Response of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> roots to lipo-chitooligosaccharide from <Emphasis Type="Italic">Bradyrhizobium japonicum</Emphasis> and other chitin-like compounds

Lipo-chitooligosaccharides (LCOs) are bacteria-to-plant signals required for the establishment of rhizobia–legume nitrogen fixing symbioses. The ability of LCO Nod Bj V (C_18:1, MeFuc)] isolated from B. japonicum (strain 532C), and of oligomers of chitosan (tetramer, pentamer) and chitin (pentamer) to affect the developmental morphology of roots in Arabidopsis thaliana (L.) Heynh ecotype Columbia (Col-0) was assessed using an interactive scanner-based image analysis system. LCOs have been shown to play a role in plant organogenesis at nanomolar concentrations. LCO and the chitin pentamer promoted root growth and development in Arabidopsis at concentrations of 10 nM and 100 μM, respectively. The LCO treated Arabidopsis plants had about 35% longer roots than untreated control plants. Similarly, treatment with 100 μM chitin pentamer (CHIT5) resulted in 26% longer roots than the untreated plants; however, chitosan oligomer (CH4 or CH5) treated plants did not differ from the control plants at either concentration (100 or 1 μM). Both LCOs and the chitin pentamer at higher concentrations increased root surface area, mean root diameter and number of root tips. However, leaf area increase was observed only in plants treated with LCO at 10 nM.