Abstract: In the present study， the sugarcane variety YT55 was selected as study material. Under drought and normal conditions， the activity of P5CS， δOAT and their gene expression， and contents of free proline and chlorophyll were tested under 6 Mn concentrations， respectively. It was shown that all indexes tested exhibited a first increasing and then decreasing trend with the elevated Mn application rates under two water conditions. Under drought stress， the proline content reached the maximum when manganese concentration was 0.8 g·kg-1， the activity of δOAT and P5CS activity and chlorophyll content reached the peak under 0.4 g·kg-1 Mn， and the gene expression level of δOAT and P5CS reached the maximum when manganese concentration was 0.2 g·kg-1. Under normal conditions， changes of chlorophyll and proline contents and δOAT activity were similar to those under drought stress. The activity of P5CS reached maximum when manganese concentration was 0.8 g·kg-1. The simple， partial correlation and direct path coefficients of δOAT activity and proline content reached significant level under drought stress， while the simple， partial correlation and direct path coefficients of P5CS activity and proline content reached significant level under normal condition. This study suggested that manganese application amount should be 0.2-0.4 g·kg-1 for sugarcane production in latosol soil， and the stress resistance of sugarcane was strong under this condition. Due to the influences of manganese， the ornithine pathway dominated the proline biosynthesis of sugarcane under drought stress， while the glutamic pathway was dominant under normal water condition.

Key words: sugarcane, manganese, proline, P5CS, δOAT, gene expression