Regulatory Effects And Its Mechanism Of Fulvic Acid Potassium On Growth Of Flue-cured Tobacco Under Drought Stress

Fulvic acid potassium is an important plant growth regulator,it was reported that fulvic acid potassium played an important role in improving growth and stress resistance of higher plants.Previous studies indicated that,fulvic acid potassium could improve the ability of resistance to abiotic stress in many different kinds of plants,while the mechanism of alleviating stress-induced damage in tobacco has not yet been clearly studied.Effects of fulvic acid potassium（foliar spraying）on growth of flue-cured tobacco seedlings under drought stress through physiological and molecular biological methods were investigated by hydroponic experiments.We mainly discussed the morphological structure,photosynthetic and chlorophyII fluorescence characterisitic,osmolyte,active oxygen scavenging system,content of endogenous ABA and the genetic expression of key enzymes that control ABA synthesis and decomposition in two cultivars under different treatments,and explicated the mechanism of fulvic acid potassium on flue-cured tobacco drought-tolerance.The main research results were as follows:1.Four flue-cured tobacco cultivars were studied by using different concentrations of PEG-6000simulated drought conditions,the most suitable concentrations of PEG-6000 was 5%according to the drought-injure index of the cultivars,and drought-tolerance of the four flue-cured tobacco cultivars were compared,drought resistance capacity of them was honghuadajinyuan>K326>zhongyan 100>yunyan 100.2.The most suitable concentration of fulvic acid potassium was 0.1%,respectively,when two flue-cured tobacco cultivars seedlings was treated with different concentrations of fulvic acid potassium（0,0.05%,0.1%,0.2%,0.4%）.The most suitable concentrations of fulvic acid potassium could mitigate the injuries caused by drought stress by promoting the growth of root,increasing biomass accumulation,and enhancing chlorophyll contents,root activity and NR activity of flue-cured tobacco seedlings.3.Under drought stress,the leaf thickness,thickness ration of palisade/spongy and cell tightness rate（CTR）were significantly decreased,while scattered rate（SR）was increased.Compared with drought stress alone,foliar spraying fulvic acid potassium could increase the leaf thickness,palisade tissue thickness,spongy parenchyma thickness,thickness ration of palisade/spongy and cell tightness rate（CTR）,while scattered rate（SR）was decreased.Therefore,fulvic acid potassium could effectively maintain the structural integrity of flue-cured tobacco leaves under drought stress.4.Under drought stress,the seedling growth of two flue-cured tobacco cultivars was inhibited and the dry matter accumulation was decreased,chlorophyll contents,net photosynthetic rate,stomtal conductance,intercellular CO₂concentration,transpiration rate,PSII maximum photochemical efficiency,PSII potential activity,PSII effective quantum efficiency,PSII actual photochemical quantum efficiency,photosynthetic electron transport rate,photochemical quenching coefficient and the energy of photochemical reactions were all significantly decreased,while leaf water use efficiency,stomatal limitation index and non-photochemical quenching coefficient were all significantly enhanced.Compared with drought stress alone,foliar spraying fulvic acid potassium could improve seedling growth,inhibit the degradation of chlorophyll,and alleviate the decline of net photosynthetic rate and transpiration rate.Meanwhile,fulvic acid potassium addition alleviated stress-induced damage to leaf PSII and enhanced photochemical efficiency of flue-cured tobacco leaves grown under drought stress.5.Under drought stress,the water contents,K⁺contents and water potential in leaves of two flue-cured tobacco seedlings were significantly decreased,and the accumulation of proline and soluble sugar were significantly increased.Compared with drought stress alone,foliar spraying fulvic acid potassium could effectively improve the contents of soluble sugar,soluble protein,and proline to maintain high osmotic potential in cells,alleviate the decline of water contents,K⁺contents and water potential in leaves,therefore enhanced water-absorbing ability of flue-cured tobacco seedlings,and improved its drought resistance.6.Under drought stress,the O₂^-.production rate and H₂O₂contents in leaves of flue-cured tobacco seedlings were significantly increased,and the higher levels of reactive oxygen species（ROS）facilitated the production of malondialdehyde（MDA）.Moreover,the activities of superoxide dismutase（SOD）,peroxidase（POD）and catalase（CAT）were all significantly enhanced under drought stress,as well as the content of glutathione（GSH）was significantly increased in the initial period of drought stress,while the content of ascorbic acid（AsA）was decreased.Compared with drought stress alone,foliar spraying fulvic acid potassium could effectively improve the activity of antioxidase（SOD,POD and CAT）and the amount of antioxidants（AsA and GSH）to decrease the excessive ROS level（the content of superoxide anion and hydrogen peroxide）,therefore alleviating the damage of membrane lipid peroxidation.7.The expression level of NCEDs is up-regulated,the expression of CYP707A3 is down-regulated,and ABA contents is enhanced in the initial period of drought stress.Compared with drought stress alone,foliar spraying fulvic acid potassium could down-regulate the expression of NCEDs and CYP707A3,this caused the content of ABA was lower than that of single drought stress.In the later stage of drought stress,the content of ABA was higher than that of single drought stress,this indicate that fulvic acid potassium could delay the degradation of ABA in leaves of flue-cured tobacco seedlings under drought stress.In conclusion,fulvic acid potassium could alleviate stress-induced damage to flue-cured tobacco seedlings and improve its drought-tolerance through enhancing root growth,regulating photosynthesis,alleviating oxidative damage,increasing accumulation of osmolyte and ABA.