Characterization of root hair curling and nodule development in soybean-rhizobia symbioses

Abstract

Abstract Aims Root hair is the initial infection site for symbiotic (rhizobia) process including rhizobia attaching, root hair deforming, and nodule organ forming. Since roots and nodules are blocked by soil and are hard to be perceived, little knowledge is available on the process of soybean root hair deformation and nodule development over time. Methods In this study, adaptive microrhizotrons and root hair processing method were used to observe root hairs and to investigate detailed root hair deformation and nodule formation. Results It was found that root hairs were not always straight even in uninfected group with relatively small angle (<30°), but root hair curling angle in infected group were large ranging from 32° to 80° since S2 to S6. Nodule was an organ developed late than root hair curling. It initiated from root axis and began to swell in S3, with color changing from light to dark brown in S5. In order to eliminate the observing error, diameter over 1 mm was converted to real diameter with relative formulation. And after conversion, diameter of nodule reached 5 mm in S6. Relationship between root hair curling number/angle and nodule number/diameter indicated that curling angle was strongly related to log nodule diameter (R2 0.84), and curling number was strongly linear to nodule number (R2 0.91). Conclusions Thus, nodule number could be calculated through the derived formulation and nodule diameter could be observed and converted to real diameter nondestructively.