Figure 2.

Viability staining of the roots and crown of alfalfa. Plants were dug from field plots on December 2, 1997, frozen to −6°C, −10°C, and −14°C, and stained with nitroblue tetrazolium to detect viability. Cells stained red have active respiration and are considered alive. Those stained white have been injured. There is essentially no difference in the injury seen between control and SOD-transgenic plants at any freezing temperature examined.