Preparation and surface characteristics of root cell walls of soybean and maize seedlings

Surface characteristics of root cell walls are thought to closely relate to the effects of root cell walls on nutrient uptake and accumulation as well as resistance or tolerance to environmental stresses in plants. This study used a modified homogenizing-washing scheme to extract cell wall materials from roots of soybean (Glycine max L., a plant with Type I cell wall) and maize (Zea mays L., a plant with Type II cell wall) seedlings, rendering root cell wall materials with good purities. The cation exchange capacities (CECs) of extracted root cell wall materials and intact roots were measured, and the dissociation constant and amount of each type of functional group on the surface of root cell walls were estimated by fitting and resolving of the potentiometric titration curves of the root cell walls. It is indicated that the CEC of soybean root cell wall is significantly (p0.05) higher than that of maize root cell wall, with values of 425±5 and 162±7 μmol/g, DW, respectively. The root CEC of soybean is also significantly (p0.05) higher than that of maize, which is consistent with the difference between the CECs of root cell walls of the two plants. Only one functional group on the surface of root cell walls of either soybean or maize was identified, which is thought to be the carboxylic acid group with an apparent pKa equivalent to 5.78. The estimated amount of carboxylic group in the root cell wall of soybean was also significantly (p0.05) higher than that of maize, with values of 604±15 and 252±4 μmol/g, DW, respectively. The higher CEC of soybean roots or root cell walls is related to more carboxylic groups appeared in Type I cell walls. Further discussed was the effect and significance of surface characteristics of root cell walls on nutritional processes as well as resistance or tolerance to environmental stresses in plants with Type I or Type II cell wall.