Non-pretreated Plants Research Articles

Seed priming with plant growth-promoting rhizobacteria and supplementation of culture medium with biochar alleviated salinity damages in Prosopis koelziana seedlings

The Prosopis koelziana genus, a member of the Fabaceae family, is crucial to the ecology and economy of arid areas. It is commonly used to restore deserts, forests, and degraded soil with low fertility and high salt concentration. However, recent studies found that the seedlings of P. koelziana are highly susceptible to salinity stress despite having a high tolerance to it. To address this issue, an experiment was conducted to determine if plant growth-promoting rhizobacteria (PGPR) pretreatment and biochar application could enhance the seedlings’ tolerance to saline conditions. The research showed that salinity stress decreased seedling growth but increased proline content, soluble sugar content, and antioxidant enzyme activity. Na+ ions increased in plants under salt stress, while K+ ions decreased. The results indicated that the pretreatment of plants with biochar and bacteria increased the fresh weight of seedlings by about 23%, 58%, and 50% in 200, 400, and 600 mM NaCl, respectively, compared with non-pretreated plants. Biochar and bacteria application also increased the proline content by about 62%, 46%, 32%, and 45% in 0, 200, 400, and 600 mM NaCl. This experiment showed that bacteria and biochar pretreatment of plants reduced oxidative stress and sodium uptake (20%, 28%, and 10% decrement of root Na uptake in 200, 400, and 600 mM NaCl). Therefore, these two bio stimulators should be used together for more significant effects on the salinity mitigation of P. Koelziana seedlings and the production of resistant seedlings that have a high ability to transfer to the field.

Cross-Priming Approach Induced Beneficial Metabolic Adjustments and Repair Processes during Subsequent Drought in Olive

Cross-tolerance to abiotic stresses is a typical phenomenon in plants which occurs when exposure to one form of stress confers tolerance to a variety of stresses. Our study aims at investigating whether salinity priming could induce, after a recovery period (2 months), drought tolerance in olive cv. Chétoui. Here, our results revealed that this method of cross-adaptation had further enhanced the olive’s subsequent response to drought. In fact, relative to the non-pretreated plants, the salt-pretreated ones displayed an enhancement in terms of shoot biomass accumulation, photosynthetic performance, water-use efficiency, and hydration status. Furthermore, the attenuation of oxidative stress and the maintenance of structural lipid contents, as well as their fatty acid composition in salt-pretreated plants, also supported the beneficial effect of this method. From our results, it seems that salt priming substantially modulated the physiological and biochemical responses of olive plants to subsequent drought. Accordingly, metabolite adjustments (soluble sugars and proline), the enzymatic antioxidant system (superoxide dismutase (SOD), catalase (CAT), and guaiacol peroxidase (GP) activities) as well as the nonenzymatic one (phenols), and the increase in leaf density together with the raise of structural lipids content, to a lesser extent, seemed to perform a major role in the development of this improved tolerance to drought. The ameliorative response found in salt-primed olive plants, when subsequently exposed to drought, indicates an efficient cross-tolerance reaction. This could be particularly important in the Mediterranean area, where olive orchards are mainly cultivated under dry-land farming management.

Polyamines Metabolism Interacts with γ-Aminobutyric Acid, Proline and Nitrogen Metabolisms to Affect Drought Tolerance of Creeping Bentgrass.

Due to increased global warming and climate change, drought has become a serious threat to horticultural crop cultivation and management. The purpose of this study was to investigate the effect of spermine (Spm) pretreatment on metabolic alterations of polyamine (PAs), γ-aminobutyric acid (GABA), proline (Pro), and nitrogen associated with drought tolerance in creeping bentgrass (Agrostis stolonifera). The results showed that drought tolerance of creeping bentgrass could be significantly improved by the Spm pretreatment, as demonstrated by the maintenance of less chlorophyll loss and higher photosynthesis, gas exchange, water use efficiency, and cell membrane stability. The Spm pretreatment further increased drought-induced accumulation of endogenous PAs, putrescine, spermidine, and Spm, and also enhanced PAs metabolism through improving arginine decarboxylases, ornithine decarboxylase, S-adenosylmethionine decarboxylase, and polyamine oxidase activities during drought stress. In addition, the Spm application not only significantly improved endogenous GABA content, glutamate content, activities of glutamate decarboxylase and α-ketoglutarase, but also alleviated decline in nitrite nitrogen content, nitrate reductase, glutamine synthetase, glutamate synthetase, and GABA aminotransferase activities under drought stress. The Spm-pretreated creeping bentgrass exhibited significantly lower ammonia nitrogen content and nitrite reductase activity as well as higher glutamate dehydrogenase activity than non-pretreated plants in response to drought stress. These results indicated beneficial roles of the Spm on regulating GABA and nitrogen metabolism contributing towards better maintenance of Tricarboxylic acid (TCA) cycle in creeping bentgrass. Interestingly, the Spm-enhanced Pro metabolism rather than more Pro accumulation could be the key regulatory mechanism for drought tolerance in creeping bentgrass. Current findings provide a comprehensive understanding of PAs interaction with other metabolic pathways to regulate drought tolerance in grass species.

Use of Silicon to Preserve Sucrose in Sugarcane Desiccated with Paraquat and Diquat

Sugarcane studies have shown that the desiccants Paraquat and Diquat cause severe sucrose losses as a result of interrupted photosynthesis and abnormal behavior of sugar-metabolizing enzymes. It was theorized that an appropriate agent, selective for the sucrose-limiting enzymes, could modify the sugar-destroying features of otherwise useful chemicals. Experiments are reported herein in which silicon (Si), an in vitro inhibitor of cane enzymes, was applied to sugarcane foliage prior to treatment with Paraquat and Diquat. There were three objectives: 1, To incorporate sufficient Si into living tissues to control hydrolytic and oxidative enzymes; 2, to help retain photosynthetic activity; and 3, to maintain higher sucrose levels as a consequence of lessened sugar metabolism and continued photosynthesis. Plants of the variety P.R. 980 were grown in sand culture and treated with the following percent solutions of Paraquat and Diquat: 0, 0.0002, 0.0006, 0.0018, 0.0054, and 0.0162. For each experiment half of the plants were pretreated with 500 p.p.m. of Si (Na2SiO3-9H2O) as a foliar spray at 8, 4, and 1 day prior to desiccant application. The following results were obtained: 1. The 0.0018 to 0.0162 percent levels severely damaged cane foliage, desiccated leaves and sheaths, and caused major sucrose losses in plants not pretreated with Si. 2. Si-pretreated plants retained near-normal foliage and near-normal sucrose levels for approximately two Paraquat increments above those of non-pretreated plants. For example, damage typical of the 0.0018 percent level, without Si, did not appear until the 0.0162 percent level was reached when Si was present. 3. Paraquat desiccation, as reflected by sheath-moisture values, was ultimately constant regardless of Si treatment. 4. Paper chromatography revealed ribose in leaf extracts of Paraquat-and Diquat-treated plants. Si pretreatment retarded the appearance of ribose below the 0.0162 percent level of Paraquat, and at all Diquat levels. This indicated a Si "protection" of photosynthetic reactions, possibly those of phosphoribose isomerase. 5. The leaf enzymes phosphatase, ATP-ase, and peroxidase were suppressed by increasing desiccant concentrations. Si pretreatments acted to preserve near normal enzyme levels regardless of desiccant action. Leaf amylase, and invertase from immature storage tissue, were greatly stimulated by Paraquat. In these instances Si served to suppress the excessive enzyme activity. 6. Si did not seem to act as an inhibitor in living tissues, as it is known to do in the test tube. Rather, a series of Si-enzyme complexes appeared to form and to retard activity shifts in either direction. 7. A third experiment involving 0.001 percent Paraquat, and a single Si pretreatment given 1 day prior to Paraquat, generally verified the sucrose, enzyme, and visible foliar effects noted earlier with more severe desiccant and Si treatments. The results support the thesis that undesirable effects of a chemical on plants can be selectively modified by control of critical enzymes. The value of this concept in increasing the scope and productivity of agricultural chemicals is noted.

The effect of electromagnetic eretreatment on lemon balm (<em>Melissa officinalis</em> L.) seeds subjected to static magnetic fields

The effects of magnetic waves as natural environmental factors on the growth and development of plants is not well known. The present study evaluated the effects of a static magnetic field (SMF) (4 and 6mT for 30 and 120 min) on the growth, contents of proline and total soluble sugar, phenolic compounds, accumulation of hydrogen peroxide (H2O2) and malondialdehyde (MDA) of pretreated seeds. The activity of antioxidant enzymes and the essential oil composition of lemon balm seedlings subjected to SMF treatment (4 and 6mT for 30 and 120 min for 7 days) were also examined. The SMF treatments decreased plant growth by reducing the contents of photosynthetic pigments and inducing oxidative stress; however, pretreated plants had greater contents of pigments, proline, soluble sugars, total phenol and flavonoids than non-pretreated plants. The contents of MDA and H2O2 were decreased in pretreated plants compared to non-pretreated plants; this result was associated with the reduction in antioxidant enzyme activity. The exposure of seeds to SMF also increased the yield and altered the chemical composition of essential oils compared to both non-pretreated and control plants. These results indicate that pretreatment of lemon balm seeds with SMF can be effectively used as a pre-sowing treatment to increase essential oil yield for medical purposes.

Exogenous hydrogen sulfide reduces cadmium uptake and alleviates cadmium toxicity in barley

Greenhouse hydroponic experiments were conducted to evaluate the ameliorative effects of NaHS, a donor of hydrogen sulfide (H2S), on different levels of cadmium (Cd) stress in barley seedlings. The results showed that Cd stress dramatically reduced plant biomass, chlorophyll and soluble protein contents. Exogenous application of H2S significantly alleviated Cd-induced growth inhibition and reductions in chlorophyll content, and dramatically depressed leaf malondialdehyde (MDA) accumulation. Addition of H2S markedly reduced Cd concentration in plants and increased leaf soluble protein contents compared with the corresponding Cd-only treatments. Supplemental H2S counteracted Cd-induced alterations of certain antioxidant enzymes, e.g. elevated depressed superoxide dismutase in leaves and roots and depressed Cd-induced increase in leaf catalase and ascorbate peroxidase activities. Pretreatment with 200 μM NaHS markedly reduced the accumulation of hydrogen peroxide (H2O2) and superoxide ions (O 2 ⋅− ) in roots tissues treated with 5 and 25 μM Cd, which was consistent with the result of histochemical staining of roots. Compared with non-pretreated plants, exogenous H2S significantly increased reduced glutathione contents and ascorbate contents in barley given the 25 μM Cd treatment. These results indicate that the mitigated Cd toxicity by H2S is involved in the reduced Cd uptake/translocation and decreased MDA, H2O2 and O 2 ⋅− accumulation, and increased chlorophyll.

Root Abscisic Acid Contributes to Defending Photoinibition in Jerusalem Artichoke (Helianthus tuberosus L.) under Salt Stress.

The aim of the study was to examine the role of root abscisic acid (ABA) in protecting photosystems and photosynthesis in Jerusalem artichoke against salt stress. Potted plants were pretreated by a specific ABA synthesis inhibitor sodium tungstate and then subjected to salt stress (150 mM NaCl). Tungstate did not directly affect root ABA content and photosynthetic parameters, whereas it inhibited root ABA accumulation and induced a greater decrease in photosynthetic rate under salt stress. The maximal photochemical efficiency of PSII (Fv/Fm) significantly declined in tungstate-pretreated plants under salt stress, suggesting photosystem II (PSII) photoinhibition appeared. PSII photoinhibition did not prevent PSI photoinhibition by restricting electron donation, as the maximal photochemical efficiency of PSI (ΔMR/MR0) was lowered. In line with photoinhibition, elevated H2O2 concentration and lipid peroxidation corroborated salt-induced oxidative stress in tungstate-pretreated plants. Less decrease in ΔMR/MR0 and Fv/Fm indicated that PSII and PSI in non-pretreated plants could maintain better performance than tungstate-pretreated plants under salt stress. Consistently, greater reduction in PSII and PSI reaction center protein abundance confirmed the elevated vulnerability of photosystems to salt stress in tungstate-pretreated plants. Overall, the root ABA signal participated in defending the photosystem’s photoinhibition and protecting photosynthesis in Jerusalem artichoke under salt stress.

Benzothiadiazole and nitrogen source modify the nitrogen metabolism in cucumber infected with Pseudomonas syringae pv. lachrymans

The influence of nitrogen source and benzothiadiazole (BTH) pretreatment on nitrogen metabolism-related enzyme activities was studied in cucumber plants infected with Pseudomonas syringae pv. lachrymans (Psl). The plants were grown hydroponically in media containing nitrate and urea at different ratios: 100% NO3− (100N), 75% NO3−/25% urea (75N) and 50% NO3−/50% urea (50N) and pretreated with BTH prior to Psl inoculation.In the presence of urea in the nutritional medium the activities of most enzymes in the control plants decreased. Disease development was influenced by nitrogen nutrition and the weakest symptoms occurred in the 75N plants. The BTH-induced disease restriction was dependent on the type of nitrogen nutrition and was most visible in the 50N plants (about 2-fold reduction of infected leaf area compared to the plants not pretreated with BTH). The nitrogen metabolism was modified by BTH and this effect was stronger than that of urea. Irrespective of the type of nitrogen nutrition, in the BTH-treated plants, the activities of nitrate reductase, ferredoxin- and NADH-dependent glutamate synthase decreased whereas those of NADH-dependent glutamate dehydrogenase (NADH-GDH), aminotransferases and NADP-dependent isocitrate dehydrogenase were enhanced compared to the controls. After infection, in all nutritional variants, the strongest effect of BTH pretreatment was observed for NADH-GDH on the 2 day, when its activity increased by 85–256% compared to the infected non-pretreated plants. Our results concerning the glutamate-metabolizing enzymes suggest that BTH treatment combined with low dose of urea may have a positive influence on the nitrogen management leading to the inhibition of disease symptom progress.

Salt priming improved salt tolerance in sweet sorghum by enhancing osmotic resistance and reducing root Na+ uptake

This study attempted to explore how salt priming affected salt tolerance in sweet sorghum with emphasis on root Na+ uptake. After 10 days of pretreatment with 150 mM NaCl, plants were stressed with 300 mM NaCl. After salt stress for 7 days, dry matter of root and shoot decreased by 58.7 and 69.7 % in non-pretreated plants and by 37.9 and 41.3 % in pretreated plants. Consistently, pretreated plants maintained higher photosynthetic rate during salt stress, suggesting the enhanced tolerance by salt priming. Salt priming enhanced osmotic resistance, as proline and relative water contents in the leaf were higher in pretreated plants under salt stress. Salt priming alleviated salt-induced oxidative damage not by improving antioxidant protection due to lower increase in leaf malondialdehyde content and no extra induction on ascorbate peroxidase, catalase, superoxide dismutase, ascorbic acid and reduced glutathione in pretreated plants. After 7 days of salt stress, root Na+ efflux increased by 8.5- and 3.9-folds in pretreated and non-pretreated plants, suggesting that salt priming reduced root Na+ uptake, and then root and leaf Na+ accumulation were mitigated in pretreated plants. However, root Na+ extrusion became indifferent between pretreated and non-pretreated plants under salt stress after inhibiting plasma membrane (PM) Na+/H+ antiporter. Thus, the greater Na+ extrusion induced by salt priming had relation to PM Na+/H+ antiporter. Overall, salt priming improved salt tolerance in sweet sorghum by enhancing osmotic resistance and reducing root Na+ uptake.

Salt pretreatment alleviated salt-induced photoinhibition in sweet sorghum

Sweet sorghum is an important energy crop. This study aimed to investigate the effects of salt pretreatment on the interaction between photosystem II (PSII) and photosystem I (PSI) upon salt stress. In this study, sweet sorghum was pretreated with 150 mM NaCl for 10 days, and subsequently, the pretreated plants were subjected to severe salt stress at 300 mM NaCl. PSII and PSI photoinhibition occurred in non-pretreated plants after 4 days of salt stress, as the maximum quantum yield of PSII (Fv/Fm) and the maximal photochemical capacity of PSI (Delta MR/MR0) significantly decreased, and their normal coordination was destroyed. The significant positive correlation between Fv/Fm and Delta MR/MR0 under salt stress indicated that PSII photoinhibition was in relation to PSI photoinhibition, and PSI photoinhibition might lead to PSII photoinhibition through inhibiting electron transport at the acceptor side of PSII. Salt stress did not induce PSII photoinhibition in salt-pretreated plants, and thus, salt pretreatment protected PSI against photoinhibition not by aggravating PSII photoinhibition. Salt pretreatment mitigated the decrease in CO2 assimilation, reduced the feedback inhibition on photosynthetic electron transport and then contributed to suppressing PSI and PSII photoinhibition in sweet sorghum under salt stress. Therefore, the normal coordination between PSII and PSI was maintained in salt-pretreated plants. In conclusion, salt pretreatment ensured normal PSII and PSI coordination by preventing photoinhibition in sweet sorghum under salt stress.

Physiology of acclimation to salinity stress in pea (Pisum sativum)

Pea (Pisum sativum L.) seedlings were grown in half strength Hoagland solution and exposed to 0, 10, 25mM NaCl and 2.5% PEG 6000 for 1 week (pre-treatment). Thereafter plants were exposed to 0 and 80mM NaCl for 2 weeks (main treatment). The control plants were maintained in half strength Hoagland solution without NaCl. Various physiological parameters were recorded from control, pretreated and non-pretreated plants. There was no negative effect of the pre-treatments on growth (total fresh and dry matter production), and plants pre-treated with 10mM NaCl had biomass accumulation equal to control plants. The beneficial effect of salt acclimation was also evident in the prevention of K+ leakage and Na+ accumulation, primary in roots, suggesting that here the physiological processes play the major role. 2.5% PEG 6000 was not as efficient as salt in enhancing salt tolerance and acclimation appears to be more related to ion-specific rather than osmotic component of stress. We also recorded an increase of the xylem K/Na in the salt acclimated plants. Therefore, the present study reveals that short-term exposure of the glycophyte P. sativum species activates a set of physiological adjustments enabling the plants to withstand severe saline conditions, and while acclimation takes place primary in the root tissues, control of xylem ion loading and efficient Na+ sequestration in mesophyll cells are also important components of this process.

Effect of 24-epibrassinolide on drought stress-induced changes in Chorispora bungeana

Brassinosteroids (BRs) have been proposed to increase the resistance of plants to drought stress. The effect of foliar application of 0.1 μM 24-epibrassinolide (EBR) on chlorophyll (Chl) content, photosystem 2 (PS 2) photochemistry, membrane permeability, lipid peroxidation, relative water content (RWC), proline content, and the antioxidant system in drought-stressed Chorispora bungeana plants was investigated. The results showed that polyethylene glycol (PEG) induced water stress decreased RWC, Chl content and variable to maximum Chl fluorescence ratio (Fv/Fm) less in plants pretreated with EBR than in non-pretreated plants. In addition, lipid peroxidation, measured in terms of malondialdehyde content, membrane permeability and proline content in drought-stressed plants were less increased in EBR pretreated plants, while antioxidative enzyme activities and reduced ascorbate and glutathione contents were more increased in EBR pretreated than in non-pretreated plants. These results suggested that EBR could improve plant growth under drought stress

Influence of Exogenous Glycine Betaine and Abscisic Acid on Papaya in Responses to Water-deficit Stress

The effects of exogenous foliar glycine betaine (GB) and abscisic acid (ABA) on papaya responses to water stress were investigated under distinct water regimes. Papaya seedlings (Carica papaya L. cultivar “BH-65”) were pretreated with GB or ABA and subsequently subjected to consecutive periods of drought, rehydration, and a second period of drought conditions. Results indicated that water stress induced ABA, jasmonic acid (JA), and proline accumulation but did not modify malondialdehyde (MDA) concentration. In addition, water deprivation reduced photosynthetic rate, stomatal conductance, relative water content (RWC), leaf fresh weight, and increased leaf abscission. GB applied prior to drought imposition decreased the impact of water stress on ABA, JA, proline accumulation, leaf water status, growth, and photosynthetic performance. However, ABA-pretreated plants did not show alteration of most of these parameters under water stress conditions when compared with non-pretreated plants except a clear induction of JA accumulation. Taken together, the data suggest that GB may modulate ABA, JA, and proline accumulation through the control of stomatal movement and the high availability of compatible solutes, leading to improvement of leaf water status, growth, and photosynthetic machinery function. In contrast, exogenous ABA did not stimulate papaya physiological responses under drought, but interestingly ABA in combination with drought could induce progressive JA synthesis, unlike drought alone, which induces a transitory JA increase and may trigger endogenous ABA accumulation. The data also suggest that irrespective of the pretreatments, papaya did not suffer oxidative damage.

Exogenously-supplied trehalose protects thylakoid membranes of winter wheat from heat-induced damage

The effects of trehalose pretreatment on thylakoid membranes of winter wheat were investigated under heat stress. Under normal growth conditions, the winter wheat synthesized 502 μg g-1(f.m.) trehalose, which increased to 1250 μg g-1(f.m.) under heat stress and to 1658 μg g-1(f.m.) in trehalose-pretreated seedlings. Under heat stress, proteins in the thylakoid membranes and the photosynthetic capacity were protected by trehalose pretreatment. Moreover, the electrolyte leakage, contents of malondialdehyde, superoxide anion and hydrogen peroxide, and lipoxygenase activity in trehalose-pretreated seedlings were lower than in the non-pretreated plants.

Abscisic Acid Decreases Leaf Na+ Exclusion in Salt-Treated Phaseolus vulgaris L.

Previous results showed that in short-term NaCl-treated beans increased leaf abscisic acid (ABA) concentration was triggered by Na+ but not by Cl-. In this work, the specificity of ABA signaling for Na+ homeostasis was studied by comparing the plant’s responses to solutions that modified accumulation of ABA and/or Na+ uptake and distribution, such as supplemental Ca2+, increased nutrient strength, different isosmotic composition, application of exogenous ABA, fluridone (an ABA inhibitor) and aminooxiacetic acid (AOA, an ethylene inhibitor). After fluridone pretreatment, salt-treated beans had lower Na+ uptake and higher leaf Na+ exclusion capacity than non-pretreated plants. Moreover, Na+ uptake was increased and leaf Na+ exclusion was decreased by AOA and ABA. NaCl and KCl similarly increased leaf ABA and decreased transpiration rates, whereas supplemental Ca2+ and increased strength nutrient solution decreased leaf ABA and leaf Na+. These results show (1) a non-ion-specific increase in ABA that probably signaled the osmotic component of salt, and (2) increased ABA levels that resulted in higher leaf Na+ concentrations due to lower Na+ exclusion or increased root-shoot Na+ translocation.

Absorption and Translocation of Foramsulfuron in Dallisgrass (Paspalum dilatatum) Following Preapplication of MSMA

Several field studies have observed increased foramsulfuron efficacy for the control of dallisgrass when foramsulfuron is applied after MSMA. Therefore, laboratory studies were conducted with mature dallisgrass to study the absorption and translocation of 14C-foramsulfuron, and then examine the impact of preliminary applications (preapplications) of MSMA or foramsulfuron on herbicide absorption and movement. Herbicide absorption increased rapidly through 4 h, and by 8 h, differences in absorption between pretreated and control plants were evident. After 48 h, foramsulfuron absorption in non-pretreated plants was 55%, whereas plants that received either pretreatment absorbed 70% of the herbicide. Translocation above (younger tissue) and below (older tissue) the treated leaf was 0.65 and 0.62% for non-pretreated plants, respectively. Pretreatment with foramsulfuron resulted in the translocation of 2.12 and 1.55% of applied radioactivity above and below the treated leaf, respectively. Pretreatment with MSMA resulted in the translocation of 2.33 and 2.34% of applied radioactivity above and below the treated leaf, respectively. These data indicated that pretreatment of mature dallisgrass with either foramsulfuron or MSMA results in an increase in both uptake and translocation of foramsulfuron applied 2 wk after pretreatment. The increase in absorption and translocation of foramsulfuron in the pre–MSMA-treated plants may explain the increase in control observed in the field when comparing it to the pre–foramsulfuron-treated dallisgrass plants.

Salicylic acid, hydrogen peroxide and calcium-induced saline tolerance associated with endogenous hydrogen peroxide homeostasis in naked oat seedlings

This study investigates the role of salicylic acid (SA), hydrogen peroxide (H2O2) and calcium chloride (CaCl2) singly or in combination, in inducing naked oat plant tolerance to sodium chloride (NaCl). Two-week-old naked oat plants were pretreated with both single and double of 0.5 mM SA, 0.5 mM H2O2 and 5 mM CaCl2 by adding them to the culture solution for 24 h. At the end of the pretreatment, the plants were subjected to 200 mM NaCl exposure for 7 days. Data were collected on plant biomass, H2O2 level, antioxidant enzyme activity, non-enzymatic antioxidant content and malondialdehyde (MDA) content. Results showed that exposure to salt significantly inhibited plant growth, and the shoot and root dry weights were reduced 47.5% and 63.4%, and the H2O2 levels elevated 5.8 and 2.4 times in comparison with those in the control, respectively. Under the saline stress, the activities of superoxide dismutase (SOD) and catalase (CAT) were induced, but the contents of ascorbic acid (AA) and glutathione (GSH) decreased, and MDA largely accumulated. The various pretreatments efficiently counteracted the salt-caused growth inhibition, especially with H2O2 + CaCl2 the shoot and root dry weights reduced only 9.4% and 24.4% of the non salt-stressed plants. The determination of endogenous H2O2 level demonstrated that the pretreatments induced H2O2 accumulation, with H2O2 + CaCl2 being most efficient, but the effect was transient. After 7 days of saline stress, the H2O2 contents in the pretreated shoots and roots accounted for 23.7–41.8% and 31.7–57.3% of the non-pretreated plants, varying according to the different pretreatments. Under saline stress, SOD and CAT further increased, AA and GSH maintained higher levels and MDA decreased in the pretreated plants compared to the untreated plants. With application of diphenylene iodonium (DPI) during the pretreatment, which inhibited the accumulation of H2O2, the ameliorative effect of the pretreatment on salt-caused plant growth inhibition was reduced. However, applied DPI at the immediate end of the pretreatment did not alter its favorable role, indicating a H2O2 peak formed at the early time of saline stress might play an important role in regulating plant tolerance to saline stress.

Rice can acclimate to lethal level of salinity by pretreatment with sublethal level of salinity through osmotic adjustment

The physiological ability to adapt for various environmental changes is known as acclima- tion. When exposed to sublethal level of stress, plants develop the ability to withstand severe stress, as ac- quired tolerance. The present study was conducted to explicate the physiological basis of acquired tolerance in rice. Rice seedlings (variety IR 20) were grown in half strength Hoagland solution, and after 22nd day, they were kept in half strength Hoagland solution containing 50 mM NaCl (sublethal dose) for 7 days followed by half strength Hoagland solution contain- ing 100 mM NaCl (lethal dose) for another 7 days. The non-pretreated 29 days old rice seedlings main- tained in half strength Hoagland solution were directly transferred to half strength Hoagland solution con- taining 100 mM NaCl (lethal dose) solution for 7 days. The control plants were maintained in half strength Hoagland solution without NaCl. Various morphological and physiological parameters were recorded on 29th and 36th days old seedlings from control, pretreated and non-pretreated plants. The re- sults revealed significant reduction in growth param- eters (shoot length, root length, leaf area and total dry matter production) of non-pretreated plants below that of pretreated plants. The pretreated plants showed increased values to the extreme of 19.8 per cent in leaf water potential (ww), 9 per cent in relative water content (RWC), 26 per cent in photosynthetic rate (PN), 28 per cent in leaf stomatal conductance, and 47 per cent in chlorophyll a over non-pretreated plants. The same trend was also observed in chlorophyll a/b ratio (6.6%) and Fv/Fm ratio (19.3%). However, a reverse trend was seen in Fo value. The pretreated plants showed improved ionic regulation as evident from low Na + ,C l ) and high K + contents, which is attributed to enhanced plant water status and photo- synthesis. Both pretreated and non-pretreated plants had higher contents of osmolytes viz., sucrose, leaf soluble sugars and proline contents than control plants. However, starch content revealed an inverse trend. Therefore, the present study reveals that rice can acclimate to lethal dose of salinity stress by pre- treatment with sublethal dose of NaCl.

Induction of systemic resistance to Xanthomonas oryzae pv. oryzae by salicylic acid in Oryza sativa (L.)

The effect of salicylic acid (SA) is hypothesized to be a natural signal that triggers the systemic induction of phenolics, pathogenesis-related proteins and disease resistance in rice against the bacterial leaf blight pathogen Xanthomonas oryzae pv. oryzae (Xoo). Rice plants pretreated with 1000 μmol/l Sa showed resistance to challenge inoculation with Xanthomonas oryzae pv. oryzae and the effectiveness persisted in the susceptible cv. ‘Ir 50’ for at least 3 days prior to inoculation with Xoo. To investigate the role of SA in rice disease resistance, we examined the endogenous levels of SA in the Sa-pretreated rice plants with Xoo inoculation. A three-fold increase in the endogenous Sa levels was observed in the rice tissues pretreated with 1000 μmol/l Sa and the resistance persisted for at least 3 days after Sa treatment prior to inoculation with Xoo. Increasing the endogenous level of Sa in rice leaves to those naturally observed during systemic acquired resistance resulted in increased resistance to Xanthomonas oryzae pv. oryzae, expressed as a reduction in leaf blight lesion length. Immunoblot analysis revealed an induction of a 25 kDa protein cross-reacting with rice thaumatin-like protein (TLP) antiserum in response to Sa-pretreated and Sa non-pretreated rice plants followed by pathogen inoculation. A significant increase in the induction of Tlps 3 days after Xoo inoculation in the tissues pretreated with Sa was observed when compared with the 2 days and 1 day after Xoo inoculation in SA-treated plants. Increased phenolics content and enhanced activities of some pathogenesis-related (PR) proteins, viz., TLP, chitinase and β-1,3-glucanase were observed in rice plants treated with SA. Based on these experiments, it was investigated that the defense responses are induced locally at the infection site only after pathogen attack and are augumented when the rice tissue has been pretreated with Sa. These data further support the hypothesis that the defense responses in rice can be rapidly triggered and induced in a genetically susceptible cultivar after treatment with SA.

Maternal transmission of adaptive modifications in salt‐treated Sorghum bicolor: a first stage in ecotypic differentiation?

Following a 3‐wk pretreatment with 150 mM NaCl, Sorghum plants were able to survive exposure to 300 mM NaCl, a lethal concentration for nonpretreated plants. This response is termed salt adaptation. Although the population was initially homogeneous, Na‐includer and Na‐excluder individuals coexisted after the achievement of the salt‐adaptation response, and a large diversity in size of the seeds produced was observed at the end of the life cycle. Offspring of salt‐adapted plants were exposed to a new salt‐adaptation treatment. Even in the absence of selection, the proportion of Na‐excluder individuals in the progeny was significantly increased. Offspring germinated from small seeds differed significantly from plants first‐exposed to a salt‐adaptation treatment, whereas offspring from large seeds displayed intermediate characteristics. This suggests that some of the adaptive changes were transmitted through embryo imprinting. The importance of this phenomenon for emergence of a newly adapted ecotype is discussed.