Electrolyte Leakage Rate Research Articles

Different Chilling-Induced Symptoms and the Underlying Oxidative Stress and Antioxidative Defense in the Exocarp and Mesocarp of Immature Sponge Gourd (Luffa cylindrica) Fruit

Immature sponge gourd fruit is consumed as a vegetable with a limited shelf life. Although cold storage is a simple and powerful tool for maintaining postharvest fruit quality, storage at a low temperature may not be appropriate for vegetables as some chilling injury (CI) of the immature sponge gourd fruit may occur. Therefore, this research aimed to elucidate the relationship between CI, oxidative stress, and the antioxidative defense mechanisms in the exocarp and mesocarp of immature sponge gourd fruit. After storage at 5°C for 6 days, visual CI symptoms, including browning and surface pitting, were found in the peel (exocarp) but not in the mesocarp. There were, however, more dead cells (stained by Evans blue) in the mesocarp of the fruit stored at 5°C. There was a more considerable increase in the electrolyte leakage rate in both fruit tissues held at 5°C than 25°C. The CI was correlated with malondialdehyde (MDA) levels in the tissues. The MDA of fruit exocarp at 5°C was 1.6 fold higher than that at 25°C on day 6, while the lipoxygenase (LOX) activity in mesocarp was 50% higher in fruit stored at a lower temperature. The action of ascorbate peroxidase (APX) was high in the exocarp of the fruit stored at 5°C, but there appeared to be a continuous depletion of the co-substrate or ascorbic acid. In conclusion, the CI in the exocarp was mainly associated with a high level of reactive oxygen species (ROS). In contrast, the CI in the mesocarp appeared to be primarily associated with increased lipid peroxidation by the elevated LOX activity under cold stress compared to storage at 25°C.

Foliar-applied polystyrene nanoplastics (PSNPs) reduce the growth and nutritional quality of lettuce (Lactuca sativa L.).

Currently, there is a lack of information about the influence of foliar-applied nanoplastics on crop growth and nutritional quality. To fill the knowledge gap, soil-grown lettuces (Lactuca sativa L.) were foliar-exposed to polystyrene nanoplastics (PSNPs) at 0, 0.1 and 1mg/L for one month. Foliar exposure to PSNPs significantly decreased the dry weight, height, and leaf area of lettuce by 14.3%-27.3%, 24.2%-27.3%, and 12.7%-19.2%, respectively, compared with the control. Similarly, plant pigment content (chlorophyll a, b and carotenoid) was considerably reduced (9.1%, 8.7%, 12.5%) at 1mg/L PSNPs. However, the significant increase in electrolyte leakage rate (18.6%-25.5%) and the decrease in total antioxidant capacity (12.4%-26%) were the key indicators of oxidative stress in lettuce leaves, demonstrating the phytotoxicity of PSNPs by foliar exposure. In addition, the remarkable reduction in micronutrients and essential amino acids demonstrated a decrease in nutritional quality of lettuce caused by PSNPs. Besides, SEM and TEM analysis indicated the possible absorption of PSNPs through leaves stoma and the translocation downwards to plant roots. This study provides new information about the interaction of airborne NPs with plants. It also warns against atmospheric NPs pollution that the adverse effects of airborne NPs on crop production and food quality should be assessed as a matter of urgency.

The Possibilities of Using Ultrasonically Activated Streams to Reduce the Risk of Foodborne Infection from Salad

In this study, we investigated the effects of an ultrasonically activated stream (UAS) on the removal of microbial contaminants from spinach leaves. The microbial loads on samples cleaned with and without UAS were enumerated using the cell culture method and compared against unwashed samples on day 0 and day 6 after cleaning. The effects of UAS cleaning on leaf quality were also examined through both macroscopic and microscopic inspection, as well as measurement of the electrolyte leakage rate. Results showed that the microbial load on samples cleaned with UAS for 2 min was significantly lower on day 6 after cleaning than on those treated without ultrasound. Comparison between the cleaning effects of UAS for 40 s versus 2 min indicated that a cleaning duration of 2 min allowed sufficient time for UAS to disaggregate and detach the microbial contamination more effectively. In this case, the induction of bacteria into a viable but non-culturable state does not affect the shelf-life test results as much as it does with a 40 s clean. UAS cleaning for 2 min did not produce significant surface damage, which can affect overall leaf quality. These findings highlight the potential of UAS systems in the salad industry to improve the microbiological quality and shelf life of salads.

Si fertigation attenuates water stress in forages by modifying carbon stoichiometry, favouring physiological aspects

AbstractClimate change has aggravated the occurrence of drought periods, affecting pasturelands in different regions of the world. Silicon attenuates water deficiency in several species, but there is a lack of research to verify whether Si can modify C stoichiometry and its effects in mitigating water deficit in forage plants. To this end, this research was carried out with the aim of evaluating whether Si supply via fertigation causes an increase in its absorption, stoichiometric modification of C and improvement in physiological variables and in the growth of Brachiaria cultivated under two soil water regimes (70% and 40% of water holding capacity in the soil). Two experiments were carried out with the cultivars BRS RB331 Ipyporã and Mavuno grown in pots filled with Quartzipsamments. In the experiments, the same treatments arranged in a 2 × 2 factorial scheme were applied, with Si application via fertigation applied to the soil and control (Si omission) combined with two soil water regimes (70% and 40% of the water retention capacity in the soil, adequate and deficient water contents, respectively). The two forages that received silicon via fertigation specially cultivated under water deficit had a greater accumulation of Si in the shoot, decreased C content and C:Si ratio and increased C use efficiency, and decreased rate of electrolyte leakage with increased relative water content, leaf water potential, chlorophyll b content, quantum efficiency of photosystem II and, consequently, increased growth and dry matter production. The present research shows that the use of Si via fertigation promotes a new strategy to mitigate water deficit in forages, based on the improvement of the physiological aspects of the plant resulting from the modification of carbon stoichiometry, thereby increasing C use efficiency.

Transcriptomic analyses show that 24-epibrassinolide (EBR) promotes cold tolerance in cotton seedlings.

In plants, brassinosteroids (BRs) are a class of steroidal hormones that are involved in numerous physiological responses. However, the function of BRs in cold tolerance in cotton has not been explored. In this study, cotton seedlings were treated with five concentrations (0, 0.05, 0.1, 0.2, 0.5 and 1.0 mg/L) of 24-Epibrassinolide (EBR) at 4°C. We measured the electrolyte leakage, malondialdehyde (MDA) content, proline content, and net photosynthesis rate (Pn) of the seedlings, which showed that EBR treatment increased cold tolerance in cotton in a dose-dependent manner, and that 0.2 mg/L is an optimum concentration for enhancing cold tolerance. The function of EBR in cotton cotyledons was investigated in the control 0 mg/L (Cold+water) and 0.2 mg/L (Cold+EBR) treatments using RNA-Seq. A total of 4,001 differentially expressed genes (DEGs), including 2,591 up-regulated genes and 1,409 down-regulated genes were identified. Gene Ontology (GO) and biochemical pathway enrichment analyses showed that EBR is involved in the genetic information process, secondary metabolism, and also inhibits abscisic acid (ABA) and ethylene (ETH) signal transduction. In this study, physiological experiments showed that EBR can increase cold tolerance in cotton seedlings, and the comprehensive RNA-seq data shed light on the mechanisms through which EBR increases cold tolerance in cotton seedlings.

The ThSOS3 Gene Improves the Salt Tolerance of Transgenic Tamarix hispida and Arabidopsis thaliana.

The salt overly sensitive (SOS) signal transduction pathway is one of the most highly studied salt tolerance pathways in plants. However, the molecular mechanism of the salt stress response in Tamarix hispida has remained largely unclear. In this study, five SOS genes (ThSOS1–ThSOS5) from T. hispida were cloned and characterized. The expression levels of most ThSOS genes significantly changed after NaCl, PEG6000, and abscisic acid (ABA) treatment in at least one organ. Notably, the expression of ThSOS3 was significantly downregulated after 6 h under salt stress. To further analyze ThSOS3 function, ThSOS3 overexpression and RNAi-mediated silencing were performed using a transient transformation system. Compared with controls, ThSOS3-overexpressing transgenic T. hispida plants exhibited greater reactive oxygen species (ROS)-scavenging capability and antioxidant enzyme activity, lower malondialdehyde (MDA) and H2O2 levels, and lower electrolyte leakage rates under salt stress. Similar results were obtained for physiological parameters in transgenic Arabidopsis, including H2O2 and MDA accumulation, superoxide dismutase (SOD) and peroxidase (POD) activity, and electrolyte leakage. In addition, transgenic Arabidopsis plants overexpressing ThSOS3 displayed increased root growth and fresh weight gain under salt stress. Together, these data suggest that overexpression of ThSOS3 confers salt stress tolerance on plants by enhancing antioxidant enzyme activity, improving ROS-scavenging capability, and decreasing the MDA content and lipid peroxidation of cell membranes. These results suggest that ThSOS3 might play an important physiological role in salt tolerance in transgenic T. hispida plants. This study provides a foundation for further elucidation of salt tolerance mechanisms involving ThSOSs in T. hispida.

Modeling and optimizing the changes in physical and biochemical properties of table grapes in response to natural zeolite treatment

The Response Surface Methodology (RSM) was used to establish a predictive model for the effects of natural zeolite at different concentration and different storage times, as independent variables, on shelf life, physical and chemical properties, quality parameters and phytochemicals compounds of table grapes. The response surface models (RS model) had satisfactory R2 and Adj.R2 and models had non-significant lack of fit (P > 0.05). The parameters of the RS model had a good predictive performance and can be considered validated. The results demonstrated that natural zeolite is able to significantly improve the table grape tissue firmness, enhance different phytochemicals and antioxidants, and decrease water loss, electrolyte leakage, malondialdehyde production and decay extension rates. Treated fruit had a higher superoxide dismutase, ascorbate peroxidase and total antioxidant activity and phenolics, flavonoids and carotenoids contents. Using desirability function method treatment of table grapes with zeolite at 6% and storage for 60 days was found to be the optimized condition.

Contrastive Interpretation of Storage Temperatures on Physiological and Microbiological Parameters of Chemically Treated Button Mushroom ( <i>Agaricus Bisporus</i>) Stored Under Modified Atmospheric Packaging (MAP)

Button mushrooms have always been cherished and admired for their massive role in treating various human diseases. Its delicious taste, flavour and aroma make them desired the main course for everyone's plate. Button mushrooms are highly putrescible in nature due to their higher transpiration rate and thin epidermis, which causes decay within two days from harvesting. So, the current experiments were done to investigate the effect of different temperature, chemical and MAP treatments on physico-chemical and microbiological parameters. Chemically treated button mushrooms with CaCl2, citric acid and 0.1% sorbitol were packed in two MAP air compositions followed by storage at 8°oC and 12°oC for 16 days and observations were recorded at an interval of 4 days for 16 days. Chemically treated button mushrooms with the gas composition of 12% CO2; 6% O2 exhibit better quality retention parameters at 8oC, resulting in a shelf life of around 16 days. Button mushrooms with this treatment provide limited changes in total polyphenol contents, ascorbic acid content, total soluble solids, electrolyte leakage rate and microbiological analysis. Blanched samples exhibit more tissue exudation and browning, responsible for fast tissue degradation and quality loss. Blanched samples without modified atmosphere packaging underwent spoilage and decay after eight days at 8°oC.

The Effect of Alginate-Based Edible Coating Enriched with Citric Acid and Ascorbic Acid on Texture, Appearance and Eating Quality of Apple Fresh-Cut

ABSTRACT Incorporating antibrowning agents into the edible coating is a conventional processing technique for fresh-cut preparation. The main quality attributes of fresh-cuts, i.e., appearance color, taste and texture may be affected by coating formulation and its additives at different and sometime contradictory rates. In this study, the impacts of using alginate coating alone or in combination with citric acid and/or ascorbic acid were studied on browning index, microbial load, textural properties, and some taste and nutritional parameters of apple fresh-cut. Lowering weight loss, decline in browning index, increasing acidic taste and changes in some textural properties (hardness, chewiness, and springiness) in response to adding citric acid to the coating formula can be attributed to the competition of H+ ions with calcium cations and therefore physical alteration of forming gel features. On the other side, adding ascorbic acid, as an active antioxidant compound, led to elevated antioxidant capacity, lowered browning index, and least rates of electrolyte leakage. Totally, after 7 days of storage at 4°C, lowest values of weight loss (0.33%), microbial load (2.95 log CFU/g), electrolyte leakage (35.5%) and highest rates of lightness (96.11) and antioxidant capacity (11.03 mmol Fe2+/Kg) were detected when the coating formulation was enriched with both citric acid and ascorbic acid compounds.

Effect of Titanium Dioxide Nanocomposite Material and Antimicrobial Agents on Mushrooms Shelf-Life Preservation

Mushrooms have limited shelf-life and it can be prolonged if suitable conditions and treatments are effectively applied. In this study, nanocomposite material and antimicrobial agents with a combination of chitosan were used as novel packaging material for mushroom preservation. The microbiological analysis, physicochemical properties, headspace gas analysis, and polyphenol oxidase activity (PPO) during cold storage were investigated. As compared with control, coated mushrooms with chitosan (CHS), and nano-titanium dioxide CHSTiO2 thymol + tween-80 CHSTiO2/TT80 coating treatment showed significantly (p ≤ 0.05) lower respiration rate, microbial contaminations (4.27 log CFU/g), and (5.93 log CFU/g) for total yeast/mold and aerobic plate counts, respectively. The weight loss ratio was the lowest for CHSTiO2/TT80 (10.88% loss) followed by CHSTiO2 (11.76% loss). CHSTiO2/TT80 recorded a higher electrolyte leakage rate (25.84%) and acidity. While the lowest PPO activity was established for CHSTiO2 (17.09 U mg−1 Protein), while the lowest values for total soluble solid concentrations were reported for CHSTiO2/TT80 mushrooms (4.91%). These results indicated that CHSTiO2/TT80 coating treatment might delay the aging degree of white button mushrooms and be investigated as a novel packaging material for other food products in the future.

Effects of biochar and biofertilizer on cadmium-contaminated cotton growth and the antioxidative defense system

Consistent use of large amounts of fertilizers, pesticides, and mulch can cause the accumulation of harmful substances in cotton plants. Among these harmful substances, cadmium (Cd), an undegradable element, stands out as being particularly highly toxic to plants. The objective of this study was to evaluate the ability of biochar (3%) and biofertilizer (1.5%) to decrease Cd uptake, increase cotton dry weight, and modulate the activities of photosynthetic and peroxidase (POD), superoxide dismutase (SOD), catalase enzyme (CAT) in cotton (Gossypium hirsutum L.) grown in Cd-contaminated soil (0, 1, 2, or 4 mg Cd kg−1 soil) in pots. These studies showed that, as expected, exogenous Cd adversely affects cotton chlorophyll and photosynthesis. However, biochar and biofertilizer increased cotton dry weight by an average of 16.82% and 32.62%, respectively. Meanwhile, biochar and biofertilizer decreased the accumulation of Cd in cotton organs, and there was a significant reduction in the amount of Cd in bolls (P < 0.05). Biochar and biofertilizer have a positive impact on cotton chlorophyll content, net photosynthesis, stomatal conductance, transpiration rate, and intercellular CO2 concentration. Thus, the addition of biochar and biofertilizer promote cotton growth. However, biochar and biofertilizer increased the SOD activity of leaves (47.70% and 77.21%), CAT activity of leaves (35.40% and 72.82%), SOD activity of roots (33.62% and 39.37%), and CAT activity of roots (36.91% and 60.29%), respectively, and the addition of biochar and biofertilizer decreased the content of MDA and electrolyte leakage rate. Redundancy analyses showed that biochar and biofertilizer also improved SOD and POD activities by reducing the heavy metal-induced oxidative stress in cotton and reducing Cd uptake in cotton organs. Therefore, biochar and biofertilizer have a positive effect on the growth of cotton.

Antimicrobial efficacy of nisin, oregano and ultrasound against Escherichia coli O157:H7 and Listeria monocytogenes on lettuce

Ready-to-eat vegetables such as lettuce are prone to bacterial contamination, predominantly from Escherichia coli and Listeria monocytogenes, the leading causes of foodborne illnesses globally. Chlorine is widely used as a decontaminant in the fresh produce industry, however, potential carcinogenic risks limit its usage. As an alternative, green methods and hurdle technology are gaining interest. In this paper, the efficacy of a combination of nisin, oregano and ultrasound on the reduction of E. coli and L. monocytogenes on lettuce was studied using response surface methodology/Box-Behnken model design, and was found to be reliable (p < 0.05). A combination of 771.2 IU/g nisin, 0.185% v/v oregano and 14.65 min ultrasound was the most effective treatment on both pathogens, showing log reductions of 3.43 and 9.20 CFU/mL for E. coli and L. monocytogenes, respectively. The treated lettuce samples did not show any significant differences in textural properties; however, mild colour changes and a slight increase in the electrolyte leakage rate was observed, within permissible limits. Interestingly this is the first report on the combination of nisin, oregano and ultrasound, as a promising alternative to chemical treatments for the reduction of E. coli and L. monocytogenes on lettuce, without compromising its appearance and quality.

Antimicrobial activity of honeybush (Cyclopia intermedia) ethanol extract against foodborne pathogens and its application in washing fresh-cut Swiss chard

This study aimed to determine the antimicrobial activities of honeybush ethanol extract (HBE) against Listeria monocytogenes and Escherichia coli O157:H7, and to define whether it could be used to wash fresh-cut Swiss chard. HPLC analysis showed that HBE contained the phenolic compounds, hesperidin, luteolin, kaempferol, mangiferin, and epicatechin, indicating potential antimicrobial activities. The results of disc diffusion tests, time-kill assays, and analyses of the released intracellular compounds revealed that HBE was more effective against L. monocytogenes than E. coli O157:H7. Moreover, scanning electron microscopy images showed that HBE damaged and shriveled the cells of both pathogens. Washing fresh-cut Swiss chard spiked with L. monocytogenes and E. coli O157:H7 with HBE (6 mg/mL) resulted in 2.31–2.67 log reductions in the populations of these bacteria compared with those in the controls. These results were similar to those of washing with sodium hypochlorite (2.20–2.58 log reduction). In addition, washing with HBE maintained the marketable qualities of fresh-cut Swiss chard, namely, color, texture, and electrolyte leakage rates that indicated tissue deterioration. In contrast, the electrolyte leakage rate of the samples washed with sodium hypochlorite increased. These results indicate that HBE could replace sodium hypochlorite and serve as a novel washing agent to ensure the safety and quality of fresh-cut leafy vegetables.

Overexpression of an aquaporin gene PvPIP2;9 improved biomass yield, protein content, drought tolerance and water use efficiency in switchgrass (Panicum virgatum L.)

AbstractSwitchgrass (Panicum virgatum L.) is a prime candidate for non‐grain‐based bioenergy feedstock production. Improved drought tolerance and higher water use efficiency (WUE) are important for its successful field establishment and production, especially on marginal lands. Aquaporins are key channels and regulators for water transportation and maintenance of cellular water status. In this study, the functional role of an aquaporin gene, PvPIP2;9, in switchgrass was studied. Expression of PvPIP2;9 was regulated by diurnal oscillation and osmotic stress. Constitutive over‐expressing PvPIP2;9 in switchgrass significantly improved its leaf length, plant height, aboveground biomass and biomass protein contents under both drought‐ and non‐stressed conditions, and also resulted in higher cellulose content in drought‐stressed transgenic than wild‐type plants. Under 21 days of drought treatment, transgenic plants showed less electrolyte leakage rates, but higher relative water contents, photochemical efficiencies, chlorophyll contents and WUE, indicating that PvPIP2;9 positively regulated plant drought tolerance. Moreover, expression patterns of all 14 switchgrass PIP2 subfamily genes were checked during the drought treatment, and the result showed that over‐expressing PvPIP2;9 also affected transcript levels of most other PIP2 genes. Together, this study showed that improved biomass yield, drought tolerance and higher WUE can be achieved by manipulating the expression of PvPIP2;9 and also suggested PIP2 subfamily genes were transcriptionally regulated in a coordinated manner, which can be used for potential targets for crop drought resistance breeding efforts.

Influences of 1-methylcyclopropene-containing papers on the metabolisms of membrane lipids in Anxi persimmons during storage

Abstract Objectives The aim of this work was to analyse the effects of 1-methylcyclopropene (1-MCP) treatment on the metabolisms of membrane lipids in postharvest Anxi persimmons during storage. Materials and methods Anxi persimmon (Diospyros kaki L. f. cv. Anxi) fruits were treated by paper containing 1-MCP with a concentration of 1.35 μl/l. The cellular membrane permeability was analysed by the electric conductivity meter. The activities of lipoxygenase (LOX), phospholipase (PLD) and lipase were determined by spectrophotometry. The component and relative amounts of membrane fatty acids were determined using gas chromatograph (GC). Results The 1-MCP-treated Anxi persimmons manifested a lower electrolyte leakage rate, lower LOX, PLD and lipase activities, higher levels of unsaturated fatty acids (USFAs), higher ratio of USFAs to saturated fatty acids (SFAs) (U/S), higher index of USFAs (IUFA), but lower levels of SFAs. Conclusions The degradation and the metabolisms of membrane lipids could be suppressed by 1-MCP treatment, which might be accountable for the delaying softening of postharvest Anxi persimmons during storage.

EFFECIVENESS OF SOME AROMATIC OILS TREATMENTS ON QUALITY CONSERVATION OF PEPPERMEN FRESH CUT HERB UNDER COLD STORAGE

The effect of lavender, lemongrass and thyme volatile oils as a supplementary cold storage treatments on quality preservation of fresh cut herb of Menthe piperita L. , during storage for 15 days at 5°C and 7°C followed by 5 days at 20°C, as a marketing condition simulation, was evaluated during 2018 and 2019 seasons. Physical properties, chemical constituents, respiration rate and volatile oil contents were recorded. The results illustrated that discarded herb %, weight loss %, and external appearance (scale) were greatly affected by both factors of the study. The great effect in this respect was obtained with storage at 5°C than 7°C and the effect was also continuous during marketing period at 20°C. An evident decrease in discarded herb % and weight loss % were obtained due to the applied treatments, whereas external appearance values were higher with applied treatments than control during cold storage durations and marketing period. Aromatic oils treatments with 0.50% of lavender, lemongrass and thyme oils were effective than 0.25% of the three aromatic oils. However, chemical constituents i.e total chlorophyll, L-ascorbic acid and total phenols of fresh cut herb were scored highly increases by storage at 5°C than at 7°C storage conditions. Furthermore, The richest chemical constituents mentioned above were obtained with 0.50% of the three aromatic oils treatments and with superior for marketing durations for 5 days at 20°C. On contrary, total acidity of fresh cut herb recorded the minimum values with applied treatments than control (except the treatment of 0.25% thyme oil) during all cold storage durations and marketing period. On the reverse , electrolyte leakage and respiration rate values were controlled and minimized with the applied aromatic oils treatments under 5°C or 7°C cold storage conditions and followed by 5 days at 20°C as a marketing period. The decreases of both electrolyte leakage and respiration rate of fresh cut herb either with cold storage or due to the applied treatments are considered a good indicators to increase storage longevity and high quality. Meanwhile, volatile oil was greatly affected by both cold storage conditions and supplementary refrigeration treatments with lavender, lemongrass and thyme aromatic oils. Conclusively , it could be concluded that the peppermint fresh cut herb can be treated with lavender, lemongrass and thyme aromatic oils before storage at 5°C for 15 days , handling and marketing under 20°C to conserve the quality of the herb.

Browning of Early and Late-Harvested ‘Empire’ Apples Affected by Cold Storage and 1-MCP

The effects of harvest time, 1-methylcyclopropene (1-MCP) and air storage time on the susceptibility of flesh browning in ‘Empire’ apples were studied during a seven-day shelf life period after air storage at 0.5 °C for seven months. Early- or late-harvested ‘Empire’ apples without 1-MCP increased production of ethylene, respiration rates and internal ethylene concentration during the shelf life. Respiration rates increased in the late-harvested fruit for the shelf life period with/without 1-MCP treatment. The 1-MCP-treated fruit was approximately 10 N firmer than fruit not treated with 1-MCP at an early harvest for the entire shelf life duration. Peroxidase activity and percent change in electrical conductivity in the flesh were elevated in late-harvested fruit for the shelf life duration, whereas polyphenol oxidase activities were found to be stimulated by 1-MCP treatment, regardless of harvest time. Late-harvested fruit treated with 1-MCP exhibited increased susceptibility to flesh browning during shelf life, mostly due to reduction of the antioxidant defense mechanism of the fruits to stress in extending storage life, increasing polyphenol oxidase (PPO) activity and electrolyte leakage rate.

The rice Aux/IAA transcription factor gene OsIAA18 enhances salt and osmotic tolerance in Arabidopsis

In plants, auxin/indoleacetic acid (Aux/IAA) proteins are transcriptional regulators, which regulate developmental process and responses to phytohormones and stress treatments. A previous study has shown that the rice Aux/IAA transcription factor gene OsIAA18 is induced by salt and osmotic stresses. However, little is known about the regulatory functions of this gene. In this study, the OsIAA18 gene was successfully cloned from rice. Subcellular localization analysis in onion epidermal cells indicated that OsIAA18 was localized to the nucleus. Expression analysis in yeast showed that the full length OsIAA18 exhibited transcriptional activation. Heterologous expression of OsIAA18 significantly enhanced salt and osmotic tolerance in transgenic Arabidopsis plants. Real-time quantitative PCR analysis showed that constitutive expression of OsIAA18 up-regulated genes involved in abscisic acid (ABA) biosynthesis, proline biosynthesis, stress responses, and reactive oxygen species scavenging under salt and osmotic stresses. Enzymatic analyses found that the transgenic plants had higher 9-cis-epoxycarotenoid dioxygenase, pyrroline-5-carboxylate synthase, superoxide dismutase, and peroxidase activities than wild-type plants under salt and osmotic stresses. In the transgenic plants, ABA and proline content significantly increased, whereas H2O2 and malondialdehyde content significantly decreased. In addition, the transgenic plants had also a lower electrolyte leakage and water loss rate. These overall results indicate that the OsIAA18 gene is involved in enhancing salt and osmotic tolerance in transgenic Arabidopsis plants. The OsIAA18 gene has a potential to be used to enhance the tolerance to abiotic stresses in other plant species.

Understanding the early cold response mechanism in IR64 indica rice variety through comparative transcriptome analysis

BackgroundCellular reprogramming in response to environmental stress involves alteration of gene expression, changes in the protein and metabolite profile for ensuring better stress management in plants. Similar to other plant species originating in tropical and sub-tropical areas, indica rice is highly sensitive to low temperature that adversely affects its growth and grain productivity. Substantial work has been done to understand cold induced changes in gene expression in rice plants. However, adequate information is not available for early gene expression, especially in indica variety. Therefore, a transcriptome profile was generated for cold shock treated seedlings of IR64 variety to identify early responsive genes.ResultsThe functional annotation of early DEGs shows enrichment of genes involved in altered membrane rigidity and electrolytic leakage, the onset of calcium signaling, ROS generation and activation of stress responsive transcription factors in IR64. Gene regulatory network suggests that cold shock induced Ca2+ signaling activates DREB/CBF pathway and other groups of transcription factors such as MYB, NAC and ZFP; for activating various cold-responsive genes. The analysis also indicates that cold induced signaling proteins like RLKs, RLCKs, CDPKs and MAPKK and ROS signaling proteins. Further, several late-embryogenesis-abundant (LEA), dehydrins and low temperature-induced-genes were upregulated under early cold shock condition, indicating the onset of water-deficit conditions. Expression profiling in different high yielding cultivars shows high expression of cold-responsive genes in Heera and CB1 indica varieties. These varieties show low levels of cold induced ROS production, electrolytic leakage and high germination rate post-cold stress, compared to IR36 and IR64. Collectively, these results suggest that these varieties may have improved adaptability to cold stress.ConclusionsThe results of this study provide insights about early responsive events in Oryza sativa l.ssp. indica cv IR64 in response to cold stress. Our data shows the onset of cold response is associated with upregulation of stress responsive TFs, hydrophilic proteins and signaling molecules, whereas, the genes coding for cellular biosynthetic enzymes, cell cycle control and growth-related TFs are downregulated. This study reports that the generation of ROS is integral to the early response to trigger the ROS mediated signaling events during later stages.

Two distinct time dependent strategic mechanisms used by Chlorella vulgaris in response to gamma radiation

Microalgae as one of the key components of food chains in aquatic environments are promising biological models for investigating gamma irradiation effects on eukaryotic organisms. Understanding resistance mechanisms in these organisms as simple models might illuminate how gamma irradiation resistance improves in these algae and even more complex organisms. The present study aimed to investigate the effects of ionizing irradiation on Chlorella vulgaris as a stress-tolerant microalga and to find how the eukaryotic cells would tolerate such stressful conditions. The physiological responses and biochemical alterations of C. vulgaris were analyzed at three different time points (0, 16, and 48 h) after 600 Gy gamma irradiation. Compared to the control, gamma-irradiated algae had slower growth rate with significantly longer lag phase, less chlorophyll and protein contents at time 0, which were compensated and recovered during the next 48 h. The results also showed spontaneous H2O2 burst accompanied by a higher rate of lipid peroxidation and electrolyte leakage, a rapid increase of catalase activity and more ferric reducing antioxidant power immediately after irradiation. During a 48-h period, most alterations stabilized. Raising trends were observed in the carotenoid contents, the ratios of carbohydrates, amide I and amide II to fatty acids. Principal component analysis and hierarchical clustering suggest two possible distinct mechanisms: a “quick” one including spontaneous responses by boosting H2O2, amplifying enzymatic antioxidant systems, and increasing compatible solutes like proline and a “delayed” responsive strategy including the increase of soluble carbohydrates, carotenoids, and stress-related proteins triggered several hours after irradiation.