Brassinosteroids participate in many physiological processes in plants; however, their regulatory roles on the activities of the enzymes involved in dark phase of photosynthesis remains elusive. In this study, detached leaves and protoplasts of maize seedlings were treated with epi-brassinolide (EBR) and brassinazole followed by the determination of the contents of chlorophyll (a+b) and soluble sugars, and the activity of dark reaction enzymes and the expression of the relevant genes. The results showed that chlorophyll (a+b) content increased by 7.4% under 0.1 μM EBR treatment for 48 h; furthermore, chlorophyll (a+b) content increased by 34% in detached leaves that were continuously soaked in brassinazole. In addition, the transcription levels of glyceraldehyde-3-phosphate dehydrogenase subunit A (GAPA), cytoplasmic FBPase (cyFBPase), ribulose-1,5-bisphosphate carboxylase small subunit (rbcS), phosphoenolpyruvate carboxylase (PEPC), fructose-1,6-bisphosphatase (FBPase), Rubisco activase β subunit (RCAβ), ribulose-l,5-bisphosphate carboxylase large subunit (rbcL), and glutathione reductase (GR) were 96.8%, 48.4%, 79.3%, 41%, 85.6%, 133.3%, 68.8%, and 119.8% higher, respectively, in 0.1 μM EBR than in the control group. The activity of RCA and Rubisco and soluble sugar content increased by 53.4%, 28.7%, and 35.4% under 0.1 μM EBR. Brassinazole inhibits the expression of these genes. However, the transcription level, protein content, and activity of some dark-reaction enzymes cannot be increased at the same time under EBR treatment. These results indicate that the effect of EBR on dark-reaction is mainly in transcription level.

Zea mays; epi-brassinolide; brassinazole; rbcL; RCA; PEPC; soluble sugar