Do sunflower 2S albumins play a role in resistance to fungi?

Many proteins exerting antifungal activity in vitro have been isolated alth ough in certain cases their contribution in plant resistance to fungal atta ck is unclear. Screening for antifungal proteins from sunflower seeds, we h ave detected a basic polypeptide (Ha-AP15) homologous to the previously des cribed storage protein 2S albumin. Results reported here indicate that Ha-A P15 exerts a weak inhibition of hyphal elongation of some fungi but no acti vity was detected against the seed pathogen Alternaria alternata. Ha-AP 15 did not show a synergistic enhancement of the antifungal activity of anothe r antimicrobial protein present in sunflower seeds, and the activity of Ha- AP15 is blocked in the presence of physiological concentrations of CaCl2. I n addition, we show that two sunflower genotypes which differ by 10-fold in their content of Ha-AP15 were equally susceptible to A. alternata attack. In conclusion, even if 2S albumins exert antifungal activity in assays deve loped in vitro, our results indicate that it seems improbable that these st orage proteins could also play a role as antimicrobial compounds protecting sunflower seeds from fungal pathogens. (C) 2001 Editions scientifiques et medicales Elsevier SAS.