Study On Hypergravity Response Mechanism Of Malus Hupehensis

Malus Hupehensis is one of the good rootstocks for apple,which has developed root system and good disease resistance.In this study,Pingyi sweet tea seeds were treated for 1h,3h and 5000r/min at 5000r/min,10000r/min and 15000r/min.The germination rate,chlorophyll content and physiological and biochemical indexes of the seedlings were measured.The changes of endogenous hormones and internal reference genes were analyzed based on HPLC and real-time fluorescence quantitative analysis.The differential expression of genes in different treatments was analyzed based on transcriptome sequencing..The results were as follows:1.In different experimental treatments,the intensity of high gravity treatment had direct effect on germination rate,germination potential and germination index.There was no significant change in germination rate and germination potential under low intensity（5000r/min）high gravity treatment.Under the medium intensity（10000r/min）high gravity treatment,the seed germination rate and germination potential increased,and reached the maximum value in 3h.Under high intensity（15000r/min）high gravity treatment,the germination rate and germination potential of seeds decreased significantly.2.High gravity treatment inhibited the growth of Malus Hupehensis seedlings.With the increase of high gravity intensity,the plant height and root length of seedlings decreased by 0.08-0.36% and0.06-0.19% respectively3.The chlorophyll content of Malus Hupehensis seeds after high gravity treatment was significantly higher than that of the control,and the chlorophyll content was positively correlated with the gravity intensity.The content of chlorophyll a / Breached the peak value at 5000r/min for 3h.4.Malus Hupehensis directly affected the important enzyme activities in Pingyi sweet tea seedlings.The activities of peroxidase（POD）and superoxide dismutase（SOD）in the seedlings were significantly increased,but the activities of superoxide dismutase（SOD）were significantly decreased.The activity of pod in seedlings reached 35.899g/·g^-1FW · min^-1 at 10000r/min for 1h,and the activity of SOD was the lowest at 10000r/min for 5h.The activity of cat in seedlings was correlated with treatment intensity and treatment time.The activity of cat was significantly increased at 10000r/min for 3h and the lowest at 15000r/min for 5h.5.The content of calcium in leaves was lower than that in roots,and the change of calcium content in leaves was consistent with that in roots.The calcium content of leaves reached the maximum value at the gravity intensity of 5000r/min for 5h.The calcium content of roots reached the maximum when the gravity intensity was 5000r/min for 5h.6.The results showed that high gravity treatment could affect the content of endogenous hormones in the seeds of Malus hupehensis,and the content of seven endogenous hormones measured had a good linear correlation.Properly increasing the high gravity was conducive to the growth of Pingyi sweet tea,while the high gravity treatment changed the ratio of IAA/ABA and reached the maximum value after 3h of 15000r/min high gravity treatment,thus promoting the plant growth process.7.The most stable internal reference genes after high gravity treatment are glyceraldehyde3-phosphate dehydrogenase gene（GAPDH）and polyubiquitinase gene（UBQ）,followed by actin gene（ACT-7）;Tubulin gene（α-TUB）,transcription elongation factor gene（EF-2）and adenine phosphoribose converting enzyme gene（APRT-5）have poor gene stability and are not suitable as internal reference genes for Malus hupehensis.8.The results of transcriptome analysis showed that the genetic information of seeds changed significantly after high gravity treatment,and the distribution and enrichment of base content were different.Under the same high gravity treatment intensity,the gene expression of seeds with different treatment time changed significantly.Among them,78 genes were up-regulated,but 428 genes were down-regulated.However,there were 97 up-regulated genes and 68 down regulated genes under the same treatment time and different high gravity intensity.Differential genes are widely distributed in plant cell components,biological processes and molecular metabolism.