Effects of light intensity during acclimatization on antioxidative enzyme activities and growth in mericlone plantlets of a cattleya hybrid

Abstract

Mericlone plantlets of Brassolaeliocattleya Sanyan Ruby 'Shinmei' with one leaf transplanted into pots with sphagnum moss were acclimatized at 230 (high), 83 (intermediate) and 50 μmol·m-2·s-1 (low light intensity) for 4 weeks in growth cabinets under a 16-h photoperiod and 25°C. The main objective was to determine the antioxidative enzyme activities and the growth of the potted mericlone plantlets. At the intermediate light intensity superoxide dismutase (SOD) that disproportionations superoxide to hydrogen peroxide, and catalase (CAT) reduced activities in both leaves and roots. However, CAT in roots increased 6 h after the onset of acclimatization and then remained constant. Ascorbate peroxidase (APX) activity with participation of ascorbate in roots and CAT activity in roots did not changed significantly. At the high light intensity, activities of SOD and APX of leaf and of the three antioxidative enzymes of roots increased. After 4 weeks, foliar SOD and APX activities were markedly higher under the high light intensity than under the intermediate one. Under the low light intensity, these three enzyme activities in both leaves and roots increased. Activities of foliar SOD and CAT decreased after 2 weeks and then remained constant as the activity of APX increased. The three enzymes in the roots maintained higher activities under the low light intensity than under the intermediate one; CAT activity declined rapidly 2 weeks later and reached a level similar to those at the intermediate light intensity. After 4 months of acclimatization, leaves under the high light intensity were shorter than those under intermediate and low ones; roots under the low light intensity were shorter than those of other light intensities. These findings indicate that high light intensity affects leaves of cattleya mericlone plantlets more than their roots, while low light intensity has a reverse effect. The mericlone plantlets were difficult to acclimatize quickly to high light conditions, while they were easy under low light. The antioxidative enzymes are also shown to be possible indexes for light acclimatization.