| Alfalfa(Medicago sativa L.)is a kind of high-quality legume with high protein content and good palatability.Alfalfa was primarily planted in northwest and northwestern China.Most agricultural land in China is in arid and semi-arid areas due to its high-water requirement during the growth cycle.To some extent,alfalfa cultivation is prohibited.Alfalfa seedings were used as materials in this study,and PEG-6000 was used to simulate drought environment.The effects of exogenous strigolactones on physiological indexes and related molecular mechanisms of alfalfa under drought stress were explored by sand culture and hydroculture methods.The following are the main research findings:1.The effects of different concentrations of synthetic analogue GR24 on the growth of alfalfa were not consistent.Compared with the control group,plant height,root length and fresh weight of alfalfa were increased after spraying with 0.1 μM GR24.Compared with the drought stress group,the root length and fresh weight of leaves increased significantly by 36.7%and 66.7%,respectively,when treated with 0.1 μM GR24.Different concentrations of GR24 could alleviate the degradation effect of drought stress on chlorophyll content of alfalfa.The concentrations of 0.01 μM and 0.1 μM GR24 significantly increased the contents of osmotic regulatory substances in alfalfa leaves and roots,and GR24 concentrations of 1 μM decreased the contents of soluble protein in leaves.Different concentrations of GR24 decreased the relative conductivity and malondialdehyde content of leaves under drought stress,alleviating the damage to membrane permeability caused by drought stress.Different concentrations of GR24 significantly increased the antioxidant oxidase activities in alfalfa leaves and roots under drought stress compared with that in the drought treatment group.Spraying with 0.1 μM GR24 increased the antioxidant oxidase activities in leaves and roots to the maximum extent,and the activities of POD and CAT in leaves were increased by 26.1%and 27.6%,respectively.2.Alfalfa leaves sprayed with 0.1 μM GR24 were selected as materials for transcriptome high-throughput sequencing analysis.In the comparison groups of different treatment groups,72 differentially expressed genes were discovered.In the comparison between the drought stress group and the GR24 treatment group,the most enrichmentest KEGG pathway is plant hormone signal transduction pathway,and the highly amount of GO functional enrichments were transcriptional regulatory activity and DNA-binding transcription factor activity.The 24 differential genes were verified by qRT-PCR,and it was found that the differential genes were enriched in ABA signaling pathway,which mainly enriched PYL/PYR and PP2C gene families.It is concluded that GR24 may reduce the damage caused by drought stress by regulating stomatal closure and reducing water evaporation via ABA signaling.3.JIP test was used to analyze the mechanism of photosynthesis of alfalfa leaves alleviated by GR24 under drought stress.The results showed that spraying with GR24 under drought stress could improve the transient curve of chlorophyll a fluorescence OJIP,which was shown as follows:The GR24 treatment increased the Fo,Fj,Fi and Fm values of alfalfa under drought stress,significantly increased the quantum yield and efficiency,decreased the specific energy flux,and increased the Pi_ABS and PItotal values.In addition,qRT-PCR was used to determine the expression levels of seven genes related to photosynthesis,and it was found that the expression levels of genes related to photosynthesis and cytochrome synthesis were up-regulated after spraying with GR24.4.Metabolomics analysis was performed to identify metabolites in root exudates of alfalfa after spraying with GR24 leaves under drought stress after planting materials with hydroponics.In the drought and the GR24 treatment,14 different metabolites were enriched in 12 different metabolic pathways.Among them,5 metabolites were down-regulated and 9 metabolites were up-regulated after spraying with GR24.GR24 can improve the respiration of plant roots by enhancing the TCA cycle and pentose phosphate pathway,increase the content of rorosemary,improve the antioxidant enzyme activities of roots and remove excessive reactive oxygen species,so as to alleviate the negative effects of plants caused by drought stress.In conclusion,drought stress caused negative effects to the growth and physiology of alfalfa plants.Spraying with 0.1 μM GR24 could alleviate the negative effects caused by drought stress by enhancing the photosynthetic capacity of leaves,regulating stomatal closure and reducing water evaporation.In addition,spraying with 0.1 μM GR24 can improve root activity by enhancing root respiration and removing excessive reactive oxygen species.The results provided a theoretical basis for improving drought resistance of alfalfa with GR24. |
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