Figure 4.

Expression of active PPO in transgenic alfalfa. Leaf extracts of alfalfa transformed with red clover PPO1, PPO2, or PPO3 were incubated at room temperature with (+) or without (−) exogenously added PPO substrate (caffeic acid [CA] 3 mm final concentration). Leaf extracts of red clover (RC) and alfalfa transformed with the pILTAB357 vector only (Control) served as positive and negative controls, respectively. Browning was apparent within 2 to 5 min for GM alfalfa expressing red clover PPO genes. The control alfalfa extract showed no apparent browning, even after 24 h.