encounters water stress, different regions of the root respond in different ways. The very tip of the root continues to elongate and grow very much like well-watered roots. Growth in this region is primarily a result of cells dividing to make more cells. However, the 4-8 mm region just above the root tip stops growing. In this upper root region, cells elongate and that causes the observed growth. The root growth reduction in the upper root region causes a smaller shoot to be formed and can lead to reduced yield of the crop species in question. This work compares the proteins present in each of these two regions in soybean roots in drought conditions to identify proteins present in the tip that allow for continued growth and proteins in the upper region that may inhibit growth. Lignin biosynthesis was increased in the upper region. Lignin is a rigid component of the cell wall, so making more rigid cell walls will inhibit cell elongation and growth. Proteins and chemicals involved in protection from stress caused by reactive oxygen compounds were also increased.
Technical Abstract: In water-stressed soybean primary roots, elongation was maintained at well-watered rates in the apical 4 mm (region 1) but was progressively inhibited in the 4-8 mm region (region 2), which exhibits maximum elongation in well-watered roots. These responses are similar to previous results for the maize primary root. To understand these responses in soybean, spatial profiles of soluble protein composition were analyzed. Among the changes, the results indicate that region-specific regulation of phenylpropanoid metabolism may contribute to the distinct growth responses in the different regions. Several enzymes related to isoflavonoid biosynthesis increased in abundance in region 1, correlating with a substantial increase of isoflavonoid content in this region which could contribute to growth maintenance via various potential mechanisms. In contrast, caffeoyl-CoA O-methyltransferase, which is involved in lignin synthesis, was highly up-regulated in region 2. This response was associated with enhanced accumulation of lignin, which may be related to the inhibition of growth in this region. Several proteins which increased in abundance in both regions of water-stressed roots were related to protection from oxidative damage. In particular, an increase in the abundance of ferritin proteins effectively sequestered more iron and prevented excess free iron in the elongation zone under water stress.