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Some aspects of phenolic metabolism have been followed during the development of durum wheat grain. Bound ferulic (FA) and p-coumaric (PCA) acids have been extracted after alkaline hydrolysis and quantified by high-performance liquid chromatography. They increased to reach a maximum during the hydrical step and then decreased rapidly during grain dehydratation. Changes in phenylalanine ammonia-lyase (PAL) (E.C. 4.1.1.5) and l-tyrosine ammonia-lyase (TAL) (E.C. 4.3.1.5) activities have been monitored all along the development of the grain. TAL activity was maximal 2 days before PAL, at the beginning of the hydrical step. The presence of a maximal peroxidasic activity at the end of the hydrical step should be linked to the decrease of alkaline-resistant bound forms of FA. These results may suggest a possible role of peroxidase in the progressive changes from ester-linked forms of phenolic acids to insoluble derivatives, resistant to alkaline hydrolysis. Keywords: Phenolic acids; ammonia-lyases; peroxidases; durum wheat grain; development

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.

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