Morphological development and photosynthetic acclimation of Panax ginseng seedlings to irradiation by light-emitting diodes (LEDs)

Abstract

To determine the optimal light intensity and enable plants to cope with various environmental stresses in plant factories, the morphological and photosynthetic characteristics of ginseng seedlings, including the secondary metabolites, were investigated under six light intensities: 25, 50, 75, 100, 125, and 150 mu mol m(-2) s(-1). The shoot length increased with lower light intensity up to 75 mu mol m(-2) s(-1), and the leaf area and specific leaf weight were greatest at 100 and 75 mu mol m(-2) s(-1), respectively. Stomata frequency was higher from 100 mu mol m(-2) s(-1) with higher light intensity, and single stomatal pore length also increased at 150 mu mol m(-2) s(-1). Net photosynthetic rate at light saturation and net photosynthetic rate in growth condition increased sequentially up to 100 mu mol m(-2) s(-1) before rapidly decreasing at 150 mu mol m(-2) s(-1). The dark respiration rate and light compensation point were significantly high at 150 mu mol m(-2) s(-1) only. Fv/Fm and chlorophyll content statistically differed from 63 and 84 days after seedling stand, respectively. Thus, the leaves withered to death with higher light intensity. The ginsenoside content in the roots significantly increased according to the light intensity, and the panaxadiol/panaxatriol (PT) ratio tended to decrease as the PT-type ginsenosides increased further. Taken together, the range of 75-100 mu mol m(-2) s(-1) was found to be beneficial for growth, photosynthetic acclimation response, and total accumulated ginsenosides of ginseng seedlings.