Effects And Mechanisms Of Uniconazole On Alleviating Drought Damage In Cannabis Sativa L.at Seedling Stage

Drought has become one of the most important abiotic stress factors that limit crop growth and development,and decrease crop yield.With the rapid development of industrial hemp（Cannabis sativa L.）industry in recent years,it is widely planted all over the world.The long and severe drought,and the lack of irrigation equipment in most areas will shorten the growth period of industrial hemp,bud and blossom early,and decrease the plant height,which will reduce the fiber yield.Uniconazole,as a triazole plant growth retarder with high efficiency and low toxicity,has a significant effect on plant stress resistance and increasing production.However,there is little research on the mechanism of uniconazole alleviating industrial hemp under drought stress now.Therefore,the study was conducted in Daqing Branch of Heilongjiang Academy of Sciences using two different genotypes of industrial hemp varieties（Huoma 1 and Hanma 2）as test materials with the way of pot water control set drought stress treatment.The uniconazole on the morphogenesis,physiological biochemical and molecular physiological regulation mechanism,and yield regulation effect in industrial hemp conditioning drought stress were studied.The main results and conclusions are as follows:1.The morphogenesis,photosynthesis,antioxidant defense system and osmotic regulation of industrial hemp seedlings under exogenous uniconazole and drought stress were analyzed.With the extension of drought stress,the seedling morphology indexes of the two industrial hemp varieties were inhibited obviously,the RWC of leaves was decreased,the photosynthetic system of the leaves was damaged,the distribution and accumulation of ROS was increased dramatically,and membrane lipid peroxidation degree of the leaves was aggravated.Among them,Hanma 2 was more sensitive to drought stress and the above indexes recovered after rehydration.Under drought stress,seed soaking with exogenous uniconazole could significantly inhibit the plant height of industrial hemp,reduce leaf area,improve the dry and fresh weight of roots,restore shoot dry and fresh weight in the later stage of stress,promote the ability of root growth（increase root length,root surface area,root volume,root projected area and root tips number,etc.）,and maintain the integrity of leaf cell structure（palisade tissue and spongy tissue）,increase starch granules in mesophyll cells;It could increase the relative water content of leaves;It could improve chlorophyll content（chlorophyll a,chlorophyll b,total chlorophyll and carotenoid content）,increase chlorophyll fluorescence parameters（ETR and Fv/Fm）,improve photosynthetic gas exchange parameters（C_i、g_sand E）,enhance photosynthetic rate and reduce the damage of photosynthetic system;It could improve the activity of antioxidant enzymes（SOD,POD and CAT）,regulate the osmotic regulatory substances in leaves effectively（increase the content of soluble sugar and soluble protein,reduce the content of proline）,and then inhibit the accumulation of reactive oxygen species(O₂^·–and H₂O₂)in leaves,significantly reduce MDA content and cell membrane permeability,alleviated the oxidative damage of industrial hemp leaves caused by drought stress.2.Transcriptome analyzed the leaves of industrial hemp variety Hanma 2 that were treated with drought stress for 2 days and 4 days after foliar spraying with water and exogenous uniconazole.Identification of DEGs revealed 5,736 DEGs between D2＿vs＿DS2 and D4＿vs＿DS4,of which 1,701 were commonly regulated across different treatment periods,which provided a new supplement for the genomic informatics research of hemp stress response.GO enrichment results showed that DEGs induced by exogenous application of uniconazole in industrial hemp plants under drought stress were mainly enriched in oxidation-reduction process,starch biosynthetic process and glucose metabolic process at BP level,chloroplast stroma,chloroplast envelope and chloroplast at CC level,and oxidoreductase activity at MF level.KEGG enrichment analysis revealed that exogenous uniconazole promoted the expression of DEGs in metabolic pathways of plant hormone signal transduction,photosynthesis,photosynthesis-antenna proteins,porphyrin and chlorophyll metabolism,starch and sucrose metabolism,carbon metabolism and nitrogen metabolism under drought stress.3.The key metabolism pathways of industrial hemp seedlings under exogenous uniconazole and drought stress were analyzed.D2＿vs＿DS2 and D4＿vs＿DS4comparison showed that DEGs involving AUX1,IAA,SAUR,GH3,AHK2＿3＿4,ARR-A,DELLA,PP2C and Sn RK2 in IAA,CTK,GA and ABA metabolic process and signal transduction pathway of industrial hemp leaves were regulated commonly by uniconazole under drought stress.And uniconazole application dramatically increased the contents of IAA,ABA and ZT,and decreased GA₃content in the leaves of industrial hemp under drought stress,played a regulatory role in the biosynthesis of endogenous hormones.11 DEGs involving hem A,chl H,acs F,chl E,por,NOL and NYC1,etc.in the porphyrin and chlorophyll metabolic pathway of industrial hemp leaves were regulated commonly by uniconazole under drought stress.The expression of DEGs effectively inhibited the decrease of Chl and Car contents in industrial hemp leaves.7 light-harvesting chlorophyll a/b binding proteins in photosynthesis-antenna proteins of industrial hemp leaves were induced by uniconazole under drought stress,which maybe affect light energy absorption to regulate the drought resistance mechanism of plants.Uniconazole regulated commonly the DEGs in photosynthesis of industrial hemp leaves under drought stress and significantly increased the P_N.It can be seen that photosynthesis plays an important role in the response of uniconazole to drought stress.Uniconazole regulated the DEGs（SPS and Su Sy genes）in the starch and sucrose metabolism pathways of industrial hemp leaves under drought stress,significantly improved the activities of S-AI,NI and SS,decreased SPS activity,increased starch content,and reduced sucrose content,which played a key role in sucrose and starch metabolism.4.The fiber yield of industrial hemp plants under exogenous uniconazole and drought stress were analyzed.Drought stress at trefoil stage significantly reduced the fresh stem weight,dry stem weight,dry bast weight,fresh stem fibre percentage and dry stem fibre percentage of industrial hemp plants at technical maturing stage.Uniconazole（seed soaking with uniconazole and foliar spraying with uniconazole）effectively alleviated the decrease of industrial hemp fiber yield of technical maturing stage.After 8 days of drought stress,soaking seeds with uniconazole could reduce the yield loss of fresh stem fibre percentage and dry stem fibre percentage in HM1 and HM2 by 24.31%,22.82%and 20.34%,23.12%,respectively.Foliar spraying with uniconazole could decrease the yield loss of fresh stem fibre percentage and dry stem fibre percentage in HM1 and HM2 by 4.46%,14.94%and 24.57%,20.59%,respectively.In conclusion,uniconazole plays an important role in promoting industrial hemp growth and development,enhancing plant drought resistance and improving the fiber yield,and provides theoretical basis and technical support for the stress resistant cultivation of industrial hemp.