**5.1 Possible mechanisms of protection**

Because of its ability to act as an osmoprotectant without interfering with normal cellular processes and biochemical reactions proline has been used in a range of different cryopreservation protocols both for animal and plants cells and tissues, however the exact mode by which protection is achieved is still a matter of considerable debate in the scientific literature. Proline could potentially acting as storage reserve of carbon and nitrogen, a compatible osmolyte, a buffer for cytosolic pH, a scavenger of reactive oxygen species (ROS) and as an aid to balancing cellular redox status (Smirnoff & Cumbes 1989; Hare & Cress, 1997). It has also been proposed that proline could act as a molecular chaperone, helping to stabilize the structure of proteins, and as part of the signal transduction chain alerting plant cells to the presence of a stressor and hence triggering adaptive responses (Maggio et al. 2002).
