Putrescine Depletion Affects Arabidopsis Root Meristem Size by Modulating Auxin and Cytokinin Signaling and ROS Accumulation oleh Ahmed M. Hashem, Simon Moore, Shangjian Chen, Chenchen Hu, Qing Zhao, Ibrahim Eid Elesawi, Yanni Feng, Jennifer F. Topping, Junli Liu, Keith Lindsey, Chunli Chen