Katharina Pawlowski, Department of Ecology, Environment and Plant Sciences, Plant Physiology Unit, SU

katharina.pawlowski@su.se

Datisca glomerata is the only herbaceous plant that can form a nitrogen-fixing root nodule symbiosis with actinobacteria of the genus Frankia which grow as a mycelium. The Frankia microsymbiont of D. glomerata cannot be cultured – it seems to be an obligate symbiont. Therefore, crushed nodules or soil samples from underneath infected plants have to be used for the infection of new plants.

 
Frankia host
 

So how does an obligate symbiont survive in the absence of its host? For culturable Frankia strains it has been shown that they can survive long periods as spores in the soil. As a rule, spores are not formed in nodules, only in the soil. Evidence suggests that the soil from underneath infected D. glomerata plants contains Frankia spores. So we have to assume that Frankia hyphae grow out of D. glomerata nodules and form spores in the soil.

 
Frankia
 

In order to prove that, two approaches are possible:
• we can obtain nodulated D. glomerata plants in a sterile system, preferentially in a sterile system that either allows direct observation (growth on Phytagel) or that allows for easy identification of spores (perlite).
• we can surface-sterilize greenhouse nodules and observe them on phytagel plates
Then, the development of a sterile spot infection system is possible that can be tested for early symbiosis-related gene expression.

Techniques involved:
- Sterile plant culture
- Light microscopy
- Plant RNA isolation
- RT-PCR