Stress-induced Proline Accumulation Research Articles

Metabolism of carbohydrates and activity of the antioxidant system in mosses on a post-technogenic salinized territory

Adaptive physiological and biochemical reactions of mosses Didymodon rigidulus Hedw., Barbula unguiculata Hedw. and Brachythecium campestre (Müll. Hal.) Schimp. to salt stress have been investigated from the territory of the tailings storage of the Stebnyk Mining and Chemical Enterprise “Polymineral” (Lviv region, Ukraine). The peculiarities of carbohydrate metabolism in mosses under salinity conditions have been studied. The content of soluble carbohydrates and proline, the antioxidant activity, the content of ascorbate and reduced glutathione as well as the activity of enzymes of their metabolism – ascorbate peroxidase and glutathione reductase at the initial stages of the stress (salt shock) and prolonged stress exposure (salt stress) have been evaluated. It has been found that the increase of α-amylase activity, enhancement of the hydrolysis of starch and the increase of the concentration of soluble carbohydrates under salt stress were the reactions of the studied species of mosses. It has been established that there was an increase in the concentration of soluble carbohydrates by 1.2–1.5 times in moss shoots under salinity conditions, compared with plants from the background area (vicinity of Stebnyk). Experimental studies have shown that under salinity conditions sucrose dominates in the pool of soluble carbohydrates (59.0–79.5% of the total sugars content). The sucrose content was 1.5–2.0 times higher in the plants B. unguiculata and D. rigidulus from the highly saline area of the tailings storage. It has been indicated that under stress conditions constitutive adaptive mechanisms are more expressed in resistant moss species, and plants with a lower level of resistance adapt to the stressor, mainly due to induced protective systems. Experimental studies have shown that plants B. unguiculata and D. rigidulus, which are resistant to abiotic stressors, have a high constitutive pool of soluble carbohydrates both at the beginning of the experiment and under prolonged exposure of the salt stress. In the shoots of the sensitive moss B. campestre the stress-induced character of the sugars accumulation has been revealed. The accumulation of proline in mosses cells under salt stress depended on their species characteristics. The stress-induced accumulation of proline can be considered as a part of the bryophytes’ protective system, but this osmolyte does not play a key role in the formation of the mosses’ resistance to salt stress. Obviously, soluble carbohydrates are the main osmolytes in the moss cells. It has been found that resistant moss species have a high constitutive antioxidant status, while in the sensitive moss B. campestre the increase in the antioxidant activity occurred during prolonged salt stress, which may indicate its induced nature. It has been shown that the resistant mosses B. unguiculata and D. rigidulus have 3–4 times higher levels of glutathione and ascorbate content and 1.6–2.5 times higher activity of enzymes of their metabolism – glutathione reductase and ascorbate peroxidase, compared to plants of the less tolerant moss species B. campestre, which provided reduction of the lipid peroxidation process in plasma membranes and decreased the content of TBA-active products under stress.

Differential Contribution of P5CS Isoforms to Stress Tolerance in Arabidopsis.

Proline accumulation is a widespread response of plants to salt stress as well as drought and cold stress. In most plant species, two isoforms of pyrroline-5-carboxylate synthetase (P5CS) catalyze the first step in proline biosynthesis from glutamate. In Arabidopsis, these isoforms differ in their spatial and temporal expression patterns, suggesting sub-functionalization. P5CS1 has been identified as the major contributor to stress-induced proline accumulation, whereas P5CS2 has been considered important for embryo development and growth. In contrast to previous results, our analysis of P5CS1- and P5CS2-GFP fusion proteins indicates that both enzymes were exclusively localized in the cytosol. The comparison of the susceptibility of p5cs1 and p5cs2 mutants to infection with Pseudomonas syringae and salt stress provided novel information on the contribution of the two P5CS isoforms to proline accumulation and stress tolerance. In agreement with previous studies, salt-stressed p5cs1 mutants accumulated very little proline, indicating that P5CS1 contributed more to stress-induced proline accumulation, whereas its impact on stress tolerance was rather weak. Germination and establishment of p5cs2 mutants were impaired under ambient conditions, further supporting that P5CS2 is most important for growth and development, whereas its contribution to stress-induced proline accumulation was smaller than that of P5CS1. In contrast to p5cs1 mutants or wildtype plants, p5cs2 mutants were only weakly affected by sudden exposure to a high NaCl concentration. These findings show that proline content, which was intermediate in leaves of p5cs2 mutants, was not directly correlated with stress tolerance in our experiments. In rosettes of NaCl-exposed p5cs2 mutants, nearly no accumulation of Na+ was observed, and the plants showed neither chlorosis nor reduction of photosynthesis. Based on these data, we suggest a function of P5CS2 or P5CS2-mediated proline synthesis in regulating Na+ accumulation in leaves and thereby salt stress tolerance.

Participation of Jasmonate Signaling Components in the Development of Arabidopsis thaliana’s Salt Resistance Induced by H2S and NO Donors

The effect of donors of hydrogen sulfide (50 μM sodium hydrosulfide NaHS) and nitric oxide (500 μM sodium nitroprusside, SNP) on the salt resistance of wild type (Col-0) Arabidopsis plants (A-rabidopsis thaliana L. Heynh.) and those defective in jasmonate signaling—coi1 (mutant for the gene encoding protein COI1 involved in the removal of repressor proteins of transcriptional factors of jasmonate signaling) and jin1 (mutant defective in the gene encoding the transcription factor JIN1/MYC2)—have been compared. NO and H2S donors had a similar positive effect on the salt resistance of wild-type plants, which was manifested in a decrease under their influence of water deficiency of leaves, a decrease in oxidative damage, and stabilization of membrane permeability and chlorophyll content under the influence of 175 mM NaCl. The activity of superoxide dismutase (SOD) and catalase (CAT) also increased under the influence of NaHS and SNP treatment during salinization in Col-0 plants but the stress-induced accumulation of proline decreased. Pretreatment of coi1 and jin1 mutants with NO and H2S donors did not prevent the increase in lipid peroxidation caused by the action of NaCl and did not contribute to a decrease in membrane permeability and preservation of the pool of chlorophylls under stress conditions. In both mutants treated with NaHS or SNP, there was no increase in the activity of SOD and CAT under the action of salt. Donor treatment of NO and H2S did not affect the magnitude of the water deficit and the content of proline in the leaves of the mutant jin1. However, the mutant coi1 presalt treatment with NaHS or SNP reduced the manifestation of water deficiency and proline accumulation. The conclusion is drawn on the involvement of jasmonate signaling components in the implementation of the stress-protective action of donors of hydrogen sulfide and nitric oxide. It is assumed that the transcription factor JIN1/MYC2 plays a more important role in the processes of salt resistance induction of Arabidopsis plants by exogenous NO and H2S compared to protein COI1.

The cloning and characterization of hypersensitive to salt stress mutant, affected in quinolinate synthase, highlights the involvement of NAD in stress-induced accumulation of ABA and proline.

Nicotinamide adenine dinucleotide (NAD), a ubiquitous coenzyme, is required for many physiological reactions and processes. However, it remains largely unknown how NAD affects plant response to salt stress. We isolated a salt-sensitive mutant named hypersensitive to salt stress (hss) from an ethyl methanesulfonate-induced mutation population. A point mutation was identified by MutMap in the encoding region of Quinolinate Synthase (QS) gene required for the de novo synthesis of NAD. This point mutation caused a substitution of amino acid in the highly-conserved NadA domain of QS, resulting in an impairment of NAD biosynthesis in the mutant. Molecular and chemical complementation have restored the response of the hss mutant to salt stress, indicating that the decreased NAD contents in the mutant were responsible for its hypersensitivity to salt stress. Furthermore, the endogenous levels of abscisic acid (ABA) and proline were also reduced in stress-treated hss mutant. The application of ABA or proline could alleviate stress-induced oxidative damage of the mutant and partially rescue its hypersensitivity to salt stress, but not affect NAD concentration. Taken together, our results demonstrated that the NadA domain of QS is important for NAD biosynthesis, and NAD participates in plant response to salt stress by affecting stress-induced accumulation of ABA and proline.

Polyphenol-enriched spelt husk extracts improve growth and stress-related biochemical parameters under moderate salt stress in maize plants

Biostimulants improve yield, quality, and stress acclimation in crops. In this work, we tested the possibility of using phenolics-rich extracts from spelt (Triticum dicoccum L.) husks to attenuate the effects of salt stress (100–200 mM NaCl) in maize. Two methanolic extracts were prepared from the soluble-conjugated (SC), and the insoluble-bound (IB) phenolic acid fractions of the spelt husk, and their effects were investigated on several stress-associated biochemical parameters, such as proline, lipid peroxidation, H2O2, GSH levels, and ion content. Results show that SC and IB fractions of husk extracts behaved very differently, no doubt due to their greatly divergent chemical composition, as revealed by both GC-MS and HPLC analyses. The efficacy of treatments in mitigating salt stress was also dose- and timing-dependent. IB, even at the lower concentration tested, was able to recover the performance of stressed plants in terms of growth, photosynthetic pigments content, and levels of salt stress markers. Recovery of shoot growth to control levels and reduction of stress-induced proline accumulation occurred regardless of whether plants were pre-treated or post-treated with IB, whereas only pre-treatment with the higher dose of IB was effective in mitigating oxidative stress. Although in some cases SC and even methanol alone exerted some positive effects, they could also be deleterious whereas IB never was. Overall, results indicate that a polyphenol-containing extract obtained from spelt by-products can behave as biostimulant in maize plants and can mitigate their response to salt stress, by acting on different biochemical targets.

Stress Adaptive Plasticity: Aegilops tauschii and Triticum dicoccoides as Potential Donors of Drought Associated Morpho-Physiological Traits in Wheat.

The inconsistent prevalence of abiotic stress in most of the agroecosystems can be addressed through deployment of plant material with stress adaptive plasticity. The present study explores water stress induced plasticity for early root-shoot development, proline induction and cell membrane injury in 57 accessions of Aegilops tauschii (DD-genome) and 26 accessions of Triticum dicoccoides (AABB-genome) along with durum and bread wheat cultivars. Thirty three Ae. tauschii accessions and 18 T. dicoccoides accessions showed an increase in root dry weight (ranging from 1.8 to 294.75%) under water stress. Shoot parameters- length and biomass, by and large were suppressed by water stress, but genotypes with stress adaptive plasticity leading to improvement of shoot traits (e.g., Ae tauschii accession 14191 and T. dicoccoides accession 7130) could be identified. Water stress induced active responses, rather than passive repartitioning of biomass was indicated by better shoot growth in seedlings of genotypes with enhanced root growth under stress. Membrane injury seemed to work as a trigger to activate water stress adaptive cellular machinery and was found positively correlated with several root-shoot based adaptive responses in seedlings. Stress induced proline accumulation in leaf tissue showed marked inter- and intra-specific genetic variation but hardly any association with stress adaptive plasticity. Genotypic variation for early stage plasticity traits viz., change in root dry weight, shoot length, shoot fresh weight, shoot dry weight and membrane injury positively correlated with grain weight based stress tolerance index (r = 0.267, r = 0.404, r = 0.299, r = 0.526, and r = 0.359, respectively). In another such trend, adaptive seedling plasticity correlated positively with resistance to early flowering under stress (r = 0.372 with membrane injury, r = 0.286 with change in root length, r = 0.352 with change in shoot length, r = 0.268 with change in shoot dry weight). Overall, Ae. tauschii accessions 9816, 14109, 14128, and T. dicoccoides accessions 5259 and 7130 were identified as potential donors of stress adaptive plasticity. The prospect of the study for molecular marker tagging, cloning of plasticity genes and creation of elite synthetic hexaploid donors is discussed.

Arabidopsis AMINO ACID PERMEASE1 Contributes to Salt Stress-Induced Proline Uptake from Exogenous Sources.

Stress-induced proline accumulation in plants is thought to result primarily from enhanced proline biosynthesis and decreased proline degradation. To identify regulatory components involved in proline transport, we screened for Arabidopsis thaliana T-DNA mutants with enhanced tolerance to toxic levels of exogenous proline (45 mM). We isolated the proline resistant 1-1 (pre1-1) mutant and map-based cloning identified PRE1 as AMINO ACID PERMEASE1 (AAP1, At1g58360), which encodes a plasma membrane-localized amino acid permease. AAP1 expression is induced by salt stress and abscisic acid, but not by proline. In pre1-1 mutants, a 19-nucleotide deletion in the AAP1 coding region produced a premature stop codon. When grown on proline-containing medium, pre1-1 mutants accumulated significantly less proline than did the wild type. Under salt stress, proline uptake decreased significantly in pre1-1 mutants. By contrast, proline uptake increased significantly in the wild type. These results suggest that AAP1 functions in the increase of proline uptake during salt stress. In addition, proline uptake promotes salt tolerance in Arabidopsis seedlings. We conclude that plants can increase proline accumulation by AtAAP1-mediated proline uptake from exogenous source, which help to improve the salt tolerance of seedlings.

Water stress induced proline accumulation and antioxidative enzymes in groundnut (Arachis hypogaea L.)

Thirty days grown seedlings of eight genotypes of groundnut viz. RHRG-6083, TAG-24, TG-60(LC), Karad-4-11, SB-XI, RHRG-6097, RHRG-6021, and RHRG-6055 were subjected to moisture stress by withholding irrigation for 15 days in pot culture experiment in order to evaluate its effect of on RWC , proline accumulation, soluble proteins, chlorophyll content and activities of superoxide dismutase (SOD), peroxidase (POX), glutathione reductase (GR) and lipid peroxidation (MDA).The levels of proline, soluble protein and the activity of all four antioxidative enzymes were found to be increased with MDA content in all genotypes of groundnut during water stress, however the chlorophyll and RWC content were found to be decreased. This study revealed that under water stress condition SB-XI, TAG-24 and RHRG-6021 showed higher increase of proline content and activities of antioxidative enzymes with lower reduction in RWC and chlorophyll. These three genotypes are stable during stress and seems to be promising for drought tolerance.

Identification of Δ1-pyrroline 5-carboxylate synthase (P5CS) genes involved in the synthesis of proline in Lotus japonicus

ABSTRACTProline accumulation is a common response of plants to different biotic and abiotic stresses. In the model legume Lotus japonicus, osmotic stress-induced proline accumulation is one of the first responses of the plant, converting proline in a reliable stress marker. The main biosynthetic pathway of proline is from glutamate and the reaction catalyzed by the enzyme Δ1-pyrroline 5-carboxylate synthase (P5CS) is the rate limiting step. L. japonicus has been suggested to have three different P5CS genes. Here the predicted P5CS genes of L. japonicus were analyzed in silico and their expression under osmotic stress was determined. Contrary to previous suggestions this study demonstrated that L. japonicus has two different P5CS genes, as most dicotyledonous plants do. The gene that is inducible by osmotic stress and is located on chromosome 1, was called LjP5CS1, and the one located on chromosome 2 and not inducible by osmotic stress was called LjP5CS2.

Effects of Calcium and Calmodulin Antagonists on Chilling Stress-Induced Proline Accumulation in Jatropha curcas L.

Regulation of proline accumulation in plants under chilling stress remains unclear. In this paper, we treated Jatropha curcas seedlings under chilling stress with exogenous calcium chloride (CaCl2), the plasma membrane Ca2+-channel blocker lanthanum chloride (LaCl3), calmodulin antagonists, chlorpromazine (CPZ), and trifluoperazine (TFP) and investigated the effects of calcium and calmodulin (CaM) on proline accumulation and chilling tolerance. The results showed that CaCl2 treatment significantly enhanced chilling stress-induced proline accumulation. CaCl2 also induced an almost immediate and rapid increase of Δ1-pyrroline-5-carboxylate synthetase (P5CS) and glutamate dehydrogenase activities, the key enzymes in the glutamate pathway of proline biosynthesis, and up-regulated P5CS expression, but it decreased the activity of proline dehydrogenase (ProDH), a key enzyme of proline degradation, and inhibited ProDH expression. Treatment with LaCl3, CPZ, and TFP exhibited the opposite effects to those by CaCl2 treatment. Moreover, CaCl2, LaCl3, CPZ, and TFP had little effect on the activities of ornithine aminotransferase and arginase, the key enzymes in the ornithine pathway of proline biosynthesis. These results indicated that Ca2+-CaM might be involved in signal transduction events, leading to proline accumulation in J. curcas seedlings under chilling stress, and that Ca2+-induced proline accumulation is a combined result of the activation of the glutamate pathways of proline biosynthesis and the simultaneous inhibition of the proline degradation pathway. In addition, CaCl2 treatment increased tissue vitality, decreased the content of the lipid peroxidation product malondialdehyde (MDA), and alleviated electrolyte leakage in J. curcas seedlings under chilling stress, indicating that exogenous Ca2+ can enhance chilling tolerance, and proline might be a key factor in this increased chilling tolerance.

Effects of Ascorbic Acid and Reduced Glutathione on the Alleviation of Salinity Stress in Olive Plants

ABSTRACTThe aim of this study was to evaluate the effects of low molecular mass antioxidants and NaCl salinity on growth, ionic balance, proline, and water contents of ‘Zard’ olive trees under controlled greenhouse conditions. The experiment was carried out by spraying 2 mM of ascorbic acid (Asc) and 3 mM of reduced glutathione (GSH) on the plants that were treated with two salinity levels (0 and 100 mM NaCl) on their root medium. Plant growth parameters (leaf fresh weight, leaf dry weight, leaf number, total fresh weight, and total dry weight) were significantly improved by Asc compared with growth parameters in GSH and control plants. Higher concentrations of Na+ and Cl– were observed in salt-stressed plants, while Na+ and Cl– concentrations were decreased in the olive leaves that were sprayed with Asc. Salinity in the root zone caused a considerable decline in both K+ concentration and K/Na ratio. K+ concentration and K/Na ratio were significantly increased by application of Asc on plant leaves. Salinity caused an increase in electrolyte leakage (EL) compared with the control plants. Lowest EL and tissue water content (TWC) was obtained in Asc-sprayed plants, whereas TWC was increased in salt-stressed plants. Plants were subjected to salt stress and showed a higher relative water content (RWC) than the control plants. Salt stress induced proline accumulation in olive leaves. In conclusion, exogenous application of Asc is recommended to improve tolerance of olive plants under saline conditions.

Hydrogen peroxide produced by NADPH oxidases increases proline accumulation during salt or mannitol stress in Arabidopsis thaliana.

Many plants accumulate proline, a compatible osmolyte, in response to various environmental stresses such as water deficit and salinity. In some stress responses, plants generate hydrogen peroxide (H2 O2 ) that mediates numerous physiological and biochemical processes. The aim was to study the relationship between stress-induced proline accumulation and H2 O2 production. Using pharmacological and reverse genetic approaches in Arabidopsis thaliana, we investigated the role of NADPH oxidases, Respiratory burst oxidase homologues (Rboh), in the induction of proline accumulation was investigated in response to stress induced by either 200 mM NaCl or 400 mM mannitol. Stress from NaCl or mannitol resulted in a transient increase in H2 O2 content accompanied by accumulation of proline. Dimethylthiourea, a scavenger of H2 O2 , and diphenylene iodonium (DPI), an inhibitor of H2 O2 production by NADPH oxidase, were found to significantly inhibit proline accumulation in these stress conditions. DPI also reduced the expression level of Δ(1) -pyrroline-5-carboxylate synthetase, the key enzyme involved in the biosynthesis of proline. Similarly, less proline accumulated in knockout mutants lacking either AtRbohD or AtRbohF than in wild-type plants in response to the same stresses. Our data demonstrate that AtRbohs (A. thaliana Rbohs) contribute to H2 O2 production in response to NaCl or mannitol stress to increase proline accumulation in this plant.

Δ1‐pyrroline‐5‐carboxylate reductase from Arabidopsis thaliana: stimulation or inhibition by chloride ions and feedback regulation by proline depend on whether NADPH or NADH acts as co‐substrate

Δ(1)-pyrroline-5-carboxylate (P5C) reductase (P5CR) catalyses the final step of proline synthesis in plants. In Arabidopsis thaliana, protein levels are correlated neither to the corresponding mRNA copy numbers, nor to intracellular proline concentrations. The occurrence of post-translational regulatory mechanisms has therefore been hypothesized, but never assessed. The purification of A. thaliana P5CR was achieved through either a six-step protocol from cultured cells, or heterologous expression of AtP5CR in Escherichia coli. The protein was characterized with respect to structural, kinetic, and biochemical properties. P5CR was able to use either NADPH or NADH as the electron donor, with contrasting affinities and maximum reaction rates. The presence of equimolar concentrations of NADP(+) completely suppressed the NADH-dependent activity, whereas the NADPH-dependent reaction was mildly affected. Proline inhibited only the NADH-dependent reaction. At physiological values, increasing concentrations of salt progressively inhibited the NADH-dependent activity, but were stimulatory of the NADPH-dependent reaction. The biochemical properties of A. thaliana P5CR suggest a complex regulation of enzyme activity by the redox status of the pyridine nucleotide pools, and the concentrations of proline and chloride in the cytosol. Data support a to date underestimated role of P5CR in controlling stress-induced proline accumulation.

DNA methylation involved in proline accumulation in response to osmotic stress in rice (Oryza sativa)

Proline accumulation is involved in plant osmotic stress tolerance. Given that DNA methylation is related to almost all metabolic processes through regulation of gene expression, we suspected that this epigenetic modification and proline biosynthesis are probably related. To test this, we investigated whether osmotic stress-induced proline accumulation is associated with DNA methylation modifications in rice. We assessed DNA methylation and expression of 3 key genes (P5CR, P5CS, and δ-OAT) involved in proline biosynthesis, and measured proline content under both osmotic stress (15% polyethylene glycol) and control conditions. After osmotic stress, selfed progenies of osmotic-stressed plants accumulated higher concentrations of proline in leaves under both normal conditions and under osmotic stress than the unstressed control plants. Concomitantly, under osmotic stress, the selfed progeny plants showed higher expression levels of P5CS and δ-OAT than the control. This up-regulated expression was stably inherited by the subsequent generation. Methylation-sensitive Southern blotting indicated that 2 of the 3 genes, P5CS and δ-OAT, had greater DNA demethylation in the selfed progenies than in the control. Apparently DNA demethylation facilitated proline accumulation by up-regulating expression of the P5CS and δ-OAT genes in response to osmotic stress.

A novel Δ1-pyrroline-5-carboxylate synthetase gene of Medicago truncatula plays a predominant role in stress-induced proline accumulation during symbiotic nitrogen fixation

Proline accumulates in environmentally stressed plant cells including those of legume roots and nodules, but how its level is regulated is poorly understood. Δ1-Pyrroline-5-carboxylate synthetase (P5CS), the committed-step enzyme of proline biosynthesis, is encoded by two duplicated genes in many plants. Here, we isolated MtP5CS3, a third gene, from Medicago truncatula, whose predicted polypeptide sequence is highly similar to those of previously isolated MtP5CS1 and MtP5CS2 except an extra amino-terminal segment. MtP5CS3 was strongly expressed under salinity and drought in shoots and nodulating roots, while MtP5CS1 was constitutive and MtP5CS2 induced by abscisic acid. Under salinity, MtP5CS3 promoter was more active than those of MtP5CS1 and MtP5CS2, as shown by GUS fusions. Translationally fused MtP5CS1-GFP was localized in the cytoplasm, whereas significant proportions of MtP5CS2-GFP and MtP5CS3-GFP were co-localized with rubisco small subunit protein-fused RFP in transformed hairy root cells. Under salinity, RNA silencing of MtP5CS1 or MtP5CS2 strongly induced MtP5CS3 expression, while that of MtP5CS3 decreased free proline content and nodule number. Consistently, Mtp5cs3, a loss-of-function mutant, accumulated much less proline, formed fewer nodules, and fixed nitrogen significantly less efficiently than the wild type under salinity. Thus, MtP5CS3 plays a critical role in regulating stress-induced proline accumulation during symbiotic nitrogen fixation.

Активність та ізоферментний склад пероксидази клітин Dunaliella salina при сольовому стресі

The effect of elevated NaCl concentrations (0.5–4.0 M) on the proline content and activity of free peroxidase in green alga Dunaliella salina have been investigated. It was revealed that the tolerance of the alga to NaCl effect was determined by the functioning of the complex of metabolic reactions including both the necessary stress-induced accumulation of proline and high activity of the free peroxidase. The obtained data demonstrate testify to a deep reorganization of metabolic processes, occurring in alga cells during the adaptation to elevated salinity conditions.

A greenhouse investigation of responses to different water stress regimes of Laurus nobilis trees from two climatic regions

Plants from two populations of Laurus nobilis (Tunisia issued from a semi-arid inland site and Algeria originating from a coastal sub-humid area) were exposed during three months under similar controlled conditions to two stress intensities of permanent stress (60% (S1) and 20% (S2) of field capacity) or to cyclic water stress, plants being re-watered when the soil moisture dropped to 60% (S11) or 20% (S22) of field capacity. One-year old plants displayed contrasting physiological strategies to cope with water stress. Algeria exhibited a higher decrease in osmotic potential ( Ψs) in relation to stress-induced proline accumulation. Glycinebetaine accumulated in response to drought in response to permanent stress (Algeria) or cyclic stress (Tunisia). The two populations had similar net photosynthesis ( A) but Algeria exhibited higher water use efficiency (WUE) than Tunisia. A drought-induced increase in the apoplastic water content (AWC) was noticed in response to mild stress intensities (S1 and S11) in Tunisia and in response to higher stress intensities (S2 and S22) in Algeria in relation to a stress-induced accumulation of pectin and proportion of arabinose within the pectic fraction. Bulk modulus of elasticity (ɛ) increased in Tunisia in response to permanent drought and in Algeria in response to cyclic stress, as a result of a stress-induced increase in cellulose (Algeria) or hemicellulose (Tunisia). It is concluded that water stress tolerance could be achieved by both osmotic and elastic adjustment in the coastal population which did not exhibit a prodigal water use comparatively to the inland population. Differences between populations are strongly influenced by the kinetics of water stress application.

Proline antioxidant role in the common ice plant subjected to salinity and paraquat treatment inducing oxidative stress

Leaves of 4-week-old (juvenile) and 9-week-old (adult) plants of the halophyte Mesembryanthemum crystallinum L. (the common ice plant), cultured under controlled conditions in the phytotron, were treated with paraquat (0.1 μM), which produces superoxide radical, and (or) paraquat combined with introduction of NaCl (100 mM) or proline (5 mM) into nutrient medium. After a 20-h dark period (23°C), plants were transferred into light (4 h at 54.1 W/m2 of photosynthetically active radiation) for stimulation of O°2− formation in plastids. Activities of antioxidant enzymes, the contents of MDA, H2O2, chlorophyll, and free proline were measured in leaves. Plant responses in two age groups, which differed in the type of photosynthesis (juvenile plants had C3 type of photosynthesis, whereas adult plants were at the transition stage to Crassulacean Acid Metabolism (CAM) photosynthesis), differed in the levels of constitutive proline and proline, induced by NaCl and paraquat, as well as in activities of superoxide dismutase (SOD) and catalase. Changes in SOD activity and proline accumulation in response to paraquat treatment combined with NaCl revealed opposite dependence to accumulation of proline: the more proline accumulated in leaves, the lower activity of the enzyme. In response to paraquat treatment, the content of chlorophylls a and b most drastically declined in juvenile plants. Negative effect of salinity on the content of chlorophylls was lower than that of paraquat and was almost the same in plants of both age groups. Protective effect of exogenous proline was most profound in the case of paraquat treatment. Exogenous proline decreased the rate of lipid peroxidation, the content of superoxide radical and, consequently, SOD activity (almost fivefold), and increased the content of chlorophylls (a and b) in leaves of adult plants. The obtained data suggest that stress-induced accumulation of proline in the common ice plant has both osmoprotectory and antioxidant functions.

Proline accumulation and transcriptional regulation of proline biothesynthesis and degradation in Brassica napus

To understand the molecular mechanism underlying proline accumulation in Brassica napus, cDNAs encoding Delta(1)-pyrroline-5-carboxylate synthetase (BnP5CS), ornithine delta-aminotransferase (BnOAT) and proline dehydrogenase (BnPDH) were isolated and characterized. Southern blot analysis of BnP5CSs in B. napus and its diploid ancestors suggested a gene loss may have occurred during evolution. The expression of BnP5CS1 and BnP5CS2 was induced, while the expression of BnPDH was inhibited under salt stress, ABA treatment and dehydration, prior to proline accumulation. The upregulation of BnOAT expression was only detected during prolonged severe osmotic stress. Our results indicate that stress-induced proline accumulation in B. napus results from the reciprocal action of activated biosynthesis and inhibited proline degradation. Whether the ornithine pathway is activated depends on the severity of stress. During development, proline content was high in reproductive organs and was accompanied by markedly high expression of BnP5CS and BnPDH, suggesting possible roles of proline during flower development. [BMB reports 2009; 42(1): 28-34].

Effect of water stress on proline accumulation of genetically modified potatoes ( Solanum tuberosum L.) generating fructans

This study aimed to investigate the effect of water stress on the accumulation of proline in the leaves of transgenic potato lines generating fructans. The results of the series of bifactorial experiments in 2002 and 2003 indicated an increase of the proline level in leaves of all potato lines examined under water deficit. In addition, an increase in proline concentration during plant development was observed. The proline content was related to leaf water potential and relative water content (RWC), which indicates that proline could be involved in osmoregulation of potato plants under the experimental conditions. Surprisingly, under water deficit, the proline level was lowest in most of the transgenic SST/FFT-lines, which generate fructan molecules with a high degree of polymerization. Therefore, a pleiotropic effect can not be excluded as the reason for the divergence in behavior of these transgenic lines. The present results suggest that the modification of carbohydrate metabolism, especially the high content of soluble carbohydrates, may affect water stress-induced proline accumulation.