Ionome Response Characteristics And Ion Homeostatic Mechanism Of Cotton Under Different Salt Stresses

?Object?In this study we investigated the ionome response characteristics of cotton under different saline-alkali stress?NaCl?Na₂SO₄ and NaHCO₃+Na₂CO₃?.To explored the relationship between cotton ionome and physiological metabolism.Elucidation of the molecular mechanism of Na⁺transport in different salt-tolerant varieties?genotypes?cottons.Reveal the mechanism of cotton ion homeostasis under different saline-alkali stresses initially from the perspective of transcriptomics.Provide theoretical basis for ion regulation and rational fertilization of cotton in saline soil.At the same time,it also provides a reference for the breeding of cotton salt-tolerant varieties.?Method?This study consists of three experiments:seed germination experiment,pot experiment and soil column experiment.The seed germination experiment was conducted in2015.Three types of salt were set up in the experiment:NaCl,Na₂SO₄,Na₂CO₃+NaHCO₃,set five solution concentration levels for each type of salt-alkaline stress,and treated with distilled water as control?CK?.Choose 6 varieties of cotton as follow:X45,X61,L24,L28,Z43,and Z49.Each treatment was repeated four times.Germination experiment mainly discusses the effect of saline-alkali stress on cotton seed germination.Pot experiment was conducted in 2016,the cotton varieties and salt types tested were consistent with the germination test.The amount of salt added to the soil treated in NaCl was set 5 levels:0,0.1%,0.2%,0.3%,and 0.4%?accounting for dry soil weight?and Na2SO4stress was:0,0.1%,0.3%,0.5%,and 0.7%.The pH of the soil solution treated with alkaline salt?Na₂CO₃:NaHCO₃=1:1?was 7.8,8.5,8.7,9.0,9.5?the corresponding soil addition amount was 0,0.10%,0.15%,0.20%,0.25%,0.33%respectively?.Each treatment was repeated four times.This experiment mainly discussed the effects of different saline-alkali stress on cotton growth and physiological.Comparing the differences response of different cotton varies to three types of saline and alkali stress.Screen out a resistant variety and a salt-sensitive variety on this basis,lay the foundation for future research.Soil column experiment was conducted in 2017,two cotton varieties?salt-tolerant and salt-sensitive?and three types of salt treatment?NaCl?Na₂SO₄?Na₂CO₃+NaHCO₃?was chosen.Three soil salt and alkalization levels are set as follow:non-salted soil?CK?,slight salt?alkali?,moderate salt?alkali?.Each treatment was repeated six times.This part mainly studied the changes of ionome in cotton plants under different saline-alkali stress.To explored the relationships between elements and elements,elements and salt resistance physiological in cotton under salt stress.To revealed the ionome response characteristics,and combined with transcriptome to determine the ion balance mechanism of cotton in response to different saline-alkali stress.?Result??1?The germination coefficient,average germination rate,relative germination index,relative germination potential and relative germination rate of six cotton cultivars were all decrease with the increased concentration of saline and alkali stresses.The stress of Na2SO4 on seed germination is more serious than that of NaCl at the same molar concentration.The seeds no longer germinate when pH=10.47 under Na2CO3+NaHCO3 stress.The membership function analysis showed that the dominant species under the stress of NaCl and Na₂CO₃+NaHCO₃ was L24.Under the Na₂SO₄ stress,the dominant variety is Z92,and followed by L24.Z73 was most inhibited among the six varieties under NaCl stress;X61 was most inhibited under Na₂SO₄ and Na₂CO₃+NaHCO₃ stress.?2?With the increase of saline-alkali concentration,the emergence rate,plant height and of six cotton varieties were decreased,L24 had the highest seedling rate,plant height and relative biomass among the six varieties,and X45 was the lowest.The chlorophyll content decreased with the increase of NaCl and Na2CO3+NaHCO3 stress.However,low concentration of Na2SO4 stress increases chlorophyll content.Both REC and MDA increased with the increase of salt-alkali stress.The increase in REC is expressed as:NaCl>Na₂SO₄>Na₂CO₃+NaHCO₃,the increase of MDA is:Na₂CO₃+NaHCO₃>Na₂SO₄>NaCl.Therefore,the damage caused by Na₂SO₄ and NaCl stress on cotton is mainly osmotic stress,and Na₂CO₃+NaHCO₃ are oxidative stress.The activity of SOD increased with the increase of NaCl and Na₂CO₃+NaHCO₃ stress,but it increased first and then decreased with the increase of Na2SO4 stress.Saline-alkali stress increased Pro content in cotton leaves,but under high NaCl stress,Pro content was lower than control.The GB content of cotton leaves increased first and then decreased with the increase of salt-alkali stress.Under the salt-alkali stress,L24has the highest activity of SOD,POD,CAT and Pro content among the six varieties.According to the analysis of membership function,L24 has good tolerance to salt-alkali stress and is a salt-tolerant variety,X45 is most inhibited under salt-alkali stress and is a salt-sensitive variety.?3?Saline-alkali stress significantly reduced cotton biomass,but the inhibition of cotton growth by salt stress and alkali stress had different performances in the aboveground and below ground.Salt stress?NaCl and Na2SO4?is mainly inhibit shoot growth at low concentrations,high concentration stress inhibited the growth of shoots and roots significantly.However,alkali stress can inhibit the growth of cotton below and above ground regardless of low concentration or high concentration.This indicates that cotton roots are more sensitive to alkaline stress.According to the above experimental results,the salt-tolerant cotton variety L24 and the saline-alkali sensitive variety X45 were obtained.The ionome characteristics of these two cottons under salt-alkaline stress were analyzed.Under salt-alkali stress,the concentration of Na in cotton roots and leaves increased significantly.NaCl stress reduced the concentration of K,Cu,B,and Mo in cotton roots,and Mg and S in leaves.Na₂SO₄ stress reduces the concentration of K,Ca,Cu,B,and Mo in roots and Ca in leaves.Alkali?Na₂CO₃+NaHCO₃?stress reduced the concentration of K,Ca,S,Cu,B,and Mo in roots and Ca,Mg,S,Mo in leaves.Compared with neutral salt stress,alkali stress reduces more elements'concentration.Salt stress only reduces few elements in the tissue but more is to change the distribution,transport and balance of elements.The three elements K,Cu and B are transported to the leaves under salt-alkali stress,which may be one of the strategies of cotton to resist salt-alkali stress.Na₂SO₄(due to the large amount of SO₄^2-)and alkali stress can lead to the lack of Ca in cotton.Synthesis of three salt stresses,salt-tolerant variety L24 will maintain a high K content in the root system,but transported more Na to the shoot and stored in the leaves.In addition,L24 have a stronger mineral transport capacity and it will transport most of the elements to the leaves.?4?The expression of Na⁺regulatory genes?GhSOS1,GhNHX1,GhHKT and GhAKT1?in cotton leaves under neutral salt stress was greater than that under alkaline stress?except for GhAKT1 expression in L24?.However,in roots,the expression levels of GhSOS1 and GhNHX1 are not different between salt and alkali.The expression levels of GhHKT and GhAKT1 consistent with leaves were slightly higher than alkali stress in salt stress.The expression of Na⁺regulatory genes was similar under two neutral salt stresses.Comparing the two varieties,the Na⁺partitioning ability of the L24 is stronger than that of the X45,and the Na⁺efflux ability of the X45 is stronger than that of the L24.?5?The transcriptome profiles of Salt-tolerant cotton variety L24 and salt-sensitive cotton variety X45 were analyzed by Illumina deep-sequencing.A total of 36.12 Gb of pure data was obtained,and the purity data of each sample reached 6.02 Gb.Q30 base percentage is 85.00%and above.Comparison efficiency ranges from 76.19%to 83.11%.There were 807?303-up/504-down?differentially expressed genes in X45 and 382?197-up/185-down?in L24under NaCl stress.773?229-up/544-down?DEGs X45 and 194?99-up/95-down?DEGs in L24 under alkaline stress.We selected 18 differentially expressed genes for real-time quantitative PCR?qRT-PCR?analysis.The results are consistent with the trend of transcriptome?Illumina?sequencing results,indicating that the transcriptome sequencing results are reliable.Go enrichment analysis showed that the responses of the two varieties to saline-alkali stress were completely different,the main difference is reflected in the function of transport activity.Most of the genes involved in ion transport?ABC transporter,Eam-like transporter family,POT family et al.?are up-regulated in L24 and down-regulated or not in X45 both in salt stress and in alkaline stress.And these genes are up-regulated in salt stress more than alkaline stress.The result showed that L24 is more capable of ion transport than X45,Alkaline stress has a greater impact on ion transport than salt stress.?Conclusion?Saline-alkali stress reduced cotton germination rate,emergence rate,plant height and biomass.Neutral salt stress?NaCl and Na₂SO₄?inhibits shoot growth at low concentrations,and root growth is affected when the concentration reaches a high level.However,alkali stress can inhibit the growth of cotton below and above ground regardless of low concentration or high concentration.The main hazard of Na2SO4 and NaCl on cotton is osmotic stress,Na2CO3+NaHCO3 mainly produce oxidative stress.Compared with neutral salt stress,alkali stress inhibits and reduces more elements.Salt stress only reduces few elements in the tissue but more is to change the distribution,transport and balance of elements.Different varieties of cotton have different salt tolerance mechanism.The salt-tolerant variety L24 used in this paper has a higher Na⁺partitioning capacity than the salt-sensitive variety X45,but the X45's Na⁺efflux ability is stronger than the L24.Regardless of neutral salt stress or alkali stress,cotton maintains the ion homeostasis in leaves as the main salt tolerance mechanism.Na⁺compartmentalization in vacuoles and the transport of more mineral elements to the shoots are important and effective salt tolerance mechanisms.