Potato Tuber Formation Mechanism And Its Response Tocultivars And Nitrogen Content

Potted experiment was performed with Jizhangshu 12(J12)and Youjia 70(Y70)potato cultivars.The tuberization and growth mechanism of potato under natural conditions was understood initially by systematically studying the variation of plant morphological,dry matter content,carbon-nitrogen metabolism,mineral elements content,hormone content,and the differences in gene expression in the process of tuber formation.The effects of nitrogen content and different nitrogen efficiency varieties on the formation of tubers were also studied.It is expected to provide theoretical basis for increasing potato production efficiently and promote the development of potato industry.The main results were as follows:1.Effects of different nitrogen efficiency varieties on tuberization and growth of potato(1)Compared with Y70 which is a nitrogen low-efficient cultivar,the same ripening period cultivar J12 which is a nitrogen-efficient cultivar formed tubers earlier,and the duration of tuber formation period of J12 was shorter,but the duration of the tuber expansion period of J12 was longer.(2)During tuberization and growth of potato,comparing with Y70,J12 which is a nitrogen-efficient cultivar had higher stem,root,stolon,tuber dry matter accumulation and root-shoot ratio.J12 had a higher distribution rate of underground dry matter,while Y70 has a higher distribution rate of above-ground dry matter.Compared with Y70,J12 contained higher starch,sucrose,glucose,fructose content,AI,NI,SS activity and S/N ratio in stolon during tuber induction period(the stage of S1-S2);J12 had sucrose,glucose and fructose content in tuber during tuber formation period(the stage of S2-S4);glucose and fructose content in J12 were lower,but the starch and sucrose content in J12 were higher in tuber during tuber fexpansion period(the stage of S4-S5).Therefore a higher sucrose,glucose and fructose content in stolons or tubers were beneficial to tubers occurrenced and formed early.2.Effect of nitrogen content on tuberization and growth of potato(1)Low nitrogen(6 mmol/L)promoted the early occurrence of tubers and shortened the duration of tuber formation,while high nitrogen(24 mmol/L)delayed the occurrence of tubers and prolonged the duration of tuber formation.(2)High nitrogen promoted the stem,leaf and plant dry matter accumulation in stolon elongating stage,inhibited the accumulation of tuber dry matter accumulation significantly in the period of tuber formation;promoted the accumulation of stem dry matter,but significantly inhibited the accumulation of tuber dry matter in the period of tuber expansion.Low nitrogen inhibited the accumulation of the stem,leaf,plant dry matter and growth of plant height,while improved the accumulation of the stem during the period of tuberization and growth of potato during tuberization and growth of potato.During tuberization and growth of potato,high nitrogen was beneficial to distribute dry matter to the stem and leaf in above-ground,reducing the shoot-root ratio,while the low nitrogen dry matter was distributed friendly to the roots and stolons or tubers in underground,increasing the shoot-root ratio.High nitrogen reduced the content of sucrose in leaf in stolon elongating and the tuber formation period,and decreased sucrose content,while improved the activities of AI,NI,SS,SPS in the leaf during tuberization and development.Low nitrogen increased sucrose content of leaf in stolon elongating and the pre-stage tuber formation period,improved the sucrose content of tuber in stolon elongating and the pre-stage tuber expansion period,but decreased the sucrose content of tuber in late stage tuber expansion period,and reduces the activities of AI,NI,SS,SPS in leaf during potato tuberization and growth.High nitrogen reduced the NC/N ratio,in contrast,low nitrogen increased the NC/N in leaf and stolon or tuber during tuberization and growth.High nitrogen and low nitrogen conditions cause the imbalance of carbon-nitrogen ratio in plants to affect the distribution of carbohydrates,which in turn affects potato tuberization and growth.3.Under potted condition,the duration of tuber formation period(9?17 d)was much shorter than tuber expansion period(32?42 d).Except leaf and root,the dry matter of other organs increased rapidly during the tuber induction period.The accumulation of organs dry matter increased slowly during tuber formation period excepting leaf matter increased rapidly in late stage of tuber formation period.In the tuber expansion period,excepting the stolon in late stage of tuber expansion period,the dry matter of other organs increased rapidly.The stolon elongating period is the slow growth period of potato plant,and the pre-stage tuber formation period is the period of stagnation,and late stage tuber formation period and expansion period is the rapid growth period.4.During tuber induction period,the glucose,fructose and starch content in leaf and stolon changed in reverse,in which glucose content in leaf and fructose and starch content in stolon increased,while glucose content in stolon and fructose and starch content in leaf decreased.sucrose content reduced significantly,however AI,NI,SS,SPS activity in both leaf and stolon during tuber induction period.The process of diameter from the stolon subapical swelling to the tuber reached 3.0 cm,namely tuber formation period.The starch content and SPS activity in leaf significantly fluctuated falling first and rising later;oppositely glucose content significantly rised first and falled later;SS activity increased significantly;fructose,sucrose content,AI,NI activity increased slowly in leaf.Meanwhile,starch,sucrose,fructose,glucose content and SPS activity firstly decreased and then rose,among which the content of starch,sucrose,fructose and glucose showed a significant fluctuation;AI,NI and SS activity generally rised first and falled later in tuber.After the morphogenesis of tubers is completed(when tuber diameter is 3.0-6.0 cm,namely the stage of S4-S5),the substances in tuber supported tuber expansion in a relatively balanced state.During tuber induction period,glucose/fructose ratio in stolon decreased by 44.8%,while in leaf increased by 135.3%,and flowing tuber swelled,the ratio of glucose/fructose in the leaf and the stolon gradually decreased,and the decrease in leaf had a larger amplitude.There was a higher NC/N ratio in the stolons in the stolon hook period,before tuberization,during stolon subapical swelling,the ratio of NC/N in stolons decreased gradually.The trend of S/N was highly consistent with NC/N in the process of potato tuberization and development.Therefore,The carbon-nitrogen metabolism and balance relationship between sugar and nitrogen is closely related to tuberization.5.SA,JA,IAA,ABA and GA had a moderation effect on potato tuberization.The content of SA,JA,IAA,ABA,GAi,GA3 decreased in tuber during tuber induction period,and change were reached significantness except the ABA;then the content of SA,GA3 and ABA in tuber significantly fluctuated,while JA,IAA and GA1 content decreased,and reached the significant level at S3 point.During tuberization and growth,GA1/ABA,GA3/ABA,(GA1+GA3)/ABA,IAA/ABA ratio in stolon or tuber decreased significantly to S3 point,then the ratio changed smoothly.6.Mg,K,Ca,and Fe were all involved in the potato tuber induction process.Mg and Ca content significantly reduced,while K,Fe and Mn content significantly increased in stolon during tuber induction period,and then the content of Mg,K,Ca and Fe in tuber showed significant fluctuation,while the content of Mn was continuing to rise significantly.7.Through transcriptomics analysis,there were 115,1290,and 3541 different genes in S2vsS1,S3vsS2,S4vsS3 comparison groups respectively.There are 18 different genes in common,which mainly associated with heat shock protein(DnaJ,Hsp40,Hsp20),extensin domain,BAG domain,ribosome hibernation promoting factor(S30EA ribosomal protein and Sigma 54 modulation),regulator of chromosome condensation and signal transduction response regulator.8.According to analysis of the top 50 GO terms in comparison groups respectively,the differential genes concentrated GO semantics in S2vsS1 contrast group were mainly related to response to heat,glycine metabolic process,oxidation-reduction process,plant-type cell wall organization,GDP-mannose biosynthetic process,serine family amino acid catabolic process,nucleobase-containing compound biosynthetic process,peptidase regulator activity,nodulation,sequence-specific DNA binding.The differential gene concentrated GO semantics in S3vsS2 contrast group were mainly related to oxidation reduction process,photosynthesis,phenylpropanoid metabolic process,lignin catabolic process,regulation of peptidase activity,cell wall organization or biogenesis,photosystem and thylakoid part,oxidoreductase activity.The differential gene concentrated GO semantics in S4vsS3 contrast group were mainly related to oxidation-reduction process,microtubule-based movement,phenylpropanoid metabolic process,response to cytokinin,cell cycle process,chloroplast,plastid part,apoplast,microtubule binding,cytoskeletal protein binding,carbohydrate binding.9.Through the analysis of KEGG of differential expression genes,there were 60 different genes concentrated to 22 KEGG pathways in S2vsS1,in which only the pathway of protein processing in endoplasmic reticulum was significantly enriched and contained the largest number of different expression genes.There were 656 different gene concentrated to 90 KEGG pathways in S3vsS2,in which the pathway of photosynthesis,cutin,suberine and wax biosynthesis,phenylpropanoid biosynthesis,phenylalanine metabolism,starch and sucrose metabolism were significantly enriched.There were 1803 different gene concentrated to 114 KEGG pathways in S4vsS3,in which the pathway of cysteine and methionine metabolism,phenylpropanoid biosynthesis,plant hormone signal transduction,starch and sucrose metabolism had more number of different expression genes.There are 7 pathway of KEGG in common in S2vsS1,S3vsS2 and S4vsS3 contrast groups,which include plant hormone signal transduction,dierpenoid biosynthesis,fructose and mannose metabolism,carotenoid biosynthesis,zeatin biosynthesis and protein processingin endoplasmic reticulum,phenylpropanoid biosynthesis.