Research Progress of Dendrobium officinale Kimura et Migo

Ying WANG Miao ZHANG XueJing DONG Liba XU Yongpeng WEI Hua ZHU

Abstract The effects of light on the quality and related genes of Dendrobium officinale were summarized， and the main chemical components and pharmacological effects of D. officinale were analyzed. The biomass accumulation of D. officinale is related to light quality and light intensity. Monochromatic light quality can make polysaccharide accumulate， and mixed light quality can promote cell proliferation and component accumulation of D. officinale. Under different light intensity， the polysaccharide content of D. officinale is different， and it changes with the change of light intensity. When a certain intensity is exceeded， the polysaccharide content decreases with the increase of light intensity. The chemical components of D. officinale are polysaccharides， alkaloids， amino acids， volatile components， etc. The analysis of the growth and components of D. officinale provides reference and basis for improving the quality and chemical components of D. officinale and promotes the research and development of related products of D. officinale.

Key words Dendrobium officinale Kimura et Migo; Light quality; Illumination intensity; Chemical composition

Received： June 6， 2022  Accepted： August 8， 2022

Supported by National Natural Science Foundation of China （82060695）; Guangxi Key Laboratory of Zhuang and Yao Ethnic Medicine （GKJZ［2014］32）; Collaborative Innovation Center of Zhuang and Yao Ethnic Medicine （ZYYDC-02）; Collaborative Innovation Center of Zhuang and Yao Ethnic Medicine （GJKY［2013］20）; Guangxi Key Discipline： Zhuang Pharmacology （GJKY［2013］16）; First-class Discipline in Guangxi： Chinese Pharmacology （0501802815）; Development of a New Zhuang Medicine Huotanmu Capsule for the Treatment of Hepatitis B （NKF［2018］11）; The 8th Batch of Specially Appointed Experts Project in Guangxi （GRCTZ［2019］13）.

Ying WANG （1993-）， female， P. R. China， master， devoted to research about identification and development of traditional Chinese medicine and ethnic medicine.

*Corresponding author. E-mail： zhuhuagx@163.com.

Dendrobium officinale Kimura et Migo is a plant of Orchidaceae［1］， which is listed as a top medicine in Shennongs Classic of Materia Medica as "D. officinale tastes sweet and is neutral in nature. It is mainly used for the injure of the middle warmer energy， removing Bi syndrome， reducing dampness， replenishing the weakness of the five internal organs and improving marked emaciation， and strengthening yin. Long-term use can enhance the function of the spleen and stomach， thereby making the body flexible， enhancing immunity and prolonging life."［2］. At present， the research on D. officinale by scholars at home and abroad is more concentrated on the research of chemical components and pharmacological effects， such as polysaccharides［3］， alkaloids［4］， various amino acids and trace elements［5］， mannose［6］， total phenols［7］. In terms of pharmacological effects， for example， Wu et al.［8］ studied the immunity-improving effect of D. officinale polysaccharides， and scholars also studied its effects in glandular secretion and organ movement［9］， liver protection［10］， oxidation resistance［11］， tumor resistance［12］ and digestion promotion［13］. D. officinale is a perennial epiphytic herb that grows on semi-shady rocks in mountains with an altitude of 1 600 m. It is mainly distributed in Anhui， Zhejiang， Fujian， Guangxi， Sichuan， and Yunnan［14］. The wild resources of D. officinale are on the verge of extinction， and it has been listed as a national key protected medicinal plant， an endangered second-class protected plant in China， and a second-class protected plant in the world［15］， and has been included in the Plant Protection Red Book［16］. At present， the demand for D. officinale has increased sharply， and various researchers have made more extensive research on the growth of D. officinale. Therefore， the biological changes of D. officinale under different light qualities， main components， and genes were summarized， so as to facilitate the subsequent development and research of D. officinale.

Effects of Light on Plants

The development and growth of plants are not only related to their own genetic inheritance， but also to the surrounding environment of their growth， including soil， water， nutrients， and light environment［17］. Plant growth is a process of photomorphogenesis. Light plays an important role in regulating the morphological process of plant growth. The light environment includes light intensity， light distribution， photoperiod， and light quality. By changing the light environment of plant growth， plant growth and development and related metabolism can be affected［18］. Tang et al.［19］ studied the growth and development of D. officinale by simulating the growth environment of D. officinale. They found that light was the primary factor affecting the chlorophyll content， biomass and polysaccharide content of D. officinale.

Effects of light quality on D. officinale

Light quality refers to the spectrum of different wavelengths， and plants respond significantly to different light qualities［20］. Light quality is closely related to the growth and differentiation of plant callus， the culture of plant organs in vitro， and the synthesis of endogenous substances in plants［21］. Because plants have wavelengths that can be sensed by photoreceptors， photoreceptors are sensed by intracellular signaling pathways and transmit different light signals， regulate corresponding gene expression， control cell metabolism， division， and apoptosis， so that plant organisms change adaptively in accordance. Studies have shown that different light qualities have different effects on plant growth［22］. Wen et al.［23］ studied the growth and chlorophyll fluorescence parameters of D. officinale by different LED light sources， and found that monochromatic red light could effectively promote the accumulation of polysaccharides in a short term， and the combined light of red， blue and yellow was more conducive to the growth， dry matter accumulation and polysaccharide accumulation of D. officinale. Lin et al.［24］ studied the changes in the content of active components of D. officinale and the proliferation of protocorms through different light quality changes. With different parts of D. officinale as materials， the experiment found that the proliferation of D. officinale protocorms was different under different light quality conditions， and red light could promote the accumulation of carbohydrates， which was beneficial to the increase of polysaccharide content. Wang et al.［25］ studied the effect of light treatment on the reproduction and growth of D. officinale， and found that the light quality ratio of red to blue light at 1：1 was the light quality for robust growth of D. officinale seedlings. Shang et al.［26］ used test-tube D. officinale plantlets as the test material， and studied the growth of test-tube D. officinale plantlets under different red and blue light quality ratios of LED light sources. It was found that the ratio of red to blue light at 1∶1 was beneficial to the growth of test-tube D. officinale plantlets， the synthesis of chlorophyll and the accumulation of dry matter and sugar.

Effects of light intensity on D. officinale

Light intensity is one of the important factors affecting the growth and development of D. officinale. Appropriate light intensity can promote cell division of D. officinale， which is beneficial to improving the photosynthetic rate， dry weight and axillary bud number of D. officinale， thereby promoting the growth and development of D. officinale［27］. In the process of cultivating D. officinale， high-quality D. officinale can be obtained by adjusting the light intensity［28］. Xu et al.［29］ found that the net photosynthetic rate of D. officinale was relatively high from 8 to 10 in the morning， and then the photosynthetic rate decreased with the increase of light intensity and temperature. Light intensity has an effect on all growth parts of D. officinale. Light intensity can affect the root growth of D. officinale， and appropriate high light intensity is beneficial to improving the root growth of D. officinale plants［30］. When the light intensity changes from weak to strong or from strong to weak， the value of photosynthetic characteristic parameters of leaves will change［31］. Chou et al.［32］ studied the growth and metabolism of D. officinale by setting different light intensities. They found that when the light intensity was low， the amount of soluble protein and plant height increased， but the weight increase was less， and the cell proliferation was less， and the metabolism was slow. When light intensity increased， photosynthesis increased and consumption increased. Xu et al.［33］ investigated the changes of D. officinale protocorm biomass and main medicinal components under different light intensities， and found that the biomass and polysaccharide content increased under the light intensity of 2 000 lx after a period of time. Bao et al.［27］ studied the growth and development of D. officinale tissue culture plantlets by adjusting and controlling the light intensity， humidity and CO2 concentration of D. officinale in a plant factory. When the humidity， temperature and photoperiod are set， the light intensity was set according to a gradient， and it was found that the polysaccharide content accumulated with the increase of light intensity， and when it exceeded a certain intensity， the polysaccharide content decreased with the increase of light intensity. Gong et al.［34］ adjusted the light intensity by shading annual D. officinale， and studied the effect on the growth of D. officinale under this condition. It was found that when the light transmittance was 55%， the fresh weight， stem diameter and plant height of the plants all increased， and the light transmittance， which was favorable for the accumulation of polysaccharides， was 43%. Shao et al.［35］ used the number of shade net layers to adjust the light intensity of D. officinale， determined the polysaccharide content according to the Chinese Pharmacopoeia by phenol-concentrated sulfuric acid method， and discussed the changing law of polysaccharides in stems and leaves of D. officinale under different light conditions. It was found that the polysaccharide content in stems of D. officinale was higher than that in leaves under the single-layer shading net， and the polysaccharide content of the stems under the single-layer shading net was more than those under other layers of shading net， while under full light conditions， the polysaccharide content of D. officinale leaves was high， but the polysaccharide content decreased near the flowering stage.

Chemical Constituents and Pharmacological Studies of D. officinale

Chemical composition of D. officinale

D. officinale contains a variety of chemical components， including polysaccharides and mannose that have been recorded in the pharmacopoeia in terms of content determination. In addition， D. officinale also contains alkaloids［36］， proteins［37］， phenols［38］， stilbenes［39］， amino acids［40］， volatile components［41］ and various trace elements［42-43］.

Polysaccharides

The chemical composition of D. officinale differs little in various parts， but the polysaccharide contents of various growth parts are different. Xin et al.［44］ studied the components of different flowering stages and flower parts， and found that the polysaccharide contents of different parts were different， and the polysaccharide content of perianth was higher than those of the gynostemium and ovary. Cao et al.［45］ detected the content of flowers， leaves and stems of D. officinale， and found that the polysaccharide content in stems was higher than those in leaves and flowers， and the polysaccharide content in the flower was the lowest， and the polysaccharide contents in the upper and lower stems of D. officinale were not significantly different［46］. Shang et al.［47］ measured the polysaccharide content of the whole plant of D. officinale， and the polysaccharide content in the middle of the stem was the highest， followed by the upper or lower stem， and the leaves in sequence， and the roots had the lowest content. Yan et al.［48］ found that the polysaccharide content of D. officinale of two years old was higher than those of D. officinale of three years and four years old， and the polysaccharide content of D. officinale decreased in the fourth year. Zhu et al.［49］ tested the polysaccharide content of artificially cultivated D. officinale， and found that the polysaccharide content of two-year-old D. officinale was higher than those of one year and three years old， and determined that the harvest period of D. officinale in Zhejiang was from two years in winter to three years before flowering. After years of artificial cultivation， the polysaccharide content of D. officinale was similar to that of the wild product， and the polysaccharide distribution in various parts was consistent with that of the wild product， stems>leaves>roots［50］.

Xin et al.［51］ used different drying processes to dry D. officinale， and then measured its polysaccharide content. It was found that the polysaccharide content of D. officinale dried by hot air was the highest， followed by vacuum drying， vacuum freeze-drying， and natural air drying. Hot air drying led to a high polysaccharide content， and has the advantages of simple operation and low energy consumption， and can be popularized and used. In the drying temperature range from 40 to 80 ℃， the higher the drying temperature， the higher the extraction rate of polysaccharides［52］. When the drying temperature of the oven drying method was 90 ℃， and the time was controlled within 24 to 36 h， the loss of polysaccharide was less［53］. Water-soluble polysaccharides mainly contain glucose and mannose， while alkali-soluble polysaccharides contain galacturonic acid， mannose， glucose， galactose and xylose［54］. Luo et al.［55］ used column chromatography to separate and purify the crude polysaccharide of D. officinale， and found that it was an acidic pyranose in β-configuration. Chen et al.［56］ used cellulose column to separate and purify crude polysaccharide of D. officinale to obtain an acidic polysaccharide extract. Combined with molecular weight and physicochemical properties， it was analyzed to contain glucose， mannose， galactose， arabinose， rhamnose and galacturonic acid.

The main components of D. officinale are polysaccharides. The polysaccharides contained in D. officinale are water-soluble polysaccharides， while polysaccharides are composed of monosaccharides. The main monosaccharides for synthesizing polysaccharides are mannose， glucose， and xylose［57］， and related genes include UDP-glucose pyrophosphosphprylase （UGPase）， sucrose synthase gene （DOSS1）［58］， sucrose phosphate synthase （SPS）［59］， RHM， and SPS［60］， while UGPase is one of the important kinases in plant growth and sugar metabolism pathways， and plays a crucial role in the growth and sugar accumulation of D. officinale［61］. Wang et al.［62］ studied the effects of endophytic fungi on the expression of key enzymes in the synthesis of D. officinale polysaccharides and alkaloids. By regulating the expression of UGPase and affecting the synthesis of polysaccharides， combined with the accumulation of polysaccharides， it was speculated that UGPase might be the key enzyme in the polysaccharide synthesis pathway of D. officinale. Xie et al.［63］ studied the differences in gene expression related to polysaccharide accumulation in D. officinale from different sources. The correlation analysis of polysaccharide gene expression and polysaccharide content showed that the expression of β-1，3-GS gene and DONI gene was positively correlated with polysaccharide content， but UGPase gene expression was also proportional to polysaccharide content， and the correlation coefficient was high. Wang et al.［64］ took D. officinale seedlings as the research object， and analyzed the content of D. officinale polysaccharides and the gene expression of UDP-glucose pyrophosphosphprylase （UGPase）， a key enzyme in the synthesis pathway， by endophytic fungi. It was found that endophytic fungi might affect the synthesis of polysaccharides by regulating the expression of UGPase. Combined with the accumulation of polysaccharides， it was speculated that UGPase might be the key enzyme in the polysaccharide synthesis pathway of D. officinale. Lyu et al.［65］ studied the expression of UGPase in different tissues of D. officinale， and predicted that the DoUGPase1 gene was proportional to the activity of polysaccharide accumulation during the growth process of D. officinale.

Alkaloids

The roots， stems and leaves of D. officinale all contain alkaloids， and the alkaloid content of D. officinale varies in different parts and years. Shang et al.［66］ detected the alkaloids in tissue culture plantlets， wild plants and cultivated plants， and found that the alkaloid contents in different parts of stems ranked as the upper part of stem>leaves≈roots>the middle part of stem≈the lower part of stem， and the alkaloid contents at different harvest stages were in order of 1 year old≥ 2 years old ≥ wild type. The content of alkaloids varied greatly between different parts， but less between different harvest stages. Wen et al.［67］ conducted alkaloid detection on different stems of D. officinale， and found that it was consistent with the previous detection results： the upper part of stem > the middle part of stem > the lower part of stem. Yao et al.［68］ tested the contents of D. officinale alkaloids in different harvesting periods， and found that the changes in total alkaloid content were not very different. Yang et al.［69］ tested the content of dendrobine in different planting methods， and found that the content of dendrobine in imitation wild planting was higher than those in greenhouse and pot planting. Yuan et al.［70］ used a flash extraction method to optimize the enzymatic hydrolysis conditions to detect the alkaloid content of D. officinale， and found that the alkaloid yield was improved. The adopted method is simple and low in cost， and is suitable for popularization and use. Liu et al.［71］ optimized the ultrasonic extraction method of D. officinale total alkaloids by orthogonal and single factor experiments. They determined the sampling amount， particle size， ultrasonic time， and the ratio of the amount of extraction reagent to the sampling amount. The alkaloid content of Dendrobium could be detected in batches in a short period of time， providing a fast and effective detection method for the rapid detection of alkaloid content.

Amino acids

Amino acids are not only important nutrients but also have certain pharmacological effects， while the health care effects and certain medicinal effects of Dendrobium have a certain relationship with certain amino acids. With the continuous recognition and development of the medicinal efficacy and health care function of D. officinale， studies were carried out on amino acids in different parts of D. officinale. It was found in the process of the research that D. officinale contains essential amino acids for the human body. Zhou et al.［72］ analyzed the amino acids in D. officinale flowers and found that there were 17 kinds of amino acids in D. officinale flowers， of which seven are necessary for human body. Huang et al.［73］ analyzed the amino acids of D. officinale flowers at different flowering stages， and found that the amino acids of D. officinale flowers in full bloom were complete and accounted for a high proportion. Zhang et al.［74］ measured the amino acid content of different parts of D. officinale， and found that its contents ranked as leaf>upper stem>lower stem， all of which contained glutamic acid， leucine， aspartic acid， and alanine. Huang et al.［75］ analyzed the amino acid composition of D. officinale and found that it contained 17 kinds of amino acids， which is consistent with the analysis results of Zhou Jinye. Zhang et al.［76］ studied the changes of amino acid content in D. officinale， and found that the average content of various amino acids in one to three years increased with the increase of growth time， and the amino acid content could be increased by prolonging the growth time.

Volatile components

Kang et al.［77］ used SPME-GC-MS to analyze the volatile oil of D. officinale， and the results showed that it contained alkanes， aldehydes， ketones， alkenes， alcohols and esters. Huo et al.［78］ extracted the volatile oil from D. officinale flowers and analyzed the composition and results. The results showed that D. officinale flowers contained 89 components， of which 59 chemical components were identified. The ones with higher contents included nonanal， trans-2-decenal， n-pentacosane， α- cedrol， isoalantolactone， trans-2-heptanal， E， E-2， 4-decadienal， β-phorone， etc. Li et al.［79］ identified 43 components from D. officinale flowers， including alkyls， lipids， etc. Cao et al.［80］ used solid-phase microextraction combined with SPME/GC-MS to analyze the volatile components in D. officinale flowers， and found that it mainly contained α-pinene， limonene and eucalyptol. Shao et al.［81］ used GC-MS to identify and analyze the chemical components of D. officinale stems and leaves. The results showed that from D. officinale stems were isolated 80 components， of which 73 were identified， and in leaves were isolated 42 chemical components， of which 36 chemical components were identified. The main components of stems and leaves both include limonene， nonanal and cis-3-hexenol.

Others

Luo et al.［82］ analyzed the trace elements in D. officinale flowers and found that the flowers contained manganese， zinc， selenium， iron， copper and were rich in zinc and selenium. Li et al.［83］ tested the elements of D. officinale from different production areas， and found that it contained 20 elements， eight main essential elements， five heavy metals and harmful elements， but the quality measurement results were within the qualified ranges specified in the pharmacopoeia. Zhu et al.［84］ studied the contents of metal elements in D. officinale， and the results showed that in 1 to 3 years， the potassium content of D. officinale decreased with the prolongation of growth time， and the contents of zinc and copper increased with the prolongation of growth time， while the contents of calcium， magnesium and chromium did not change much. And the content of manganese was higher in the third year.

Conclusions

Light is closely related to plant growth and development， and different light qualities have different effects on plant growth and also affect the "quality" of plants. After taking light quality as the experimental condition and D. officinale as the research object， it was found that yellow light was beneficial to the growth of lateral buds， and red light could promote the accumulation of carbohydrates， which is beneficial to the increase of polysaccharide content. In addition， the compound light quality will also have different effects on the growth of D. officinale， and the mixed light of red and blue contributes to the accumulation of polysaccharides［85］. Different light intensities have different effects on various parts of D. officinale， such as stomatal opening［86］， fresh weight， polysaccharide accumulation［87］， and photosynthetic rate［88］. D. officinale contains alkaloids， amino acids， volatile components， etc.， and polysaccharides are one of its main components. Studies have found that UGPase is one of the important kinases in plant growth and sugar metabolism pathways， and the DoUGPase1 gene is proportional to the activity of polysaccharide accumulation during the growth and development of D. officinale. With the improvement of the quality of D. officinale and the deepening of the research on chemical components and related genes， it is conducive to the excavation of medicinal efficacy and accumulation of active ingredients of D. officinale， and a theoretical basis is provided for the comprehensive development of D. officinale resources.

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