Quercetin alleviates seed germination and growth inhibition in Apocynum venetum and Apocynum pictum under mannitol-induced osmotic stress.

Quercetin is one of the main flavonoids in the human diet and mainly found in different plant tissues, including seeds, flowers, leaves, stems, and roots. However, its biological function in plant tissues, especially in seeds, is unknown. In this study, the seed germination and subsequent seedling growth of Apocynum pictum and A. venetum under osmotic stress (400 mmol L-1 mannitol) supplemented with 5 μmol L-1 quercetin were evaluated after 7, 14, and 21 days of germination. Results showed that quercetin improved the germination percentage and seed vigor, as indicated by the higher germination energy, shoot length, root length, dry weight, fresh weight, and chlorophyll content in A. pictum and A. venetum seedlings under the mannitol compared with those under the mannitol alone. Quercetin decreased H2O2 and O2- production and cell membrane damage, and mostly increased the gene expression of superoxide dismutase, peroxidase, catalase, chalcone synthase and flavonol synthase in A. pictum and A. venetum seedlings under the mannitol compared with those under the mannitol alone. In addition, the germination energy of A. pictum was 21.57% higher than that of A. venetum, and the gene expression of key enzymes in quercetin biosynthesis in A. pictum was mostly higher than that in A. venetum after 1 and 7 days of germination. These results indicated that quercetin was an effective anti-osmotic agent that alleviated the adverse effect of mannitol-induced osmotic stress on seed germination and seed vigor, and A. pictum seeds were more osmotic resistant than A. venetum seeds.