Rorippa indica Regeneration via Somatic Embryogenesis Involving Frog Egg-like Bodies Efficiently Induced by the Synergy of Salt and Drought Stresses

Frog egg-like bodies (FELBs), novel somatic embryogenesis (SE) structures first observed in Solanum nigrum , were induced in Rorippa indica . NaCl-mediated salt and mannitol-mimicked drought stresses induced FELBs in R . indica , which is very different from the induction by plant growth regulators (PGRs) under low light condition that was used in S . nigrum FELB induction. It demonstrated that NaCl or mannitol supplements alone could induce FELBs in R . indica , but with low induction rates, while the synergy of NaCl and mannitol significantly increased the FELB induction rates. For the combination of 5.0 g/L mannitol and 10.0 g/L NaCl the highest FELB induction rate (100%) was achieved. It suggests that the synergy of drought and salt stresses can replace PGRs to induce FELBs in R . indica . On medium supplemented with 1.0 mg/L gibberellic acid all the inoculated in vitro FELBs developed into multiple plantlets. Morphological and histological analyses confirmed the identity of FELBs induced in R . indica and revealed that FELBs originate from root cortex cells.