Stimulus-responsive mechanism of salt-responsive polymer and its application in saturated saltwater drilling fluid

AM-AMPS-TAC polymers with different charge distribution are synthesized using acrylamide(AM),2-acrylamido-2-methylpropanesulfonate(AMPS)and 3-acrylamidopropyl trimethylammonium(TAC)at different feed ratios by polymerization in solution.The salt-responsive behavior,reasons leading to salt-responsiveness,and effects of polymers molecular structure on salt-responsiveness are studied by laboratory experiments to find out the adaptability of the polymers.Rheology test under stepwise shear mode shows that the AM-AMPS-TAC polymers have salt responsiveness,and the closer the feeds of AMPS and ATC,the more significant the salt responsiveness will be.Conformation change of polymers molecular chain under salt stimulus is studied by turbidity test and micro-morphology analysis,and the responsive mechanism is further investigated by intrinsic viscosity test and copolymer composition analysis.Results indicate that the salt-responsive behavior of AM-AMPS-TAC polymers derives from the"curled to expanded"transition of chain conformation under salt stimulus,and this transition is led by the screening effect of salt which weakens polymers intramolecular ionic bond.Application in saturated saltwater drilling fluid shows that the AM90-AMPS5-TAC5 polymer has the best salt-tolerance and temperature-tolerance when used together with fluid loss controller PAC-Lv.The drilling fluid saturated with NaCl can maintain stable viscosity,good dispersion and low fluid loss for long time under 150℃.

A saturated saltwater drilling fluid based on salt-responsive polyampholytes

Based on special antipolyelectrolyte effect of zwitterion polymer with same quantity of anionic and cationic charges, we developed two types of salt-responsive polyampholytes, one with high molecular weight and low charge density(HvL) and the other with low molecular weight and high charge density(LvH), by inverse emulsion polymerization. Molecular structure and salt-responsiveness of them were characterized by 1 H-NMR and rheology measurement, respectively. HvL and LvH were evaluated in saturated-salt bentonite suspension and influences of their ratio on apparent viscosity and fluid loss were investigated as well. The results indicate that HvL is better at decreasing fluid loss while LvH is better at maintaining low viscosity. A saturated saltwater drilling fluid centering on HvL and Lv H with simple formula was designed and applied. It is indicated that salt-responsive polyampholytes are fundamentally better than AM-AMPS anionic copolymer and AM-AMPS-DMDAAC amphoteric copolymer. The saturated saltwater drilling fluid has excellent thermal stability, tolerance to bentonite and shale cuttings, and certain resistance to CaCl_2. Salt-responsive polyampholytes can be used in KCl-saturated drilling fluid, with universal adaptability.

Molecular cloning, expression analysis and chromosomal mapping of salt-responsive cDNAs in rice (Oryza sativa L.)

By using differential display PCR (DD-PCR) technique, two salt-inducible and one salt-repressed cDNA fragments were isolated from rice. The three cDNA fragments were characterized respectively as partial sequence of rice S-adenosylmethionine decarboxylase (SAMDC) gene, a new member of translation elongation factor lA gene (named REF1A), and a novel gene whose function is unknown (named SRG1). The full-length cDNA of SAMDC gene (named SAMDC1) was further isolated by RT-PCR approach and the deduced polypeptide was found to be homologous to SAMDC proteins of other plants, yeast and human. Northern hybridization revealed that expression of SAMDC1 and REF1A was induced, while SRG1 was dramatically repressed, by salinity stress. Southern blot analysis demonstrated that SAMDC 1 and SRG1 were present as a single copy gene in rice genome, whereas rice REF1A gene was organized as a gene family. The REF1A, SAMDC1, and SRG1 genes were located on chromosome 3,4, and 6 respectively by RFLP mapping approach using ZYQ8/JX17 DH population and RFLP linkage maps.

Comparative Transcriptome Analysis of Salt-Stress-Responsive Genes in Rice Roots

Soil salinity greatly impairs plant growth and crop productivity.Rice(Oryza sativa L.)is a salt-sensitive crop.To better understand the molecular mechanisms of salt tolerance in roots,the BGISEQ-500 sequencing platform was employed to elucidate transcriptome changes in rice roots after 0,3,24,and 72 h of salt stress.The results showed that root K+content decreased and Na+content increased rapidly after the initial stage of salt stress,but that fresh and dry weight in root did not significantly reduce.Compared to the control(no salt stress),1,292,453,and 486 differentially expressed genes(DEGs)were upregulated,respectively,and 939,894,and 646 DEGs were downregulated,respectively,after 3,24,and 72 h of salt treatment.The number of DEGs was higher during the early stage of salt stress(3 h)than in later stages(24 and 72 h).A number of DEGs involved in the response and adaptation to salt stress were related to protein kinase and calcium-binding,plant hormone signaling and metabolism,transcriptional regulation,metabolic pathways,antioxidant activity,and ion transport.Many of these DEGs were activated during the early stage of salt stress(3 h).The present study reports candidate salt-stressresponsive genes with the potential to genetically improve salt tolerance in rice elsewhere.