Naringenin inhibits seed germination and seedling root growth through a salicylic acid-independent mechanism in Arabidopsis thaliana

Flavonoids fulfill an enormous range of biological functions in plants. In seeds, these compounds play several roles; for instance proanthocyanidins protect them from moisture, pathogen attacks, mechanical stress, UV radiation, etc., and flavonols have been suggested to protect the embryo from oxidative stress. The present study aimed at determining the role of flavonoids in Arabidopsis thaliana (L.) seed germination, and the involvement of salicylic acid (SA) and auxin (indole-3-acetic acid), two phytohormones with the same biosynthetic origin as flavonoids, the shikimate pathway, in such a putative role. We show that naringenin, a flavanone, strongly inhibits the germination of A. thaliana seeds in a dose-dependent and SA-independent manner. Altered auxin levels do not affect seed germination in Arabidopsis, but impaired auxin transport does, although to a minor extent. Naringenin and N-1-naphthylphthalamic acid (NPA) impair auxin transport through the same mechanisms, so the inhibition of germination by naringenin might involve impaired auxin transport among other mechanisms. From the present study it is concluded that naringenin inhibits the germination of Arabidopsis seeds in a dose-dependent and SA-independent manner, and the results also suggest that such effects are exerted, at least to some extent, through impaired auxin transport, although additional mechanisms seem to operate as well.