Analysis of nodulation kinetics in Frankia - Discaria trinervis symbiosis reveals different factors involved in the nodulation process.

GABBARINI, L; WALL, LG

PHYSIOLOGIA PLANTARUM

WILEY-BLACKWELL PUBLISHING, INC

Año: 2008 p. 1 - 10

0031-9317

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 descriptors parameters revealed different factors related to the nodulation process. The initial time for nodulation (t0), the initial nodulation rate (v0), and the total time of nodule development (tNOD), were defined and consequently quantified in different experimental conditions: co-inoculation of Discaria trinervis with increasing concentrations of different non-infective bacteria together with the full compatible infective Frankia strain (the indicator strain) used at a limiting concentration; or by changing plant factor(s) concentration. All the above nodulation parameters were modified by changing doses of full compatibility infective strain Frankia BCU110501; v0 appears to be an expression of symbiotic recognition between partners since only fully symbiotic indicator Frankia BCU110501 was able to change it; t0 seems not to reflect symbiotic recognition because it can also be modified by non infective Frankia but suggest the existence of a basic level of plant microbe recognition. t0, reflecting the time required for the early interactions towards nodulation, is an inverse measure of the ability to establish early interactions towards nodulation.  The increase in plant factors concentration also reduces t0 values suggesting that a plant factor is involved and favors very early interactions. Increases 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 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.