Absence Of Salt Stress Research Articles

Putrescine Transport in a Cyanobacterium Synechocystis sp. PCC 6803

The transport of putrescine into a moderately salt tolerant cyanobacterium Synechocystis sp. PCC 6803 was characterized by measuring the uptake of radioactively-labeled putrescine. Putrescine transport showed saturation kinetics with an apparent K(m) of 92 +/- 10 microM and V(max) of 0.33 +/- 0.05 nmol/min/mg protein. The transport of putrescine was pH-dependent with highest activity at pH 7.0. Strong inhibition of putrescine transport was caused by spermine and spermidine whereas only slight inhibition was observed by the addition of various amino acids. These results suggest that the transport system in Synechocystis sp. PCC 6803 is highly specific for polyamines. Putrescine transport is energy-dependent as evidenced by the inhibition by various metabolic inhibitors and ionophores. Slow growth was observed in cells grown under salt stress. Addition of low concentration of putrescine could restore growth almost to the level observed in the absence of salt stress. Upshift of the external osmolality generated by either NaCl or sorbitol caused an increased putrescine transport with an optimum 2-fold increase at 20 mosmol/kg. The stimulation of putrescine transport mediated by osmotic upshift was abolished in chloramphenicol-treated cells, suggesting possible involvement of an inducible transport system.

Functional analysis of CHX21: a putative sodium transporter in Arabidopsis

The functional role of CHX21, a member of the Arabidopsis thaliana CHX cation transporter family, has been investigated in plants growing under "ideal" conditions and in the presence of elevated NaCl levels. In public databases, AtCHX21 (At2g31910) is annotated as a putative Na+/H+ antiporter. In this study, Southern analysis was used to identify a genotype that contained a single transposon insertion within its genome; using PCR, this insertion was shown to be within the CHX21 locus. No CHX21 transcript was detectable in Atchx21 (mutant) plants using RT-PCR. In the absence of salt stress, Atchx21 showed significant quantitative differences from the wild type (AtCHX21) in development with respect to characters such as rosette width and flowering time. In the presence of 50 mM NaCl, (i) roots of Atchx21 elongated more slowly than the wild type, (ii) the leaf sap Na+ concentration was significantly lower in Atchx21 compared with the wild type, and (iii) the concentra) in the xylem was lower compared with the wild type. The concentration of Na+ exported from the leaf in the phloem was unchanged. Thus, loading of Na+ into the root xylem could explain changes in leaf concentration of Na+. This hypothesis was supported by immunolocalization which demonstrated that the AtCHX21 transporter could only be detected in root endodermal cells. Immunogold labelling of ultra-thin sections, followed by transmission electron microscopy, demonstrated the localization of the protein in the plasma membrane. The data demonstrate that the CHX21 transporter may play a role in regulation of xylem Na+ concentration and, consequently, Na+ accumulation in the leaf.

Salinity-induced ion flux patterns from the excised roots of Arabidopsis sos mutants

The SOS signal-transduction pathway is known to be important for ion homeostasis and salt tolerance in plants. However, there is a lack of in planta electrophysiological data about how the changes in signalling and ion transport activity are integrated at the cellular and tissue level. In this study, using the non-invasive ion flux MIFE technique, we compared net K+, H+ and Na+ fluxes from elongation and mature root zones of Arabidopsis wild type Columbia and sos mutants. Our results can be summarised as follows: (1) SOS mutations affect the function of the entire root, not just the root apex; (2) SOS signalling pathway is highly branched; (3) Na+ effects on SOS1 may by-pass the SOS2/SOS3 complex in the root apex; (4) SOS mutation affects H+ transport even in the absence of salt stress; (5) SOS1 mutation affects intracellular K+ homeostasis with a plasma membrane depolarisation-activated outward-rectifying K+ channel being a likely target; (6) H+ pump also may be a target of SOS signalling. We provide an improved model of SOS signalling and discuss physiological mechanisms underlying salt stress perception and signalling in plants. Our work shows that in planta studies are essential for understanding the functional genomics of plant salt tolerance.

Salt‐induced expression of peroxisome‐associated genes requires components of the ethylene, jasmonate and abscisic acid signalling pathways

ABSTRACTPeroxisomes participate in many biological functions including detoxification of reactive oxygen species and biosynthesis of oxylipin signalling molecules. Peroxisome protein and enzyme activities have been reported to change in response to salt stress. To investigate the relationship between peroxisomes and salt stress the level of expression of three peroxisome‐associated genes, thiolase (PED1), PEX10 and PEX1 was analysed by quantitative real‐time polymerase chain reaction. The steady‐state transcript level of all three genes was increased by salt and ABA treatment, and was blocked in the abi1‐1 mutant. Salt‐dependent increase of transcript for all three genes also required the JAR1 gene as it was prevented in the jar1‐1 mutant. Expression of thiolase, and to a lesser extent PEX1, was increased in the jar1‐1 mutant in the absence of salt, suggesting jasmonate may negatively regulate these genes in the absence of salt stress. PEX1 was up‐regulated in the ethylene over‐producer eto1‐1 and salt had an additive effect on PEX1 transcript level, but salt induction may be inhibited in the ethylene‐insensitive line etr1‐1. Consistent with this, PEX1 was also up‐regulated in transgenic plants over‐expressing the ethylene response element binding factors AtERF1 and AtERF5.

Thermoprotection of Bacillus subtilis by exogenously provided glycine betaine and structurally related compatible solutes: involvement of Opu transporters.

Bacillus subtilis possesses five osmotically regulated transporters (Opu) for the uptake of various compatible solutes for osmoprotective purposes. We have now found that compatible solutes also function as thermoprotectants for B. subtilis. Low concentrations of glycine betaine enhanced the growth of the B. subtilis wild-type strain JH642 at its maximal growth temperature (52 degrees C) but did not allow an extension of the upper growth limit. A similar enhancement in the growth of B. subtilis was also observed by the addition of several other compatible solutes that are structurally related to glycine betaine or by the addition of proline. Each of these compatible solutes was taken up under heat stress by the cell through the same Opu transporters that are used for their acquisition under osmostress conditions. Northern blot analysis revealed a moderate increase in transcription of the structural genes for each of the Opu transport systems in cells that were propagated at 52 degrees C. In contrast, the uptake level of radiolabeled glycine betaine was very low under high-temperature growth conditions but nevertheless allowed the buildup of an intracellular glycine betaine pool comparable to that found in cells grown at 37 degrees C in the absence of salt stress. Although exogenously added glutamate has only a limited osmoprotective potential for B. subtilis, it was found to be a very effective thermoprotectant. Collectively, our data demonstrate thermoprotection by a variety of compatible solutes in B. subtilis, thus ascribing a new physiological function for this class of compounds in this microorganism and broadening the physiological role of the known osmoprotectant uptake systems (Opu).

Improved tolerance of maize plants to salt stress by arbuscular mycorrhiza is related to higher accumulation of soluble sugars in roots.

The effect of colonization with the arbuscular mycorrhizal (AM) fungus Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe on the growth and physiology of NaCl-stressed maize plants ( Zea mays L. cv. Yedan 13) was examined in the greenhouse. Maize plants were grown in sand with 0 or 100 mM NaCl and at two phosphorus (P) (0.05 and 0.1 mM) levels for 34 days, following 34 days of non-saline pre-treatment. Mycorrhizal plants maintained higher root and shoot dry weights. Concentrations of chlorophyll, P and soluble sugars were higher than in non-mycorrhizal plants under given NaCl and P levels. Sodium concentration in roots or shoots was similar in mycorrhizal and non-mycorrhizal plants. Mycorrhizal plants had higher electrolyte concentrations in roots and lower electrolyte leakage from roots than non-mycorrhizal plants under given NaCl and P levels. Although plants in the low P plus AM fungus treatment and those with high P minus AM fungus had similar P concentrations, the mycorrhizal plants still had higher dry weights, soluble sugars and electrolyte concentrations in roots. Similar relationships were observed regardless of the presence or absence of salt stress. Higher soluble sugars and electrolyte concentrations in mycorrhizal plants suggested a higher osmoregulating capacity of these plants. Alleviation of salt stress of a host plant by AM colonization appears not to be a specific effect. Furthermore, higher requirement for carbohydrates by AM fungi induces higher soluble sugar accumulation in host root tissues, which is independent of improvement in plant P status and enhances resistance to salt-induced osmotic stress in the mycorrhizal plant.

Characterization of rice (Oryza sativa L.) F3 populations selected for salt resistance. I. Physiological behaviour during vegetative growth

Plants belonging to a somaclonal family (R3-1-23, obtained from a salt-resistant callus of the salt-sensitive cultivar I Kong Pao (IKP, salt-sensitive)) were crossed with this intital cultivar IKP or with plants of the elite breeding line IR31785 (IR31, extremely salt-sensitive). Two other crosses were also performed: IR31 × IKP and IKP × Aiwu, where Aiwu is a moderatly salt-resistant cultivar. The physiological behaviour of F3 populations was analysed after 21 and 42 days of exposure to 0 or 30 mM NaCl and compared to the behaviour of plants selected within parental populations. A clear improvement in terms of survival percentages was demonstrated for plants issued from IR31 × 1-23 and IR31 × IKP. These F3 populations exhibited lower Na accumulation in shoots, higher Ca accumulation in roots, higher ratios of shoot P/root P than the parents after 42 days of salt exposure. Salt stress induced a decrease of shoot K, an increase of shoot Cl and proline and a decrease of osmotic potential in all populations. Correlation analysis indicated that no physiological parameter recorded in the absence of salt stress may be used as a reliable selection marker to predict the plant behaviour in salt stress conditions. K/Na ratio recorded in the stressed plants was significantly correlated with surviving percentages recorded after 90 days of salt stress, suggesting that this physiological parameter in stress conditions appears to be the most reliable selection criterion for salt resistance in rice.

A new genetic locus in sinorhizobium meliloti is involved in stachydrine utilization

Stachydrine, a betaine released by germinating alfalfa seeds, functions as an inducer of nodulation genes, a catabolite, and an osmoprotectant in Sinorhizobium meliloti. Two stachydrine-inducible genes were found in S. meliloti 1021 by mutation with a Tn5-luxAB promoter probe. Both mutant strains (S10 and S11) formed effective alfalfa root nodules, but neither grew on stachydrine as the sole carbon and nitrogen source. When grown in the absence or presence of salt stress, S10 and S11 took up [14C]stachydrine as well as wild-type cells did, but neither used stachydrine effectively as an osmoprotectant. In the absence of salt stress, both S10 and S11 took up less [14C]proline than wild-type cells did. S10 and S11 appeared to colonize alfalfa roots normally in single-strain tests, but when mixed with the wild-type strain, their rhizosphere counts were reduced more than 50% (P </= 0.01) relative to the wild type. These results suggest that stachydrine catabolism contributes to root colonization. DNA sequence analysis identified the mutated locus in S11 as putA, and the luxAB fusion in that gene was induced by proline as well as stachydrine. DNA that restored the capacity of mutant S10 to catabolize stachydrine contained a new open reading frame, stcD. All data are consistent with the concept that stcD codes for an enzyme that produces proline by demethylation of N-methylproline, a degradation product of stachydrine.

Is salinity tolerance related to Na accumulation in Upland cotton (Gossypium hirsutum) seedlings

Physiological responses to salt stress were studied in two cotton cultivars previously selected on the basis of growth under salinity. Plants were grown in nutrient solutions under controlled conditions. In the first experiment, the genotypes were grown at different salt concentrations (0, 100 and 200 mM NaCl) and growth rates, water contents and ion accumulation were determined. In a second experiment, both genotypes were grown at the same salt concentration (200 mM NaCl). Dry matter partitioning in individual leaves, stem and roots, water contents, specific leaf area (SLA), ion accumulation (K ,N a ,C l ) and leaf water potentials were measured. Finally, an experiment with low salt levels (2.7 and 27 mM NaCl) was run to compare K and Na uptake and distribution. There were no differences in growth between the cultivars in the absence of salt stress, whereas under stress genotype Z407 had higher leaf area and dry matter accumulation than P792. Leaf water potential and leaf water content were lower in cv P792 than in cv Z407. There were no significant differences in the levels of Cl accumulation between genotypes. The main feature of the tolerant genotype (Z407) was a higher accumulation of Na in leaves and an apparent capacity for K redistribution to younger leaves. We postulate that the higher tolerance in Z407 is the result of several traits such as a higher Na uptake and water content. Adaptation through adequate, but tightly controlled ion uptake, typical of some halophytes, matched with efficient ion compartmentation and redistribution, would result in an improved water uptake capacity under salt stress and lead to maintenance of higher growth rates.

The participation of phytochrome in the signal transduction pathway of salt stress responses inMesembryanthemum crystallinumL.

Continuous irradiation of Mesembryanthemum crystallinum plants with light of equal amounts of photosynthetically active radiation, but widely different red :far red ratios was used to intervene in phytochrome-mediated signal transduction pathways in the presence and absence of salt stress. Light with a low ratio of red :far red (in contrast to light with a high ratio of red :far red), caused induction of PEP carboxylase activity, accumulation of the CAM isoform of PEP carboxylase, and the accumulation of malate anion. Taking these as indicators of CAM induction it is concluded that phytochrome can participate in the signal transduction pathway leading to CAM in M. crystallinum. A low ratio of red :far red light acted synergystically with salt stress in the induction of these CAM indicators. The simplest interpretation of this interaction is that the phytochrome-mediated effects and salt stress effects acted on the same signal transduction pathway. The accumulation of pinitol was also increased by light with a low ratio of red :far red, consistent with the existence of a stress syndrome in M. crystallinum which utilizes a common transduction pathway. A low ratio of red :far red light induced a strong shade avoidance response and, compared to light with a high red :far red ratio, modified chlorophyll content and betacyanin pigment complement. Plants grown in light with a low ratio of red :far red flowered earlier than plants grown in light with a high red :far red ratio. It is concluded that phytochrome can participate in the signal transduction pathway leading to the induction of both CAM and the processes which result in pinitol accumulation and pigmentation in M. crystallinum, as well as in the mediation of shade avoidance and flowering responses.

Effect of NaCl Salinity on Growth and Development of Jojoba Clones: I. Young Plants

Summary Young jojoba (Simmondsia chinensis) plants of four high-yielding commercial clones grown in sand culture were irrigated over a period of 1y2 years with nutrient solutions having EC values of 2, 4, 8, and 12 dS m-' (corresponding to addition of 0, 20, 60, and 100 mole m-3 NaCl. All clones with the exception of clone 64, the best producer among Israeli selections in the absence of salt stress, developed reasonably well up to 8 dS m-', growth parameters such as shoot elongation and node production remaining unaffected. At 12 dS m-' all clones showed signs of salinity stress, clone 154 proving most tolerant and clone 64 most sensitive. Exposure to 12 dS m-' reduced the number of viable flower buds in three of the four clones, clone 64 being most affected. Although clone 64 produced the highest number of flower buds at 2 and 4 dS m-', clone 154 performed best at 12 dS m-', with twice the number of viable flower buds. In all clones a high percentage of flower buds wilted or degenerated at the highest salinity level. Salinity treatments increased both leaf thickness and succulence. Unlike many other perennial woody plants, jojoba does not exclude Na and Cl ions from leaves, but rather accumulates them in high concentrations in mature leaves. The most sensitive clone, 64, accumulated the highest amount of Na and Cl ions. Potassium content was only slightly affected by salinity, and at 12 dS m-' its content in mature leaves and roots decreased by about 30 % compared with that of control plants. Salinity inhibited net photosynthesis during part of the day, presumably due to the steeper decline in water potential in the saline-treated plants.

Salt stress in cultured rice cells: effects of proline and abscisic acid

Abstract. The presence of 1 and 10 mol m−3 proline in media containing 100 and 200 mol m−3 of NaCl, had little effect on the growth of salt‐adapted callus of rice. However, in such callus proline accumulation was stimulated by 10 mol m−3 proline in the presence of 100 mol m−3 NaCl. On the other hand, with 100 mol m−3 NaCl, both 1 and 10 mol m−3 proline significantly increased both the growth and proline content of salt‐unadapted callus. On replacing NaCl with KCl (100 and 200 mol m−3), growth of saltadapted as well as unadapted callus was inhibited, but the presence of 10 mol m−3 proline had an ameliorating effect. Abscisic acid (ABA) supressed the growth of both salt‐adapted and unadapted callus of rice in the absence of salt stress. ABA inhibited the growth of callus adapted to and grown in 100 and 200 mol m−3 of NaCl or when it was replaced by equimolar concentrations of KCl. Growth of 100 mol m−3 NaCl adapted cells was inhibited when they were transferred to a medium containing 200 mol m−3 of NaCl, but in the presence of ABA it was stimulated. ABA increased the growth of unadapted cells when subjected to different salts. Also, ABA accelerated the adaptation of cells exposed to salt but not to water deficits imposed by nonionic solutes.

Transport and catabolism of proline betaine in salt-stressed Rhizobium meliloti

Exogenous proline betaine (N,N-dimethylproline or stachydrine) highly stimulated the growth rate of Rhizobium meliloti, in media of inhibitory concentration of NaCl whereas proline was ineffective. High levels of proline betaine uptake occurred in cells grown in media of elevated osmotic strength; on the contrary, only low activity was found in cells grown in minimal medium. The apparent Km was 10 μM with a maximal transport rate of 25 nmol min-1 mg-1 of protein in 0.3 M NaCl-grown cells. The concentrative transport was totally abolished by KCN (2 mM), 2,4-dinitrophenol (2 mM), and carbonyl cyanide-m-chlorophenyl hydrazone (CCCP 10 μM) but was insensitive to arsenate (5 mM). Glycine betaine was a very potent inhibitor of proline betaine uptake while proline was not. Proline betaine transport was not reduced in osmotically shocked cells and no proline betaine binding activity was detected in the crude periplasmic shock fluid. In the absence of salt stress, Rhizobium meliloti actively catabolized proline betaine but this catabolism was blocked by increasing the osmotic strength of the medium. The osmolarity in the growth medium regulates the use of proline betaine either as a carbon and nitrogen source or as an osmoprotectant.

Response of salt-stressed wheat seedlings to kinetin

The response of wheat ( Triticum aestivum L.) seedlings to kinetin and salt-stress treatment was studied. Kinetin, in the absence of salt-stress, reduced root growth significantly even at 1 μM but in shoot significant growth reduction was observed after 5 μM. Increase in NaCl concentration in the growth media decreased seedling growth but simultaneous application of kinetin partially reversed the inhibitory effect of salt-stress.