Effect of CaCl2treatment on the acclimatisation of mericlone seedlings ofCattleyaandPhalaenopsis

SummaryTo increase resistance to environmental stress during the acclimatisation of mericlone seedlings of Cattleya and Phalaenopsis, seedlings were treated with CaCl2. The effectiveness of CaCl2 treatment on acclimatisation was determined by investigating the levels of anti-oxidative enzyme activity and reactive oxygen species (ROS), the amounts of chlorophyll and malondialdehyde (MDA), the net rate of photosynthesis (A), and the area of leaf-burn caused by high temperature injury. The activities of four anti-oxidative enzymes [superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POD)] in mericlone seedlings of Cattleya and Phalaenopsis increased with CaCl2 treatment. The highest increase was in the treatment with 4 mM CaCl2. Mericlone seedlings treated with 4 mM CaCl2 had increased SOD, CAT, APX, and POD activities compared with the controls after 35 d of acclimatisation in a greenhouse. The levels of superoxide anions (O2•–) and hydrogen peroxide (H2O2) were also low. In line with this, any decrease in chlorophyll content, increase in MDA content, drop in A, or injury due to high temperature stress were mitigated by CaCl2 treatment. These results show that CaCl2 treatment is effective for the acclimatisation of mericlone seedlings of Cattleya and Phalaenopsis by increasing their resistance to environmental stress.