| Water is the key factor determining plant growth,but soil water that are too high or too low will result in abnormal development and reduced production..Water stress has become one of the main abiotic stresses affecting crop growth and development,yield and quality.Apple(Malus Xdomestica Borkh)is one of the main cultivated fruit tree species in China,and its area and yield rank first in the world.The apple industry has become an important industry for farmers’ income growth,agriculture and rural economic development in China.However,abiotic stresses such as drought and waterlogging seriously affect the yield and quality of apple.Therefore,clarifying the adaptation mechanism of apple rootstocks to water stress and mining related genes are of great significance for apple resistant breeding and high quality and high yield cultivation.In this study,M.hupenensis Rehd.and M.toringoides Rehd were used as materials to study the alleviation effect of melatonin on apple rootstock seedlings under water stress,and the differential expression genes were investigate of melatonin on apple rootstock under water stress using Illumina Hi Seq 2500,.The aim is to provide a theoretical basis for the biological function and stress resistance improvement of apple.The main findinggs are as follows:1.The physiological responses of M hupenensis Rehd and M.toringoides Rehd were different to drought stress,and M.toringoides Rehd exhibited superior drought tolerance.Under drought stress,exogenous melatonin could significantly alleviate the damage of drought on rootstock and improve the drought resistance of apple rootstocks.Compared with drought treatment,the melatonin-treated M hupenensis Rehd delayed the symptoms of phenotypic stress for 2 days,and the symptoms of phenotypic traits changed.Melatonin treatment can promote the accumulation of dry matter such as plant height,shoot,shoot and leaf dry quality under drought stress.Under drought stress,the chlorophyll content of increased first and then decreased.Net photosynthetic rate(Pn),stomatal conductance(Gs)and transpiration rate(Tr)decreased with continued drought stress.Melatonin treatment could alleviate drought stress.The results of paraffin section observation showed that the thickness of the leaves,the thickness of the upper epidermis,the thickness of the epidermis and the tightness of the mesophyll structure of the apple rootstock decreased under drought stress.The leaf thickness of melatonin-treated M.hupenensis Rehd increased 97%compared with the control treatment,the leaf thickness of melatonin treated with M.toringoides Rehd increased by 18.4%compared with the control.The relative conductivity of the leaves of apple rootstocks increased under drought stress.The relative conductivity of melatonin treatment in M.hupenensis Rehd decreased by 5.3%compared with the drought treatment.The relative conductivity of melatonin treatment decreased 2.7%compared with drought treatment.The leaf relative water content(RWC)decreased slowly in the early stage of drought stress,With the prolongation of drought stress,the RWC of M.hupenensis Rehd and M.toringoides Rehd decreased to the lowest on the 5th day after stress.2.Transcriptome analysis of melatonin regulation of apple rootstock resistance under drought stress.The transcriptome sequencing analysis of the control,drought and melatonin-treated rootstock was carried out on the 4th day of drought stress.The results showed that the changes of physiological indexes of apple rootstock and melatonin could improve the drought resistance of rootstock and its transcriptome level.Compared with the control,7170 genes were differently expressed in M.hupenensis Rehd under drought stress,2672 genes were up-regulated and 4498 genes were down-regulated.2969 genes were differently expressed in M.toringoides Rehd,950 genes were up-regulated and 2019 genes were down-regulated..Compared with drought stress,1491 genes were differently expressed in M hupenensis Rehd by exogenous melatonin under drought stress,465 genes were up-regulated and 1026 genes were down-regulated.1384 genes were differently expressed in M.toringoides Rehd by exogenously added melatonin under drought stress,586 genes were up-regulated and 798 genes were down-regulated.3.The physiological responses of M hupenensis Rehd and M.toringoides Rehd,were different for waterlogging stress.The adaptability of M hupenensis Rehd exhibited superior drought tolerance Under waterlogging stress,exogenous melatonin significantly alleviated the damage of rooting seedlings caused by waterlogging and improved the waterlogging-tolerance of apple rootstocks.The symptoms of phenotypic were delayed by 1 day after treatment with melatonin,and the symptoms of waterlogging stress did not appear in M.hupenensis Rehd.Under waterlogging stress,plant height,dry mass,dry mass and dry weight of apple rootstock seedlings were all reduced.Under the waterlogging stress,Pn of M hupenensis Rehd first decreased and then increased,while M.toringoides Rehd showed a downward trend.The contents of Chla,Chlb and Chlt also showed a downward trend.Under waterlogging stress,the leaf thickness of M.toringoides Rehd increased by 7.4%by application melatonin compared with the control,while the leaf thickness of M hupenensis Rehd decreased by 2.6%.The relative conductivity of waterlogging stress increased compared with the control,Under the waterlogging stress,RWC of M hupenensis Rehd showed a trend of slow rise,decline and then rise,while M.toringoides Rehd to show a downward trend.4.The transcriptome sequencing analysis was carried out on the day 4.Compared with the control,8842 genes were differently expressed in M.hupenensis Rehd under waterlogging stress,5110 genes were up-regulated and 3732 genes were down-regulated.For M.toringoides Rehd,7525 genes were differently expressed under waterlogging stress,3204 genes were up-regulated and 4321 genes were down-regulated.Compared with waterlogging stress.5847 genes were differently expressed in M.hupenensis Rehd by exogenously application melatonin under waterlogging stress,2118 genes were up-regulated and 3729 genes were down-regulated.For M.toringoides Rehd,2400 genes were differently expressed,1227 genes were up-regulated and 1173 genes were down-regulated. |
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