Study On The Influence Of Different Light Intensity On The Quality Of Dendrobium Officinale

Dendrobium officinale Kimura et Mi-go is a perennial herbaceous plant of Dendrobium orchidaceae,with high edible and medicinal value and strong ornamental value.It is widely planted in Yunnan,Zhejiang and Fujian in China.In recent years,with the development of the Chinese medicine industry and the improvement of people’s health awareness,the market demand for D.officinale has been increasing.Through market research and literature research in the early stage,it was found that light intensity,as an important ecological factor in the habitat of D.officinale,had a great influence on its growth and quality.At present,the setting of light intensity in D.officinale production is relatively random,and there is a lack of normative standards.Therefore,this study carried out the effects of different light intensities on the growth and quality of D.officinale under artificial control,and systematically analyzed the gene differential expression between treatments by transcriptome sequencing,and clarified the regulatory mechanism of light intensity on the growth and quality of D.officinale.The main findings were as follows:1.The influence of light intensity on the physiological and biochemical indexes of D.officinale.With the increase of light intensity,the growth and development of D.officinale changed significantly,and the color of the stems and leaves of the plants changed from green to red even under high light intensity.Among them,the light intensity had a significant effect on the longitudinal growth of D.officinale stems.When the light intensity reached 15500 Lux,it began to show a tendency to inhibit the elongation of the stem;in terms of dry matter accumulation,the light intensity was optimal at about 11000 Lux.In addition,the antioxidant enzyme activity and MDA content under different light intensity treatments showed similar trends,and the lowest values all appeared at 6500 Lux-11000 Lux,indicating that this range was more suitable for plant growth.The increase of light intensity would appropriately increase the content of soluble sugar and soluble protein,which reached the peak at the 32 d and 4 d respectively,and cooperated with each other inside the plant in response to changes in light intensity.Under each treatment,the significant difference of SPAD value appeared at the 32 d,in which SPAD value under 2000 Lux was significantly higher than other treatments,while the SPAD value at 20000 Lux was significantly lower than other treatments.Overall,the growth and development of D.officinale were more suitable under 6500 Lux-11000Lux.2.The effect of light intensity on the quality of D.officinale.The results of the study showed that with the prolongation of the treatment time,the polysaccharide and total flavonoid content reached a relatively high value on the 64 d,and the polysaccharide content at 20,000 Lux was significantly higher than other treatments;the total flavonoid content at15500 Lux was significantly higher other treatments.Under the treatments of the same period,the dendrobine content of D.officinale at6500 Lux treatment was significantly higher than other treatments,and11000 Lux was slightly inferior.The change of cellulose content showed the highest peak at 20,000 Lux on the 8 d.In addition,the correlation of metabolic components showed that with the increase of light intensity,the correlation coefficient between cellulose and polysaccharides,alkaloids,total flavonoids gradually increased,and the antagonism between alkaloids and cellulose decreased obviously.It showed that light intensity could affect the synthesis and conversion of cellulose to improve the medicinal quality of plants.Sensory evaluation and juice yield indicators showed that the stems were red at 11000 Lux,with high viscosity,less residue and easier to chew and the indicators were well coordinated,better met fresh food standards and had a higher juice yield.The above results showed that properly increasing the light intensity could improve the edible and medicinal quality.3.Different gene expression of D.officinale under different light intensity.The stem samples of D.officinale under 2000 Lux,11000 Lux,15500 Lux and 20000 Lux were analyzed by Illumina sequencing technology.A total of 144,576 independent genes were obtained using Illumina sequencing technology,with a total length of 104,774,033 bp,an average length of 724 bp,and an N50 of 1,398 bp.Futhermore,STEM software was used for KO enrichment analysis and a total of 2,629differentially expressed genes（DEGs）were enriched.And KO enrichment analysis showed that DEGs mainly focused on plant hormone transduction pathway,Ca²⁺-CAM signaling system,linoleic acid metabolism,gluconeogenic pathway and biosynthesis of flavonoids.Through in-depth analysis of the differential genes in key metabolic pathways,it was initially clarified that light intensity by promoting the signal transduction of zeatin（CISZOG1,CKX6）and jasmonic acid（TIFY10B）,inhibiting auxin（IAA4,SAUR32）and abscisic acid（GAM1）signal transduction,down-regulating the key enzyme genes CPK10,CPK11,CPK17,Unigene0027659,CML27,CML46 of Ca²⁺-CAM signaling system to increase Ca²⁺concentration,could not only regulate the metabolism of linoleic acid in the downstream pathway（LOX2.3,PLA2-ALPHA）,promote linoleic acid metabolites to enter the gluconeogenesis pathway（Os03g0267300,Unigene0111044,Unigene0029293）to generate glucose,and provide a substrate for cellulose synthesis,and could also promote the synthesis of flavonoids（Os03g0267300,Unigene0111044,Unigene0029293）composite flavonoids,enhance the inhibitory effect on auxin,promote the fibrocyte to enter the rapid deposition period of cellulose,thereby molecularly regulate the biosynthesis of cellulose of D.officinale.And through the above pathway locked including jasmonic acid synthesis inhibitory factor TIFY10B,Ca²⁺-CAM calcium-dependent protein kinase CPK11,linoleic acidmetabolismlipoxygenasegeneLOX2.3,the fructose-1,6-bisphosphatase gene Os03g0267300 and the 6-phosphate glucose 1-epimerase gene Unigene0111044 in the gluconeogenesis pathway,and the flavonoid synthesis chalcone synthase gene CHS8、chalcone isomerase gene CHI seven key regulatory genes.In summary,different light intensities had a significant impact on the growth and quality of D.officinale,and could further affect the edible and medicinal quality of D.officinale by affecting the synthesis and conversion of cellulose.Therefore,the light intensity was controlled at about 11000 Lux which palyed an important role in ensuring the normal growth and development of D.officinale,improving the quality and economic value of D.officinale.