Alleviation Of The Effects Of Exogenous Hydrogen Sulfide On Physiological Characteristics Of Tobacco Seedlings Under Drought Stress

In this study,tobacco variety Yuyan 10 was used as experimental material,PEG-6000 was used to simulate drought stress,NaHS was used as an exogenous hydrogen sulfide donor,and different concentrations of NaHS were added to the nutrient solution to pretreat tobacco seedlings.The effects of exogenous hydrogen sulfide on drought stress were analyzed from physiological and biochemical characteristics,photosynthetic parameters and fluorescence parameters.The main results of the study on the effects of tobacco seedlings are as follows:1.Under drought conditions,the growth of tobacco seedlings will be significantly inhibited,water content will decrease,chlorophyll will be degraded and the content of chlorophyll will decrease at the same time,affecting the normal physiological response.0.4 mmol/L NaHS treatment could effectively improve the physiological status of seedlings,relieve the inhibition effect of drought stress on tobacco growth to a certain extent.The contents of proline and soluble sugar in seedling leaves increased significantly,the water potential and water content of leaves increased significantly,the activity of protective enzymes increased significantly,and the stability of chloroplast structure was effectively protected,and the content of chlorophyll increased.Exogenous hydrogen sulfide pretreatment has obvious concentration gradient phenomenon.NaHS treatment with appropriate concentration can improve the tolerance of tobacco seedlings.Higher concentration will produce more obvious toxicity and aggravate the stress state.0.4 mmol/L NaHS treatment can effectively enhance the drought tolerance of tobacco seedlings.2.Drought stress can lead to serious oxidative stress in tobacco seedlings,and the content of hydrogen peroxide is significantly increased.At the same time,the antioxidant enzymes in tobacco play a role and increase their activity.However,the dynamic balance of reactive oxygen species in tobacco is destroyed,malondialdehyde is produced in large quantities,resulting in serious lipid peroxidation,cell membrane structure is destroyed,the conductivity of tobacco leaves is significantly increased,and the cell content is increased Root activity was also affected by material outflow,and water and nutrient uptake capacity decreased.Exogenous hydrogen sulfide pretreatment effectively enhanced the activities of major antioxidant enzymes such as superoxide dismutase,peroxidase,catalase and ascorbic acid peroxidase in tobacco leaves,effectively eliminated some peroxides in leaves,decreased malondialdehyde content,decreased leaf conductivity,and increased root activity,which enhanced water and nutrition in adversity environment.Absorption of substances.3.Under drought conditions,photosynthetic parameters of tobacco seedlings will decrease in varying degrees,destroying normal respiration and photosynthesis.After pretreatment with exogenous hydrogen sulfide,the net photosynthetic rate,transpiration rate and stomatal conductance of seedlings increased significantly,while the intercellular CO2 concentration and water use efficiency decreased significantly.The results showed that exogenous hydrogen sulfide treatment could increase CO2 uptake,alleviate photosynthesis decline caused by stomatal constraints to a certain extent,and keep seedlings under drought stress.Strong photosynthetic capacity under conditions.4.Drought stress can cause the fluorescence parameters of tobacco seedling leaves to decrease significantly,reduce photosynthetic rate and inhibit energy transfer.Drought stress can reduce the maximum photochemical quantum yield(Fv/Fm),actual photochemical efficiency(PSII),photochemical quenching coefficient(qP)of PS Ⅱ and increase the non-photochemical quenching coefficient(NPQ).After the pretreatment with exogenous hydrogen sulfide,the Fv/Fm,PSII,qP and other coefficients of flue-cured tobacco increased,reducing the NPQ coefficient and reducing the effect of heat dissipation on Photosynthetic mechanism.5.Drought stress can cause the separation of cytoplasmic wall of tobacco seedling leaves,the degradation of chloroplast internal structure and the increase of osmiophilic particles,which lead to the decrease of light conversion efficiency and photosynthetic rate.In the leaves pretreated with exogenous hydrogen sulfide,the cell structure is protected to a certain extent,and the organelle morphology is better.Although the internal structure of chloroplast is affected,it can still be clearly distinguished.These results showed that the use of exogenous hydrogen sulfide pretreatment could effectively improve the drought tolerance of tobacco.6.The water content of tobacco seedlings decreases with the increase of stress time.The decrease of water causes the seedling osmotic substances to increase first and then decrease.With the increase of stress time,the insufficiency of antioxidant enzymes activity causes the continuous increase of malondialdehyde content and the increase of plasma membrane permeability.The tobacco seedlings pretreated with exogenous hydrogen sulfide can maintain higher antioxidant enzymes activity.Maintaining oxidative balance in vivo,and increasing root activity and chlorophyll content are conducive to the survival of seedlings under adversity.Exogenous hydrogen sulfide is helpful to maintain the stability of substances in seedlings during the period of drought stress treatment.