Effects Of Light Quality On The Growth, Photosynthesis And Accumulation Of Secondary Metabolism In Gynostemma Pentaphyllum

Light is one of the important environmental factors in plant growth. Not only canlight controls photosynthesis as one of energy source, but also as a trigger signal toaffect plant growth. Researches of the relationship among light quality and plant growthand accumulation of secondary metabolism have become hot issues in recent years. As akind of shade-tolerant plant, Gynostemma pentaphyllum showed sensitive responses tolight in morphogenesis, photosynthetic physiology and accumulation of secondarymetabolism. Many researches had conduced on the relationship between light intensityand G. pentaphyllum, however, little was known about the interrelation between lightquality and G. pentaphyllum.In this thesis, the seedlings of tissue culture of G. pentaphyllum were used as theexperimental material. Light-emitting diodes (LED) with red light (625±20nm), greenlight (525±20nm), blue light (470±20nm) and white light (compound light, controlcheck) were employed as light source to irradiate the seedlings for60days. Then theeffects of light quality on the growth, photosynthesis and accumulation of secondarymetabolism in G. pentaphyllum were determined. The obtained main results were asfollows.1. The optimal explant for tissue culture of G. pentaphyllum was the shoot tip,while MS+6-BA1.0mg of/of+NAA0.02mg/L as the optimum medium, in whichthe callus induction rate arrived at94.3%. The propagation coefficient of adventitiousbuds could increase to14for3weeks of enrichment cultured, inoculated in MS+6-BA1.0mL/L+NAA0.02mL/L culture medium. The transplant survive ratio ofregenerate plant was90.5%.2. Red light could improve the accumulation of biomass of G. pentaphyllum. Thepetiole length and stem length in red, green and blue light were larger than those incontrol check, which were favorable to capture more light sources for seedlings. Greenand blue light inhibited the thickening of the blade, especially the thickening of palisadetissue. The thickening of main vein was inhibited significantly in red, green and bluelight, compaired to the white light. The leaf structure in white light had the trend of thecharacter of sun plant, and that in red light had the trend of the character of tolerantplant, whil that in green light and blue light were similar to shade plant.3. The diurnal change in net photosynthetic rate of G. pentaphyllum presented adouble-peak curve under red light, blue light and white light, while a single-peak curvewas observed in green light. The descending order of the maximum photosynthetic ratesin different light quality for G. pentaphyllum was white light> red light> blue light>green light, and the lowest light saturation point and light compensation point weremeasured in green light. The photosynthetic light response curves were closed in redand blue light. In addition, the transpiration rate and the stomatal conductance werechanged synchronously in the daily time, register as positive correlation for all kinds of light. However, the net photosynthetic rate was negatively correlated with theintercellular co2concentration in the daily time under four kinds of light.4. Red light had significant ability in accumulating total gypenosides, and bluelight came the second, while green light inhibited the accumulation of gypenosides. Red,green and blue light inhibited the accumulation of total flavonoids, especially greenlight most againsting the accumulation of total flavonoids. In summary, affected bydifferent quality of lights, G. pentaphyllum was forced to adapt to the change of lightenvironment, adjusting the morphology and structure of its stems and leavies, leading tothe difference of photosynthesis, which could be reflected by the accumulation ofsecondary metabolism.5．Red, green and blue light were conducive for the absorption and enrichment ofCa, Fe, Zn, Cu, Se, but had the adverse effects in absorption and enrichment of P andMn.