Effects of light quality on growth, total gypenosides accumulation and photosynthesis in <em>Gynostemma pentaphyllum</em>

Gynostemma pentaphyllum is a kind of shade–tolerant plants. It can synthesize and accumulate gypenosides in large amounts. The gypenosides are a valuable medicine. To develop effective cultivation techniques of the plant, effects of light quality on growth, accumulation of total gypenosides and photosynthesis in G. pentaphyllum were investigated in this study. Results showed that light quality had remarkable effect on plant growth. White light had a significant effect on the increase in growth, especially in highest biomass, stem diameter and newly sprouted leaves. Red light accelerated stem length, new leaf formation and biomass when compared with blue and green lights. By contrast, green light had influence on inhibiting the increase of growth and biomass. And moreover, the content of total gypenosides was different in seedlings under different lights. The content of total gypenosides was the highest rank under red and white lights, followed by the content under blue light. The content was the least under green light. The diurnal variation of net photosynthetic rate exhibited a typical double-peak curve when the plant grown under white, red and blue lights respectively, while that under green light presented a single-peak curve. The net photosynthetic rate (Pn) under red light was higher than those under either blue or green lights, but obviously lower than that under white light. The diurnal variation curve of stomatal conductance closely paralleled to that of transpiration rate curve, whereas the curve of intercellular CO2 concentration exhibited an opposite trend to that of Pn under any of the four lights. It was suggested that the influence of monochromatric light quality on growth and the accumulation of total gypenosides was associated with photosynthesis efficiency.