Effects of exogenous Putrescine on plant growth and photosynthesis of perennial ryegrass under drought stress

• ZHANG Jinpeng, 
• GAO Shikong, 
• YU Qiao, 
• ZHAO Yifan, 
• WANG Zongsen, 
• GAO Junjun, 
• HAO Xiaojun, 
• HU Tianming, 
• FU Juanjuan