Effects of light irradiation on essential oil biosynthesis in the medicinal plant Asarum heterotropoides Fr. Schmidt var. mandshuricum (Maxim) Kitag.

Asarum heterotropoides Fr. var. mandshuricum (Maxim) Kitag (Chinese wild ginger) is an important medicinal herb. Essential oil extracted from its roots is the key ingredient and is mainly composed of phenylpropanoid compounds. As a skiophyte plant, light is a crucial factor for A. heterotropoides var. mandshuricum growth and metabolism. To investigate the effects of light irradiation on the essential oil biosynthesis in A. heterotropoides var. mandshuricum, the plants were cultivated in four light irradiation treatments (100, 50, 24 and 12% full sunlight). The photosynthetic capacity, essential oil content and composition, activities of several enzymes and levels of some secondary metabolites involved in the shikimic acid and cinnamic acid pathways were analyzed. The leaf mass per area, average diurnal net photosynthetic rate, and the essential oil content increased significantly with increasing light intensity. Phenylalanine, cinnamic acid, and p-coumaric acid in the cinnamic acid pathway were at their highest levels in plants cultivated in 100% full sunlight. The highest content of shikimic acid in the shikimic acid pathway was obtained in plants grown in 50% sunlight transmittance. The activity of the enzymes 3-Deoxy-D-arabino-heptulosonate-7-phosphate synthase, phenylalanine ammonia lyase, cinnamate-4-hydroxylase and 4-coumarate:CoA ligase increased proportionally with light intensity. Overall, we conclude that high light irradiation promotes high net photosynthetic rate, high activity of enzymes and high amounts of phenylpropanoid precursor metabolites leading to significant biosynthesis of essential oil in A. heterotropoides var. mandshuricum.

[Photosynthetic characteristics and active ingredients differences of Asarum heterotropoides var. mandshuricum under different light irradiance].

Chlorophyll content,leaf mass to per area,net photosynthetic rate and bioactive ingredients of Asarum heterotropoides var. mandshuricum,a skiophyte grown in four levels of solar irradiance were measured and analyzed in order to investigate the response of photosynthetic capability to light irradiance and other environmental factors. It suggested that the leaf mass to per area of plant was greatest value of four kinds of light irradiance and decreasing intensity of solar irradiance resulted in the decrease of leaf mass to per area at every phenological stage. At expanding leaf stage,the rate of Chla and Chlb was 3. 11 when A. heterotropoides var. mandshuricum grew in full light irradiance which is similar to the rate of heliophytes,however,the rate of Chla and Chlb was below to 3. 0 when they grew in shading environment. The content of Chla,Chlb and Chl( a+b) was the greatest value of four kinds of light irradiance and decreasing intensity of solar irradiance resulted in its decreasing remarkably( P<0. 05). The rate of Chla and Chlb decreased but the content of Chla,Chlb and Chl( a+b) increased gradually with continued shading. The maximum value of photosynthetically active radiation appeared at 10: 00-12: 00 am in a day. The maximum value of net photosynthetic rate appeared at 8: 30-9: 00 am and the minimum value appeared at 14: 00-14: 30 pm at each phenological stage if plants grew in full sunlight. However,when plants grew in shading,the maximum value of net photosynthetic rate appeared at about 10: 30 am and the minimum value appeared at 12: 20-12: 50 pm at each phenological stage. At expanding leaf stage and flowering stage,the average of net photosynthetic rate of leaves in full sunlight was remarkably higher than those in shading and it decreased greatly with decreasing of irradiance gradually( P < 0. 05). However,at fruiting stage,the average of net photosynthetic rate of leaves in full sunlight was lower than those in 50% and 28% full sunlight but higher than those in 12% full sunlight. All photosynthetic diurnal variation parameters of plants measured in four kinds of different irradiance at three stages were used in correlation analysis. The results suggested that no significant correlation was observed between net photosynthetic rate and photosynthetically active radiation,and significant negative correlation was observed between net photosynthetic rate and environmental temperature as well as vapor pressure deficit expect for 12% full sunlight. Positive correlation was observed between net photosynthestic rate and relative humidity expect for 12% full sunlight. Significant positive correlation was observed between net photosynthetic rate and stomatal conductance in the four light treatments. Only,in 12% full sunlight,the net photosynthetic rate was significantly related to photosynthetically active radiation rather than related to environmental temperature,vapor pressure deficit and relative humidity. In each light treatment,a significant positive correlation was observed between environmental temperature and vapor pressure deficit,relative humidity as well as stomatal conductance. Volatile oil content was 1. 46%,2. 16%,1. 56%,1. 30% respectively. ethanol extracts was 23. 44%,22. 45%,22. 18%,21. 12% respectively. Asarinin content was 0. 281%,0. 291%,0. 279% and 0. 252% respectively. The characteristic components of Asarum volatile oil of plant in different light treatments did not change significantly among different groups.