TITLE:
Involvement of Root Hair during Rhizobial Invasion in Cultivated Peanut (Arachis hypogaea L.)
AUTHORS:
James Maku, Liping Wang, Fengxia Liu, Lixia Liu, Karen Kelley, Ze Peng, Jianping Wang
KEYWORDS:
Cultivated Peanut, Crack Entry, Bradyrhizobia, Root Hair, Nodulation
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.9 No.8,
July
19,
2018
ABSTRACT: Peanut
root invasion by Bradyrhizobia is
through a crack entry, which is different from many other legumes applying an
infection thread entry in root hair. Understanding the role of root hair in the
crack entry of Bradyrhizobia invasion
of peanut root and subsequent peanut nodulation would facilitate improvement of
biological nitrogen fixation in
cultivated peanut. The
objective of this study was to investigate the involvement of root hair in Bradyrhizobial invasion of peanut. Seedling roots of a nodulating peanut cultivar were
observed for root hair emergence, its life span, and nodule formation at the
base of the lateral roots with and without rhizobia inoculation for 14 days
after germination (DAG). Scanning
electron microscopy (SEM) was utilized to observe rhizobia accumulation at
lateral roots at 24 hours
after inoculation (HAI) before the emergence of root hair. Root hair emerged at 7 DAG with or without rhizobia
inoculation. Two variations of rosette hair (RoH) were observed, the
transient-thin RoH had life span of 3 days after root hair emergence and the
thick and densely distributed RoH type stayed till the time of nodule emergence
(9 days after inoculation). The lateral root devoid of root hair at the top 2 cm region was found to produce nodules. The SEM
observation of seedling roots at 24 HAI showed that Bradyrhizobia invaded the roots at epidermis, protoplasm of cortical cell, and cortical cells
of the main root near the newly emerged lateral root in the absence of RoH. The
observations validated that root hair is not required in the Bradyrhizobia invasion of peanut root in the crack entry mode. Results from this study
provided important morphological information for the hypothesis of close
relationship between RoH and peanut
nodulation for further genetic study of crack entry mechanism and signaling
pathway of symbiosis between Bradyrhizobia and peanut.