Effects Of Cooling Methods On The Postharvest Physiology And Expression Of Browning Related Genes In Late-harvest Yali Pear

Yali Pear?Pyrus bretschneideri Rehd cv.Yali?is an ancient place in Hebei,China,the larger production,storage.However,there is a serious browning phenomenon on core during storage and transportation,especially late-harvest pear's maturity is relatively high and the core is more likely to browning.According to the transcriptome data and references,this enzymatic browning was related to the key enzymes in pear tissue.Therefore,it is a great significance to study the browning mechanism of late-harvest pear fruit and to reduce the occurrence of browning,and to improve the storage quality of pear.The changes of the core browning index,weight loss rate,fruit hardness,respiration intensity,ethylene release rate,browning related genes expression and activity of the late-harvest pear under the slowly cooling and rapidly cooling were determined in the experiment.And the relationship of browning related genes expression with core browning was studied by q RT-PCR as well.The main conclusions are as bellows:1.The browning index of the pear under the slowly cooling was 0.32 at 60 d after storage,which was 18 times higher than that of the rapidly cooling fruit.The browning index of the rapidly cooling and the slowly cooling was 0.61 and 0.17 at 20 d after shelf life.On the whole,the browning index of the slowly cooling was significantly higher than that of the rapidly cooling.And after slowly cooling treatment,the hardness decreased rapidly,weight loss rate,respiration intensity and ethylene release were higher than the rapidly cooling fruit.The CO₂ and ethylene contents of ovary and respiration intensity and ethylene release of fruit and seed were closely related to the core browning.Therefore,during the storage,marketable fruit rate of the rapidly cooling was 98.38 %,while marketable fruit rate of the slowly cooling was 92.47 %.During the shelf life,marketable fruit rate of the rapidly cooling and the slowly cooling was 81.18 % and 60.47 % respectively.The results showed that the physiological indexes and storage quality of the latee-harvest pear under the rapidly cooling were better than the slowly cooling.2.The total amount of Clean Data obtained by transcriptome sequencing was 21.99 Gb,and 96 % or more of the data base error rate was less than 1/1000.The comparison rate of Clean Reads for each sample with the specified reference genome was between 54.97 % and 57.60 %.According to the cluster analysis and KEGG enrichment,the key genes related to the browning were screened.The three genes of PAL,POD and PPO were selected as the next research object.Under the slowly cooling treatment,the PAL gene and POD gene both up-regulated and down-regulated,PPO genes were up-regulated.3.By NCBI,the pear fruit has two named PAL gene family members,namely pb PAL1?accession number: GU906268.1?and pb PAL2?accession number: GU906269.1?;PPO gene family members also have two,respectively,pb PPO1?Accession number: JQ320275.1?and pb PPO2?accession number: HQ729709.2?;POD gene only one,named pb POD?accession number: JQ325052.1?.The slowly cooling treatment induced the up-regulation of the two member genes in the PAL gene family,and increased the expression of PPO1 gene,but promoted the down-regulation of POD gene,leading to the increase of PAL and PPO activity and the accelerated inactivation rate of POD.However,the expression of PAL gene was inhibited by the rapidly cooling treatment,and the PAL activity was reduced.The PPO gene expression was inhibited,and the activity of PPO was tardily increased.The higher expression of POD gene was maintained volume,so that POD activity at a high level.Indicating that the slowly cooling treatment resulted in core browning by regulating PAL,PPO gene up-regulated expression and POD gene down-regulated expression.The rapidly cooling was the opposite.