Diffusible Factors involved in early interactions of the actinorhizal symbiosis are modulated by the host plant but are not enough to break host range barrier

GABBARINI L; WALL LG

FUNCTIONAL PLANT BIOLOGY

CSIRO PUBLISHING

Año: 2011 vol. 38 p. 671 - 681

1445-4408

The induction of root nodule development in actinorhizal symbiosis would depend on the concentration of factors produced by the bacteria and the plant. A detailed analysis of nodulation kinetic revealed different factors with dose response effect related to nodulation. Initial time for nodulation (t0), initial nodulation rate (v0), total time of nodule development (tNOD), were defined and consequently quantified in different experimental conditions: co-inoculation of Discaria trinervis with increasing concentrations of a different bacteria together with the indicator Frankia strain used at a limiting concentration; or by changing plant factors concentration. All the nodulation parameters were modified when the doses of full compatibility infective strain Frankia BCU110501 were changed. v0 appears to be an expression of symbiotic recognition between partners since only Frankia BCU110501 was able to change it. t0 seems not to reflect symbiotic recognition because it can be modify also by non infective Frankia. The increase in plant factors concentration also reduced the t0 suggesting that a plant factor is involved in the very early interactions. Change in plant factors concentration also modifies the final number of nodules per plant and the nodule cluster profile along the tap root as an expression of the autoregulation phenomenon. Meanwhile Frankia inoculums concentration, either infective or not, modified tNOD in an opposite way as plant factors did. In conclusion, the analysis of nodulation kinetics appears to be an appropriate tool to investigate factors involved in the symbiotic interaction leading to the formation of nitrogen fixing nodules.