A comparative study of antioxidant protection in cryopreserved unicellular algae Euglena gracilis and Haematococcus pluvialis

Algal culture collections are required to develop robust and broadly applicable cryogenic storage methods for diverse taxonomic groups and understanding differential responses to cryoinjury helps to achieve this end. Antioxidant profiles were constructed for cryopreserved Euglena gracilis (Klebs CCAP 1224/5Z), a freeze sensitive alga, and Haematococcus pluvialis (Flotow CCAP 34/8), which is a highly freeze-tolerant. H. pluvialis had a coordinated antioxidant response with respect to catalase, superoxide dismutase (SOD) and glutathione reductase; it is postulated that this may contribute to freeze tolerance. Formation (via SOD) and removal (via catalase) of H₂O₂ were not fully coordinated in freeze-sensitive E. gracilis and this may exacerbate cryoinjury. Increased SOD activity in the absence of catalase thus compromises survival due to the formation of hydroxyl radicals (^.OH) from H₂O_2. Changes in sulfhydryl group (SH) status for non-Protein bound SH groups were greater in freeze-tolerant H. pluvialis. Therefore, the tolerant organism may have a range of coordinated protection mechanisms that ameliorate the deleterious effects of oxidative stress during cryopreservation.