Distribution And Regulation Mechanism Of Photosynthetic Products In Flue Cured Tobacco Under Different Light Conditions

In order to reveal the photosynthetic physiology and the mechanism about accumulation and distribution of photosynthetic assimilation products under different light environments and effects of Ca Cl₂ on photosynthetic characteristics and distribution of photosynthetic assimilation products,a two-year pot experiment was cultivated in a climate control chamber at modern tobacco agriculture science and Technology Park in Xuchang campus of Henan Agricultural University,includes two individual experiment:（1）Response of photosynthetic characteristics and accumulation and distribution of assimilation products in tobacco to different light environments:there were three light intensity treatments(shading:（400±15）-（500±15）μmol·m-2·s-1;natural light:（800±15）-（1000±15）μmol·m-1·s-1;high light:（1500±15）-（1800±15）μmol·m-2·s-1.LI-6400 photosynthetic apparatus and the 13 C pulse labeling technique were used to system study the lighting conditions on photosynthetic and physiological characteristics of tobacco and photosynthesis assimilates distribution in plant-soil system.（2）Effects of Ca Cl₂ on photosynthetic physiology and the mechanism about accumulation and distribution of photosynthetic assimilation products of flue-cured tobacco under intense light stress:15 days after transplanting,consistent growth of tobacco were transferred to artificial climate room which was sprayed with30 m mol·L-1Ca Cl₂ for 4 days,net photosynthesis,fluorescence parameters and superoxide dismutase（SOD）,malondialdehyde（MDA）and related physiological indexes were measured to analysis the exogenous Ca Cl₂ on the photosynthetic characteristics and activity of antioxidant enzymes under the strong light and to investigate the effects of Ca Cl₂ on the relationship between the ability to adapt to the strong light and maintain photosynthetic function in tobacco leaves.The results showed that:（1）With the decline of light intensity,net photosynthetic rate（Pn）,stomatal conductance（gs）,transpiration rate（Tr）were decreased,but the intercellular CO2 concentration（Ci）increased.The maximum net photosynthetic rate（Amax）,light saturation point（LSP）,light compensation point（LCP）,dark respiration rate（Rd）reached the maximum value of tobacco under the condition of high light,however,low Light Condition have a larger apparent quantum efficiency.With the increase of light intensity,the maximum photochemical efficiency Fv/Fm,actual photochemical efficiency ФPSⅡand photochemical quenching coefficient q P of Photosystem Ⅱwere showing a trend of increasing first and then decreasing,but the Non-photochemical quenching factor NPQ continued to rise.Larger proportion of light energy were lost by the chemical process which were absorbed flue-cured tobacco under the condition of high light.It is a “harmless disposal “of excess light energy which is not accompanied by photosynthetic rate reduction.（2）There were significantly affected one the antioxidant enzyme system of flue-cured tobacco under different light environment.SOD,POD,CAT activity of shade treatment T1 and strong light T3 were significantly higher than light intensity T2,the activity of SOD and POD were increased by 16.53% and 75.4% respectively compared with T2 under the condition of low light,and effectively alleviated the harm of low light intensity on tobacco leaf.When the light intensity reached at 1500-1800±15 μmol·m-2·s-1,the activities of the three protective enzymes were significantly increased to the maximum value,the results showed that high light intensity was more conducive to improving the antioxidant capacity of flue-cured tobacco and to ensure the normal photosynthesis.With the increase of light intensity,MDA content and soluble protein showed a trend of "falling first and then rising",too low or too high of the light can cause the increase of MDA content and soluble protein and it is more obvious of the increasing trend which under low light stress.The results showed that the flue-cured tobacco leaves were most affected bylow light stress.（3）Different light intensity has a significant impact on the quality of flue cured tobacco,with the increasing of light intensity,the content of reducing sugar and total sugar increased,but content of nitrogen compounds increased under the shading treatment,the ratio of sugar to alkali decreased,and the content of potassium and chlorine decreased.The effects of different light treatments on the contents of neutral aroma components and aroma components in flue-cured tobacco leaves were analyzed: phenylalanine and cembratriendiol catabolite,in addition to the total amount of neophytadiene to the minimum amount of T2 treatment,and T1 and T3 treatment respectively increased.It show that shade and high light are conducive to these kinds of aroma components increased.The browning reaction products,carotenoid degradation products,neophytadiene and other classes increased with the increase of light intensity,T3 treatment reached the maximum,which was 13.94% and 58.18% higher than that of T1 treatment.The results showed that the strong light promoted the formation of browning reaction products and the formation of carotenoid,neophytadiene and other aroma compounds,and the content of neophytadiene increased remarkably.（4）With the decrease of light intensity,the biomass of each component of tobacco and the ratio of root to shoot decreased gradually.Light intensity also affected the absorption,accumulation and distribution of 13 C,under the condition of weak light,the proportion into the root of tobacco enriched 13 C significantly fewer,but more distribution to the upper;With the increase of sampling time,the deposition efficiency of rhizosphere increased,pulse labeling after 1day,the deposition efficiency of ¹³C-SOC was 0.009%-0.016%,and to the pulse labeled 30 day,the rhizosphere deposition efficiency increased to 0.021%-0.037%.In addition,the proportion of 13 C in the leaves decreased gradually with the extension of the sampling time,and the proportion of the underground parts increased gradually with the growth stage,Increased from 9.85%-13.54% to28.12-30.91%,which may be related to the transport of assimilate to the lower part of the soil.It can be seen that the change of the external light environment not only significantly affects thephotosynthetic characteristics and biomass accumulation of tobacco leaves,but also changes the distribution pattern of photosynthetic carbon in tobacco plant soil system.（5）Spraying with Ca Cl₂,the chlorophyll content of the flue-cured tobacco leaves was significantly higher than that of the control group.The Pn,Gs and Tr were all increased,and the Ci was lower than that of the control group,while the content of Ca Cl₂ was decreased;The AQY,Amax and LSP of the light response curve were increased by 27.08%,16.17% and 21.43%respectively compared with the control CK of distilled water,and the carbon assimilation rate increased significantly;The system has maintained a high degree of openness,Fv/Fm,Phi PSII,q P were significantly increased,NPQ decreased.The results indicated that the application of exogenous Ca Cl₂ could protect the photosynthetic apparatus from the strong light and reduce the photoinhibition.At the same time,pretreatment with Ca Cl₂ significantly activated the SOD and POD activity of flue-cured tobacco leaves under strong light stress,and effectively inhibited the decrease of CAT activity under continuous strong light stress;The content of MDA and soluble sugar were decreased（P<0.05）,and the content of soluble protein was significantly increased.To avoid the membrane peroxidation,so as to reduce the damage of strong light stress on flue-cured tobacco leaves,in a certain extent to protect the cells of photosynthetic performance,enhance the light tolerance of tobacco.（6）The biomass,the value and concentration of 13 C in tobacco treated by Ca Cl₂ showed an increasing trend compared with that of CK in distilled water.After the end of isotope-labeled 1day,under the strong light condition and the natural light intensity,the delta 13 C value was10.08% and higher than that of the control CK.The results showed that exogenous Ca Cl₂ could promote the growth of tobacco plant,increase the growth rate of tobacco plant,and increase the photosynthetic capacity of Flue-cured tobacco.Furthermore,the accumulation of photosynthetic carbon assimilation products of tobacco plants increased,and the degree of Ca Cl₂ was more significant than that under natural light treatment under the strong light.