| Due to the depletion of stratospheric ozone levels leads to an increase of solar UV-B (280～320 nm) radiation reaching the Earth's surface. Some direct and indirect effects were triggered by enhanced UV-B, including damage to DNA, protein and lip membrane, changes in photosynthesis, plant growth, morphology, and reproduction, as well as regulation to antioxidative system and second metabolism. In the recent years, comparing to studies conducted in the greenhouse or growth chamber, there are less studies conducted in the field. While the former, due to the unbalance between different spectra, may exaggerate the negative effects of enhanced UV-B irradiance. In numerous studies, radiation period of UV-B was shorter, and more seedlings were used, without considering about physiology-biochemistry in lower leaves of the plant. Based on the background above, our study worked out in the field, taking Scutellaria baicalensis as subject with two intensities of UV-B radiation and long-term UV-B radiation period. Both the upper leaves exposed to enhanced UV-B radiation and lower leaves in the plant were used in order to understand the changes towards growth and physiology-biochemistry of S. baicalensis under enhanced UV-B radiation. In recent years, increasing attention has payed to effects of UV-B radiation on plant secondary metabolism, research subjects were not limited to UV-absorbing compounds, especially leaf surface flavonoids and related metabolic pathway, it also involved a large number of active ingredients of medicinal plants. In order to understand effects of long-term enhanced UV-B radiation on flavonoids in S. baicalensis, HPLC method was used to analyze active ingredients in root of S. baicalensis, LC-MS and HPLC were also used in this research for qualitative and quantitative analysis on several flavonoids in leaves of S. baicalensis. Fourier transform infrared spectroscopy(FTIR) was attempted to analyze the effects of UV-B radiation on chemical composition of different parts of S. baicalensis. Results indicated that: 1. Long-term enhanced UV-B radiation causes leaf morphology changes, growth inhibition and biomass allocation changes. Physiology-biochemistry and flower numbers are influenced by long-term enhanced UV-B radiation.2. Effects of long-term enhanced UV-B radiation is greater on the biomass of shoot syatem than the root system, meanwhile physiology-biochemistry in the lower leaves of plant is less influenced by UV-B radiation. We speculate that under long-term enhanced UV-B radiation, S. baicalensis is more inclined to adapt to stress environment on the whole;3. Although UV-B radiation has greater influence on physiology-biochemistry in upper leaves than lower leaves, and the impacts of enhanced UV-B radiation is greater on the shoot system than the root system, however, inhibitory effects are shown by decrease in the biomass of both the shoot system and the root system. At the micro level, it seems that "cell communication" may play a role in plant. We need to understand signal transduction process and communication between cells under UV-B radiation, and then understand cell signaling transduction process between different parts of plant, which could help us to explain the findings at more macro-level. In the researches from this respect, soluble sugar should not only be considered as osmotic adjustment substance, the role of sugar as signaling molecule deserves further research.4. Changes in contents of active ingredient in the root are not significant under enhanced UV-B radiation. However, flavonoids in leaves of S. baicalensis significantly changes under long-term enhanced UV-B radiation. Some flavonoids are significantly increased according to HPLC analysis, although analysis on UV-absorbing compounds (mainly flavonoids) content showed that total content of UV-absorbing compounds has not influenced by long-term enhanced UV-B radiation, We believe that induction on flavonoids by enhanced UV-B radiation is selective. At the same time, structure identification for the flavonoids induced by UV-B radiation is need.5. UV-B radiation increase contents of alcohols, phenols, flavonoids and their glycosides in root and leaf of S. baicalensis. While UV-B radiation reduce the contents of flavonoids, unsaturated lipids and esters in stem, indicating that secondary metabolism of S. baicalensis changes under enhanced UV-B radiation. At the same time, there is trade-off in secondary metabolism between different parts of the plant.
|
PDF Full Text Request