Leaf H2O2 Research Articles

An Optimized in situ Quantification Method of Leaf H2O2 Unveils Interaction Dynamics of Pathogenic and Beneficial Bacteria in Wheat.

Hydrogen peroxide (H2O2) functions as an important signaling molecule in plants during biotic interactions. However, the extent to which H2O2 accumulates during these interactions and its implications in the development of disease symptoms is unclear. In this work, we provide a step-by-step optimized protocol for in situ quantification of relative H2O2 concentrations in wheat leaves infected with the pathogenic bacterium Pseudomonas syringae pv. atrofaciens (Psa), either alone or in the presence of the beneficial bacterium Herbaspirillum seropedicae (RAM10). This protocol involved the use of 3-3′diaminobenzidine (DAB) staining method combined with image processing to conduct deconvolution and downstream analysis of the digitalized leaf image. The application of a linear regression model allowed to relate the intensity of the pixels resulting from DAB staining with a given concentration of H2O2. Decreasing H2O2 accumulation patterns were detected at increasing distances from the site of pathogen infection, and H2O2 concentrations were different depending on the bacterial combinations tested. Notably, Psa-challenged plants in presence of RAM10 accumulated less H2O2 in the leaf and showed reduced necrotic symptoms, pointing to a potential role of RAM10 in reducing pathogen-triggered H2O2 levels in young wheat plants.

Gibberellic acid-induced generation of hydrogen sulfide alleviates boron toxicity in tomato (Solanum lycopersicum L.) plants

It was aimed to examine the role of gibberellic acid (GA) induced production of hydrogen sulfide (H2S) in alleviating boron toxicity (BT) in tomato plants. Two weeks after germination, a solution consisting of GA (100 mg L−1) was sprayed once a week for 14 days to the leaves of cv. “SC 2121” of tomato under BT stress (BT; 2.0 mM). Before starting BT treatment, half of the seedlings were retained in a solution containing a scavenger of H2S, 0.1 mM hypotaurine (HT), for 12 h. Boron toxicity led to a substantial decrease in dry biomass, leaf water potential, leaf relative water content, chlorophyll a, chlorophyll b, photosynthetic quantum yield (Fv/Fm), ascorbate (AsA) and glutathione (GSH) in the tomato plants. However, it increased the accumulation of hydrogen peroxide (H2O2), malondialdehyde (MDA), endogenous hydrogen sulfide (H2S), and free proline as well as the activities of catalase, superoxide dismutase and peroxidase. The supplementation of GA mitigated BT by increasing the endogenous H2S, and leaf Ca2+ and K+, and reducing the contents of leaf H2O2, MDA, and B as well as membrane leakage. GA-induced BT tolerance was further enhanced by the supplementation of sodium hydrosulfide (0.2 mM NaHS), an H2S donor. A scavenger of H2S, hypotaurine (0.1 mM HT) was supplied along with the GA and NaHS treatments to assess if H2S was involved in GA-induced BT tolerance of tomato plants. Addition of HT reversed the beneficial effect of GA on oxidative stress and antioxidant defence system by reducing the endogenous H2S without changing L-DES activity, suggesting that H2S participates in GA-induced tolerance to BT of tomato plants.

Sulfur-enriched leonardite and humic acid soil amendments enhance tolerance to drought and phosphorus deficiency stress in maize (Zea mays L.)

Soil amendments are known to promote several plant growth parameters. In many agro-ecosystems, water scarcity and drought induced phosphorus deficiency limits crop yield significantly. Considering the climate change scenario, drought and related stress factors will be even more severe endangering the global food security. Therefore, two parallel field trials were conducted to examine at what extent soil amendment of leonardite and humic acid would affect drought and phosphorus tolerance of maize. The treatments were: control (C: 100% A pan and 125 kg P ha−1), P deficiency (phosphorus stress (PS): 62.5 kg P ha−1), water deficit stress (water stress (WS): 67% A pan), and PS + WS (67% A pan and 62.5 kg P ha−1). Three organic amendments were (i) no amendment, (ii) 625 kg S + 750 kg leonardite ha−1 and (iii) 1250 kg S + 37.5 kg humic acid ha−1) tested on stress treatments. Drought and P deficiency reduced plant biomass, grain yield, chlorophyll content, Fv/Fm, RWC and antioxidant activity (superoxide dismutase, peroxidase, and catalase), but increased electrolyte leakage and leaf H2O2 in maize plants. The combined stress of drought and P deficiency decreased further related plant traits. Humic acid and leonardite enhanced leaf P and yield in maize plants under PS. A significant increase in related parameters was observed with humic acid and leonardite under WS. The largest increase in yield and plant traits in relation to humic acid and leonardite application was observed under combined stress situation. The use of sulfur-enriched amendments can be used effectively to maintain yield of maize crop in water limited calcareous soils.

Use of Nitric Oxide and Hydrogen Peroxide for Better Yield of Wheat (Triticum aestivum L.) under Water Deficit Conditions: Growth, Osmoregulation, and Antioxidative Defense Mechanism.

The present experiment was carried out to study the influences of exogenously-applied nitric oxide (NO) donor sodium nitroprusside (SNP) and hydrogen peroxide (H2O2) as seed primers on growth and yield in relation with different physio-biochemical parameters, antioxidant activities, and osmolyte accumulation in wheat plants grown under control (100% field capacity) and water stress (60% field capacity) conditions. During soaking, the seeds were covered and kept in completely dark. Drought stress markedly reduced the plant growth, grain yield, leaf photosynthetic pigments, total phenolic content (TPC), total soluble proteins (TSP), leaf water potential (Ψw), leaf turgor potential (Ψp), osmotic potential (Ψs), and leaf relative water content (LRWC), while it increased the activities of enzymatic antioxidants and the accumulation of leaf ascorbic acid (AsA), proline (Pro), glycine betaine (GB), malondialdehyde (MDA), and H2O2. However, seed priming with SNP and H2O2 alone and in combination mitigated the deleterious effects of water stress on growth and yield by improving the Ψw, Ψs, Ψp, photosynthetic pigments, osmolytes accumulation (GB and Pro), TSP, and the antioxidative defense mechanism. Furthermore, the application of NO and H2O2 as seed primers also reduced the accumulation of H2O2 and MDA contents. The effectiveness was treatment-specific and the combined application was also found to be effective. The results revealed that exogenous application of NO and H2O2 was effective in increasing the tolerance of wheat plants under drought stress in terms of growth and grain yield by regulating plant–water relations, the antioxidative defense mechanism, and accumulation of osmolytes, and by reducing the membrane lipid peroxidation.

Exogenous Isoprene Confers Physiological Benefits in a Negligible Isoprene Emitter (Acer monspessulanum L.) Under Water Deficit.

Isoprene, the main volatile released by plants, is known to protect the photosynthetic apparatus in isoprene emitters submitted to oxidative pressures caused by environmental constraints. Whether ambient isoprene contributes to protect negligible plant emitters under abiotic stress conditions is less clear, and no study has tested if ambient isoprene is beneficial during drought periods in plant species that naturally release negligible isoprene emissions. This study examines the effect of exogenous isoprene (20 ppbv) on net photosynthesis, stomatal conductance and production of H2O2 (a reactive oxygen species: ROS) in leaves of Acer monspessulanum (a negligible isoprene emitter) submitted to three watering treatments (optimal, moderate water stress and severe water stress). Results showed that A. monspessulanum exhibited a net photosynthesis increase (+30%) and a relative leaf H2O2 decrease when saplings were exposed to an enriched isoprene atmosphere compared to isoprene-free conditions under moderate water deficit. Such physiological improvement under isoprene exposure was not observed under optimal watering or severe water stress. These findings suggest that when negligible isoprene emitters are surrounded by a very high concentration of isoprene in the ambient air, some plant protection mechanism occurs under moderate water deficit probably related to protection against ROS damage eventually impeding photosynthesis drop.

Streptomyces alleviate drought stress in tomato plants and modulate the expression of transcription factors ERF1 and WRKY70 genes

Application of PGPRs that are tolerant to abiotic stresses is a promising approach to reduce the negative effects of drought stress and increase crop production. This study was designed to select and evaluate stress-tolerance PGP Streptomyces strains based on in vitro and in vivo experiments. Our results showed that only a small percentage (14 %) of 107 Streptomyces can produce ACCD. The effect of two selected isolates, IT25 an ACCD producing and C-2012 which did not have this ability but was able to tolerate NaCl 13 %, was evaluated on the growth and yield of tomato plants under normal and drought stress conditions. Under normal conditions, strain IT25 and C-2012 increased tomato yield 35 and 32 % respectively. Besides, decreased in fruit weight (by 60 %) under drought stress was significantly ameliorated in plants treated with Streptomyces strains. Both isolates, increased leaf RWC, proline, MDA, H2O2 and total sugar content and APX activity and decreased CAT and GPX activity under stress conditions. Plants exposed to drought stress exhibited a highly increased expression of ERF1 and WRKY70 in the roots. Both isolates inhibited expression of the genes under stress conditions. Streptomyces strains suppress stress signals, at biochemical and molecular levels to halt the plant's understanding of stress whereas, through increasing leaf RWC, compensated for the decrease in the yield. In conclusion, ACCD producing and salt tolerant Streptomyces both have the potential to prevent yield losses in tomato fruits under drought stress. However, the precise mechanism of their impact on the plant still needs to be addressed in future researches.

Biochar alleviates Cd phytotoxicity by minimizing bioavailability and oxidative stress in pak choi (Brassica chinensis L.) cultivated in Cd-polluted soil

The production of leafy vegetables such as Brassica chinensis L. in cadmium (Cd)-polluted soil causes serious threats to human health and food safety around the globe. A pot culture was established to examine the efficacy of rice-straw induced biochar (applied to soil at the rate of 0%, 2.5% and 5%, w/w) on growth, gaseous exchange attributes, antioxidative capacities and Cd uptake in pak choi (Brassica chinensis L.), when soil was spiked with Cd (CdCl2) at 0, 5, 10 and 20 mg kg−1 soil. The results revealed that Cd stress significantly (P < 0.05) reduced plant biomass and physiological attributes, and accumulated higher Cd concentrations in plant tissues with the increasing rate of Cd concentration in the soil. However, incorporation of biochar at 5% application rate prominently increased the shoot (98.27%) and root (85.96%) dry biomass, net photosynthesis (45.52%), transpiration rate (161.34%), stomatal activity (111.76%) and intracellular CO2 concentration (32.25%) when Cd was added at 20 mg kg−1 soil, relative to the respective treatment without biochar. Whereas, incorporation of biochar at 5% significantly reduced the bioavailable Cd by 16.64% under 20 mg kg-1 soil, compared to respective Cd treatment without biochar.Similarly, Cd accumulation in shoots and roots was decreased by 42.49% and 29.23%, and thereby reduced leaf MDA and H2O2 contents by 21.45% and 31.28%, respectively, at 20 mg Cd kg−1 spiked soil relative to without biochar amended soil. An increment was noticed in the activities of guaiacol peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathione (GSH) by 37.31%, 66.35%, 115.94%, 122.72% and 59.96%, respectively, with 5% biochar addition in 20 mg kg−1 Cd spiked soil. Moreover, biochar induced a synergistic impact on plants by increasing soil alkalinization and thereby reducing Cd phytotoxicity throughimmobilization. Overall, results proposed that rice-straw biochar has an ability to restore Cd polluted soil and increased pak choi production and thereby reduced food security risks in polluted soil.

Climate and development modulate the metabolome and antioxidative system of date palm leaves.

Date palms are remarkably tolerant to environmental stresses, but the mechanisms involved remain poorly characterized. Leaf metabolome profiling was therefore performed on mature (ML) and young (YL) leaves of 2-year-old date palm seedlings that had been grown in climate chambers that simulate summer and winter conditions in eastern Saudi Arabia. Cultivation under high temperature (summer climate) resulted in higher YL H2O2 leaf levels despite increases in dehydroascorbate reductase (DHAR) activities. The levels of raffinose and galactinol, tricarboxylic acid cycle intermediates, and total amino acids were higher under these conditions, particularly in YL. The accumulation of unsaturated fatty acids, 9,12-octadecadienoic acid and 9,12,15-octadecatrienoic acid, was lower in ML. In contrast, the amounts of saturated tetradecanoic acid and heptadecanoic acid were increased in YL under summer climate conditions. The accumulation of phenolic compounds was favored under summer conditions, while flavonoids accumulated under lower temperature (winter climate) conditions. YL displayed stronger hydration, lower H2O2 levels, and more negative δ 13C values, indicating effective reactive oxygen species scavenging. These findings, which demonstrate the substantial metabolic adjustments that facilitate tolerance to the high temperatures in YL and ML, suggest that YL may be more responsive to climate change.

EFFECT OF SALICYLIC ACID FOLIAR APPLICATION ON Vitis vinifera L. cv. ‘SULTANA’ UNDER SALINITY STRESS

The current survey aimed to study the effect of exogenous salicylic acid (SA) application on salinity stress of grapevine cv. ’Sultana’. The leaves of hydroponically cultivated grapes that were under 0, 75 and 150 mM salinity conditions treated with 0, 0.5, 1 and 1.5 mM SA and after two weeks, the factors such as Na+, K+, proline and MDA contents, leaf electrolyte leakage and enzymatic activities were measured. The results showed that all SA treatments were significantly effective at tolerance enhancement by reduction in Na+/K+ ratio, leaf electrolyte leakage, MDA and H2O2 values and promotion in proline content and the enzymatic activities (POD, APX, CAT and SOD) of grapes. These results indicated that SA application at salinity condition could be applied as a promising method for increasing the salinity tolerance of ‘Sultana’ grapes.

Nitrate supplementation attenuates As(V) toxicity in Solanum lycopersicum L. cv Pusa Rohini: Insights into As(V) sub-cellular distribution, photosynthesis, nitrogen assimilation, and DNA damage

The present study investigates As(V) toxicity in tomato (Solanum lycopersicum L. cv Pusa Rohini) and its alleviation by exogenous supplementation of nitrate. The seven days old seedlings were grown up to thirty days under defined levels of As(V) concentrations (0, 2.5, 6.25, and 12.5 mg/250 g soil) in alone or/and in combination with 20 mM nitrate. The arsenic accumulation, lipid peroxidation, DNA damage, photosynthesis, nitrogen assimilation, and AsA-GSH cycle were evaluated. Results revealed that As(V) exposure significantly (P ≤ 0.05) enhances the root, leaf and leaf sub-cellular arsenic accumulation, H2O2 and MDA contents in a dose-dependent manner. Comet assay indicated a progressive enhancement in the DNA damage with maximum tail length (58.33 ± 9.87 μm) and tail moment (25.05 ± 2.80) at 12.5 As(V) exposure. Nitrate supplementation counteracted As(V) toxicity on photosynthesis, nitrogen assimilation, and boosts AsA-GSH cycle at each respective As(V) treatments. The net photosynthesis was increased by 18% at 6.25 As(V), however, stomatal conductance and Fv/Fm were increased by 26%, and 11%, respectively, at 2.5 As(V) exposure. The activities of NR and GS were enhanced by 29% and 18%, respectively; contents of NO3−, NO2− and NH4+ were improved by 21%, 56%, and 13%, respectively, at 6.25 As(V) exposure. The activities of APX and GR were increased concomitantly with the ratios of AsA/DHA and GSH/GSSG. The study demonstrates that nitrate supplementation significantly (P ≤ 0.05) decreases As(V) accumulation, boosts the performance of AsA-GSH cycle, and consequently enhances the photosynthesis and nitrogen assimilation. Based on present findings, nitrate supplementation could be recommended as a promising approach to ameliorate the As(V) toxicity in plants.

The expression of the genes involved in redox metabolism and hydrogen peroxide balance is associated with the resistance of cowpea [Vigna unguiculata (L.) Walp.] to the hemibiotrophic fungus Colletotrichum gloeosporioides

Correlations between the transcriptional responses of genes that encode superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxiredoxin (Prx) enzymes and Colletotrichum gloeosporioides development in cowpea leaves were assessed. Each of these genes is involved in the redox metabolism and hydrogen peroxide balance. Although electron microscopy revealed that conidia adhered to and germinated on the leaf cuticle, the inoculated cowpea leaves did not show any characteristic anthracnose symptoms. The adhered and germinated conidia showed irregular surfaces and did not develop further. This was apparently due to increased leaf H2O2 levels in response to inoculation with C. gloeosporioides. During the early stages post inoculation, cowpea leaves elevated the H2O2 content and modulated the defense gene expression, as well as associated pathways. During the later stages, the increased expression of the CuZnSODI and CuZnSODII genes suggested an active superoxide dismutation to further elevate H2O2 levels, which indicated that higher H2O2 content may function as a toxic agent that kills the fungus. The second increase in H2O2 production above the threshold level was correlated with the expression of the APXI, CATI, CATII, PrxIIBCD, and PrxIIE genes, which resulted in a coordinated pattern to establish an appropriate balance between H2O2 generation and scavenging. Therefore, appropriate H2O2 content in cowpea leaves inhibited C. gloeosporioides development and maintained intracellular redox homeostasis to avoid uncontrolled programmed cell death and necrosis in cowpea leaves.

Drought tolerance of sugarcane propagules is improved when origin material faces water deficit.

Drought stress can imprint marks in plants after a previous exposure, leading to plant acclimation and a permissive state that facilitates a more effective response to subsequent stress events. Such stress imprints would benefit plants obtained through vegetative propagation (propagules). Herein, our hypothesis was that the propagules obtained from plants previously exposed to water deficit would perform better under water deficit as compared to those obtained from plants that did not face stressful conditions. Sugarcane plants were grown under well-hydrated conditions or subjected to three cycles of water deficit by water withholding. Then, the propagules were subjected to water deficit. Leaf gas exchange was reduced under water deficit and the propagules from plants that experienced water deficit presented a faster recovery of CO2 assimilation and higher instantaneous carboxylation efficiency after rehydration as compared to the propagules from plants that never faced water deficit. The propagules from plants that faced water deficit also showed the highest leaf proline concentration under water deficit as well as higher leaf H2O2 concentration and leaf ascorbate peroxidase activity regardless of water regime. Under well-watered conditions, the propagules from plants that faced stressful conditions presented higher root H2O2 concentration and higher activity of catalase in roots as compared to the ones from plants that did not experience water shortage. Such physiological changes were associated with improvements in leaf area and shoot and root dry matter accumulation in propagules obtained from stressed plants. Our results suggest that root H2O2 concentration is a chemical signal associated with improved sugarcane performance under water deficit. Taken together, our findings bring a new perspective to the sugarcane production systems, in which plant acclimation can be explored for improving drought tolerance in rainfed areas.

Abscisic acid cross-talking with hydrogen peroxide and osmolyte compounds may regulate the leaf rolling mechanism under drought

Leaf rolling observed in some crops such as maize, rice, wheat and sorghum is an indicator of decreased water status. Moderate leaf rolling not tightly or early increases the photosynthesis and grain yield of crop cultivars under environmental stresses. Moreover, the effects of exogenous abscisic acid (ABA) on stomatal conductance, water status and synthesis of osmotic compounds are a well-known issue in plants subjected to water deficit. However, it is not clear how the cross-talk of ABA with H2O2 and osmolyte compounds affects the leaf rolling mechanism. Regulation mechanism of leaf rolling by ABA has been first studied in maize seedlings under drought stress induced by polyethylene glycol 6000 (PEG 6000) in this study. ABA treatment under drought stress reduced hydrogen peroxide (H2O2) content and the degree of leaf rolling (%) while the treatment-induced ABA synthesis, osmolyte levels (proline, polyamine and total soluble sugars) and some antioxidant enzyme activities in comparison to the plants that were not treated with ABA. Furthermore, exogenous ABA up-regulated the expression levels of arginine decarboxylase (ADC) and pyrroline-5-carboxylate synthase (P5CS) genes and down-regulated polyamine oxidase (PAO), diamine oxidase (DAO) and proline dehydrogenase (ProDH) gene expressions. When endogenous ABA content was decreased by the treatment of fluoridone (FLU) that is an ABA inhibitor, leaf rolling degree (%), H2O2 content and antioxidant enzyme activities increased, but osmolyte levels, ADC and P5CS gene expressions decreased. Finally, the treatment of ABA to maize seedlings exposed to drought stress resulted in the stimulation of the antioxidant system, osmotic adjustment and reduction of leaf rolling. We concluded that ABA can be a signal compound cross-talking H2O2, proline and polyamines and thus involved in the leaf rolling mechanism by providing osmotic adjustment. The results of this study can be used to provide data for the molecular breeding of maize hybrids with high grain yield by means of moderately rolled leaves.

Physiological and biochemical responses of two sugarcane genotypes growing under free-air ozone exposure

Biomass accumulation, physiological and biochemical responses of sugarcane to ozone (O3) were evaluated in two genotypes (IACSP94-2094 and IACSP95-5000) in a realistic free-air O3 exposure system. Our aims were to investigate the mechanisms involved in O3 detoxification and verify whether such mechanisms are genotype-dependent. Plants were exposed to ambient air (Amb.) and ambient air plus 40% increase in O3 concentration (x1.4) for 90 days. Plants at x1.4 O3 showed reductions in leaf gas exchange and biomass production with consistent differences between the genotypes. Photosynthesis of IACSP95-5000 was more sensitive to elevated O3 as compared to IACSP94-2094. As a primary response, IACSP94-2094 showed reductions in stomatal conductance due to elevated O3, thus avoiding oxidative stress and maintaining CO2 assimilation for longer. As a consequence, IACSP94-2094 produced more biomass, and stalks had more soluble sugar concentration than IACSP95-5000. Leaf concentrations of O2− and H2O2 in plants exposed to x1.4 O3 were not enhanced, with such unexpected result suggesting that sugarcane plants have an effective antioxidant system to avoid O3-induced damage. In both genotypes, increases in ascorbate peroxidase activity was directly related to decreases in leaf H2O2 concentration. In IACSP94-2094, however, catalase pathway was also stimulated for detoxifying H2O2. We concluded that sugarcane sensitivity to O3 is genotype-dependent and then it is possible to reduce the deleterious effects of high O3 levels on sugarcane physiology and biomass production by growing tolerant genotypes in polluted areas.

Physiological alterations due to field salinity stress in melon (Cucumis melo L.)

This study was aimed to assess physiological responses of melon (Cucumis melo L.) cultivars to salinity stress under field conditions. Seventeen melon cultivars including 16 widely distributed native and one exotic (‘Galia’) were subjected to 2-year (2014–2015) field salinity stress. Leaf relative water content (RWC), membrane stability index (MSI), pigments [chlorophyll a, b, total chlorophyll (TChl), carotenoid (Car) and their ratios], malondialdehyde (MDA), H2O2 content, proline content (Pro), total soluble sugar content (TSC), salinity tolerance and susceptibility indices as well as yield were evaluated. The results of combined analysis of variance showed significant genotypic variation for all the traits and significant effect of salinity stress on all the traits with the exception of Chla/Chlb and TChl/Car ratios. Overall, field salinity stress caused an increase in leaf MDA, H2O2, Chla, Chlb, TChl, Car, Pro and TSC and caused a reduction in leaf MSI and RWC as well as yield. The results of correlation coefficients showed that accumulation of osmolytes (proline and TSC) led to an increase in RWC and a decrease in MDA contents. In addition, the results of multiple regression analysis showed that leaf MDA, TSC, MSI and Chla contents were the most important predictors of yield justifying 72% total variation of yield under saline conditions. These results may highlight a dynamic interplay among biomarkers for lipid peroxidation (MDA), sugar osmolytes (TSC) and photosynthetic pigment (Chla) to maintain cell viability and cell wall integrity under salinity stress conditions in melon.

Exogenous Application of Humic Acid Mitigates Salinity Stress in Maize (Zea mays L.) Plants by Improving some Key Physico-biochemical Attributes

Application of salt stress (100 mM) through root growing medium caused a considerable decrease in plant fresh and dry biomass, maximum quantum yield (Fv/Fm), chlorophyll contents, leaf water potential, and leaf Ca, K, P and N concentrations of two maize cultivars (Apex 836 and DK 5783). However, salt-induced increase was observed in leaf osmolality (LO), proline, hydrogen peroxide (H2O2), malondialdehyde (MDA), Na+ concentration and activities of enzymatic antioxidants, such as catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD). Of five humic acid (HA) levels used under non-stress and stress conditions in an initial experiment, 100 mg L−1 was chosen for subsequent studies. Exogenous application of humic acid (HA) at the rate of 100 mM as a foliar or pre-sowing seed treatment significantly increased the plant biomass, Fv/Fm, chlorophyll pigments and proline contents, while it considerably reduced the leaf water potential, H2O2 and MDA contents as well as the activities of all the afore-mentioned enzymatic antioxidants. Of both modes of exogenous treatment, foliar spray was better in improving plant biomass, chlorophyll contents, LO, leaf Na+ as well as the accumulation of all nutrients measured, however, in contrast, seed pre-treatment was more effective in altering leaf proline, H2O2 and MDA contents. Of both maize cultivars, cv. DK 5783 excelled in plant biomass, chlorophyll contents and leaf N, Ca and K concentrations as well as in the activities of all three antioxidant enzymes, whereas cv. Apex 836 was superior in leaf Na+ and P concentrations, H2O2 and MDA contents. Cv. DK 5783 was comparatively better in salt tolerance as compared to cv. Apex 836. Overall, exogenous application of HA was effective in improving salinity tolerance of maize plants which can be attributed to HA-induced increase in plant biomass, chlorophyll contents, mineral nutrients and activities of key antioxidant enzymes.

MiR156 switches on vegetative phase change under the regulation of redox signals in apple seedlings

In higher plants, miR156 regulates the vegetative phase change via the target SBP/SPL genes. The regulation of miR156 during ontogenetic processes is not fully understood. In the apple genome, of 31 putative MdMIR156 genes that encode pre-miR156, seven were dominantly expressed. However, the transcript levels of only MdMIR156a5 and MdMIR156a12 decreased significantly during the vegetative phase change, which was consistent with the mature miR156 level, indicating that miR156 is under transcriptional regulation. Leaf H2O2 content was higher in the adult phase than in the juvenile phase because of excess H2O2 accumulation in chloroplasts. When in vitro shoots were treated with menadione, diphenyleneiodonium, L-2-oxothiazolidine-4-carboxylic acid or buthionine sulphoximine, the expressions of MdMIR156a5, MdMIR156a12, and as well miR156 were coordinated with reduced glutathione (GSH) contents and glutathione/glutathione disulfide ratio but not H2O2 contents. Alteration of miR156 expression level by MdMIR156a6-overexpressing or miR156-mimetic transgenic Nicotiana benthamiana did not cause a corresponding change in reactive oxygen species or GSH status. Collectively, the results indicate that the vegetative phase change in apple is controlled by the MdMIR156a5 and MdMIR156a12 transcriptional regulatory network in response to the plastid–nucleus redox signals, such as GSH.

Better tolerance to water deficit in doubled diploid ‘Carrizo citrange’ compared to diploid seedlings is associated with more limited water consumption

Tolerance to water deficit in diploid (2x) and doubled diploid (4x) ‘Carrizo citrange’ (Citrus sinensis [L.] Osbeck × Poncirus trifoliata [L.] Raf) was investigated. Water deficit was applied for 4 weeks. Physiological parameters, including stomatal conductance (g s), photosynthesis (A), transpiration (E), leaf and soil water potentials (Ψ leaf; Ψ soil), and pot water loss, were monitored throughout the stress. Moreover, ABA, H2O2 contents, and the expression of genes involved in ABA biosynthesis (NCED3), regulation of abscisic acid signaling (ABI1), and coding for a catalase enzyme (CAT2) known to favor H2O2 scavenging were monitored. During the experiment g s, A, and E values were most of the time higher in 2x compared to 4x. During the water deficit period, pot water loss decreased faster in 2x compared to 4x, leading to a faster decrease in all physiological parameters in 2x. The higher sensitivity of 2x compared to 4x was correlated with more numerous thinner roots, higher leaf ABA and H2O2 contents, and with the lower leaf water potential. ABI1 and NCED3 expression was not strictly correlated with the ABA content. However, the higher CAT2 expression in 4x was correlated with the lower leaf H2O2 contents. Therefore, the better tolerance observed in 4x ‘Carrizo citrange’ compared to 2x was associated with more limited water consumption and better and H2O2 scavenging.

Using controlled salt stress and β-aminobutyric acid signaling to decrease transplant failure

Root injuries, heat and desiccation after transplanting are abiotic stresses that may cause transplant failure. Stress signal transduction for preventing transplant failure due to root injuries and growing in hot dry conditions was evaluated using Pistacia vera, a species highly sensitive to transplanting, as the model plant. Pistachio seedlings were primed by exposure to salt stress using 100mM CaCl2 100mM KNO3, 50mM CaCl2+50mM KNO3, and three foliar applications of 2.0mM β-aminobutyric acid (BABA) for 7days. After removing 30% of the root length, the plants were then grown under hot dry conditions for 60days. Significant increases were observed in the plasma membrane thermostability and proline and malondialdehyde leaf concentrations after the priming treatments. The BABA and KNO3 treatments increased leaf H2O2 content by 26% while the KNO3+CaCl2 treatment increased it by 63%. Detached leaves of non-primed plants lost water more quickly than leaves of primed plants. The BABA and KNO3+CaCl2 treatments were most effective at limiting water loss from detached leaves. Transplanting killed all the non-primed plants. The CaCl2 treatment increased transplant survival by 42.9% and the KNO3+CaCl2 treatment by 100%. The survival rate of BABA and KNO3 primed plants was 57.1%. These results suggest controlled salt stress could be a simple, rapid and efficient method of for controlling transplant shock.

Effects of Low pH on Photosynthesis, Related Physiological Parameters, and Nutrient Profiles of Citrus.

Seedlings of “Xuegan” (Citrus sinensis) and “Sour pummelo” (Citrus grandis) were irrigated daily with a nutrient solution at a pH of 2.5, 3, 4, 5, or 6 for 9 months. Thereafter, the following responses were investigated: seedling growth; root, stem, and leaf concentrations of nutrient elements; leaf gas exchange, pigment concentration, ribulose-1,5-bisphosphate carboxylase/oxygenase activity and chlorophyll a fluorescence; relative water content, total soluble protein level, H2O2 production and electrolyte leakage in roots and leaves. This was done (a) to determine how low pH affects photosynthesis, related physiological parameters, and mineral nutrient profiles; and (b) to understand the mechanisms by which low pH may cause a decrease in leaf CO2 assimilation. The pH 2.5 greatly inhibited seedling growth, and many physiological parameters were altered only at pH 2.5; pH 3 slightly inhibited seedling growth; pH 4 had almost no influence on seedling growth; and seedling growth and many physiological parameters reached their maximum at pH 5. No seedlings died at any given pH. These results demonstrate that citrus survival is insensitive to low pH. H+-toxicity may directly damage citrus roots, thus affecting the uptake of mineral nutrients and water. H+-toxicity and a decreased uptake of nutrients (i.e., nitrogen, phosphorus, potassium, calcium, and magnesium) and water were likely responsible for the low pH-induced inhibition of growth. Leaf CO2 assimilation was inhibited only at pH 2.5. The combinations of an impaired photosynthetic electron transport chain, increased production of reactive oxygen species, and decreased uptake of nutrients and water might account for the pH 2.5-induced decrease in CO2 assimilation. Mottled bleached leaves only occurred in the pH 2.5-treated C. grandis seedlings. Furthermore, the pH 2.5-induced alterations of leaf CO2 assimilation, water-use efficiency, chlorophylls, polyphasic chlorophyll a fluorescence (OJIP) transients and many fluorescence parameters, root and leaf total soluble proteins, H2O2 production, and electrolyte leakage were all slightly greater in C. grandis than in C. sinensis seedlings. Hence, C. sinensis was slightly more tolerant to low pH than C. grandis. In conclusion, our findings provide novel insight into the causes of low pH-induced inhibition of seedling growth and leaf CO2 assimilation.