Showing papers in "Plant Growth Regulation in 2015"

Phytohormones and plant responses to salinity stress: a review

Abstract: Plants are exposed to a variety of abiotic stresses in nature and exhibit unique and complex responses to these stresses depending on their degree of plasticity involving many morphological, cellular, anatomical, and physiological changes. Phytohormones are known to play vital roles in the ability of plants to acclimatize to varying environments, by mediating growth, development, source/sink transitions and nutrient allocation. These signal molecules are produced within the plant, and also referred as plant growth regulators. Although plant response to salinity depends on several factors; nevertheless, phytohormones are thought to be the most important endogenous substances that are critical in modulating physiological responses that eventually lead to adaptation to salinity. Response usually involves fluctuations in the levels of several phytohormones, which relates with changes in expression of genes involved in their biosynthesis and the responses they regulate. Present review described the potential role of different phytohormones and their balances against salinity stress and summarized the research progress regarding plant responses towards salinity at physiological and molecular levels. We emphasized the role of abscisic acid, indole acetic acid, cytokinins, gibberellic acid, salicylic acid, brassinosteroids, jasmonates, ethylene and triazoles in mediating plant responses and discussed their crosstalk at various baseline pathways transduced by these phytohormones under salinity. Current progress is exemplified by the identification and validation of several significant genes that enhanced crops tolerance to salinity, while missing links on different aspects of phytohormone related salinity tolerance are pointed out. Deciphering mechanisms by which plant perceives salinity and trigger the signal transduction cascades via phytohormones is vital to devise salinity related breeding and transgenic approaches.

Salicylic acid in plant salinity stress signalling and tolerance

Abstract: Soil salinity is one of the major environmental stresses affecting crop production worldwide, costing over $27Bln per year in lost opportunities to agricultural sector and making improved salinity tolerance of crops a critical step for sustainable food production. Salicylic acid (SA) is a signalling molecule known to participate in defence responses against variety of environmental stresses including salinity. However, the specific knowledge on how SA signalling propagates and promotes salt tolerance in plants remains largely unknown. This review focuses on the role of SA in regulation of ion transport processes during salt stress. In doing this, we briefly summarise a current knowledge on SA biosynthesis and metabolism, and then discuss molecular and physiological mechanisms mediating SA intracellular and long distance transport. We then discuss mechanisms of SA sensing and interaction with other plant hormones and signalling molecules such as ROS, and how this signalling affects activity of sodium and potassium transporters during salt stress. We argue that NPR1-mediated SA signalling is pivotal for (1) controlling Na+ entry into roots and the subsequent long-distance transport into shoots, (2) enhancing H+-ATPase activity in roots, (3) preventing stress-induced K+ leakage from roots via depolarisation-activated potassium outward-rectifying channel (KOR) and ROS-activated non-selective cation channels, and (4) increasing K+ concentration in shoots during salt stress. Future work should focus on how SA can regulate Na+ exclusion and sequestration mechanisms in plants.

Exogenous melatonin improves seedling health index and drought tolerance in tomato

Abstract: The melatonin molecule is well-known for its benefits to human health. It also mediates many physiological processes in plants. In the current study, the effects of melatonin on the health index and drought tolerance of tomato seedlings have been investigated. Under drought stress, chlorophyll contents and net rates of photosynthesis in tomato seedlings were significantly decreased. As the stress was prolonged, the kinetics of chlorophyll fluorescence was also significantly altered. However, plants pretreated with melatonin (0.1 mM) significantly alleviated these negative outcomes caused by the drought stress and enabled plants to maintain their photosynthetic capacity. The results show that application of melatonin to tomato plants enhances their root vigor, mitigates their stress-related damage to PSII reaction centers, minimizes the negative impact of drought by regulating the antioxidant system and reduces the cellular content of toxic substances of the plants. Current study provides valuable information for growers and breeders to use this approach to produce stronger and drought-tolerant tomato seedlings.

Drought priming at vegetative growth stages improves tolerance to drought and heat stresses occurring during grain filling in spring wheat

Abstract: Plants of spring wheat (Triticum aestivum L. cv. Vinjett) were exposed to moderate water deficit at the vegetative growth stages six-leaf and/or stem elongation to investigate drought priming effects on tolerance to drought and heat stress events occurring during the grain filling stage. Compared with the non-primed plants, drought priming could alleviate photo-inhibition in flag leaves caused by drought and heat stress episodes during grain filling. In the primed plants, drought stress inhibited photosynthesis mainly through decrease of maximum photosynthetic electron transport rate, while decrease of the carboxylation efficiency limited photosynthesis under heat stress. The higher saturated net photosynthetic rate of flag leaves coincided with the lowered non-photochemical quenching rates in the twice-primed plants under drought stress and in the primed plants during stem elongation under heat stress. Compared to the non-priming treatment, drought priming either applied once or twice alleviated the grain yield reduction by drought stress during grain filling, and priming during the stem elongation stage alleviated yield loss by heat stress at grain filling. The higher concentration of abscisic acid in primed plants under drought stress could contribute to higher grain yield compared to the non-primed plants. Taken together, the results indicate that drought priming during vegetative stages improved tolerance to both drought and heat stress events occurring during grain filling in wheat.

Nitric oxide mediates hydrogen peroxide- and salicylic acid-induced salt tolerance in rice (Oryza sativa L.) seedlings

Abstract: Nitric oxide (NO), hydrogen peroxide (H2O2), and salicylic acid (SA) are well-known signaling molecules that play multifaceted roles in the stress tolerance of plants; however, their interactions during stress alleviation have not been well studied. We investigated the possible regulatory role of NO in H2O2- and SA-induced reduction of oxidative damage in salt-exposed rice seedlings. For this purpose, hydroponically grown 14-day-old seedlings were pretreated with 100 μM H2O2 or 100 μM SA in the presence or absence of 100 μM hemoglobin (Hb, a potent NO scavenger) for 24 h followed by salt stress (200 mM NaCl) for 72 h. Salt stress significantly increased the levels of H2O2, malondialdehyde, and proline whereas H2O2 and SA pretreatment reduced the values of these parameters. H2O2 and SA pretreatment also inhibited salt-induced loss of total chlorophyll and relative water content. Histochemical detection of reactive oxygen species [ROS: superoxide (O 2 ·− ) and H2O2] indicated evident oxidative burst in the seedlings stressed with salt alone. Salt stress modulated the non-enzymatic and enzymatic antioxidants differentially; however, H2O2 and SA treatment prior to salt stress enhanced these antioxidants compared with the salt-stressed seedlings alone. H2O2 and SA pretreated salt-stressed seedlings also showed higher induction of the methylglyoxal (MG) detoxification system. Endogenous NO content was elevated following H2O2 and SA pretreatment over the experimental period. Adding Hb reduced the level of NO and subsequently abolished the beneficial effects of H2O2 and SA. Our results, therefore, suggest that NO might be involved in H2O2- and SA-induced reduction of oxidative damage through the upregulation of the antioxidant defense and MG detoxification systems to confer salt tolerance in rice seedlings. The data are of considerable value in elucidating the biochemical mechanisms of salt-stress tolerance and will augment the goal of developing appropriate and efficient methods for crop protection in saline environment.

Potassium application mitigates salt stress differentially at different growth stages in tolerant and sensitive maize hybrids

Abstract: A pot experiment was conducted to investigate the role of potassium (K) in extenuating the injurious effect of salt stress on maize hybrids differing in salt tolerance at different growth stages. One salt-sensitive viz. 8441 and one salt-tolerant viz. 26,204 maize hybrids were sown in pots having 12 kg soil. The recommended dose of nitrogen and phosphorus @ 200 and 150 kg ha−1 with different rate of potassium (75, 150 and 300 kg ha−1) and salinity level (10 dS m−1) was developed in soil before filling the pots. Salinity stress reduced plant growth by affecting plant morphological characteristics, reducing relative water contents and membrane stability index, decreasing photosynthetic activities, altering K+/Na+ ratios and antioxidant activities of both maize hybrids at all three growth stages. However, results also depicts that maximum relative water contents, membrane stability index, gas exchange attributes, photosynthetic pigments, antioxidant enzymes activities and proline contents was observed at reproductive growth stage as compared to vegetative and grain development growth stages in both hybrids. The inhibitory effect of salt stress was more pronounced on maize hybrid 8441 than 26,204. But, addition of potassium significantly alleviates harmful effect of salinity by improving the plant growth, gas exchange parameters, enhancing K+/Na+ ratios and antioxidant activities of both maize hybrids. Potassium application (300 kg K ha−1) was found more effective in alleviating perilous effect of salinity as compared to other two levels. Salt tolerant maize hybrid (26,204) produced more biomass, less shoot Na+ concentration, high K+ concentration, exhibited more chlorophyll contents, gas exchange parameters and antioxidant enzymes activities under salt stress condition at all growth stages as compared to salt sensitive maize hybrids (8441). These results suggested that potassium application counteracted the unfavorable effects of salinity on growth of maize by civilizing photosynthetic capacity of maize plants against salinity-induced oxidative stress and maintaining ion homeostasis, however, these alleviating effects were cultivar specific.

Exogenously applied spermidine improves drought tolerance in creeping bentgrass associated with changes in antioxidant defense, endogenous polyamines and phytohormones

Abstract: Improvement of endogenous polyamine (PA) levels by exogenous spermidine (Spd) application in leaves may promote drought tolerance of plants In this study, leaves of creeping bentgrass (cv ‘Penn-A4’) were pretreated with 02 mmol Spd every another day for three cycles before water was limited for 15 days in a growth chamber The application of exogenous Spd elevated the accumulation of endogenous PA, including putrescine, Spd and spermine in leaves of creeping bentgrass under drought stress Exogenous Spd effectively alleviated the damage effects from drought stress, as demonstrated by lower O2 ·− generation rate, H2O2 and malondialdehyde content, higher relative water content, chlorophyll content and antioxidant enzyme activities (superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase) as compared to untreated plants Additionally, the pretreatment with Spd resulted in a lower accumulation of indole-3-acetic acid (IAA) and gibberellin A3 (GA3) after 15 days of drought stress, but an unchanged accumulation of abscisic acid compared to the untreated ones These results suggest that ameliorating drought stress through exogenously applied Spd may be associated with increased antioxidant protection capability and after a longer stress treatment with changed IAA and GA3 accumulation level on account of improved endogenous PA content In addition, drought tolerance mechanisms related to PA regulation of phytohormones are very complex and deserve further investigation

Differences in photosynthesis, yield and grain cadmium accumulation as affected by exogenous cadmium and glutathione in the two rice genotypes

Abstract: Greenhouse pot experiments were conducted using Cd-tolerant (Bing97252) and sensitive (Xiushui63) rice genotypes to investigate genotypic differences in yield, Cd accumulation and photosynthesis at different growth stages in response to different Cd levels and as affected by glutathione (GSH). Yield of the two genotypes were impaired when soil Cd levels higher than 5 mg kg−1 (Cd2), with Xiushui63 being more affected. Application of GSH at seedling, elongation or the both stages significantly increase yield in Bing97252 and at elongation stage in Xiushui63. Cd concentration in leaves showed dose-dependent responses at seedling and elongation stages except Xiushui63 which showed a slight reduction under Cd5 (100 mg kg−1) treatment over Cd4 (50 mg kg−1). At harvest stage, leaf Cd concentration also increased with Cd levels in both genotypes. Grain Cd concentration showed dose-dependent increase in Xiushui63, but this increase was only found from control to Cd3 (10 mg kg−1) treatments in Bing97252. Addition of GSH markedly decreased grain Cd concentration in both genotypes. Regression equations between grain and leaf Cd concentrations at seedling/elongation stage were established, and the calculated critical levels of Cd in leaves at seedling (0.403 mg kg−1 DW) and elongation (0.299 mg kg−1 DW) stages were obtained for safe rice grain production. Net photosynthetic rate and stomatal conductance were not affected at different growth periods under different Cd levels in Bing97252, but significantly reduced at filling stage in Xiushui63 when soil Cd levels up to 50 mg kg−1. Intercellular CO2 concentration was significantly reduced during the whole growth period under high soil Cd level except seedling stage in Xiushui63, while the decrease was found in Bing97252 only at seedling stage. Our findings demonstrate that adoption of low Cd accumulation genotype coupled with GSH application provided a promising strategy to reduce grain Cd accumulation for safe food production, especially in slight or moderate Cd polluted soils.

Application of nitric oxide and calcium nitrate enhances tolerance of wheat seedlings to salt stress

Abstract: Nitric oxide and calcium are two kinds of signaling molecules that are the key secondary messenger. An experiment was conducted in saline culture solution to examine the cross-talk interactions of nitric oxide and calcium in common wheat under NaCl stress. Addition of 100 mM NaCl reduced plant growth, decreased the chlorophyll content and root activity, increased the reactive oxygen species (such as $$ {\text{O}}_{2}^{ \cdot - } $$ and H2O2) level, lipid peroxidation and electrolyte leakage, and suppressed the activities of antioxidant enzymes in wheat seedlings. Moreover, high Na+ resulted in the deficiency of mineral nutrients. While addition of 0.10 mM sodium nitroprusside (a NO donor) and/or 17.50 mM Ca(NO3)2 (Na/Ca = 5) alleviated a decline in chlorophyll content, root activity and soluble sugar content, stimulated the activities of antioxidant enzymes such as superoxide dismutase, peroxidase and catalase and decreased the electrolyte leakage, lipid peroxidation, H2O2 content, $$ {\text{O}}_{2}^{ \cdot - } $$ generation rate. Furthermore, the concentrations of potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn), iron (Fe) and copper (Cu) concentrations in the leaves and roots of wheat were increased, indicating that application of Ca(NO3)2 facilitated the maintenance of ion homeostasis, while the exogenous NO improved the uptake of Ca. The results suggest that the nitric oxide and calcium are effective in alleviating the adverse effects of salt stress: the nitric oxide is more actively involved in antioxidant system while the calcium is more beneficial to ion homeostasis. When applied in combination, Ca(NO3)2 could counteract the toxicity of exogenous NO to the root, while the exogenous NO may promote the selectivity of uptake and transport of Ca2+.

Effective microorganisms improve growth performance, alter nutrients acquisition and induce compatible solutes accumulation in common bean (Phaseolus vulgaris L.) plants subjected to salinity stress

Abstract: No information is available concerning effective microorganisms (EM) influence on the ionic and osmotic responses in plants grown in salty soils. Therefore, as a first approach, this study focuses on the contribution of EM to nutrient acquisition and compatible solutes accumulation in salt-stressed plants. It assesses some mechanisms underlying alleviation of salt toxicity by EM application, and also directs to establish a possible interrelationship between EM application as well as ionic and osmotic stresses tolerance in plants exposed to saline soils. Phaseolus vulgaris cv. Nebraska plants were grown under non-saline or saline conditions (2.5 and 5.0 dS m−1) with and without EM application. Salinity stress significantly decreased growth, productivity, membrane stability index, relative water content, concentrations of N, P, K+, Fe, Zn and Cu, and the ratios of K+/Na+, Ca2+/Na+ and Mg2+/Na+. However, EM application protected plants against the detrimental effect of salinity and significantly improved the above parameters. Concentrations of Ca+2, Mg+2, soluble sugars, free amino acids, proline and glycinebetaine were increased under saline conditions; moreover they further increased in salt-stressed plants treated with EM. Lipid peroxidation, hydrogen peroxide content, electrolyte leakage and Na+ level were increased in response to salinity and significantly decreased when stressed plants treated by EM. Reduction in Na uptake together with a concomitant increase in N, P, K, Ca, Mg, Fe, Zn and Cu absorption and a high compatible solutes accumulation may be an efficient mechanism used by EM-treated plants to gain tolerance against salinity stress.

Proteomic analysis of salt-stress responsive proteins in roots of tomato (Lycopersicon esculentum L.) plants towards silicon efficiency

Abstract: Salt stress is a rising threat to crop productivity, among several notable consumed crops tomato is often under threat due to salt stress. In this study, the role of Si in restraining salinity stress responses in root proteome and genes involved in stress tolerance has been studied. Fifteen days old tomato (Lycopersicon esculentum L.) plants grown hydroponically with or without NaCl were fed with 2.5 mM Si in the form of potassium silicate [K2SiO3]. The response to a combined effect of NaCl and Si were studied 5 days after treatment. Proteomic analysis indicated that 40 proteins were differentially expressed under Si and/or salt stress treatments. Twenty-four of them were up-regulated by Si supplements (50 mM +NaCl/+Si) and down-regulated in salt-stressed roots (50 mM +NaCl/−Si), and these proteins were mostly associated with stress responses, plant hormones and transcriptional regulations. The rest of them belong to other secondary metabolites. Moreover, 17 differentially expressed proteins (25 mM +NaCl/+Si), up-regulated in the Si treatments, were mostly related to stress responses, plant hormones and cellular biosynthesis, and the rest of the proteins were related to transcriptional regulation, RNA binding and other secondary metabolisms. In addition, 17 protein spots were observed absent in salinity-stressed roots (25/or 50 mM +NaCl/−Si). Moreover, the important genes associated with salt stress responses (leDREB-1, leDREB-2 and leDREB-3), antioxidants (leAPX, leSOD and leCAT genes) and Si transport (leLsi-1, leLsi-2 and leLsi-3) were analyzed by the real-time polymerase chain reaction. The physiological data such as thiobarbituric acid reactive substances, superoxide dismutase as an oxidative stress marker and concentration of Si all correlated well with proteomic and gene expression data. The observed responses to Si supply in salt stressed plants indicate that the Si has a substantial role in alleviating the salinity stress responses by improving the root proteome and activating important genes responsible for stress tolerance.

Endophytic bacteria improve nodule function and plant nitrogen in soybean on co-inoculation with Bradyrhizobium japonicum MN110

Abstract: The potential of bacterial endophytes to improve symbiotic efficiency through synergistic interactions with rhizobia can help to improve nodulation and nitrogen fixation in legume plants. In the present study, we compared the effect of endophytic plant growth-promoting bacteria on nodulation and effective rhizobial symbiosis in soybean. Nodule endophyte Bacillus megaterium LNL6 isolated from root nodules of Lesperdeza sp. and plant endophyte Methylobacterium oryzae CBMB20 isolated from rice leaves were selected as endophytic co-inoculants. Treatment of Bradyrhizobium japonicum MN110 along with B. megaterium LNL6 and M. oryzae CBMB20 exhibited an increase in nodule number in pots at 35 days after sowing compared to single inoculation of MN110. Additionally, both the co-inoculation treatments showed significant increase in nodule activity which was measured in terms of nodule leghemoglobin content, nodulated root ARA and total plant nitrogen content compared to solitary inoculation of B. japonicum MN110. Though ACCD activity of the co-inoculated strains can be attributed to increase in nodule number, the observed increase in root nitrogenase activity and leghemoglobin content in the nodules is understood as due to plant growth promotion traits of the specific endophytic strains. High levels of IAA produced by B. megaterium LNL6 can be considered to have aided development of mature nodules which thereby improved the nodular nitrogen fixation. Thus, endophytic lifestyle combined with plant growth-promoting traits, such as IAA production, ACC deaminase, cellulase and nitrogenase activity by B. megaterium LNL6 and M. oryzae CBMB20, contributes to the improvement of overall symbiotic nitrogen fixation by the plant.

Physiological and biochemical responses to drought stress in cultivated and Tibetan wild barley

Abstract: Greenhouse pot experiments were conducted to investigate genotypic differences in response to drought stress between Tibetan wild barley genotypes (XZ5 and XZ150, drought-tolerant; XZ54 and XZ147, drought-sensitive) and cv ZAU3. Drought stress of 4 % soil moisture content (SMC) significantly decreased water potential (WP) and osmotic potential (OP), while increased water saturation deficit (WSD) and the bound water content (BWC) in leaves, with the least decrease/increase in XZ5, which recorded the highest levels in WP and OP but the lowest in WSD and BWC under 4 % SMC. Under 15 % SMC, when compared with control, XZ5 and XZ150 had more elevation in soluble sugar content relative to the other 3 genotypes, while XZ5 had the least increase in soluble protein. Under 4 % SMC, endogenous ABA content increased more in XZ5 and XZ150 than in the other three genotypes, but proline content increased least in XZ5. After rewatering, the transpiration rate increased in sensitive genotypes but decreased in tolerant genotypes. The less elevated MDA accumulation was observed in XZ5 and XZ150 with higher POD and CAT activities under 15 and 4 % SMC than in the other three genotypes. Drought stress of 4 % SMC significantly up-regulated the expression levels of CAT1 and Cu/ZnSOD in XZ5 and MnSOD in XZ150.Our results indicated that drought tolerance of wild barley XZ5 is mainly associated with the osmo-regulation of soluble sugar and stomatal regulation of ABA. This mechanism could be applied to improve the drought tolerance of cultivated barley and the further marker-assisted breeding.

Chitosan enhances rice seedling growth via gene expression network between nucleus and chloroplast

Abstract: Chitosan, a partially deacetylated form of the natural and biodegradable biopolymer chitin, has been used as plant growth promoter in agriculture. The aim of this work was to investigate the growth promoting responses induced by chitosan at the physiological and molecular level in rice (Oryza sativa L.) seedlings. The combination of the degree of deacetylation (DD), molecular weight and concentration of chitosan had differing effects on the rice seedling growth. For the best enhancement, oligomeric chitosan with an 80 % DD applied at 40 mg/L significantly enhanced the vegetative growth, in terms of the leaf and root fresh weights and dry weights of rice seedlings compared to the control. At the proteomics level, of the 352 rice leaf proteins that could be resolved using the Multi Experiment Viewer software, 105 showed a significantly different expression level in rice leaves treated with chitosan compared to the control. Co-expression network analysis revealed nine of these proteins had significant coexpression with other genes from the three main biochemical network systems of photosynthesis, carbohydrate metabolism and cell redox homeostasis. More than 90 % of the genes positively co-expressed with these nine chitosan-responsive proteins were localized in chloroplasts, suggesting that chitosan enhanced the plant growth of rice seedlings via multiple and complex networks between the nucleus and chloroplast.

The alleviation of cadmium toxicity in oilseed rape (Brassica napus) by the application of salicylic acid

Abstract: To assess the potential role of salicylic acid (SA) in plants under cadmium (Cd) stress, a study was conducted on three different oilseed rape (Brassica napus) genotypes. Gas exchange parameters, photosynthetic pigments, antioxidant enzymes activities, mineral nutrients concentration, and ultrastructural analysis were carried out for assessment. Interestingly, cadmium treatment reduced gas exchange parameters, photosynthetic pigments, mineral elements [calcium (Ca), magnesium (Mg), and iron] and the activity of catalase (CAT) enzyme. Whereas, a pronounced increase was observed in malondialdehyde content and antioxidant enzymes, cadmium and zinc accumulation. Impressively, SA played its role as an alleviatory agent by reducing the damage to all parameters caused by Cd except internal CO2 concentration which was further decreased by SA. Even more, Cd and SA showed synergistic effects by increasing superoxide dismutase, peroxidases, ascorbate peroxidase, guaiacol peroxidase, glutathione reductase and decreasing CAT. Apart from affecting the enzyme activities of oilseed rape, both Cd and SA had the same inhibitory effects on Ca and Mg concentrations. Damage caused by Cd to chloroplast and other internal organelles were almost rectified by SA. Effective role of SA, in alleviating Cd toxicity, could be attributed to the SA-induced improvement of photosynthetic activities, enhancement of antioxidant enzymes activities, reduction in lipid peroxidation and Cd uptake. These findings reflect the possible role of SA as a potential inhibitor of cadmium toxicity by strengthening the internal immunity in oilseed rape.

Improvement of photosynthesis in rice (Oryza sativa L.) as a result of an increase in stomatal aperture and density by exogenous hydrogen sulfide treatment

Abstract: Hydrogen sulfide (H2S) is considered to be the third gaseous signaling molecule after NO and CO, and it plays an active role in regulating the physiological processes of plants and animals. In this work, rice cultivar ‘IIyou 084’ seedlings were treated with NaHS, which is a donor of H2S, for 10 days, and its effects on growth and physiology, including photosynthesis, photorespiration, chlorophyll fluorescence, and stomata, were investigated. The data revealed that 0.01 mM of H2S improved rice biomass and chlorophyll content, while higher concentrations of H2S had an adverse effect on these parameters. Photosynthetic rate, stomatal conductance, and ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) activity also increased under 0.01 mM H2S treatment. However, photosynthetic oxygen evolution rate, photosynthetic electron transfer, and photochemical efficiency of PSII were not affected by H2S treatment. In addition, photosynthesis oxygen sensitivity, CO2 compensation point, and glycolate oxidase (EC 1.1.3.1) activity reduced by H2S treatment, and thus photorespiration was down-regulated. Under light, stomatal aperture and density increased by treatment with 0.01 mM H2S. On the basis of these results, it can be deduced that 0.01 mM of H2S treatment improved photosynthesis in rice by increasing its stomatal aperture and density, which may result from reduced photorespiration.

Evidence of phytohormones and phenolic acids variability in garden-waste-derived vermicompost leachate, a well-known plant growth stimulant

Abstract: Cytokinins, auxins, abscisic acid, gibberellins (GAs) and brassinosteroids (BRs) as well as the phenolic acid content in three batches of vermicompost leachate (VCL) were quantified using ultra high performance liquid chromatography–tandem mass spectrometry N 6-isopentenyladenine formed the major (60 %) proportion of the CK content while dihydrozeatin had the lowest (<002 %) concentration Indole-3-acetic acid ranged from approximately 055–077 pmol/mL A total of 18 GAs including bioactive forms and metabolic end products were observed in the VCL samples Cathasterone had the highest (2,500–3,200 fg/mL) concentration while brassinolide was the lowest (1–5 fg/mL) abundant BRs found Phenolic acids quantified were protocatechuic acid (3–36 µg/mL), p-hydroxybenzoic acid (25–28 µg/mL), p-coumaric acid (1–17 µg/mL) and ferulic acid (0–4 µg/mL) These results provide an indication of the rich diversity in natural PGRs and phytochemicals in VCL which may inevitably contribute to the numerous favorable physiological responses elicited by VCL application to plants

Elimination of gibberellin from Kappaphycus alvarezii seaweed sap foliar spray enhances corn stover production without compromising the grain yield advantage

Abstract: Sustainable intensification of agricultural productivity is a global challenge. The sap of the commercially important red seaweed, Kappaphycus alvarezii, has been of interest in this regard, and its application as foliar spray has had a profound impact on the yields of many crops. It has been shown to contain indole acetic acid, kinetin, zeatin and gibberellic acid (GA3) but no study is yet reported on the interactions among these constituents, if any. In the present study, selective solvent extraction was undertaken to obtain GA3-free and indole acetic acid-free sap compositions. Another composition was prepared by autoclaving the sap which resulted in degradation of all the above growth hormones. The sap variants, along with water spray (control) and pristine sap, were applied on Zea mays as foliar spray over three consecutive seasons in dilute form. The four sap treatments were at par with one another—and significantly superior to control treatment—in so far as grain yield and quality were concerned. Pristine sap was subsequently shown to also contain choline and glycine betaine, and these were detected in similar amounts in all the sap variants, apparently indicating their profound influence on grain yield. Another important observation was that GA3-free sap led to heightened photosynthetic activity which translated into 26 % increase in corn stover yield compared to pristine sap. This is hypothesized to be on account of prevention of negative interactions between GA3 and other hormones. The study constitutes the first report of enhancement of performance of a natural seaweed plant stimulant towards increasing plant growth through simplification of its composition.

Volatile compounds from Alcaligenes faecalis JBCS1294 confer salt tolerance in Arabidopsis thaliana through the auxin and gibberellin pathways and differential modulation of gene expression in root and shoot tissues

Abstract: Volatile compounds from rhizobacteria are known to elicit and regulate plant growth and defense against various biotic and abiotic stresses. In the present study, we elucidated the biological role of volatiles from Alcaligenes faecalis strain JBCS1294 on the growth performance of Arabidopsis thaliana under salt stress. JBCS1294 volatiles promoted gains in fresh weight and shoot length of Arabidopsis Col-0 under salt stress by 61.5 and 45.8 %, respectively. Hexanedioic acid and butanoic acid were identified as major volatiles emitted from JBCS1294. However, volatiles from JBCS1294 were unable to induce salt tolerance in eir1 and gai-1 mutant lines of A. thaliana, or in auxin and gibberellin inhibitor-treated Col-0 plants. On the other hand, a significant increase of growth in cytokinin-, brassinosteroid-, and ethylene-defective mutant lines, or in respective inhibitor-treated Col-0, led us to conclude that the auxin and gibberellin pathways are mediators which confer salt tolerance in Arabidopsis upon introduction of JBCS1294 volatiles. Exposure to JBCS1294 volatiles did not alter proline content in gai-1 and gibberellin inhibitor-treated lines. Additionally, AtNHX1, AtHKT1, AtSOS1, AtAVP1, auxin and brassinosteroid pathway genes were upregulated in the roots after exposure of salt-stressed seedlings to JBCS1294 volatiles, suggesting tissue-specific remodeling of gene expression.

Effects of application of salicylic acid alleviates cadmium toxicity in perennial ryegrass

Abstract: To study the exogenous salicylic acid (SA) to alleviate the cadmium (Cd) toxicity in ryegrass (Lolium perenne L.), ryegrass plants subjected to 100 μM CdCl2 exposure were treated with different concentrations of SA, and Cd toxicity was evaluated by the decreases in plant growth and chlorophyll content. In Cd-treated plants, the activities of antioxidant enzymes, such as superoxide dismutase, peroxidase and catalase, decreased dramatically in both shoots and roots, whereas the accumulation of superoxide anion (O 2 ·- ), hydrogen peroxide (H2O2) and malondialdehyde (MDA) increased significantly. Excess Cd also decreased soluble protein and ascorbic acid (AsA) contents, increased accumulation of Cd in both shoots and roots; furthermore, the absorption of micronutrients was inhibited. Addition of 200 μM SA had the most significant alleviating effect against Cd toxicity while the addition of 400 μM SA had no significant effect with Cd treatment. Addition of 100, 200, 300 μM SA considerably increased chlorophyll content and the activities of antioxidant enzymes, increased the uptake and translocation of mineral elements, and decreased H2O2 and MDA accumulation in both shoots and roots of Cd-stressed plants. Addition of 200 μM SA not only decreased the Cd uptake in ryegrass, but also decreased the root-to-shoot translocation of Cd and changed its subcellular distribution in plants. Addition of 200 μM SA increased Cd concentrations in soluble fraction and cell wall in both shoots and roots markedly, with the majority of Cd associated with the cell wall and the soluble fraction and a minor part of Cd present in the cell organelle. Based on these results, we conclude that the optimal concentrations of exogenous SA could alleviate Cd-induced stress and promote ryegrass plant growth.

The role of the CBL–CIPK calcium signalling network in regulating ion transport in response to abiotic stress

Abstract: Plants are sessile organisms and have multiple tolerance mechanisms which allow them to adapt to the environmental stresses to which they may be exposed. Key to a plant’s tolerance of abiotic stresses is the ability to rapidly detect stress and activate the appropriate stress response mechanism. The calcineurin B-like (CBL) and CBL-interacting protein kinase (CIPK) signalling pathway is a flexible Ca2+ signalling network which allows a plant to fine tune its response to stress, via both pre- and post-translational mechanisms. Genes encoding CBLs and CIPKs have now been identified in a variety of plant species. Plants have been found to have large gene families of CBLs and CIPKs, each encoding proteins with specific upstream and downstream targets, thus providing the flexibility required to allow a plant to adapt to a variety of stresses. Characterisation of CBL and CIPK mutants have shown them to be important for a plant to survive cold, drought, heat, salinity and low nutrient stresses. Many CBLs and CIPKs have been shown to be involved in the transport of ions through a plant, either limiting the supply of toxic ions to certain tissues or maximising the uptake of beneficial nutrients from the soil. This review will provide an update into the current knowledge of CBL and CIPK interactions and their role in ion transport during abiotic stress.

IAA alleviates Cd toxicity on growth, photosynthesis and oxidative damages in eggplant seedlings

Abstract: Plant growth regulator IAA (indole-3-acetic acid), besides its role in growth and development, is gaining increased attention because of its involvement in regulation of abiotic stresses. To ascertain this hypothesis, sand culture experiments were conducted to investigate the implication of IAA in regulation of Cd (cadmium) toxicity in eggplant (Solanum melongena L.) seedlings. Cd at tested doses (Cd1: 3 mg Cd kg−1 sand and Cd2: 9 mg Cd kg−1 sand) declined growth, pigment contents and photosynthesis, and increased the rate of dark respiratory oxygen uptake, and these effects were accompanied with Cd accumulation in tissues. Photochemistry of photosystem II (PS II) was analyzed by measuring chlorophyll a fluorescence kinetics-JIP test. Cd declined the efficiency of PS II in its concentration dependent manner which is evident from the decreased values of Fv/F0, Fv/Fm (ϕP0), Ψ0, ϕE0 and PIABS and increased values of F0/Fv and energy fluxes per reaction centre: ABS/RC, ET0/RC, TR0/RC and DI0/RC. Enhanced level of oxidants: superoxide radical and hydrogen peroxide under Cd stress stimulated the rate of lipid peroxidation and electrolyte leakage, despite of appreciable rise in activity of superoxide dismutase, peroxidase, catalase, glutathione-s-transferase and contents of non protein thiol and proline. Exogenous IAA application alleviated Cd induced toxicity on growth performance by improving the structural and functional attributes of photosynthetic apparatus i.e. pigment contents and photosynthetic activity. The ameliorating effect of exogenous IAA was due to (1) significant reduction in Cd uptake in roots and its translocation to leaves and (2) further rise in level/activity of antioxidants which brought the level of oxidants under control hence, minimized the oxidative damage in eggplant seedlings.

The mitigating effect of cysteine on growth inhibition in salt-stressed barley seeds is related to its own reducing capacity rather than its effects on antioxidant system

Abstract: This research was an attempt to study the effects of exogenous cysteine (Cys) on early seedling growth, amylase activity, enzymatic and non-enzymatic antioxidant systems, reactive oxygen species (ROS), oxidative stress parameters and DNA damage of germinating barley seeds under salt stress (125 mmol l−1 NaCl). Salt stress markedly reduced root elongation and coleoptile growth; these changes could be alleviated by Cys application. Amylase activity exhibited results parallel to early seedling growth. The observed salinity-mediated reduction in amylase activity was markedly impeded by Cys. Isozyme profile confirmed the mitigating effect of Cys on salt-induced amylase inhibition. ROS production was significantly elevated under salt stress. Changes in lipid peroxidation level and DNA damage coincided with high levels of ROS. However, Cys significantly reduced salt-induced ROS production and mitigated oxidative damage to membranes and genetic material. This mitigating effect of Cys was related to low level of ROS as a conclusion its own antioxidant properties rather than its effect on enzymatic and non-enzymatic antioxidants. We found that although Cys application resulted in different effects on antioxidant system in root and coleoptiles, it had partial reducing effect as compared to stressed seedlings in both organs (especially roots). These results were supported by the isozymes activity profiles. Despite the partial reduction determined in antioxidant system in Cys-applied seedlings, low ROS levels revealed that Cys decreases the need for activation of antioxidant system by acting as a ROS scavenger. The evidence from this study suggests that Cys alleviates salt-induced growth inhibition and suppresses oxidative damage in germinating barley seeds by modulating cellular redox status due to its own antioxidant property.

Burkholderia phytofirmans-induced shoot and root growth promotion is associated with endogenous changes in plant growth hormone levels

Abstract: Plant growth promoting bacteria (PGPB) are capable of significantly altering the growth phenotype of inoculated plants. Changes in growth phenotype are often attributed to the ability of PGPB to assimilate minerals and/or increase mineral uptake, leading to increased plant root growth. However, many PGPB are also capable of either synthesizing plant hormones, such as auxins (mainly indole-3-acetic acid or IAA), gibberellins (GAs) and cytokinins (CKs) or affecting plant hormone biosynthesis (homeostasis) in planta. Burkholderiaphytofirmans strain PsJN is a PGPB capable of inducing biomass growth of several plant species, including potatoes (Solanum tuberosum L.). In this paper we examined the effect of PsJN inoculation of two potato cultivars with similar root growth, but different shoot growth patterns (faster-growing Kennebec and slower-growing Yukon gold) to asses the bacteria’s impact on growth and plant hormone homeostasis. Both cultivars showed similar and massive root growth increases after inoculation and this was associated with a twofold to threefold increase in IAA and CK (trans-zeatin or tZ) levels, expressed on a per plant basis. However, PsJN inoculation resulted in a different shoot growth response, which appeared to depend on the inherent growth characteristics of each cultivar. That is, the slower-growing Yukon gold plants matched the growth rate of faster-growing Kennebec plants 20 days after inoculation and this was associated with higher GA1 levels and lower tZ levels. It is thus concluded that B.phytofirmans strain PsJN-induced plant phenotypic changes are associated with, and likely dependent on, changes in biosynthesis of plant growth hormones.

Aminoethoxyvinylglycine (AVG) ameliorates waterlogging-induced damage in cotton by inhibiting ethylene synthesis and sustaining photosynthetic capacity

Abstract: In this glasshouse study, we investigated the mechanisms of aminoethoxyvinylglycine (AVG)-induced waterlogging tolerance in cotton. Two cotton cultivars Sicot 71BRF (moderately waterlogging tolerant) and LA 887 (waterlogging sensitive) were grown in a clay-loam soil, and exposed to waterlogging at early squaring stage (53 days after sowing). One day prior to waterlogging, shoots were sprayed with AVG (ReTain®, 830 ppm). Continuous waterlogging for 2 weeks accelerated the shedding of leaves and fruits. As the duration of waterlogging increased, shoot growth rate, biomass accumulation, photosynthesis (P n) and stomatal conductance (g s) were all reduced. Growth of LA 887 was more severely impaired than Sicot 71BRF, with a decline in leaf P n and g s after just 4 h of waterlogging. Waterlogging inhibited allocation of nitrogen (N) to the youngest fully expanded leaves, photosynthesis and biomass accumulation, while it accelerated ethylene production promoting leaf and fruit abscission. AVG blocked ethylene accumulation in leaves and subsequently improved leaf growth, N acquisition and photosynthetic parameters. In addition, AVG enhanced fruit production of both cotton cultivars under waterlogged and non-waterlogged conditions. Higher ethylene production in cotton is linked with fruit abscission, implying that AVG-induced ethylene inhibition could potentially limit yield losses in waterlogged cotton.

Elucidating multifaceted urease producing marine Pseudomonas aeruginosa BG as a cogent PGPR and bio-control agent

Abstract: Species belonging to the genus of Pseudomonas are known to possess metabolic versatility and are capable of adapting to various environments. One such strain BG, possessing urease activity, was isolated from marine water from the Gulf of Khambhat, Gujarat. 16S rRNA gene sequence analysis was performed to identify the isolate, which showed that it was the closest neighbor to be Pseudomonas aeruginosa strain BS8. Strain BG was accessed (meant to be assessed?) for multiple plant growth promoting and biocontrol traits. It tested positive for indole-3-acetic acid (IAA) production with 19 mg ml−1 of IAA yield, phosphate solubilization with 13 mg ml−1 solubilization of tri-calcium-phosphate and it showed maximum of 27 mg ml−1 of ammonia production. Further, BG isolate could produce hydrocyanic acid, siderophore, catalase and showed growth inhibition of Aspergillus flavus and Fusarium oxysporum f. sp. cubense confirming its potential antifungal activity. The marine isolate also showed 17.92 ± 1.79 unit min−1 ml−1 urease activity, and further, the presence of genes responsible for urease enzyme in strain BG was identified by amplification using gene specific primers. Talc based biofertilizer using strain BG was prepared and tested on seedling growth of Chickpea, where biofertilizer treated seeds showed enhanced growth. Thus, it was concluded that marine P. aeruginosa BG showed plant growth promotion and biocontrol abilities along with urease activity.

Role of arbuscular mycorrhiza in arresting reactive oxygen species (ROS) and strengthening antioxidant defense in Cajanus cajan (L.) Millsp. nodules under salinity (NaCl) and cadmium (Cd) stress

Abstract: Application of phosphate fertilizers and biosolids enhances Cd contamination in arid and semi-arid regions. Increased concentration of dissolved chloride (Cl−) in saline solution increases Cd solubility and bioavailability. Nodules are soft targets for NaCl and Cd stresses due to adverse effects on their functioning. Arbuscular mycorrhizal (AM) fungi enhance plant growth in contaminated sites. Greenhouse experiments were conducted to evaluate the efficacy of Funneliformis mosseae in arresting toxic ion transport and ROS generation in pigeonpea nodules and its role in improving membrane structure and antioxidant defense. Two genotypes (Sel 85N; tolerant and ICP 13997; sensitive) were subjected to NaCl (4, 6 dS m−1) and Cd (CdCl2—25, 50 mg Kg−1 dry soil) treatments. Results indicated higher phytotoxicity of Cd than NaCl which aggravated when NaCl was added along with Cd. Increment in toxic ions caused injury to nodular membranes and increased oxidative stress (H2O2 and MDA), higher in ICP 13997 than Sel 85N. Significant increase in non-protein thiols (NP-SH) and PC levels was observed under Cd and NaCl + Cd treatments. The rapid generation of ROS was counteracted by AM-induced enzymatic activities (SOD, POD, CAT and GR), non-enzymatic components (GSH–GSSG cycling, their ratio and total glutathione) and glutathione-mediated PC synthesis.

Morpho-physiological and micrographic characterization of maize hybrids under NaCl and Cd stress

Abstract: A hydroponic experiment was conducted to investigate single and combined effects of 5 µmol/L Cd and 100 mM NaCl on growth, root morphology, photosynthetic parameters, leaf and root ultra-structure of two maize hybrids (26204 and 8441) differing in salt tolerance. A more pronounced reduction on growth, root morphology, SPAD value, chlorophyll fluorescence and leaf gas exchange indicated that 8441 was more sensitive than 26204 to both Cd and NaCl stresses. Transmission electron microscopy of 8441 revealed a more severe destruction in root and leaf cells as compared to 26204. The reduction in growth and photosynthetic parameters were associated with severe disorganization of nucleus, chloroplast, mitochondrial damage, vacuolation, and increased number and size of pastoglobuli. Interestingly, the combined stress of both NaCl and Cd had obvious beneficial effect on the plant growth, photosynthetic parameters and cell ultra-structure relative to Cd or Na stress alone in the two maize hybrids. The study suggested that there is involvement of same genetic and physiological mechanisms in response to both Cd and NaCl stresses.

Changes in carbon and nitrogen allocation, growth and grain yield induced by arbuscular mycorrhizal fungi in wheat (Triticum aestivum L.) subjected to a period of water deficit

Abstract: Drought is a major abiotic factor limiting agricultural crop production. One of the effective ways to increase drought resistance in plants could be to optimize the exploitation of symbiosis with arbuscular mycorrhizal fungi (AMF). Hypothesizing that alleviation of water deficits by AMF in wheat will help maintain photosynthetic carbon-use, we studied the role of AMF on gas-exchange, light-use efficiencies, carbon/nitrogen ratios and growth and yield parameters in the contrasting wheat (Triticum aestivum L.) cultivars ‘Vinjett’ and ‘1110’ grown with/without AMF symbiosis. Water deficits applied at the floret initiation stage significantly decreased rates of photosynthetic carbon gain, transpiration and stomatal conductance in the two wheat cultivars. AMF increased the rates of photosynthesis, transpiration and stomatal conductance under drought conditions. Water deficits decreased electron transport rate and increased non-photochemical quenching (NPQ) in ‘1110’ but not in ‘Vinjett’. With AMF, nitrogen concentrations increased in roots of both cultivars, but decreased in grains of ‘Vinjett’ and in side-tiller grains of ‘1110’ regardless of water status. With water deficits, AMF colonization increased plant height in both cultivars. AMF also increased biomass and grain yield in ‘1110’ but not in ‘Vinjett’. The results showed that the improvements in growth and yield were the results of AMF-mediated increases in photosynthesis during drought stress and that the alleviating effect of AMF depended on the wheat cultivar.

Effects of exogenous application of GA4+7 and N-(2-chloro-4-pyridyl)-N′-phenylurea on induced parthenocarpy and fruit quality in Pyrus pyrifolia ‘Cuiguan’

Abstract: Parthenocarpy largely depends on the coordinated action of hormones produced in unpollinated ovaries, but can be induced by application of exogenous hormones. We evaluated the effects of gibberellins (GA4+7) and 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU) on induction and quality of parthenocarpic fruit in Pyrus pyrifolia Nakai ‘Cuiguan’ pear. Parthenocarpic fruit with a small core and a high edible ratio were induced by GA4+7 and/or CPPU. GA4+7 application induced normally shaped fruit with superior quality and normal size, whereas CPPU treatments resulted in abnormally shaped fruit with a larger size and an extraordinarily expanded calyx tube. Among all GA4+7 treatments, 500 mg L−1 GA4+7 induced the highest fruit set (91.88 %) and increased fruit size by 85 % compared with fruit induced by 200 mg L−1 GA4+7. In addition, the parthenocarpic fruit induced by GA4+7 accumulated considerably higher quantities of sucrose and less organic acids than pollinated and CPPU-induced fruit. The potential commercial application of CPPU and GA to pear in place of hand pollination is discussed.