Effect of Root Density in Incubation Medium on Root Exudate Composition of Axenic Maize Seedlings

The effect of root density in incubation medium on maize root exudate composition was examined. Sterile root exudates were studied following their collection at various root density values and their fractionation into three constitutive classes: low and high MW soluble material and particulate material. Carbohydrate and protein composition of these different classes were compared. The results indicated that the quantity of carbohydrates exuded by root was a highly variable phenomenon correlated to the density of roots in the incubation medium and mostly associated to the low MW soluble fractions. Nevertheless, these density-dependent variations did not affect their qualitative monosaccharide composition. On the contrary, soluble protein excretion by maize roots was not very sensitive to these variations while root exudation of the proteins that appeared to be linked to the particulate material increased markedly as root density increased. Consequently, two major sources of variability were evidenced in this study: low MW soluble material and particulate material. In conclusion, the density of roots in incubation medium represents a parameter that is very important in consideration of its effect on the composition of root exudates.