NaCl Induction Research Articles

NaCl-Induced Alterations in Both Cell Structure and Tissue-Specific Plasma Membrane H+ -ATPase Gene Expression.

NaCl-induced plasma membrane H+-ATPase gene expression, which occurs in roots and fully expanded leaves of the halophyte Atriplex nummularia L. (X. Niu, M.L. Narasimhan, R.A. Salzman, R.A. Bressan, P.M. Hasegawa [1993] Plant Physiol 103: 713-718), has been differentially localized to specific tissues using in situ RNA hybridization techniques. Twenty-four-hour exposure of plants to 400 mM NaCl resulted in substantial accumulation of H+ pump message in the epidermis of the root tip and the endodermis of the root elongation/differentiation zone. In expanded leaves, NaCl induction of plasma membrane H+-ATPase message accumulation was localized to bundle-sheath cells. Ultrastructural analyses indicated that significant cytological adaptations in root cells included plasmolysis that is accompanied by plasma membrane invaginations, formation of Hechtian strands and vesiculation, and vacuolation. These results identify specific tissues that are involved in the regulation of Na+ and Cl- uptake into different organs of the halophyte A. nummularia and provide evidence of the intercellular and interorgan coordination that occurs in the mediation of NaCl adaptation.

Acid sensitivity as affected by physico-chemical stresses in Aeromonas hydrophila.

This work focuses mainly on the effect of NaCl along with other mono and divalent anions and cations at pH 4 on survival and virulence properties of Aeromonas hydrophila. To find the optimum stress condition, effects of several other physical factors on NaCl induction were also assayed. A. hydrophila collected from International Center for Diarrheal Disease Research, Bangladesh (ICDDR,B) was found to be more sensitive to pH 4.0 when grown in media containing 200 mM or more salt. Induction of acid sensitivity was rapidly gained in NaCl-supplemented broth at 37 C. There was only slight sensitization after 5 min, but a marked effect was observed within 30 min. Uninduced A. hydrophila gave an average of 40% survival after exposure to pH 4.0 for 5 min. However, NaCl-induced cells of this organism reduced the survival to a great extent having an average of 0.06%. Either increase in salt concentration (100 mM through 400 mM) or decrease (50 mM) resulted in decrease in percent survival when exposed to gradually increased concentrations of salt. The most effective dose for induction was 400 mM NaCl salt. NaCl-induction was found to be more pronounced in log-phase organisms. All other monovalent and divalent anions and cations tested were almost as effective as NaCl except KCl.

Genetic Variability in Recovery Growth and Synthesis of Stress Proteins in Response to Polyethylene Glycol and Salt Stress in Finger Millet

Marked differences were found among 28 finger millet genotypes (Eleusine coracana Gaertn.) in acquired tolerance to osmotic stress as assessed by the recovery of root growth from severe stress [-1·2 MPa polyethylene glycol, (PEG) or 400 mM NaCl]. However, these differences in tolerance were observed only when the seedlings were subjected to a preceding mild induction stress (-0·6 MPa PEG or 200 mM NaCl). In two contrasting genotypes, synthesis of stress-induced proteins was studied. Proteins with apparent molecular weight of 70-72, 52, 37, 34 and 23 kDa were synthesized in the highly responsive genotype (GE 415) and poorly responsive (VL 481) genotype following a mild induction stress (200 mM NaCl). However, GE-415 synthesized a 54 kDa protein that was not observed in VL-481. Addition of abscisic acid (ABA) to the induction medium containing 200 mM NaCl enhanced the acquired tolerance of finger millet seedlings over those without ABA in association with the appearance of several ABA-responsive proteins. GE-415 required much less ABA than VL-481 to obtain the same response. With 10 μM ABA + 200 mM, A NaCl induction stress, GE-415 had significantly higher endogenous ABA. In association with higher levels of ABA, GE-415 had greater recovery root growth following severe stress from 600 mM NaCl. Pretreatment with 10 μM ABA + 200 mM NaCl induced several proteins with apparent molecular weights of 70-72, 54, 45, 36, 29 and 21 kDa in both genotypes. Qualitatively, GE-415 synthesized a unique 23-24 kDa protein and quantitatively there was significantly more of the 21 kDa protein in GE-415 compared to VL-481. The results indicate that the synthesis of stress proteins is correlated with the observed variation in acquired tolerance of the two genotypes.

Control of osmotin gene expression by ABA and osmotic stress in vegetative tissues of wild‐type and ABA‐deficient mutants of tomato

Osmotin gene expression and protein synthesis were up‐regulated in young tomato (Lycopersicon esculentum cv. Rheinlands Ruhm) plants after a short exposure (24 h) to 150 mM NaCl or 100 μM abscisic acid (ABA) or after dehydration to 80% of original plant fresh weight. Osmotically induced accumulation of osmotin mRNA was accompanied by a large increase in endogenous ABA levels. Increasing accumulation of osmotin protein was also observed during a longer exposure (7 days) to salt. Upon treatment with NaCl. osmotin mRNA levels increased in both root and leaf tissues. with an additional longer transcript induced in roots. No induction of osmotin mRNA was observed upon salt or water stress of the tomato ABA‐deficient mutant sitiens. Treatment of sitiens with exogenous ABA induced osmotin mRNA accumulation to the level normally found in salt‐treated wild‐type plants. However, salt stress alone enhanced accumulation of osmotin mRNA in plants of another tomato mutant (flacca) which is also impaired in ABA synthesis. In tobacco plants carrying an osmotin promoter/β‐glucuronidase (GUS) fusion gene, NaCl induction of GUS could be only partially blocked by the ABA inhibitor fluoridone. In flacca plants simultaneous treatment with NaCl and ABA resulted in higher levels of osmotin transcript compared to those following treatment with NaCl alone. No accumulation of osmotin protein was observed after short‐ or long‐term osmotic treatments of the mutants. Our results support previous evidence that osmotin gene expression may be triggered in part through ABA and in part through a separate pathway of gene activation.

An algD-bioluminescent reporter plasmid to monitor alginate production in biofilms

A broad-host range algD-lux bioluminescent reporter plasmid was developed to examine the role of exopolymer production in biofilm function. The algD-lux reporter plasmid will allow rapid on-line in situ detection of environmental factors that induce alginate biosynthesis. The algD promoter was stimulated by factors previously reported to induce alginate production, including ethanol and NaCl, and differences were observed with different nitrogen sources. With growth on minimal media with either glucose or succinate as a carbon source, succinate had a greater inductive effect on the algD promoter. An increase in light output of 1.3-fold and 1.7-fold was seen with cultures amended with 50 and 150 mM NaCI, respectively, compared to cultures with succinate alone. NaCl induction of the algD promoter was confirmed by algD RNA slot blots. Light output increased 2.0-fold and 1.7-fold with 0.25% and 0.5% ethanol, respectively, compared with controls grown with succinate only. While the rate of algD promoter response was initially similar when either NH4 or NO3 was used as a nitrogen source, NH4-grown cultures maintained a higher light output during late log phase compared to NO3-grown cultures.

Growth cycle stage‐dependent NaCl induction of plasma membrane H+‐ATPase mRNA accumulation in de‐adapted tobacco cells

ABSTRACTA cDNA clone encoding an isoform of the plasma membrane H+‐ATPase was isolated from Nicotiana tabacum. The steady‐state plasma membrane H+‐ATPase message levels were the same in unadapted tobacco cells and tobacco cells adapted to 428 mol m−3 NaCl. When cells adapted to 428 mol m−3 NaCl maintained in the absence of NaCl (deadapted) for an excess of 100 passages were exposed to 400 mol m−3 NaCl for 24 h, there was an increased accumulation of plasma membrane H+‐ATPase message. The NaCl responsiveness of the deadapted cells was dependent upon the growth cycle stage. Alterations in the levels of plasma membrane FT‐ATPase message during the growth cycle support a role for the H+‐ATPase in cell growth. These results document the induction by NaCl of plasma membrane FT‐ATPase message accumulation in tobacco cells, and suggest that enhanced expression of the plasma membrane FT‐ATPase has a role in the short term response of cells of NaCl, but is not necessarily involved in long‐term adaptation.