Showing papers in "Journal of Plant Growth Regulation in 2020"

Photosynthetic Response of Plants Under Different Abiotic Stresses: A Review

Abstract: Plants encounter various abiotic stresses due to their sessile nature which include heavy metals, salt, drought, nutrient deficiency, light intensity, pesticide contamination, as well as extreme temperatures. These stresses impose major constraints limiting crop production and food security worldwide. Abiotic stresses primarily reduce the photosynthetic efficiency of plants, due to their negative consequences on chlorophyll biosynthesis, performance of the photosystems, electron transport mechanisms, gas exchange parameters, and many others. A better understanding of the photochemistry of plants under these abiotic stresses can help in the development of pragmatic interventions for managing these stresses. Interestingly, in this review, we provide an overview of insight into different mechanisms affecting the photosynthetic ability of plants in relation to these abiotic factors. The present review describes how different abiotic stresses can pose deleterious impacts on plant photosynthetic machinery including cellular membranes, cell division and cell elongation, biosynthesis of photosynthetic pigments, as well as electron transport chain. It is important to understand the detrimental impacts of various abiotic stresses for better stress management because a comprehensive understanding of plant responses has pragmatic implication for remedies and management.

Brassinosteroids in Plant Tolerance to Abiotic Stress

Abstract: Brassinosteroids (BRs) are a group of plant steroid hormones with multiple roles in plant growth, development, and responses to stresses. In plants, BR deficiencies impair vital physiological processes and cause phenotypic abnormalities. A large number of studies show that BRs can positively influence plant responses to abiotic stresses such as heat, cold, drought, salinity, pesticides, and heavy metals. However, the underlying mechanisms of BR-induced stress tolerance are largely unclear. BR perception takes place in the cell surface by BR receptors, leading to a cascade of phosphorylation events to activate the central transcription factor BRASSINAZOLE-RESISTANT1 (BZR1) that controls the transcription of BR-responsive genes in the nucleus. BRs improve photosynthetic efficiency under stress conditions, which largely contributes to increased growth and biomass accumulation. Studies relating to exogenous BRs reveal a high dependency on concentrations with regards to BR effects on plants. Genetic studies show a positive correlation between the endogenous BR levels and abiotic stress tolerance, although this assumption contradicts with the performance of some BR mutants under stress conditions. Notably, plant responses to BRs greatly vary depending on the plant species, developmental stages, and environmental conditions. In addition, other hormones and signaling molecules that participate in fine-tuning the BRs effects also play an important role in plant adaptation to stress. Here, we review the involvement of BRs in plant responses to abiotic stresses. We also discuss available literature to show potential mechanisms of BR-induced abiotic stress tolerance. These studies signify the complexity of BR action in mediating stress responses in plants.

Ameliorative Effects of Biochar on Rapeseed (Brassica napus L.) Growth and Heavy Metal Immobilization in Soil Irrigated with Untreated Wastewater

Abstract: Untreated wastewater carries substantial amount of heavy metals and causes potential ecological risks to the environment, food quality, and soil health. The pot study was established to evaluate the effectiveness of woodchip-derived biochar (BC) on rapeseed biomass, photosynthetic pigments, antioxidant enzyme activities, such as peroxidase (POD), ascorbate peroxidase (APX), polyphenol peroxidase (PPO), catalase enzyme (CAT), and heavy metal-induced phytotoxicity under untreated domestic (DWW) and industrial (IWW) wastewater irrigation. Biochar was applied at three levels (0, 1, and 2%) combined with DWW and IWW treatments. Wastewater analysis indicated higher heavy metal concentrations than the safer limits set by FAO. Results revealed that DWW and IWW treatments without biochar incorporation adversely affected the rapeseed growth performance, photosynthetic pigments, and antioxidative defense system. Compared with DWW and IWW treatments, BC at 2% rate significantly enhanced shoot fresh biomass (41% and 72%), root fresh biomass (34% and 62%), total chlorophyll (79% and 85%), total pigments (77% and 108%), carotenoids (74% and 94%), and lycopene concentration (43% and 61%), respectively. In addition, BC also improved the antioxidant enzymes activities by reducing the heavy metal-induced oxidative stress in rapeseed leaves. Similarly, AB-DTPA extractable Cd was decreased by (44% and 26%), Pb (51% and 54%), Ni (59% and 56%), and Cu (45% and 41%) in soil when BC was applied at 2% application rate along with DWW and IWW treatments and thereby reduced their uptake in shoots and roots of rapeseed. Therefore, BC can be considered an efficient strategy to ameliorate the hazardous effects of untreated DWW and IWW wastewater and to enhance rapeseed biomass, physiological attributes, and antioxidant enzyme activities.

Inoculation with Azospirillum lipoferum or Azotobacter chroococcum Reinforces Maize Growth by Improving Physiological Activities Under Saline Conditions

Abstract: A pot study was performed to examine the effect of plant growth-promoting rhizobacteria (PGPR) including Azospirillum lipoferum or Azotobacter chroococcum on growth criteria (leaf area and seedlings fresh and dry weight), pigments [chlorophylls (Chl a and b) and carotenoids], osmolytes (soluble sugars, soluble proteins and proline), nutrient uptake, antioxidant enzyme activities, and oxidative stress in maize plants under normal and salt-affected soils. The results showed that salt stress induced a reduction in growth traits, pigments, soluble proteins, K+, and K+/Na+ ratio. On the other side, it increased soluble sugars, proline, Na+, malondialdehyde (MDA), and the activity of peroxidase (POD) and catalase (CAT). Meanwhile, salt stress did not significantly change the activity of ascorbate peroxidase (APX) in maize plants. The inoculation using Azospirillum lipoferum or Azotobacter chroococcum significantly enhanced growth parameters, pigments, K+, osmolytes, K+/Na+ ratio, and the activity of CAT, POD, and APX of the salt-affected maize plants as well as uninoculated control plants. In addition, the results showed that both types of bacteria have attributed to lower MDA and Na+ in maize plants. Interestingly, Azospirillum lipoferum has affected more compared to Azotobacter chroococcum in control and salt-stressed plants. We, therefore, have observed in this study that microbial inoculation significantly improved plant physiological activities and that adding bacteria such as Azospiroillum or Azotobacter to the soil could mitigate the negative effects of salt stress on maize plants.

Signal Function Studies of ROS, Especially RBOH-Dependent ROS, in Plant Growth, Development and Environmental Stress

Abstract: Reactive oxygen species (ROS) are well known for their dual functions in plants. On the one hand, ROS were once thought to be harmful to plants because their excessive accumulation might lead to oxidative stress and cause cell injury in severe cases. On the other hand, a timely and appropriate burst of ROS acts as an important signal for plant growth, development and defence against environmental stress. ROS are common molecules in various plant metabolic processes and can be generated almost anywhere in plant cells. NADPH oxidase located on the plasma membrane, also known as the RBOH protein, provides a very important ROS synthesis pathway. This article briefly summarizes the signal functions of ROS, especially RBOH-dependent ROS, in plant growth, development and defence against abiotic and biotic stress in Arabidopsis (Arabidopsis thaliana).

Approaches in Enhancing Thermotolerance in Plants: An Updated Review

Abstract: Global warming has been increasing manifold in recent times, and this may cause tremendous economic losses in the near future. Recently, heat stress is considered one of the major constraints affecting crop growth and yield at world level. Heat stress reduced the plant growth, photosynthesis, mineral nutrients, and yield attributes. Heat stress caused both ultrastructural alterations and oxidative stress in different parts of plants. Plants can tolerate certain levels of heat stress by maintaining membrane stability, adjusting antioxidants and compatible solutes, and scavenging reactive oxygen species. Heat tolerance in plants can be improved by selecting heat-tolerant cultivars, genetic engineering, and exogenous application of osmolytes, microbes, mineral nutrients, soil amendments, and proper agricultural practices. This review is devoted to discuss the plants’ physiological and biochemical responses to heat stress and various integrated approaches to improve heat stress tolerance in plants.

Supplementation of Salicylic Acid and Citric Acid for Alleviation of Cadmium Toxicity to Brassica juncea

Abstract: The reported study investigated the interaction between salicylic acid (SA) and citric acid (CA) in cadmium (Cd)-stressed Brassica juncea plants. Seedling received Cd (0.6 mM) stress through soil at 5-day stage of growth. SA (0.01 mM) and CA (0.6 mM) treatments were applied at 25 days after sowing. Growth, photosynthesis, oxidative burst, and antioxidant systems were examined at 30-day stage of growth. Growth and photosynthetic parameters reduced significantly in the presence of Cd, and elevated levels of H2O2 were indicative of oxidative burst which resulted in decline of cell viability. Foliar spray of SA and CA alone or in combination mitigated the toxic effects generated by Cd and enhanced plant growth parameters. The inhibitory effects of Cd toxicity on width of stomatal pore resulted in reduced internal CO2 concentration and carbonic anhydrase activity which consequently limited the photosynthetic rate. SA and CA alleviated the inhibitory effect of Cd on photosynthesis by stimulating the stomatal activity and pore size. The Cd-generated oxidative burst was reduced via enhanced antioxidant activity (catalase, peroxidase, and superoxide dismutase) upon follow-up treatment with SA and CA alone or in combination. A combined dose of SA and CA countered Cd-induced damage by reducing levels of reactive oxygen species and strengthening plant antioxidant defense systems, which resulted in membrane stabilization and recovery from stress. Combined dose of SA and CA proved more effective than their individual application towards Cd stress which suggests an effective synergism between the two acids.

24-Epibrassinolide Alleviates the Injurious Effects of Cr(VI) Toxicity in Tomato Plants: Insights into Growth, Physio-Biochemical Attributes, Antioxidant Activity and Regulation of Ascorbate–Glutathione and Glyoxalase Cycles

Abstract: Brassinosteroids (BRs) are well-ascertained growth regulators that play prime roles in alleviation of a stress in plants The current investigation determined the impact of epibrassinolide (EBR) applied as seed pretreatment on growth attributes, physiological attributes and antioxidant potential of tomato plants grown under Cr(VI) metal stress Applications of EBR were found to be effective in improving growth of control as well as Cr-stressed plants in terms of lengths of shoot and root and their dry weights Of the physiological parameters, stomatal conductance was the most sensitive to chromium exposure exhibiting 7215% decline, while photosynthetic rate decreased to 3316% Chromium stress led to decline in non-enzymatic antioxidants like GSH by 4185% and in total flavonoid by 6948% Application of EBR modulated more significantly the titres of antioxidants (glutathione, ascorbic acid, total flavonoids and activities of antioxidant enzymes (ascorbate peroxidase, catalase, superoxide dismutase, glutathione-S-transferase and glutathione reductase) as well as proline and glycine betaine in Cr-stressed plants compared to those in plants receiving no supply of EB Diminution of Cr stress by EBR was also maintained by higher values of stress indices, such as flavonoids, photosynthetic pigments and reduction in malondialdehyde and H2O2 levels in the Cr-treated plants than those in the controls Restricted production of ROS and improved quenching of ROS were also recorded due to EBR application under Cr stress At the same time, insignificant reduction in uptake of Cr was noticed due to application of EBR in leaves compared to that in roots of Cr-stressed plants Overall, our results reveal that application of EBR can effectively act as a growth stimulant in plants subjected to Cr stress Therefore, it can be conjectured that the interaction of 24-epibrassinolide remodulates the physiological, metabolic and defence system of the tomato thriving under chromium stress by equilibrating the Cr accumulation

Seaweed-Based Biogenic ZnO Nanoparticles for Improving Agro-morphological Characteristics of Rice ( Oryza sativa L.)

Abstract: To develop sustainable nano-agriculture, biogenic ZnO nanoparticles have been prepared using brown seaweed Turbinaria ornata (T. ornata) extract as a priming agent to promote rice seed quality and crop yield attributing to rice seeds. The results of various physico-chemical characterization analysis indicate the formation of ZnO nanoparticles. Rice seeds primed with seaweed-based biogenic ZnO nanoparticles at 10 mg/L showed that there has been enhancement in the seed germination (100%), shoot length (100 mm), shoot width (1.0 mm), root length (185.0 mm) root width (0.5 mm), seedling length (216 mm), leaf length 33.0 mm), leaf width (2.0 mm), seedling vigor (28,500 vigor index) and dry matter production (DMP) compared to the conventional hydropriming. Consequently, a micro-plot experiment has been conducted with foliar application of biogenic ZnO nanoparticles and the results revealed that at 10 mg/L recorded improvement in grain weight (653 g/m2), seed length (8.0 mm), seed thickness (1.71 mm) and seed width (3.23 mm) compared to hydroprimed seeds under. HR-SEM micrograph confirms the presence and assimilation of biogenic ZnO nanoparticles in treated seed/foliar applied leaf of rice plant. Further, ICP-MS analysis also confirmed the increase in Zn content in the nanoprimed rice seedlings and foliar applied rice crop in a dose-dependent manner. The experimental results thus demonstrate that the application of seaweed biogenic ZnO nanoparticles improving agronomical characteristics of rice.

Pseudomonas putida and Pseudomonas fluorescens Influence Arabidopsis Root System Architecture Through an Auxin Response Mediated by Bioactive Cyclodipeptides

Abstract: Plant growth-promoting rhizobacteria modulate root development through different mechanisms. This work was conducted to evaluate the effects of root colonization by Pseudomonas putida and Pseudomonas fluorescens in biomass production, lateral root formation, and activation of auxin signaling in Arabidopsis thaliana. Selected strains of P. putida and P. fluorescens were tested for modification of DR5::uidA, BA3::uidA and HS::AXR3NT-GUS auxin-related gene expression, and to promote root hair and lateral root formation in WT and tir1-1, tir1-1afb2-1afb3-1, arf7-1, arf19-1, arf7-1arf19-1, and rhd6 mutants. Production of cyclodipeptides with possible roles in auxin signaling was also determined in P. putida and P. fluorescens culture supernatants by gas chromatography–mass spectrometry. P. putida and P. fluorescens stimulated lateral root and root hair formation and increased plant biomass, which correlated with an induction of the auxin response. Genetic analyses suggested that growth promotion involves auxin signaling as tir1-1, tir1-1afb2-1afb3-1, arf7-1, arf19-1, and arf7-1arf19-1 mutants showed decreased lateral root response to inoculation and because P. putida and P. fluorescens restored root hair development in the rhd6 mutant. It was also found that these bacteria produce the cyclodipeptides cyclo(L-Pro-L-Val), cyclo(L-Pro-L-Phe), and cyclo(L-Pro-L-Tyr), which modulates auxin-responsive gene expression in roots. Our results suggest a role of cyclodipeptides for bacterial phytostimulation.

Salicylic Acid Induced Photosynthetic Adaptability of Raphanus sativus to Salt Stress is Associated with Antioxidant Capacity

Abstract: Despite the plethora of published reports on ameliorative effects of exogenously applied salicylic acid (SA) to plants under salt stress, a critical role of SA in redox balance, photosynthetic and electron transport in mediating salt tolerance in plants is still ignored. The present study was aimed to assess the beneficial effects of SA on photosynthetic electron transport in five radish cultivars during salt stress which may translate into protection from salt-induced oxidative damage. Seeds of five radish cultivars (Red Neck Purple, Early Long White, Minnu Radish, Radish 40-day and Gong Swang Radish) were allowed to germinate for five days after which seedlings were sprayed with different concentrations of SA (0, 2 and 5 mM). After 48 h of SA treatment, seedlings were subjected to salt stress (0, 100, and 200 mM NaCl). Salt stress cause reduction in biomass, chlorophyll contents and PSII photochemistry in all five radish cultivars. However, salt stress causes an increase in proline content, lipid peroxidation, ROS content and antioxidant enzymatic activity. Foliar spray of SA downregulated the absorption, trapping and photosynthetic electron transport fluxes while it increased dissipation flux consequently improving photochemistry of most of the radish cultivars under salt stress. This Improved photochemistry and enhanced antioxidant enzymes activity of radish cultivars by SA application resulted in lower ROS generation and membrane damage. Greater accumulation of compatible solutes due to foliar spray of SA might have additional protective effects on photosynthetic machinery by lowering oxidative stress. Moreover, ameliorative effects of SA were cultivar specific. The study suggested that SA could mitigate the detrimental effects of salt stress by regulating physiological and biochemical mechanisms in radish plant.

Melatonin and Gibberellic Acid Promote Growth and Chlorophyll Biosynthesis by Regulating Antioxidant and Methylglyoxal Detoxification System in Tomato Seedlings Under Salinity

Abstract: The beneficial roles of melatonin (Mel) and gibberellic acid (GA3) in the biosynthesis of photosynthetic pigments, osmoregulation, and methylglyoxal (MG) detoxification and antioxidant system were studied in tomato (Solanum lycopersicum L. cv. Five Star) seedlings under NaCl stress. The exogenous application of Mel (100 µM) and GA3 (1.4 µM) together more efficiently affected growth performance of seedlings under salt stress. The decreased chlorophyll (Chl) degradation and Chl-degrading enzyme (chlorophyllase) activity in seedlings receiving Mel plus GA3 resulted in increased Chl content by upregulating Chl synthesizing enzyme (δ-aminolevulinic acid dehydratase) under salinity. Exogenous Mel plus GA3 suppressed the overproduction of reactive oxygen species (ROS; superoxide and hydrogen peroxide) and activity of glycolate oxidase. Application of Mel with GA3 reduced MG content by enhancing the activity of enzymes (glyoxalase I and glyoxalase II) involved in the MG detoxification system. Both Mel and GA3 together protected seedlings from ROS induced damage by regulating Δ1-pyrroline-5-carboxylate synthetase activity, and content of proline (Pro) and glycine betaine (GB). Seedlings receiving Mel + GA3 exhibited a substantial upregulated activity of catalase, ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase, monodehydroascorbate reductase, glutathione peroxidase, polyphenol oxidase and lipoxygenase, and redox homeostasis that reduced oxidative damage induced by salinity. These outcomes advocate that Mel and GA3 played beneficial roles in Chl, Pro and GB biosynthesis, and improved redox homeostasis, and MG detoxification and antioxidant system under salt stress.

Overexpression of Caffeic Acid O-Methyltransferase 1 (COMT1) Increases Melatonin Level and Salt Stress Tolerance in Tomato Plant

Abstract: Melatonin is a natural phytohormone that occurs in most plants. It can regulate not only plant growth and development but also alleviate biotic and abiotic stress in plants. However, no studies have reported on endogenous melatonin increasing tomato tolerance to salt stress. In the present study, we observed that the overexpression of caffeic acid O-methyltransferase 1 (SlCOMT1) increased melatonin levels in tomato plants. We also observed that transgenic plants exhibited higher salt stress tolerance. SlCOMT1 overexpression could maintain the balance of Na+/K+ and decrease ion damage by activating salt overly sensitive (SOS) pathway under salt treatment. In addition, SlCOMT1 overexpression significantly enhanced the antioxidant capability, with higher antioxidant enzyme activity observed, including superoxide dismutase, peroxide and catalase activity, and higher ascorbic acid (AsA) and glutamate (GSH) accumulation levels. SlCOMT1 overexpression also maintained good nutrient homeostasis in the tomato plants. In addition, SlCOMT1 overexpression upregulated some stress-related genes (AREB1, AIM1, MAPK1, WRKY33 and CDPK1), which resulted in the activation of downstream signaling pathways and could be partly responsible for the improvement in salt stress tolerance.

Seed Priming with Cold Plasma and Multi-walled Carbon Nanotubes Modified Growth, Tissue Differentiation, Anatomy, and Yield in Bitter Melon ( Momordica charantia )

Abstract: This study was conducted to explore the capability of seed priming with the cold plasma and multi-walled carbon nanotubes (MWCNT), in order to improve growth and yield in Momordica charantia. The soaked seeds were primed with plasma (DBD; 0.84 W cm−2 surface power densities) under different durations (0, 60, and 120 s) and/or MWCNT (0, 50, 100, and 200 mg l−1). Seed priming with plasma and/or MWCNT led to the dramatic increase in growth-related traits, like root and shoot lengths, fresh and dry mass, vigor index, and leaf length. Moreover, simultaneous treatments with MWCNT and plasma amplified their individual effects. Uptake and transportations of MWCNTs from the root to leaves were manifested using an electron microscopy. The ultra-structural study revealed that plasma enhanced MWCNT uptake and accumulation. Modifications in organogenesis and differentiation patterns of tissues, especially vascular system, were provoked by the MWCNT and/or plasma treatments. The plasma and MWCNT reinforce conducting xylem tissue. In addition, the long-term effects of MWCNT and/or plasma treatments on reproductive stage were confirmed. The increase in the number of produced flowers, and the decrease in the time of fructifying, caused by the MWCNT and/or plasma treatments. The findings introduce a new alternative path for applications of cold plasma and MWCNT technologies in the plant, agriculture, and food sciences.

Brassinosteroids Regulate Functional Components of Antioxidative Defense System in Salt Stressed Maize Seedlings

Abstract: The purpose of current investigation was to explore the role of brassinosteroids (BRs) in Zea mays L. var. DKC 9106 seedlings subjected to salt stress. The seedlings were raised under controlled laboratory conditions and subjected to different concentrations of NaCl (0, 40, 60, 80, 100 mM) for 10 days. The impact of pre-sowing treatment of both 28-homobrassionolide (HBL) and 24-epibrassinolide (EBL) on defense system of Z. mays L. under salt stress was studied by analyzing Na+ and K+ ions, malondialdehyde content (MDA), antioxidative enzymes activities (peroxidase, POD; catalase, CAT; dehydroascorbate reductase, DHAR; monodehydroascorbate reductase, MDHAR), osmoprotectants (proline, glycine betaine, mannitol, and total osmolytes content), total phenolic content, total flavonoid content, and 1,1-diphenylpicrylhydrazyl (DPPH) free radical scavenging activity. The results of our finding showed that treatment of both HBL and EBL under high salt stress balanced the ionic status by decreasing the Na+ ions content by 21.23% and 38.94%, respectively, and enhancing the K+ ions content by 51.94% and 26.66%, respectively. Treatment of both BRs also overcome the oxidative damage induced due to salinity stress by reducing the MDA accumulation 19.50% and 45.0%, respectively, and enhancing the activities of antioxidative enzymes. The osmoprotectants: proline (50.08% and 17.03%), glycine betaine (35.57% and 28.16%), and mannitol content (2.80% and 20.98%) were markedly increased by the treatment of both HBL and EBL, respectively. Further, treatment of both HBL and EBL also increased the total phenolic content by 11.68% and 5.80%, total flavonoid content by 31.56 and 31.09% and DPPH free radical scavenging activity by 37.99% and 77.41%, respectively. Overall the treatment of BRs before seed sowing considerably conquer the salinity-induced damage by stimulating functional components of antioxidative defense system and ultimately reduced oxidative damage.

Application of Streptomyces pactum Act12 Enhances Drought Resistance in Wheat

Abstract: The use of beneficial microbes to improve drought resistance in crops has great application potential in agricultural production, yet the effects of actinomycetes upon crop resistance to drought are rarely reported. Streptomyces pactum Act12 is a known multi-functional biocontrol agent of soil-borne diseases in several horticultural crops and medicinal plants. Here, we systematically analyzed how Act12 treatment affects drought resistance in drought-sensitive wheat (Triticum aestivum L.) cultivar Xinong 979 by considering both its effects and underlying mechanisms. After seed exposure to a cell-free culture filtrate of Act12, we measured several plant growth variables, osmotic adjustment and antioxidant capacity, cell membrane peroxidation, and drought resistance-related gene expression in wheat seedlings under drought stress conditions simulated by polyethylene glycol 6000. Results showed that, under drought stress, wheat seedling exposure to Act12 cell-free filtrate facilitated plant growth, with significant increases in shoot fresh weight (21.3%), shoot length (10.3%), and root length (13.6%). Act12 treatment also significantly increased total soluble sugar content in wheat leaves while decreasing their malondialdehyde content by 20.5%. Under non-drought conditions, Act12 treatment increased the content of both proline and glutathione in wheat leaves; however, both were lowered in Act12-treated plants compared with non-treated plants at 96 h of drought stress. Further analysis revealed that Act12 treatment increased the content of leaf abscisic acid and upregulated the expression levels of several drought resistance-related genes, such as EXPA2, EXPA6, P5CS, and SnRK2. These results suggest that application of S. pactum Act12 can enhance the osmotic adjustment and antioxidant capacity of plants via induction of abscisic acid accumulation and up-regulation of drought resistance-related gene expression, thereby mitigating drought stress impact in wheat.

The key roles of salicylic acid and sulfur in plant salinity stress tolerance

Abstract: The salinization of agriculture soils over the globe has become one of the most devastating stresses and is significantly limiting cultivated land area, and crop productivity and quality. It is very imperative to explore both salinity tolerance in plants and insights into approaches (and underlying mechanisms) for effectively controlling salinity impacts. To this end, the role of phytohormone salicylic acid (SA) and plant nutrient sulfur (S) in promoting salinity tolerance has been researched in isolated studies, and SA–S interaction results have been little discussed. Given this, taking into account recent literature on SA, S and soil salinity, this paper aimed to (i) overview of the major impacts of soil salinity on plant health; (ii) highlight the significance of SA and S in improving plant salinity tolerance; (iii) discuss the role and underlying mechanism of SA, S and their interaction in the modulation of plant growth and development under salinity stress; and also to (iv) appraise the discussed literature and enlighten the major prospects.

Application of Melatonin-Enhanced Tolerance to High-Temperature Stress in Cherry Radish (Raphanus sativus L. var. radculus pers)

Abstract: The growth and development of cold-season plants are susceptible to high temperature. Melatonin is a plant growth regulator with potential to improve plant tolerance to biological and abiotic stresses. In our study, cherry radish (Raphanus sativus L. var. radculus pers) was cultured at a high temperature (35 °C/30 °C day/night) and different concentrations (0, 11.6, 17.4, 29.0, 34.8 and 67.0 mg L−1) of melatonin were applied to these high-temperature stressed plants to its effects on biomass, quality, antioxidant enzyme activity, chlorophyll and endogenous hormone contents. The plants were grown under normal temperature (25 °C/20 °C) as control and high-temperature condition as HT-stress treatment. The results revealed that under high temperature with 29.0 mg L−1 melatonin treatment, cherry radish biomass was significantly increased by 12.9%, and the soluble protein and soluble solid were increased by 18.7 and 9.2%, respectively. The activity of antioxidant enzyme, ascorbate peroxidase and peroxidase were increased by 43.7 and 45.5%, respectively. The chlorophyll a and carotenoid contents were increased by 7.4 and 20.0% compared with the control at 27 days. The auxin and abscisic acid contents were significantly increased by 28.5 and 6.7% compared with HT at 9 days. Thus, application of optimal rate of melatonin had a positive effect on cherry radish growth under high-temperature stress.

Microbial Volatile Organic Compounds Produced by Bacillus amyloliquefaciens GB03 Ameliorate the Effects of Salt Stress in Mentha piperita Principally Through Acetoin Emission

Abstract: We investigated the effects of microbial volatile organic compounds (mVOC) emitted by Bacillus amyloliquefaciens GB03 on Mentha piperita growing under different levels of NaCl stress, by evaluating their growth-promoting potential and ability to increase salt tolerance effects. Plants were exposed to bacterial VOCs without having any physical contact with the rhizobacteria. The VOCs emitted by the rhizobacteria (mVOCs) were analyzed using SPME fibers. An increase in the level of salt concentration led to a decrease in plant growth. However, these negative effects of salinity were inhibited in the plants exposed to mVOCs. Plants grown in a saline media and exposed to GB03 VOCs had significantly better morphological characteristics and higher total chlorophyll content compared to controls. The level of endogenous jasmonic acid (JA), salicylic acid, and abscisic acid increased in salt-stressed plants compared to controls. The level of JA did not show any change in plants grown in a saline media either exposed to mVOCs or not. In contrast, the amount of salicylic acid increased remarkably in salt-stressed plants exposed to mVOCs compared to controls (salt-stressed plants not exposed to mVOCs), but the levels of abscisic acid decreased in salt-stressed plants exposed to mVOCs. The chromatographic analyses of the mVOCs produced by salt-stressed GB03 bacteria were similar, regardless of the concentration of salt in the media where the bacteria were grown, although it was observed that the relative percentage of acetoin increased with salt concentration. After determining that acetoin was the main VOCs compound, we exposed plants to acetoin, which demonstrated that acetoin caused similar effects on plants grown under salt stress conditions as those exposed to GB03 mVOCs. Based on these results, the use of mVOCs from PGPR is suggested as a useful technological innovation to facilitate the growth of M. piperita in salt-stressed environments.

Assessment of Changes in Some Biochemical Traits and Proteomic Profile of UCB-1 Pistachio Rootstock Leaf under Salinity Stress

Abstract: University of California at Berkeley I or UCB-1 pistachio rootstock is propagated from the cross between Pistacia integerrima male × Pistacia atlantica female. So far, no report has been presented on the proteomic profile of Pistacia genus. In this research, 7-month-old UCB-1 rootstocks that were produced by tissue culture method and grown in pots containing 1/3 perlite, 1/3 clay and 1/3 sand were exposed to the three different concentrations of NaCl including 0, 100 and 200 mM for 30 days in the controlled conditions in the greenhouse. In the first step, under these three different concentrations of NaCl, the content of malondialdehyde and activities of guaiacol peroxidase, superoxide dismutase, catalase and peroxidase were evaluated. Malondialdehyde content increased up to 100 mM NaCl and then decreased. Activities of guaiacol peroxidase, superoxide dismutase and catalase increased with increasing concentration of NaCl, while peroxidase activity reduced. In the second step, 0 and 100 mM NaCl were selected to evaluate changes in the proteomic profile of this rootstock using MALDI-TOF/TOF method. In this study, ribonucleoside-diphosphate reductase small chain, polcalcin Phl p 7-like and golgin subfamily A member 5 were identified for the first time in response to salinity stress and have not been previously reported to be involved in the response of plant under abiotic stresses. Moreover, in this study, five unknown proteins were identified in UCB-1 pistachio under salinity stress.

Seed Priming by Cyanobacteria (Spirulina platensis) and Salep Gum Enhances Tolerance of Maize Plant Against Cadmium Toxicity

Abstract: Cadmium (Cd) is considered as a hazard for plant growth and human health. In the current study, the beneficial effects of maize (Zea mays L.) seed priming with salep gum (SG), Spirulina platensis (SP) and combination of SG and SP on seed germination, plant growth, photosynthesis performance, and Cd uptake and translocation factor were investigated on plants exposed to Cd toxicity (200 mg CdCl2 per kg of culture medium). Seed priming either by SG or SG + SP accelerated seed germination irrespective of Cd application. Improvement of plant growth due to seed priming by SP was observed in Cd-contaminated soil. SP caused Cd depletion in the shoots of the Cd-exposed plants. Cd translocation from root to shoot was significantly restricted in seed-primed plants after 12 days of sowing. Seed priming by SP improved photosynthetic electron flows and increased non-photochemical quenching in Cd-exposed maize plants. In conclusion, due to positive effects of seed priming (particularly by SP) on growth, photosynthetic capacity, and Cd accumulation and translocation, it can be effectively used to enhance plant capacity to cope with Cd toxicity in contaminated soils.

Tartaric Acid Mediated Cr Hyperaccumulation and Biochemical alterations in seedlings of Hordeum vulgare L.

Abstract: The present study was done to evaluate the effects of tartaric acid (TA) amendment on physiology of Hordeum vulgare L. seedlings under Cr(VI) stress. Cr(VI) at higher concentrations decreased the shoot and root dry weights of seedlings. However, amendment of Cr(VI) media with TA enhanced the root and shoot dry weights, activities of antioxidative enzymes (ascorbate peroxidase, guaiacol peroxidase, superoxide dismutase, catalase, and glutathione reductase), and contents of pigments (total chlorophyll and carotenoids). Cr(VI) also increased the malondialdehyde content, an indicator of lipid peroxidation and stress. However, application of TA in combination with higher concentrations of Cr(VI) reduced the malondialdehyde content. Amendment of 0.5 mM Cr(VI) with 1.5 mM TA increased the Cr uptake content in the roots of the seedlings by 208.7% with respect to treatment with 0.5 mM Cr(VI) only. The shoot and root bio-concentration factors (BCF) were enhanced with the application of TA to culture media. Further, the results were statistically analyzed by employing various multivariate techniques such as analysis of variance, multiple regression analysis, beta regression analysis, correlation analysis, principal component analysis, factor analysis, non-metric multidimensional scaling, canonical correspondence analysis, and two-block partial least squares. The present study confirmed that TA acts as an antagonist to Cr(VI) in the seedlings of H. vulgare by increasing their antioxidative potential and enhancing their capability of chromium accumulation. The present study also suggests that multivariate techniques, which are mainly applied for data analysis in the field of ecology, can also be applied for experimental biology studies.

Quantification of the Effect of Environmental Factors on Seed Germination and Seedling Growth of Eruca (Eruca sativa) Using Mathematical Models

Abstract: Eruca (Eruca sativa; Brassicaceae) is an important industrial crop due to its ability to grow under a wide range of climatic conditions and in poor fertility lands and also for the quality of seed oil and protein. Seed germination (SG) is an important event in plant’s life history which can significantly be influenced by several environmental factors such as temperature (T), water potential (ψ), salinity, pH, and burial depth. Therefore, this study aimed (i) to investigate the effects of these environmental factors on SG behavior of Eruca using several mathematical models, (ii) to determine the cardinal Ts and tolerance threshold value for each trait (i.e., 50% reduction than its maximum value) affected by the environmental factor, and (iii) to quantify the response of Eruca seedling growth to each environmental factor. The results indicated that Eruca SG and seedling growth were significantly influenced by these factors (P < 0.05). The estimated cardinal Ts were 1 °C for the base T, 30 °C for the optimum T, and 40.8 °C for the ceiling T. The salt and drought tolerance threshold values were 257 mM NaCl and − 1.2 MPa for SG and 247 mM NaCl and − 1 MPa for the seedling growth, respectively, suggesting that the seedling growth was more sensitive than SG under both salt and drought stresses in Eruca. In addition, the maximum SG and seedling growth were observed at pH 7 and burial depth 1.9 cm. In general, the models used in this study could describe well the response of Eruca SG under different levels of environmental factors and also their parameters could easily be used in Eruca SG simulation models. This information also could help us to better manage the production of this plant under stressful conditions and/or to determine its geographic range expansion in the world.

Seed Priming with Spermidine and Trehalose Enhances Chilling Tolerance of Rice via Different Mechanisms

Abstract: Chilling stress is an important limiting factor for rice growth and development. To examine the effect of spermidine (Spd) and trehalose (TH) priming in response to chilling stress of rice seed, we investigated the effects of seed priming with Spd, TH, and a mixture of Spd + TH on response and resilience of rice plants to chilling stress. Priming with Spd, TH and Spd + TH resulted in better seed vigor and seedling growth than hydro-priming and non-priming under low temperature (15 °C). In addition, Spd-, TH-, and Spd + TH-priming notably decreased malondialdehyde content but increased the proline and soluble sugar contents and antioxidant enzymes activities. Interestingly, spermine content and the expression of spermine-synthase (SPMS) gene were improved by Spd-priming. However, lower spermine content and SPMS expression was observed in the TH-primed plants. Moreover, expressions of trehalose-6-phosphate–phosphatase (TPP) genes was upregulated by TH-priming but downregulated by Spd-priming. It could be concluded from our results that (1) both Spd- and TH-priming could increase the contents of proline and soluble sugar, which were involved in osmotic adjustment, and antioxidant enzymes activities; (2) Spd-priming promoted the accumulation of endogenous spermine by upregulating SPMS1 and SPMS2, but inhibiting the expressions of TPP1 and TPP2; and (3) TH-priming increased the expressions of TPP1 and TPP2 but downregulated the expressions of SPMS1 and SPMS2. These findings suggested that seed priming with Spd and TH might enhance the chilling tolerance of rice seedling via different mechanisms.

Relationship of Nitrogen Deficiency-Induced Leaf Senescence with ROS Generation and ABA Concentration in Rice Flag Leaves

Abstract: Nitrogen (N) deficiency is one of the critical environmental factors that induce leaf senescence, and its occurrence may cause the shorten leaf photosynthetic period and markedly lowered grain yield. However, the physiological metabolism underlying N deficiency-induced leaf senescence and its relationship with the abscisic acid (ABA) concentration and reactive oxygen species (ROS) burst in leaf tissues are not well understood. In this paper, the effect of N supply on several senescence-related physiological parameters and its relation to the temporal patterns of ABA concentration and ROS accumulation during leaf senescence were investigated using the premature senescence of flag leaf mutant rice (psf) and its wild type under three N treatments. The results showed that N deficiency hastened the initiation and progression of leaf senescence, and this occurrence was closely associated with the upregulated expression of 9-cis-epoxycarotenoiddioxygenase genes (NCEDs) and with the downregulated expression of two ABA 8′-hydroxylase isoform genes (ABA8ox2 and ABA8ox3) under LN treatment. Contrarily, HN supply delayed the initiation and progression of leaf senescence, concurrently with the suppressed ABA biosynthesis and relatively lower level of ABA concentration in leaf tissues. Exogenous ABA incubation enhanced ROS generation and MDA accumulation in a dose-dependent manner, but it decreased the activities of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) in detached leaf. These results suggested that the participation of ABA in the regulation of ROS generation and N assimilating/remobilizing metabolism in rice leaves was strongly responsible for induction of leaf senescence by N deficiency.

Alkanes (C29 and C31)-Mediated Intracuticular Wax Accumulation Contributes to Melatonin- and ABA-Induced Drought Tolerance in Watermelon

Abstract: As the outermost hydrophobic layer, cuticular waxes serve as an essential waterproof barrier to protect plants from desiccation, but the mechanism of wax accumulation still remains unclear. We analyzed the response of cuticular wax composition and deposition to drought in three different watermelon germplasms, namely, M20, M08, and J5F, which showed similar stomatal response, but high, moderate, and low tolerance to drought, respectively. Among the identified 28 compounds of cuticular waxes on leaves, more alkanes with chain lengths of C29 and C31 were induced in M20, accompanied by an increased transcript levels of CER1 (very-long-chain aldehyde decarbonylase 1), when compared to that in M08 and J5F. M20 showed higher total wax amount but fewer platelet-like wax crystals on the upper epidermis of leaves under drought, suggesting the prevalence of more intracuticular waxes embedded into the cutin matrix as fillers. These distinct responses of cuticular waxes in M20 conferred low water loss and high tolerance to drought. Melatonin and abscisic acid (ABA), which can be induced by drought, promoted the biosynthesis of alkanes (C29 and C31) but inhibited the accumulation of wax crystals under drought. Moreover, melatonin inhibited the elevation of ABA levels under mild drought but promoted the ABA accumulation under severe drought, indicating that melatonin and ABA function synergistically to regulate wax compositions to limit non-stomatal water loss under severe but not mild drought in watermelon. These findings can be exploited to improve crop tolerance to drought in arid regions.

Sweet Basil Growth, Physiological and Ultrastructural Modification, and Oxidative Defense System Under Water Deficit and Silicon Forms Treatment

Abstract: The current investigation aimed to evaluate the role of silicon forms on sweet basil (Ocimum basilicum L.) biomass and essential oil (EO) production, as well as some physiological and ultrastructural modification under different irrigation regimes. Drought significantly decreased plant growth, photosynthetic pigment, ion, relative water content, catalase activity, and EO yield, meanwhile, increased organic and antioxidant solute concentration, EO percentage, peroxidase activity, and oxidative impairment criteria (hydrogen peroxide, lipid peroxidation, and membrane permeability percentage). Concerning EO constituents, linalool and methyl chavicol were the major components that decreased under drought relative to well-watered plants. Exogenous application of silicon forms under well-watered or drought condition may fully or partially compensate to some extent to sweet basil plant development and biochemical attributes (photosynthetic pigment, ion percentage, antioxidant solutes, and organic osmolytes). The maximum EO yield was obtained by 250 mg L−1 sodium metasilicate (Si) under mild drought. Cell organelles exhibited a different degree of malformation and lyse under severe drought; conversely, application of Si forms nullify the abovementioned injuries caused by drought. In conclusion, application of 250 mg L−1 Si improved drought tolerance in sweet basil herb and EO yield by accelerating their antioxidant system, osmoregulation, and maintaining organelles ultrastructure that induced herb growth and EO yield.

Benefits of Biochar for Improving Ion Contents, Cell Membrane Permeability, Leaf Water Status and Yield of Rice Under Saline–Sodic Paddy Field Condition

Abstract: Saline–sodic is one of the major conditions threatening crop production. Biochar application could alleviate the adverse impacts of saline–sodic stress in crops. But its effect on reducing Na+ uptake in rice under saline–sodic paddy field condition remains unknown. This study evaluated the effect of biochar on ion contents, cell membrane permeability, leaf water status and yield of rice in saline–sodic paddy soil using a field experiment. The soil was amended with biochar at zero-biochar (B0), 33.75 t ha−1 (B1), 67.5 t ha−1 (B2), and 101.25 t ha−1 (B3), respectively. The results indicated that biochar addition significantly reduced Na+ concentration and Na+/K+ ratio, while it remarkably increased K+ concentration of rice plant. Furthermore, biochar application significantly decreased the leaf-relative electrical leakage and increased leaf water status, plant height, and chlorophyll content index. The rice biomass production and harvested yield were significantly increased. Therefore, biochar application to saline–sodic paddy soil has benefits to alleviate saline–sodic stress and increase rice yield in saline–sodic paddy soil.

Preparation and Standardisation of Smoke-Water for Seed Germination and Plant Growth Stimulation

Abstract: Smoke-water (SW) has a positive effect on seed germination in many plant species and its application in various fields of plant science has become popular. The method of preparing SW is relatively easy and inexpensive. However, many researchers working in the field of smoke biology are still unfamiliar with preparing SW and testing it for bioactivity. Thus, the aim of this study was to develop a low-cost efficient apparatus to produce SW using grasses, its standardisation and quantification of major active biomolecules. The prepared crude SW was diluted with distilled water (SW:DW) to 75:25, 50:50 and 25:75 (v/v) and these sub-dilutions were further diluted to 1:500; 1:1000; 1:1500; 1:2000; 1:2500; 1:3000 and 1:3500 (v/v). For the standardisation of SW, lettuce seeds (Lactuca sativa L. cv. Grand Rapids) were tested to determine the best working concentration. The ratio 1:2500 (v/v) from the sub-dilution 25:75 (v/v) of SW was the best for germination of lettuce seeds in the dark, achieving 91% germination against the water control that had only 7–10% germination. This is the first study which reports the levels of stimulatory (karrikinolide 1, KAR1 and karrikinolide 2, KAR2) and inhibitory (trimethylbutenolide, TMB) compounds present in SW using ultrahigh-performance liquid chromatography–electrospray positive ionisation tandem mass spectrometry (UHPLC-ESI(+)-MS/MS).

Response of Ornamental Pepper to High-Temperature Stress and Role of Exogenous Salicylic Acid in Mitigating High Temperature

Abstract: Ornamental pepper (Capsicum annuum L.) is an important economic decorative plant well known for its abundant genetic diversity. However, high-temperature (HT) stress seriously affects its aesthetic and commercial value. In this work, we analyzed the effects of exogenous salicylic acid (SA) on seed germination and seedling growth of ornamental pepper under HT stress. The inherent physiological and biochemical basis of the alleviating effect of salicylic acid was further analyzed. The findings revealed SA with 0.01 mM and 0.1 mM was most effective in enhancing thermotolerance in seeds and seedlings, respectively. SA treatment increased the germination rate and germination potential, and reduced the oxidative damage of seeds under HT stress. For seedlings, spraying SA with 0.1 mM significantly alleviated yellow leaves and dwarfing under HT stress. SA could maintain high root vigor, inhibit water loss, and maintain the integrity of cell structure by regulating osmotic substance content under HT. SA-induced thermotolerance development involved in the activation of antioxidant defense system. SA decreased the production of reactive oxygen species (ROS), increased the activity of protective enzymes, and the content of non-enzymatic ROS scavengers in plants under HT. The changes of chlorophyll fluorescence parameters showed that SA was beneficial to maintain a high level of photosynthetic capacity of ornamental pepper seedlings under HT stress. Moreover, recovery also showed a mitigatory effect on injuries induced by HT stress. Taken together, this study provided evidence for the ability of exogenous SA application to moderate the detrimental effects by HT stress.