Abstract
Dry mass production and leaf area in relation to leaf injury and superoxide dismutase (SOD) were evaluated for eggplant (Solarium melongena L.) and pepper (Capsicum annuum L.) seed-lings grown in continuous light at different intensities with metalhalide and high-pressure sodium lamps.
Continuous light-induced leaf injury occurred in eggplants even at 50μmol m-2 s-1 PPFD. When the 2nd leaf unfolded under daily 12h light-12h dark cycle, the eggplants were transferred to three levels of light intensity; 100 (low), 250 (medium), 480 (high) μmol m-2 s-1. After 8days, the SOD activity in the 3rd leaves showing no leaf injury at low light intensity was higher than that showing chlorosis or necrosis at high light intensity. However, after 16 days when the seedlings grown at low light intensity developed leaf-necrosis, SOD activities decreased to a low level, similar to those at medium and high light intensities. SOD activity increased gradually with time under continuous light up to the point of leaf injury, and decreased rapidly thereafter. These results suggest that the superoxide radical is associated with leaf injury.
In contrast, pepper plants grew vigorously without any leaf injury, and the dry weight was the highest at a light intensity of 300-400 μmol m-2 s-1 and the largest leaf area at 150-200 μmol m-2 s-1. SOD activity in pepper plants was relatively lower and more stable compared to that of eggplants, and the pepper plants also seemingly well adapted to continuous light at an optimum intensity of 300 μmol m-2 s-1 for dry mass production in a closed environmental system.
