Effects Of Light Intensity On Leaf Growth And Physiological And Biochemical Characteristics Of Cigar

Cigar is a special tobacco product.The tobacco leaf that makes a cigar can be divided into eggplant coat,eggplant cover and eggplant core according to its use in the product,domestic also used to call outer wrapping,inner wrapping and core leaf.Due to the requirement of the outer leaf,the blade is thinner and the organization is more detailed,which requires that it cannot be exposed to too much direct sunlight.Shading cultivation is a key cultivation technique for cigar wrapper tobacco production.In this study,cigar varieties H382 and Guyin 4 were used as experimental materials to conduct different light intensity treatment to analyze the differences in response of the two cigar varieties to different light intensity.Secondly,the response of related physiological indexes such as morphological characteristics,photosynthetic characteristics and leaf tissue structure to low light intensity of the cigar varieties with greater response to light intensity was determined.The physiological mechanism of light intensity regulating the growth of cigar leaves was revealed at the transcriptional and translation levels.The main results are as follows:1.Cigar varieties H382 and Guyin 4 were used as materials,and light intensity treatment of200μmol·m^-2·s^-1 and 100μmol·m^-2·s^-1 were set.The results show that H382 and Guyin 4 have different responses to different light intensities.The differences were reflected in（1）morphological characteristics:the plant height and pitch of H382 increased significantly with the decrease of light intensity,while the plant height and pitch of Guyin 4 decreased.The leaf length,leaf width and leaf area of the two cultivars increased,but the increase amplitude was different.The leaf length,leaf width and leaf area of H382 increased by 19.8%,18%and 42%,respectively,while that of Guyin 4 increased by8.6%,9%and 16%,respectively.（2）Biomass:the biomass of all parts of the plants of the two varieties decreased with the decrease of light intensity,and the leaf dry weight of single plant H382 was larger than that of single plant Guyin 4 under low light intensity.Under the same light intensity,the total dry weight of Guyin 4 was significantly lower than that of H382.（3）In terms of photosynthesis,the chlorophyll content of Guyin 4 was lower than that of H382 under each light intensity,and the leaf Pn,LSP,LCP and Rd of H382 decreased with the decrease of light intensity,while Guyin 4 increased with the decrease of light intensity.（4）In terms of leaf tissue structure,leaf thickness of H382 decreased by15.77%under low light,and that of Guyin 4 decreased by 19.75%.2.Three different light intensity levels T200(200±15μmol·m^-2·s^-1),T100(100±15μmol·m^-2·s^-1)and T50(50±15μmol·m^-2·s^-1)were applied to H382 variety.The results showed that leaf length,leaf width,leaf area,and specific leaf area were significantly increased with a decrease in light intensity levels.Similarly,the leaf dry weight and specific leaf weight were also significantly decreased under low light intensities.The leaf photosynthetic characteristics like leaf apparent quantum efficiency（AQY）,maximum net photosynthetic rate（P_n）,light saturation point（LSP）,light compensation point（LCP）,and dark respiration rate（R_d）were also decreased in response to low light intensity.Similarly,the chlorophyll content was also decreased under low light intensity.The leaf anatomical structure analysis showed that with a decrease in light intensity levels,the upper and lower epidermis and palisade tissue became thinner,and the spongy tissue thickness was in the order T200>T50>T100.The spongy tissue under T100 and T50 had large intercellular spaces and loose cells.Moreover,auxin（IAA）and abscisic acid（ABA）contents were significantly decreased while gibberellin（GA₃）content was increased under low light.The zeatin content showed a trend of first increasing and then decreasing.Overall,the effect of low light can be demonstrated in two ways:on the one hand,low light intensity increases the GA₃content and decreases ABA content,promote leaf length and leaf width,increases leaf area and specific leaf area,and thus increases light-capturing area and light interception efficiency while decreases LCP and LSP and thus improves the ability to use low light and maintain a certain photosynthetic capacity.Therefore,on the one hand,the low light intensity increased GA3 content and decreased ABA content thus promoted leaf development;while on the other hand,IAA and chlorophyll contents were decreased which resulted in less dry matter accumulation and thinner leaves formation.3.An integrative analysis of transcriptome and proteome was also performed on cigar tobacco leaves in response to low light.Under low light intensity,the Cigar H382 variety improved light absorption and electron transfer by increasing the expression of DEGs and DEPs related to photosynthesis-antenna complex,photosystem I（PSⅠ）,and photosystem II（PSⅡ）core complex proteins in order to maintain the balance between the photosystems,protect both photosystems and to cope with the low light environment.The DEGs/DEPs involved in energy metabolism（glycolysis,sucrose and starch metabolism）were downregulated while DEGs/DEPs related to the defense/stress system was up-regulated.The results showed that the physiological and biochemical processes under low light were actively adjusted to reduce energy according to plant need,improve the scavenging ability of reactive oxygen species,and enhance the adaptability of cigar tobacco to survive and maintain growth under low light conditions.