Studies On Physiological And Biochemical Characteristics And Transcriptional Regulation Mechanism Of Light Stress Response Of Yellow Camellias

Yellow camelliasis the general name of yellow flowering species in camellia of Theaceae.It is a precious and rare species which has high medicinal and ornamental value with narrow distribution area and small ecological population.However,random excavation and mining further accelerates the population shrinkage of wild Yellow camellias.It has been listed as an endangered species,of which C.impressinervis is a very dangerous species.Yellow camellias have high requirements for habit at and are shade loving plants.Lights have significant impacts on the growth and development of Yellow camellias.Here,taking Camellia petelotii（Merr.）Sealy and C.impresinervis with different light sensitivity as materials,this paper carried out a systematic study on the physiological and biochemical characteristics and transcriptional regulation mechanism of Yellow camellis responses to light stress,and obtained the following main results:（1）Strong light stress significantly inhibited photosynthesis and plant growth of Yellow camellias.Yellow camellias has poor adapt ability to strong light environment,which leads to the decreased net photosynthetic rate,stomatal conductance and transpiration rate,the inter cellular CO₂ concentration,however,increased,the initial fluorescence（fo）,maximum fluorescence value（Fm）and maximum light energy conversion efficiency（Fv/Fm）of PSII also decreased,indicating that photo inhibition had occurred in plant growth at this time.Under the condition of 300μmol·m^-2·s^-1light,the net photosynthetic rate of plants was the highest.With the intensification of strong light and weak light,the contents of Chl and Car decreased,and Car/Chl increased with the enhancement of stress.It is suggested that plant growth was significantly inhibited by affecting photosynthesis of Yellow camellias plants under strong light stress.（2）Light stress led to a significant increase in membrane lipid peroxidation of Yellow camellias.Under stronglight stressconditions,the activities of superoxide dismutase,peroxidase and catalase increased significantly,and the content of malondialdehyde（MDA）also increased.The higher content of malondialdehyde（MDA）,the final decomposition product of membrane lipid peroxidation in the leaves of Yellow camellias proves that the peroxidation of plant membrane lipids was significantly enhanced and plant cell membrane lipids was seriously damaged by treatment of 700μmol·m^-2·s^-1 light intensity.（3）Photosynthetic system is involved in transcriptional regulation of light stress response.In the treatment of 700μmol·m^-2·s^-1,there was an obvious trend of photoinhibition.These data are consistent with the obvious disintegration of the chloroplast lamellar structure under 700μmol·m^-2·s^-1light intensity.Yellow camellias eventually led to the decline of photosynthetic rate by affecting the formation and stability of PSII and PSI complexes and electron transfer.Yellow camellias treated with 700μmol·m^-2·s^-1showed the lowest Fv/Fm value,which was also consistent with the RNA-Seq and RT-PCR results of DEGs in PSII.（4）Carbohydrate pathway is involved in the transcriptional regulation of light stress.After treated with 700μmol·m^-2·s^-1 for 5 h,one sucrosesynthase,three UDP glycosyltransferases and oneβ-Amylase,fiveβ-Glucosidase,four glycosyltransferases and three glycosylhydrolases were significantly increased,and five UDP glucose phosphatase,two cell wall invertase 2 and one hexokinase 1 were inhibited in Camellia petelotii（Merr.）Sealy,indicating that when the light intensity was too high,in order to resist the damage of strong light stress,Yellow camellias reduced the accumulation of starch in leaves and transformed it into soluble sugar to reduce the water loss of plant cells,under strong light stress,PSII has been permanently damaged,resulting in irreversible changes in chloroplast structure.（5）Flavonoid metabolic pathway is involved in the transcriptional regulation of light stress.Under strong light stress,the content of total flavonoids in the two Yellow camellias decreased significantly.36 differentially expressed genes in Yellow camellias were verified and found by fluorescence quantitative PCR,which proved that the up-regulation of gene expression in flavonoid biosynthesis pathway was the reason for the abundance of flavonoid compounds in Yellow camellias.In addition,C.impresinervis also responded to strong light stress by stabilizing the expression of phenylalanine ammonia lyase（PAL）in the stage of light damage repair.（6）Plant hormones play an important role in regulating the response of Yellow camellias to light stress.It was found that under strong light stress,Yellow camellias regulated abscisic acid（ABA）content and expression of related genes increased significantly.Thus,the damage of strong light to plants is reduced.At the same time,it was found that the variation trend of zeatin in Camellia petelotii（Merr.）Sealy,was consistent with the variation trend of cat enzyme activity,suggested that abscisic acid,zeatin and antioxidant enzyme system are involved in the regulation of its response mechanism to strong light stress,while the variation trend of zeatin in C.impresinervis was consistent with the synthesis process of flavonoids,indicating that the biosynthesis of abscisic acid,zeatin and flavonoids is involved in the regulation of the strong light stress response mechanism.This study revealed the effects of light intensity on the physicochemical characteristics,metabolic changes and differential expression of related genes of Yellow camellias,and analyzed the physicochemical characteristics and transcriptional regulation mechanism of Yellow camellias in response to light stress,which provided a theoretical reference and practical basis for the migration and protection of Yellow camellias.