A number of studies have produced transgenic plants expressing AFPs from other plants, fish, and insects. Most of these did not
produce lowered freezing temperatures in the transgenic plants.
In some systems, AFP expression in transgenic plants produced
plants whose extracts exhibited low levels of thermal hysteresis
(0.37 ◦ C/mg apoplastic protein by nanoliter osmometer, Holmberg
et al., 2001), recrystallization inhibition in vitro , or reduced electrolyte leakage in leaves after freezing . Only the expression of AFPs derived from beetle larvae unambiguously resulted in increased levels of supercooling
in the transformants, however, the freezing temperatures of the
plants were often not reported in other studies.