Effects of Acclimatization Temperatures on Antioxidant Enzyme Activities in Mericlones of a Cattleya Hybrid

Mericlones of Brassolaeliocattleya Shinmei 'Sanyang' transplanted from flasks to pots with sphagnum moss were acclimated for 4 weeks in growth cabinets controlled at 15degreesC, 25degreesC and 35degreesC under 50 mumol . m(-2) . s(-1) for 16-hr photoperiod with fluorescent lamps. Except for root CAT activity that increased at 25degreesC, superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT) activities in leaves and roots fluctuated slightly. However, those activities at 15degreesC and 35degreesC, initially changed significantly after the onset of the treatments; they became stable during the rest of the acclimation period. Based on the antioxidative enzyme activities, the responses to thermal stress were greater in roots than in leaves. These results indicate the significance of managing the root environment at transplantation time. SOD activities that were highest at 35degreesC, followed by those at 15degreesC, clearly demonstrate the effects of acclimation temperatures (thermal stress) on both leaves and roots. Thermal effects on APX and CAT differed between leaves and roots. SOD activities in both leaves and roots as affected by the high temperature became smoothly stabilized. CAT activated for 48 hrs after the onset of the. acclimation treatment reverted to its initial level and remained so for several more weeks. Activities in SOD, APX, and CAT in roots that increased at 15degreesC indicate that cattleya plants are heat- but not cold-resistant.