Flavan-Containing Cells Delimit Frankia-Infected Compartments in Casuarina glauca Nodules

Abstract

We investigated the involvement of polyphenols in the Casuarina glauca-Frankia symbiosis. Histological analysis revealed a cellspecific accumulation of phenolics in C. glauca nodule lobes, creating a compartmentation in the cortex. Histochemical and biochemical analyses indicated that these phenolic compounds belong to the flavan class of flavonoids. We show that the same compounds were synthesized in nodules and uninfected roots. However, the amount of each flavan was dramatically increased in nodules compared with uninfected roots. The use of in situ hybridization established that chalcone synthase transcripts accumulate in flavancontaining cells at the apex of the nodule lobe. Our findings are discussed in view of the possible role of flavans in plant-microbe interactions.

Nitrogen-fixing bacteria associated with leguminous and non-leguminous plants

“…More recently, a second level of compartmentalization was described in Casuarina glauca nodules based on accumulation of flavans, which occurs in uninfected cells in the endodermis and cortex. These cells form layers that delimit Frankia-infected compartments in the nodule lobe and may play a role in restricting bacterial infection to certain zones of the nodule (Laplaze et al 1999). …”

The role of flavonoids in the establishment of plant roots endosymbioses with arbuscular mycorrhiza fungi, rhizobia and Frankia bacteria

“…The use of in situ hybridization established that chalcone synthase transcripts accumulate in flavan containing cells at the apex of the nodule lobe. Laplaze et al 79 hypothesized that cell specific flavan biosynthesis and accumulation delimit cortical compartments containing Frankia-infected cells and might restrict endophyte invasion. The meaning of this compartmentation is not understood, but obviously some signal exchange with the endophyte is needed for its development.…”

“…The involvement of polyphenols in the Casuarina glauca-Frankia symbiosis was investigated. 79 Histological analysis revealed a cell specific accumulation of phenolics in C. glauca nodule lobes, creating a compartmentation in the nodule cortex. Histochemical and biochemical analyses indicated that these phenolic compounds belong to the flavan class of flavonoids.…”

Improving Casuarina growth and symbiosis with Frankia under different soil and environmental conditions—review

“…Kaempferol and quercetin, along with other phenolic compounds, were the dominant flavonoids in the tested Casuarina species in Egypt (Saleh and El-Lakany 1979). Phenolic compounds may also limit Frankia colonization compartments inside the host nodule tissues (Laplaze et al 2000). The added quercetin increased the isolated Frankia colonies, while fungal contaminants were reduced, in the isolation medium (Sayed and Wheeler 1999).…”