Effects Of Foliar Application Of Zn And Mo Salt Solution On Growth And Physiological Parameters In Mulberry Under Drought Stress

Drought stress is one of the main threats to plant growth and survival.Zinc?Zn?and molybdenum?Mo?are essential trace elements for plant growth and participate in a variety of metabolic activities in plants.However,the effects of Zn and Mo on the drought tolerance of mulberry and the underlying physiological mechanisms are not clear.In this study,saplings of the mulberry cultivar Zhongsang 5801 were foliar sprayed with distilled water?H₂O?,0.02%Zn SO₄?Zn?,0.01%Na₂Mo O₄?low Mo?,0.1%Na₂Mo O₄?high Mo?and0.02%Zn SO₄+0.01%Na₂Mo O₄?Zn+low Mo?,The normal water treatment group maintained 80%of the saturated water content of the substrate,and the drought treatment group maintained 20%of the saturated water content of the substrate for 7 days.The root morphology,growth,tissue water content,contents of photosynthetic pigment,nitrogen and phosphorus,osmoregulation substances,starch,malondialdehyde?MDA?and antioxidant enzymes were were analyzed and compared.The effects of different Zn and Mo salt solution on the drought tolerance were evaluated,and the physiological regulation mechanisms were revealed.The main results are as follows:1.Under drought stress,the rate of stem elongation,the biomass of each part and the root water content decreased,the content of chlorophyll and carotenoid increased,the content of starch in roots and leaves decreased,the content of total N in roots and leaves increased,and the content of ammonium nitrogen and nitrate nitrogen in leaves increased.The content of total P decreased in roots and increased in leaves.The content of O₂ú?in leaves decreased,while the content of H₂O₂increased.Correspondingly,the activity of APX and CAT in leaves increased,and the activity of POD decreased.2.The growth and physiological responses of different spraying treatments were different under drought stress.The growth rate of Zn+low Mo treatment was significantly higher than that of other treatments,and was close to the full watering level,suggesting that Zn and Mo had synergistic stimulating effect on growth.Under drought stress,Zn or low Mo aloneled to significant loss of chlorophyll,but the combined application of them did not form an accumulative effect.Under drought stress,the starch contents in roots of Zn+low Mo treatment group significantly decreased,while the starch contents in leaves of Zn and high Mo treatment group were the highest.Zn+low Mo treatment promoted the content of total N in roots under drought stress,while low Mo increased the content of total N,nitrate N and total P in leaves.3.Low Mo treatment significantly increased Pro content in leaves,and only under this treatment,Pro content in roots significantly increased under drought stress.Zn and Mo application alone or in combination significantly increased the content of soluble protein in roots under drought stress,while Zn+low Mo application accumulated the highest content of soluble protein in leaves.On the contrary,the application of Zn+low Mo significantly increased the soluble sugar content in leaves,and the effect was better than that of single application,which was related to the significant decrease of starch content in leaves4.Different spraying treatments had no significant effect on the content of H₂O₂ and O₂ú?and MDA.It can be seen that the effect of spraying Zn and Mo salt solution on the drought resistance of mulberry in this study may be directly related to reactive oxygen species?ROS?.In the antioxidant enzyme system,the activities of CAT in leaves and SOD in roots of the saplings treated with low Mo were higher under drought stress,suggesting that low Mo could activate the antioxidant enzyme and reduce the drought induced oxidative stress.In conclusion,Zn and low Mo could alleviate the damage of drought stress on mulberry,but the strategies of Zn and Mo involved in regulating drought tolerance might be different.Zn+low Mo increased the content of many osmoregulation substances,and may play an important role in regulating the pathway of glucose metabolism,especially the transformation of starch to soluble sugar,so as to improve the osmoregulation ability of cells and reduce the inhibition of growth under drought stress;while Zn and low Mo may play an important role in protein metabolism,especially in the regulation of antioxidant enzymes,promote the toleranceto drought induced oxidative stress...