| Cinnamomum camphora is a remarkable species of tree found in subtropical evergreen broad-leaved forests,known for its numerous benefits,such as valuable wood,medicinal properties,and use in the chemical industry.‘Gantong No.1’is a mutated ornamental camphor tree selected from the naturally mutated seedlings of the Jiangxi Provincial Key Laboratory of Ornamental Plant Genetic Improvement.Its stems are red and have high ornamental value.It has broad prospects for promotion and application.Cutting propagation is a simple and efficient method of asexual reproduction for woody plants that allows them to maintain the excellent characteristics of the original variety.One of the crucial environmental factors affecting this process is light.Light quality and intensity play a significant role in determining the survival rate of cuttings.Therefore,paying attention to light conditions during cutting propagation is essential to ensure optimal growth and development of the new plants.Preliminary experiments have indicated that the survival rate of camphor tree cuttings is significantly higher when exposed to red light as compared to white light.However,there are few reports on the effect of light on the rooting of camphor tree cuttings and its mechanism.In this study,the cuttings of’Gantong No.1’（now referred to as Red bark camphor）were taken as the research object.The LED plant factory was used to research the influence of different light intensities and light qualities on the cutting rooting of camphor cuttings,to develop the’Gantong No.1’cuttings.The cutting propagation of the whole year can provide scientific basis and technical support to speed up the promotion process of new varieties.The results of this study are as follows:（1）The rooting result of‘Gantong No.1’cuttings treated with different light intensities（100,130,160）showed that the light intensity of 100μmol·m-2·s-1 was significantly higher than that of the other two treatments,and the rooting rate reached 77%.However,the rooting rate of‘Gantong No.1’cuttings was the lowest under the light intensity of 160μmol·m-2·s-1 treatment,only 67%.Regarding the treatment conditions of different light intensit,significant variations were observed in the soluble sugar content,soluble protein content,POD,PPO activity and IAA content in the phloem of‘Gantong No.1’cuttings.During the adventitious root expression period（68 days）,our study found that the levels of soluble sugar,soluble protein content,and IAA content were significantly higher under a light intensity of 100μmol·m-2·s-1 compared to the other two treatments.Our study found minimal difference in POD（peroxidase）activity among the three treatments during the initial cutting stage to the callus formation stage（30 days）.However,at a light intensity of 100μmol·m-2·s-1,POD activity was significantly higher than in the other two treatments.In the later stages of cutting（49-68 days）,the POD activity under a light intensity of160μmol·m-2·s-1 remained consistently higher than the other two treatments.PPO activity decreased significantly in the three treatments at the initial cutting stage.The PPO activity was the highest in the adventitious root expression period（68d）when the light intensity was130μmol·m-2·s-1.（2）The rooting result of‘Gantong No.1’cuttings treated with different light quality（red,blue,white,red,and blue）showed that the red light treatment had the highest rooting rate,and the rooting rate reached 73%.However,the rooting rate of‘Gantong No.1’cuttings was the lowest under the white light treatment,only 31%.Our study found that the rooting rate of Cinnamomum camphora cuttings was significantly higher under the red light treatment than the blue light and white light treatments.Moreover,there was no significant difference in the rooting rate between the red and blue light combined treatment and the red light treatment alone.Under different light treatment conditions,there were significant changes in the levels of soluble sugar content,soluble protein content,POD,PPO activity and IAA content levels in the phloem of‘Gantong No.1’cuttings.During the period between callus formation and adventitious root expression（49 days）,our study found that the levels of soluble sugar,soluble protein content,and IAA content were significantly higher under the red light treatment than the other three treatments.During the callus formation period（30d）and adventitious root expression period（68d）,the POD activity was the highest under the red light treatment.The PPO activity was significantly lower under the red light treatment than the other three light-quality treatments.Our study found that during the adventitious root expression period（68 days）,the levels of soluble sugar,soluble protein content,IAA content,and POD（peroxidase）activity were all low under the blue light treatment.Moreover,the PPO（polyphenol oxidase）activity was highest under the white light treatment.（3）Transcriptome sequencing analysis was carried out on the phloem of Cinnamomum camphora cuttings under different light quality conditions,and the initial stage（0d）,callus formation stage（30d）,and adventitious root expression stage（68d）were selected.A total of 181.36 Gb of Clean Data were obtained.The assembled unigene sequences were compared with four major databases（Nr,KEGG,KOG,and Swissprot）for Blast comparison,resulting in functional annotation of 32,946 unigenes.GO functional analysis categorized unigenes into three categories and 46 branches,while KEGG Pathway enrichment analysis classified unigenes into 144 metabolic pathways.Based on the results of different analysis,GO annotation,and KEGG Pathway enrichment analysis,differential genes were mainly enriched in secondary metabolic processes,phenylpropanoid metabolism processes,photosynthesis,oxidoreductase activity,anchored component of plasma membrane and calmodulin binding.Different genes were also significantly enriched in metabolic pathways,biosynthesis of secondary metabolites,starch and sucrose metabolism,photosynthesis and plant hormone signal transduction.213 differential genes encoding transcription factors（AP2/EREBP,WRKY,NAC,and GRAS gene family members）played a vital role in promoting the formation of adventitious roots.Furthermore,114 genes with significant expression of starch,fructose,sucrose,and glucose were identified,indicating that genes involved in sugar anabolism are critical components in regulating adventitious root formation in plants.Moreover,differential genes involved in plant hormone signaling pathways also played an essential role in developing adventitious roots.Overall,these findings shed light on the complex molecular mechanisms involved in developing adventitious roots in red rod camphor cuttings under different light-quality treatments.These results can contribute to developing effective strategies for the propagation and cultivation of this plant species.To summarize,under red light treatment,the cuttings of‘Gantong No.1’showed the most optimal rooting effect at a light intensity of 100μmol·m-2·s-1.The results suggest that higher levels of soluble sugar,soluble protein content,and IAA content can enhance the growth of adventitious roots in‘Gantong No.1’.On the other hand,POD activity was found to have minimal impact on the growth of adventitious roots,while PPO activity may have a negative effect on their growth.The molecular regulatory mechanism underlying adventitious root formation suggests the process is closely linked to the differential expression of genes involved in plant hormone biosynthesis,glucose metabolism,and other related pathways. |
