Effects Of Melatonin On Arbuscular Mycorrhizal Symbiosis And Drought Tolerance In Kiwifruit Seedlings

Actinidia chinensis is a deciduous fruit tree belonging to the genus Actinidia in the family Actinidiaceae.Its root system is fleshy and shallow,and its leaves are large and hairy,making it more susceptible to drought than other fruit trees.Research has confirmed that pretreatment with melatonin(MT)can increase the biomass of kiwifruit seedlings by improving leaf photosynthetic capacity and carbon sequestration capacity,and improve drought resistance by promoting root elongation growth and increasing antioxidant content.Arbuscular mycorrhiza fungi(AMF)can also improve the water status of plants and enhance the ability of fruit tree roots to resist high temperatures.However,whether AMF and MT have a synergistic effect on plant drought resistance is unknown.This article studied the effects of inoculation with Rhizophagus intraradices and/or MT treatment on the growth characteristics,photosynthesis,antioxidant enzyme activity,accumulation of osmoregulation substances,and nutrient absorption of kiwifruit seedlings under two water conditions: normal watering and drought treatment.Based on this,relevant genes were analyzed using q RT-PCR,in order to further seek better measures to improve the drought resistance of kiwifruit.The main research findings are as follows:1.Inoculating AMF and applying MT can alleviate the impact of drought stress on the growth of kiwifruit seedlings,alleviate the damage to plant morphology,and facilitate the increase of plant growth indicators.The combined use of AMF and melatonin has a better effect.Combined MT treatment can promote the infection of AMF in the roots of kiwifruit seedlings,significantly increase the mycorrhizal infection rate(MC),spore density(SPD)and hyphal length density(HLD),forming a good symbiotic relationship.2.Inoculating AMF,applying MT,or both can significantly improve the photosynthetic performance of kiwifruit plants under drought treatment,increase chlorophyll content,and improve their gas exchange parameters.Application of AM and MT alone had less impact on chlorophyll content and gas exchange parameters,while the combined treatment of AM and MT had a more significant effect.Compared to CK,the contents of chlorophyll a,chlorophyll b,and total chlorophyll increased by 25.93%,11.11% and 35.19%,respectively.Pn,Gs,Ci and Tr increased by 180.96%,168.72%,38.55% and 218.99%,respectively.3.Inoculating AMF,applying MT,or a combination of both can significantly improve the osmoregulation ability of kiwifruit plants under drought treatment,reduce the MDA content and relative electrical conductivity of leaves,and increase the content of osmoregulation substances such as proline,soluble sugar and soluble protein.In addition,the combination of AM and MT had the best effect on improving osmoregulation,with MDA content and relative electrical conductivity decreased by 37.1% and 26.82%,respectively.Proline,soluble sugar and protein increased by 89.64%,21.82% and 211.17%,respectively.4.Inoculating AMF,applying MT,or a combination of both can significantly increase the antioxidant enzyme activity and the expression of related antioxidant enzyme genes in kiwifruit plants under drought stress.The combination of AM and MT has the strongest effect on improving SOD,POD and CAT activities.The expression of all antioxidant enzyme genes in mycorrhizal plants was higher than that in non-mycorrhizal plants.AM+MT significantly affected the expression of SOD,POD12,POD42 and CAT6 in leaves,but had no significant effect on the expression of SOD [Cu-Zn] and CAT1 in leaves.5.Inoculating AMF,applying MT,or a combination of both can promote nutrient uptake in kiwifruit plants under drought treatment,and significantly induce the expression of the main transporter genes for phosphorus uptake.Under drought treatment,AM could significantly increase the content of N,P,K and Fe in kiwifruit leaves,while MT could significantly increase the content of P,Fe and Zn in seedling leaves.The combined application of AM and MT can significantly increase N and K content in plant leaves,and the effect is better than that of AM and MT alone.Inoculation with AMF and MT significantly induced the predicted expression of six PHT1 s,and both AMF and MT treatments upregulated the expression of Ac PHT1;1,Ac PHT1;2 and Ac PHT1;6.In addition,MT and AMF combined treatment significantly upregulated the expression of all six genes,with a significantly higher effect than single treatment.