Optimization of Callus Induction Conditions from Immature Embryos of Maize under Stress

The embryos of maize (Zea mays L.) inbred lines GS02, GS07, GS08, GS11 and GS15 were used as receptor materials to optimize the receptor system from the aspects of genotype, medium components and stress (PEG6000, mannitol, salt and low phosphorus). The results showed that GS07 had the highest induction rate (95.2%). Orthogonal test analysis showed that the best combination of medium components in induction was A₂B₃C₁D₃₍₂₎, namely, the concentration of 2, 4-dichlorophenoxy acetic acid (2,4-D) was 4 mg·mL^-1, the concentration of L-Proline (L-Pro) was 0.8 mg·mL^-1, and the concentration of silver nitrate (AgNO₃) was 10 mg·mL^-1 (or 5 mg·mL). Interestingly, we found that the optimal medium supplemented with 30 g·L^-1 PEG6000 or 80 g·L^-1 mannitol was suitable for antioxidant enzyme activity and malondialdehyde (MDA) content in GS07 callus. Exogenous 10 mmol·L^-1 Ca²⁺ in the medium components with 100 mmol·L^-1 sodium chloride (NaCl) could improve the activity of antioxidant enzymes in GS07 callus. Callus of GS07 could divide normally and grow well in medium components with 27 mg·L^-1 KH₂PO₄. This study enhanced the adaptability of maize callus to stress and optimized the culture conditions.