Physiological And Molecular Mechanism Of Solanum Tuberosum L.in Response To Cadmium Stress

With the rapid economic and social development,various industrial and domestic waste emission have increased,coupled with the excessive application of chemical fertilizers and pesticides in agricultural production,which has led to a series of soil environmental problems.The pollution of heavy metal cadmium（Cd）is one of the most prominent ones,which has posed a serious threat to crop production and human health.As the leading’food and vegetable’crop,the healthy development of the potato industry is central to food security in China and globally.Currently,the response mechanism of potato to Cd stress is not clear,and the means to alleviate its stress are lacking.Therefore,various physiological and biochemical indicators,yield and quality of potato under Cd stress were comprehensively investigated so as to clarify the response pattern of physiological and biochemical characteristics.In addition,the molecular mechanism of potato response to Cd stress at the RNA level were studied based on transcriptome sequencing,bioinformatics and plant genetic transformation to further explore the underlying mechanisms in more depth.The main findings are as follows:1.Potato growth was inhibited by Cd stress,and the height and stem thickness were significantly lower than that of control under high Cd treatment.The antioxidant system of potato functioned after Cd treatment.The activities of SOD and POD increased with the increase of Cd concentration.Proline began to accumulate substantially,and glutathione content increased significantly when Cd concentration was greater than 500μmol/L.The photosynthetic system was also severely affected by Cd stress,Net photosynthetic rate,stomatal conductance and transpiration rate decreased with increasing Cd concentration,while intercellular CO₂ concentration continued to increase.The initial fluorescence was significantly higher under high Cd concentration,but dark-adapted maximum fluorescence,variable fluorescence and PSII maximum photochemical quantity decreased with increasing treatment concentrations.The content of relative chlorophyll was significantly reduced at Cd concentrations greater than 500μmol/L.Leaf ultrastructure observations also showed that the cells underwent plastid wall deparation,chloroplasts were damaged and basal lamellae became lax under high Cd concentration treatment.The contents of auxin and zeatin decreased,but salicylic acid,jasmonic acid and abscisic acid increased significantly after treatment.Lignin content in the root continued to accumulate after Cd treatment,while the content of organic acids secreted by roots varied differently,and the overall trend was accumulated with the increase of Cd concentration.2.Potato yield and yield components were greatly affected by Cd stress,especially at high Cd concentrations.When the Cd concentration was greater than 1000μmol/L,the large tuber rate was 0,the small tuber rate increased significantly,the rotten tuber rate was higher and the commercial tuber rate decreased significantly.After Cd stress,the quality of potato tubers deteriorated,and the contents of starch,soluble protein and vitamin C decreased significantly at Cd concentrations greater than 500μmol/L.3.With the extension of Cd stress,potato leaves gradually wilted and curled,and the contents of SA,GSH,lignin and POD activities in roots increased,while the contents of IAA and ZT gradually decreased.161 existing mi RNAs,383 known mi RNAs and 7361 new mi RNAs were identified by mi RNA-seq.Among them,18 mi RNAs were differentially expressed in response to Cd stress.7340 differentially expressed m RNAs were also screened based on m RNA-seq.Moreover,a mi RNA-target gene regulatory network consisting of 23differential m RNAs and 33 mi RNAs was constructed by mi RNA-m RNA association analysis.In addition,’glutathione metabolism’,’plant hormone signal transduction’and’phenylpropanoid biosynthesis’were found to play important roles in response to Cd stress in potato.For the first time,novel-m3483-5p was found to function in the’phenylpropanoid biosynthesis’pathway by targeting and regulating an m RNA encoding CAD.4.The key gene St CAD3 was screened out through preliminary data analysis,and the family analysis of St CAD3 was performed.The q RT-PCR analysis showed that Cd could induce the expression of St CADs,and the up-regulation of St CAD3 was the highest.Compared with wild-type Arabidopsis thaliana,the CAD content of transgenic St CAD3Arabidopsis plants was significantly higher than that of wild type after 48 h Cd treatment.The contents of POD,lignin and glutathione of transgenic St CAD3 Arabidopsis plants were significantly higher than those of wild type after 96 h Cd stress.5.After using glutathione to alleviate potato under Cd stress,the expression of PAL,CAD and POD genes increased,and the activities of PAL,CAD and POD enzyme were elevated.The lignin content significantly increased and was positively correlated with the expression of genes PG0031457,PG0005359,PG0011640 and PG0015106.In addition,both SA and JA contents were significantly increased,genes encoding TGA and PR1 were up-regulated but JAZ genes were down-regulated.Meanwhile,IAA contents were significantly decreased,AUX and ARF-related genes were down-regulated and transcriptional repressor Aux/IAA genes were up-regulated.