Showing papers in "Acta Physiologiae Plantarum in 2018"

Polyamines and their possible mechanisms involved in plant physiological processes and elicitation of secondary metabolites

Abstract: Polyamines are amine-containing, low molecular weight, and ubiquitous polycationic molecules present in almost all cells and free-living microbes, which are formed by aliphatic hydrocarbons replaced with multiple amino groups. They have been considered as a new kind of plant biostimulant, which play vital roles in diverse plant growth and developmental processes, and environmental stress responses. However, little is known regarding the effects of polyamines specifically on the elicitation of bioactive compounds in medicinal plant production. Therefore, in this review, we attempt to cover these gaps of information. Supply of polyamines, whether by exogenous application or through genetic engineering, could positively affect medicinal plant growth, productivity, and stress tolerance; however, these effects depend on type and dose of polyamine application and plant species. Furthermore, polyamines play as precursor for the several groups of alkaloids (pyrrolizidine, tropane, and quinolizidine alkaloids) and phenolamides, so these bioactive compounds could significantly increase the concentration of the above-mentioned natural products.

Regulation of photosynthesis by brassinosteroids in plants

Abstract: Brassinosteroids (BRs) regarded as plant hormone are a class of naturally occurring polyhydroxylated sterol derivatives present in all plant species. Overall growth of the plant relies on the very basic and important process of photosynthesis. BRs are found capable of preventing the loss of photosynthetic pigments either by activating or inducing the synthesis of enzymes involved in chlorophyll biosynthesis. BRs play important role in maintaining PS II efficiency by stabilizing D1 protein. It overcomes the stomatal limitations and elevates the efficiency of photosynthetic carbon fixation. BRs also act at various levels of light and dark reactions leading to enhanced carbohydrate synthesis. Therefore, it becomes important to focus and collect information related to various effects of BRs on photosynthesis and its related attributes. The present review deals with the effect of BRs on photosynthesis under normal as well as stressful conditions.

Physiological responses of wheat to drought stress and its mitigation approaches.

Abstract: Drought is a polygenically controlled stress and a major agricultural risk that reduces crop productivity and limits the successful insight of land potential throughout the world. This review article has been divided into two parts, i.e., effect of drought stress on physiology of wheat and potential drought mitigation approaches. In the first part, physiological responses of wheat to stress were discussed. Cell membrane stability, relative water content, early maturity, decreased leaf area, small plant size, increased dry weight and root–shoot ratio, and the whole-plant transpiration rate response to enhanced atmospheric vapor pressure deficit are physiological traits associated with drought tolerance in wheat. Reduction of relative water content closes stomata and thereby reduces stomatal conductance. Osmotic adjustment improves drought tolerance by allowing cell enlargement, plant growth, and stomata to stay partially open and by maintaining CO2 fixation under severe water deficit. The wheat plant accumulates several organic and inorganic solutes in its cytosol to lessen its osmotic potential for maintenance of cell turgor. Drought affects photosynthesis negatively by changing the inner structure of chloroplasts, mitochondria, and chlorophyll content and minerals. Destruction of the photosystem II (PSII) oxygen releasing complex and reaction center can disturb production and use of electrons, causing lipid peroxidation of cell membrane through the production of reactive oxygen species. In the second part, drought mitigation approaches were discussed. Seed, drought, bacterial, and hormonal priming are common approaches used to lessen the effects of water deficit. Physiological trait-based breeding, molecular breeding, marker-assisted backcrossing, aerial phenotyping, water budgeting, and resource allocation are modern approaches used to develop drought tolerant wheat cultivars. Wheat genotypes produced as a result of a combination of all these methodologies will increase food security regarding the currently changing climate.

Aspirin priming circumvents the salinity-induced effects on wheat emergence and seedling growth by regulating starch metabolism and antioxidant enzyme activities

Abstract: Though seed priming has been emerged as an effective and pragmatic approach, efforts are being made to discover and optimize the new priming agents which are cheaper and easily accessible to the farmers. Here, we established two independent experiments, to ascertain the role of aspirin priming in salinity tolerance of wheat. In the first experiment, various concentrations of aspirin (125, 250, 375, and 500 ppm) were examined for emergence and seedling growth of wheat. A non-primed control, hydropriming, and hydrogen peroxide priming treatments were also maintained for comparison. Among the different treatments, seeds primed with 125 and 250 ppm aspirin depicted better emergence, vigorous seedling growth, and higher starch metabolism. Therefore, these treatments were further used in the second experiment under salinity stress (10 dS m−1). Salinity stress caused delayed and erratic emergence hampered the shoot and root growth, chlorophyll contents, and enhanced the lipid peroxidation and phenolics content in wheat seedlings. However, wheat seed priming particularly with aspirin effectively alleviated the negative effects of salinity on most of the observed parameters. Aspirin priming also significantly enhanced the activities of antioxidant enzymes (catalase, peroxidase, and superoxide dismutase), and reduced oxidative stress in wheat seedlings. Vigorous growth and greater salinity tolerance of wheat seedlings derived from aspirin primed seeds were related with better starch metabolism, strong antioxidative defense system, and lower lipid peroxidation.

Exogenous melatonin alleviates damage from drought stress in Brassica napus L. (rapeseed) seedlings

Abstract: This study investigated the ability of exogenous melatonin (MT) to alleviate drought stress in Brassica napus L. (rapeseed) seedlings. Seedling traits under control condition, drought stress, and drought stress with exogenous MT were evaluated. The results indicated that 0.05 mmol/L exogenous MT had the greatest protective effect against simulated drought stress. Exogenous MT alleviated the seedling growth inhibition under drought stress and significantly increased the leaf area and fresh and dry weights of roots and shoots compared to stress conditions lacking MT. In addition, although the hydrogen peroxide (H2O2) content increased under drought stress, it was decreased by exogenous MT. Moreover, antioxidant enzyme activities were increased in response to drought stress, and the activities of catalase, ascorbate peroxidase, and peroxidase were significantly enhanced by exogenous MT. The results also showed that solute accumulation under stress was enhanced with exogenous MT through increases in the contents of soluble sugars and proteins. These results suggest that exogenous MT can alleviate the negative effects of drought stress and improve the growth of seedlings. The findings indicate that MT possesses antioxidative, osmotic activity-adjusting, and growth-inducing properties, thus making it beneficial for drought acclimatization.

Estimating the contribution of arbuscular mycorrhizal fungi to drought tolerance of potted olive trees (Olea europaea)

Abstract: The aim of the present study is to investigate the contribution of mycorrhization to the resilience of olive trees to drought. One-year-old olive plants were inoculated (Myc+) or not (Myc−) with arbuscular mycorrhizal fungi (AMF), and subjected to a 40-day-drought period. At regular intervals of the watering-off period and after rehydration period, water relations and gas exchanges parameters were measured. Similarly, the total soluble sugars, proline, and mineral nutrients concentrations were determined. The results revealed that Myc+ plants were less affected by drought than Myc− plants proving the involvement of the AMF in the alleviation of drought impact on olive tree. In fact, the turgor potential (Ψp) in Myc+ plants exhibited positive values during the whole treatment period, while Ψp in Myc− plants was negative mainly under severe stress intensity. Moreover, the stomatal function of Myc+ plants was less affected by drought compared to Myc− plants. The maximum of mycorrhizas relative drought alleviation rate (RDAR) was estimated to be 40% for Ψpd and RWC, 36% for the osmotic potential (ΨS), 86% for Ψp, 16% for gs, and 27% for E. The osmotic adjustment by proline was earlier in Myc+ plants than in Myc− ones. The inoculation with AMF also improved mineral uptake (K, N, Zn, and Fe). After 40 days of drought, Myc+ plants survive but not Myc− ones. In addition, the restoration of the irrigation permitted the Myc+ plants to recuperate from severe drought stress. To sum up, inoculation of young olive trees with the AMF improved their resilience to drought.

Drought tolerance in citrus rootstocks is associated with better antioxidant defense mechanism

Abstract: Citrus is one of the major fruit crops grown worldwide. Citrus trees are affected by different abiotic stresses including drought which decrease its yield. In this study, six different citrus rootstocks (Volkameriana lemon, Brazilian sour orange, Carrizo citrange, Eureka lemon, Gada dahi, and Rangpur lime) were subjected to drought stress (24 days) and leaf relative water content (LRWC), chlorophyll ‘a’ and ‘b’, antioxidant capacity (AC), total phenolic content, and proline content (PRO) were measured. Hydrogen peroxide (H2O2), lipid peroxidation (MDA), total soluble proteins (TSP), and enzymatic antioxidant activities, such as superoxidase dismutase (SOD), catalase (CAT), and peroxidase (POD), were measured in leaves and roots of the rootstocks. Drought-stressed Volkameriana lemon had the minimum LRWC but higher SOD activity in its leaves. Carrizo citrange possessed the minimum amount of Chl ‘a’ and ‘b’ in leaves and exhibited lesser MDA and H2O2 in roots but greater TSP content in leaves and roots. SOD, CAT, POD, PRO, MDA, H2O2, and AC decreased in the leaves of Eureka lemon and Rangpur lime under drought stress. MDA and H2O2 contents were observed higher in leaves of Brazilian sour orange (a drought sensitive rootstock). However, higher SOD activity in roots and higher CAT and POD activities in leaves and roots were recorded in Carrizo citrange (a drought-tolerant rootstock). The results indicated that all the studied rootstocks were different in their defense mechanism. Tolerant rootstocks exhibited less amount of MDA and H2O2 and more antioxidant enzymatic activities (SOD, CAT, and POD) to cope with reactive oxygen species produced during drought stress.

Sugar beet extract acts as a natural bio-stimulant for physio-biochemical attributes in water stressed wheat (Triticum aestivum L.)

Abstract: The present study investigated the role of sugar beet extract (SBE) as a bio-stimulant to ameliorate the adverse effects of drought on seed germination and growth of wheat (Triticum aestivum L.). Different concentrations of SBE (0, 10, 20, 30, 40 and 50%) were used for priming the wheat seeds. The experiment was conducted in laboratory (PEG-8000 was used to create water stress) as well as under natural environmental conditions (using soil with 100 and 60% field capacity). Significant ameliorating effects of seed priming with SBE were recorded on different germination attributes, i.e., time to 50% emergence (E50), germination index (GI), mean emergence time (MET), germination percentage (G%), coefficient of uniformity of emergence (CUE) and germination energy (GE) under water stress. Without priming, the plants exhibited symptoms of water stress like decreased biomass, reduction in photosynthetic pigments, e.g., chlorophyll, carotenoids. Seed pre-conditioning with SBE improved the plant growth, photosynthetic pigments, antioxidants’ activities and nutrient homeostasis of plants facing water deficit and grown under well-watered conditions. The maximum increase in biomass, content of chlorophyll, carotenoids and activities of superoxide dismutase (SOD) and peroxidase (POD) was 13.4, 8.5, 11.9, 7.6, 13.6, 42.0, 19.8%, respectively, with SBE seed priming under water stress. In conclusion, SBE seed priming effectively reduced the negativities of water stress on seed germination which resulted in better plant growth in terms of enhanced biomass, photosynthetic pigments, antioxidant defense mechanism and better nutrient homeostasis. Overall, the findings suggest that seed pre-conditioning with SBE as a bio-stimulant will be helpful for better crop stand establishment under low field capacity, especially in semi-arid and arid agricultural fields.

Growth and mineral content of coriander ( Coriandrum sativum L.) plants under mild salinity with different salts

Abstract: Soil salinity is a complex issue in which various anions and cations contribute to have a general adverse effect on plant growth. In the present study, effects of salinity from various salts including sodium chloride (NaCl), potassium chloride + sodium chloride + calcium chloride (KCl + NaCl + CaCl2), potassium sulfate + magnesium nitrate (K2SO4 + Mg(NO3)2) at two electric conductivities (EC) of 2 and 4 dS m−1 of irrigation water, and a distilled water control were evaluated on coriander plants (Coriandrum sativum L.). At EC = 2, all salts increased plant yield (shoot fresh weight) than control. Most growth traits including plant height, shoot fresh and dry weight, leaf SPAD value and vitamin C, leaf K, Mg and P concentrations were increased by K2SO4 + MgNO3, and remained unchanged by KCl + NaCl + CaCl2 treatment (except reduced plant height). Leaf’s zinc concentration reduced by either treatment. Even sodium chloride at EC = 2 showed some beneficial effects on leaf chlorophyll index, root fresh weight, leaf’s calcium and phosphorus concentration; however, most traits remained unchanged than control. Treatment of plants with NaCl or KCl + NaCl + CaCl2 at either EC increased the number of flowered shoots and leaf proline content than control. Most growth and quality traits including leaf minerals and vitamin C content were reduced by NaCl at EC = 4; however, shoot fresh and dry weights remained unchanged than control. Plant root fresh weight increased by NaCl at EC = 2 and decreased at EC = 4 than control. At EC = 4, shoot dry weight was increased and leaf Ca, P, Zn and Mn were decreased by KCl + NaCl + CaCl2, whereas shoot dry weight, leaf SPAD value and vitamin C content, leaf Mg and P were increased and leaf Zn was decreased by K2SO4 + MgNO3 than control. The results indicate that in contrast to sodium chloride, the salinity effects of other salts can not be detrimental on coriander plant growth.

Wild relatives of wheat: Aegilops–Triticum accessions disclose differential antioxidative and physiological responses to water stress

Abstract: Wild relatives of wheat are an outstanding source of resistance to both abiotic and biotic stresses. In the present study, we evaluated the activity of four antioxidant enzymes—superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and guaiacol peroxidase (GPX)—along with photosynthetic pigments and shoot biomass in 12 Aegilops–Triticum accessions with different genomic constitutions and two tolerant and sensitive control varieties under well-watered (WW; 90% FC), moderate (MS; 50% FC) and severe (SS; 25% FC) water stress treatments. The analysis of variance for measured traits indicated highly significant effects of the water stress treatments, accessions, and their interactions. The 12 domesticated and wild relatives of wheat exhibited more variability and greater activity in the expression of antioxidative enzymes than cultivated wheats. While domesticated forms of wheat, T. aestivum (AABBDD) and T. durum (AABB) seem to have a functionally active antioxidant mechanism, other accessions with alien genomes—Ae. umbellulata (UU), Ae. crassa (MMDD), Ae. caudata (CC), Ae. cylindrica (DDCC) and T. boeoticum (AbAb)—respond to water stress by increasing enzymatic antioxidants as the dominant mechanism that contributes to the retention of oxidative balance in the cell. Furthermore, abovementioned accessions with alien genomes had higher photosynthetic pigment contents (chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid) under water stress than well-watered conditions. Hence, these accessions could be used in future breeding programs to combine beneficial stress-adaptive characters of alien genomes into synthetic hexaploid wheat varieties in the field, even at limited water supply.

Strigolactones: multi-level regulation of biosynthesis and diverse responses in plant abiotic stresses

Abstract: Strigolactones (SLs) are a small class of diverse metabolites derived from the carotenoid pathway. These active biomolecules are a recent inclusion to the list of non-traditional phytohormones or plant growth regulators. Previous reports and articles have discussed their pro-regulatory roles in plant growth, development, signaling and delay of senescence. However, the multi-level control of SL biosynthesis is less known. The anabolic genes are strictly regulated through synchronized co-operation between crucial phytohormones. Epigenetic and microRNA-mediated post-transcriptional regulation fine tunes the cellular accumulation of these putative phytohormones. The question now arises that why such multi-level intricate regulation at all is required for SLs, which were originally detected as under-rated germination and rhizosphere stimulants. This review answers the question in the backdrop of the positive roles of SLs in promoting abiotic stress resilience across diverse plant species. SLs reportedly accumulate in the plant tissues in response to environmental sub-optimal conditions like drought, salinity, temperature, nutrient deprivation and oxidative stresses. Fluctuations in the light quality and intensity also trigger variable accumulation of SLs, indicating their potential in regulating light stress as well. Though the exact roles of SLs have not yet been characterized, it is predicted that they possibly induce the expression of downstream osmolytes to maintain metabolic homeostasis in the stressed cells. Thus, exogenous treatments or transgenic approaches for higher SL bioaccumulation can be potential strategies for developing multiple abiotic stress tolerance in crops and plants.

Cold plasma relieved toxicity signs of nano zinc oxide in Capsicum annuum cayenne via modifying growth, differentiation, and physiology

Abstract: Taking functional scientific devices and metal-based nanoparticles into account, the present research was carried out to evaluate the plant (Capsicum annuum) responses to cold plasma and zinc oxide nanoparticle (nZnO) in in vitro and pot conditions. Seeds were exposed to plasma (0.84 W/cm2 surface power densities) with three exposure times (0, 60, and 120 s) and/or two concentrations of nZnO (0 and 100 mgl− 1). The treated seeds were cultured in hormone-free MS medium (MS) or supplemented with 2 mgl− 1 BA and 0.5 mgl− 1 IAA (MSH). The seed pre-treatment with plasma enhanced a germination process and plant early growth, in contrast with the nZnO treatment. The treatment of nZnO significantly decreased the total fresh mass and leaf area in the seedlings grown in both culture media, while its growth-delaying impact was mitigated by the plasma treatment. The chlorophyll a and carotenoid were increased to 39.35 and 32% for the plasma-treated seedlings, respectively, than the control. The plasma and/or nZnO treatments acted as effective elicitors to induce the peroxidase activities in both culture media. Similarly, the activities of phenylalanine ammonia-lyase and soluble phenols were found to be significantly higher in the plasma and/or nZnO groups in both roots and leaves. Interestingly, inhibiting effects of nZnO on xylem differentiation was alleviated by the plasma treatments. In the pot condition, soaking seeds before the plasma treatment was the most effective method to affect plant growth. This is a first report reflecting the potential benefits of the cold plasma treatment to improve plant growth and resistance to the nanoparticle.

Effect of TIBA, fluridone and salicylic acid on somatic embryogenesis and endogenous hormone and sugar contents in the tree fern Cyathea delgadii Sternb.

Abstract: Somatic embryogenesis (SE) in the tree fern Cyathea delgadii was first described in 2015 and since then has been used to exploration of this phenomenon in cryptogamic plants. To deepen the knowledge about the hormonal control of SE, stipe explants were cultured on media supplemented with hormone biosynthesis and transport inhibitors (HBTIs). In the presence of 30 µM 2,3,5-triiodobenzoic acid (TIBA), or 40 µM fluridone or 125 µM salicylic acid (SA), somatic embryo production was totally inhibited. The quantitative analysis of the changes in endogenous hormone and sugar contents was conducted every 2 days within 10-day-long initial culture. The results showed that the concentrations of endogenous indole-3-acetic acid (IAA), abscisic acid (ABA), cytokinins (CKs) and soluble sugars were strongly modified either by TIBA and fluridone. Under their influence, the contents of cytokinins such as c-Z, c-ZR, t-Z, t-ZR, KinR were reduced to barely detectable levels. Treatment with SA results in the changes in endogenous IAA and sugar contents. It also modifies the IAA/CKs ratio; however, excluding the first 2 days of culture, the concentrations of ABA and cytokinins were kept on the control level. All HBTIs significantly increased the kinetin (Kin) content. Our work sheds new light on the relationships between the biosynthetic inhibitors and phytohormones and sugars in the process of early SE. It can be helpful to study the role of hormones in acquisition of embryogenic competence.

Transgenic plants as a source of polyhydroxyalkanoates

Abstract: Polyhydroxyalkanoates (PHAs) make a large class of biodegradable biopolymers that are naturally synthesized by numerous microorganisms. These biopolymers could be an alternative to commonly used plastics based on petroleum. Production of PHAs in bioreactors using microorganisms is not widely applied due to its unprofitability. Using transgenic plants for this purpose may be cheaper and more environmental friendly because the biosynthesis of PHAs in plants is based only on water, mineral salts, CO2 and light. Additionally, plants are not capable of degrading PHAs as bacteria do, and extraction of PHAs from plant tissues is not always necessary. The main objective of this work is a review of possibilities of PHA biosynthesis in transgenic plants and presentation of general information on properties and potential application possibilities of these biopolymers. The possibility of syntheses and accumulation of PHA in several transgenic plants has been studied for some years. Many experiments were performed on model plant Arabidopsis thaliana, however, the research has also revealed a great potential of transgenic crop plants such as camelina (Camelina sativa), tobacco (Nicotiana tabacum) or sugarcane (Saccharum officinarum) as a good sources of PHAs. The highest level of PHAs accumulation in plants was achieved in transgenic A. thaliana (up to 40% of the dry weight of the leaf), and among crop plants in C. sativa (up to 20% of the dry weight of the seed). Increasing knowledge on PHAs permits expansion of the possibilities of these biopolymers use even at a low level of their accumulation in plant tissues.

Selenium nano-particle induced alterations in expression patterns of heat shock factor A4A (HSFA4A), and high molecular weight glutenin subunit 1Bx (Glu-1Bx) and enhanced nitrate reductase activity in wheat ( Triticum aestivum L.)

Abstract: Taking account of heat shock factor A4A (HSFA4A) as a hydrogen peroxide sensor, anti-apoptosis agent, and crosslink component with critical signaling cascades, the current study was carried out to monitor possible changes in expression of this gene as well as some other important characteristics in wheat plants exposed to selenium nano-particle (nSe). Wheat seedlings were treated with nSe (0, 5, 10, and 50 mgl−1). In germinating stage, plant fresh weights were reduced in nSe-treated seedlings, among which the nSe of 50 provoked roots turned brown. The nSe triggered the increases in the expressions of HSFA4A, in the plate. In the pot condition, shoot fresh weights in nSe-supplemented seedlings were decreased by approximately 22%. The nSe of 5 and 10 mgl−1, respectively induced the expression of HSFA4A by 3.4- and 9.15-folds, contrasted with nSe50. Increasing times of sprays caused the dramatic reductions of the expression of HSFA4A in the nSe-supplemented groups. Moreover, the treatment of nSe stimulated expression of high molecular weight glutenin subunit 1Bx (Glu-1Bx) by fourfold, over the control. While the dramatic decrease in the expression of Glu-1Bx was recorded with increasing times of spray. Nitrate reductase activities were significantly improved by approximately 47% in nSe-fortified seedlings. Also, the foliar supplementation of nSe of 5 mgl−1 provoked the significant inductions in peroxidase activity by 8%, whereas two other nSe treatments declined it. It may be stated that the nSe may modify the expression of HSFA4A, thereby triggering specific signaling and altering metabolism.

A chalcone synthase gene AeCHS from Abelmoschus esculentus regulates flavonoid accumulation and abiotic stress tolerance in transgenic Arabidopsis

Abstract: Chalcone synthase (CHS) is one of the key enzymes in flavonoid biosynthesis pathway in plants. However, the roles of AeCHS gene from Abelmoschus esculentus in flavonoid accumulation and tolerance to abiotic stresses have not been studied. In this study, the AeCHS gene was cloned from Abelmoschus esculentus. The open reading frame contained 1170 nucleotides encoding 389 amino acids. The coding region of AeCHS was cloned into a binary vector under the control of 35S promoter and then transformed into Arabidopsis to obtain transgenic plants. Overexpression of AeCHS increased the production of downstream flavonoids and the expression of related genes in the flavonoid biosynthesis pathway. It also improved resistance to salt and mannitol stresses during seed germination and root development. Further component and enzymatic analyses showed the decreased content of H2O2 and malondialdehyde and the increased activities of superoxide dismutase (SOD) and peroxidase (POD) in transgenic seedlings. Meanwhile, the expression level of AtSOD and AtPOD genes was up-regulated against salt and osmotic stresses. Together, our finding indicated that changing the expression level of AeCHS in plants alters the accumulation of flavonoids and regulates plantlet tolerance to abiotic stress by maintaining ROS homeostasis. The AeCHS gene has the potential to be used to increase the content of valuable flavonoids and improve the tolerance to abiotic stresses in plants.

Physiological and biochemical changes in different drought-tolerant alfalfa ( Medicago sativa L.) varieties under PEG-induced drought stress

Abstract: Medicago sativa L. cv. Longzhong is a nutritious forage plant in dryland regions of the Loess Plateau with strong drought tolerance and broad adaptability. To understand the adaptation mechanism of alfalfa (M. sativa L. cv. Longzhong) to drought stress, growth, and physiological parameters including levels of chlorophyll content, osmotic adjustment, reactive oxygen species (ROS), and antioxidant enzymes and antioxidants were measured under simulated levels of drought (− 0.40, − 0.80, − 1.20, − 1.60, and − 2.00 MPa). The changes in M. sativa L. cv. Longzhong were compared with those of plants of M. sativa L. cv. Longdong control (Variety I) suited to moderate rainfall areas and M. sativa L. cv. Gannong No. 3 (Variety II) suited to irrigated areas. The results showed that root–shoot ratio, the chlorophyll (a + b) and osmolytes contents, the degree of lipid peroxidation and ROS production, and the levels of antioxidative enzymes and antioxidants increased significantly with increasing drought stress, whereas plant height, aboveground biomass, chlorophyll a/b ratio, leaf water potential (Ψ1), and relative water content (RWC) decreased in response to drought. The Longzhong variety responded early to beginning drought stress (between 0 and − 0.4 MPa) compared with the controls. Under drought stress (between − 0.4 and − 2.0 MPa), the Longzhong variety had significantly higher belowground biomass, root–shoot ratio, Ψ1, RWC, catalase (CAT) activity and reduced glutathione content than those of Varieties I and II, but hydrogen peroxide and hydroxyl free radical (OH·) contents were significantly lower. Step regression analysis showed that OH·, CAT, malondialdehyde, superoxide anion-free radical (O 2 ·− ), and superoxide dismutase of Longzhong had the most marked response to drought stress. In conclusion, the stronger drought tolerance of the Longzhong variety might be due to its higher water-holding capacity, root–shoot ratio, and ability to coordinate enzymatic and non-enzymatic antioxidant systems, which coordinate the peroxidation and oxidative systems.

Transverse thin cell layer ( t -TCL)-mediated improvised micropropagation protocol for endangered medicinal orchid Dendrobium aphyllum Roxb: an integrated phytomolecular approach

Abstract: Clonal propagation is an important biotechnological tool for the conservation of rare, endangered and threatened as well as commercially important plant species of which orchids are an important representative. In the present research, an attempt was made to develop a fast, clonally stable as well as phytochemically enriched regeneration protocol for propagating Dendrobium aphyllum, an important medicinal orchid using transverse thin cell layer (t-TCL) explants. Murashige and Skoog (MS) medium supplemented with 15 µM meta-topolin along with 10 µM TDZ and 10 µM AgNO3 was found to be most conducive for shoot proliferation. After 8 weeks of culture, an average of 39.41 shoots/explant proliferated; till date this is the best shooting frequency for D. aphyllum and one of the best amongst the orchids. The highest rooting frequency of 82.34% was accomplished in half-strength MS medium supplemented with 15 µM IBA. The plantlets were successfully acclimatized in greenhouse exhibiting normal developmental patterns and flowering occurred after 6 months of acclimatization with 3–4 flowers/stalk irrespective of the flowering season. The genetic homogeneity of the micropropagated plants was ascertained using IRAP and ISSR markers. A comparative assessment of the antioxidant activity (mother and micropropagated plant) was performed using DPPH and FRAP assays which was recorded to be higher amongst the in vitro-regenerated plants. A rapid, genetically stable regeneration protocol coupled with comprehensively higher phytochemical yield is reported in the present study on D. aphyllum. The results of this study confirm the use of in vitro propagation protocol for sustainable commercial utilization as well as conservation of medicinal orchid bio-resources within a limited time period.

Plant growth regulators ameliorate the ill effect of salt stress through improved growth, photosynthesis, antioxidant system, yield and quality attributes in Mentha piperita L.

Abstract: The roles of plant growth regulators (PGRs) in plants are well documented. However, there is a little information regarding their roles in alleviating salt stress in plants, particularly peppermint. This necessitated the evaluation of the efficiency of three selected PGRs in counteracting the ill effect of salt stress by conducting a pot experiment on peppermint (Lamiaceae). Three uniform size suckers were transplanted in each pot containing proper nutrients. Thirty day old plants were subjected to 4 levels of salinity, viz. 0, 50, 100 or 150 mM NaCl. Salt stress was given at 30 days after their transplantation (DAT). Plants were sprayed twice, i.e., at 60 and 75 DAT with 10−6 M each of gibberellic acid (GA3), salicylic acid (SA) or triacontanol (Tria). The sampling was made at 100 DAT and harvesting at 120 DAT. The graded levels of salinity decreased growth, photosynthesis, carbonic anhydrase (CA) activity, NPK content, peltate glandular trichome (PGT) density, essential oil (EO) and menthol content and herb, EO and menthol yield, but increased catalase (CAT), peroxidase (POX) and superoxide dismutase (SOD) activities and proline content linearly. Spray of PGRs particularly SA improved all parameters under both salt and salt free conditions. The maximum values for yields of herb, EO and menthol were noted with 0 mM NaCl × SA. However, antioxidants, proline content, PGT density and EO content were found to be maximum with 150 mM NaCl × SA.

Ectopic overexpression of maize heat shock transcription factor gene ZmHsf04 confers increased thermo and salt-stress tolerance in transgenic Arabidopsis

Abstract: In our previous study, 25 Hsf gene homologues were identified and analyzed in maize. However, the exact functions of these gene family members are unclear at present. Here, we report the isolation and characterization of a strongly heat-induced HsfA2 gene from maize, ZmHsf04, and show its function in the heat/salt-stress response. Subcellular location assays showed that the ZmHsf04 protein is localized to the nucleus. Transcription activation data demonstrate that an AHA2 domain protein is necessary for the transcriptional activity of ZmHsf04. Furthermore, the function of ZmHsf04 was characterized in detail in transgenic plants of Arabidopsis thaliana Col-0. Overexpression of ZmHsf04 in Arabidopsis enhanced thermotolerance and positively regulated short-term-acquired thermotolerance. In addition, ZmHsf04 significantly improved salt tolerance and increased the sensitivity to abscisic acid in transgenic Arabidopsis. Overexpression of ZmHsf04 in Col-0 plants significantly up-regulated the expression of heat-specific HSP genes (AtHsp25.3-P, AtHsp18.2-CI, and AtHsp70B) and stress-related genes (AtAPX2 and AtGolS1) compared to the wild type. In summary, we have characterized a transcriptional regulator, ZmHsf04, which has important functions in enhancing heat and salt tolerance in plants.

Cold stress modulates osmolytes and antioxidant system in Calendula officinalis

Abstract: Understanding the mechanism of adaptation to low-temperature stress is very crucial for developing cold-tolerant crop plants. The present study was used to investigate the response of Calendula officinalis (C. officinalis) to cold stress (CS). Seeds of C. officinalis were grown at normal temperature of 25 °C for 14 days and then shifted to a growth chamber set at 4 °C. The response of C. officinalis seedlings to cold stress was evaluated by estimating the relative growth changes, chlorophyll, electrolyte leakage (EL) and the content of malondialdehyde (MDA), proline, glycine betaine (GB), total soluble sugars, trehalose, total protein content and fatty acid profile. Enzymatic activity of antioxidants such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) was also assessed. Moreover, transcript expression of cold-responsive genes [APX, CAT, dehydration-responsive element-binding protein (DREB1), GR and SOD] was also evaluated on homology basis. We measured and compared these indices of seedlings leaves under low temperature (4 °C) and normal temperature (25 °C) and observed that on exposure to CS, C. officinalis shows higher accumulation of osmoprotectants (proline, soluble sugars, glycine betaine and trehalose), phenolics and proteins, and increased antioxidant enzyme activity (APX, GR and SOD) except CAT activity, which declined in cold-stressed plants. Transcript expression of cold-responsive genes (SOD, CAT, APX, GR and DREB1) was found to be upregulated under cold stress. Overall, our study suggests that cold exposure/CS, besides eliciting various biochemical/physiological responses, triggers various pathways causing differential gene expression, consequently leading to differential protein expression. Further, this is the first report of C. officinalis under cold stress that may help us in exploring the mechanism of cold tolerance in future.

Screening of rice landraces (Oryza sativa L.) for seedling stage salinity tolerance using morpho-physiological and molecular markers.

Abstract: Traditional rice landraces of coastal area in Bangladesh are distinct regarding their phenotype, response to salt stress and yield attributes. With characterization of these landraces, suitable candidate genes for salinity tolerance could be identified to introgress into modern rice varieties. Therefore, the aim of this experiment was to uncover prospective rice landraces tolerant to salinity. Relying on morphological, biochemical and molecular parameters 25 rice genotypes were tested for salt tolerance at germination and seedling stage. At germination stage 0 and 12 dSm−1 salinity were imposed on rice genotypes. Ward’s cluster analysis divided rice genotypes into three clusters (susceptible, moderately tolerant and tolerant) based on the physiological indices. The tolerant rice landraces to salinity were Sona Toly, Nakraji and Komol Bhog. At seedling stage screening was performed following IRRI standard protocol at 12 dSm−1 salinity level. Based on all morphological and biochemical parameters Komol Bhog was identified as the highly salinity tolerant landrace while Bolonga, Sona Toly, Dud Sail, Tal Mugur and Nakraji were found as tolerant to salinity. Molecular characterization using two simple sequence repeats (SSR) markers, viz. RM121 and RM337 displayed Bolonga, Til Kapor, Panbra, Sona Toly, Bina Sail, Komol Bhog, Nakraji, Tilkapur, Gajor Goria and Gota were tolerant landraces through genetic similarity in dendrogram. These identified salt-resistant landraces can be used as promising germplasm resources for breeding salt-tolerant high-yielding rice varieties in future.

Methyl jasmonate effects on volatile oil compounds and antioxidant activity of leaf extract of two basil cultivars under salinity stress

Abstract: Basil (Ocimum basilicum L.) as an economic and culinary herb is used in traditional medicine. In this research, a pot experiment was conducted, as factorial based on randomized completely design with three replications, to examine the influence of methyl jasmonate (MeJA) on volatile substances and chemical components as well as antioxidant activity of leaf’s extract from two commercial cultivars (Genove and Rubi) of sweet basil under salinity stress. The treatments were comprised MeJA (0 and 0.5 mM) and salinity stresses (0, 30, 60, and 90 mM). Using MeJA foliarly meaningfully raised the essential oil content in the Rubi cultivar at 0 and 30 mM of salinity and in the Genove cultivar just on 30 mM of salinity. MeJA treatment increased the essential oil content and also showed noticeable effects on the main components of the oils. The foliar application of MeJA raised the percentages of linalool and 1,8-cineole, whereas reduced the percentages of α-cadinol, α-bergamotene, β-maaliene, and eugenol in the extracted oil. In both basil cultivars, the MeJA significantly enhanced the antioxidant activity. The highest antioxidant activities in the Rubi and Genove cultivars were obtained at 0 mM (control) and 60 mM of salinity with the MeJA application, respectively. In conclusion, the foliar application of MeJA caused to different responses in the cultivars and reduced the negative effects of salt stress.

Effects of exogenous myo-inositol on leaf water status and oxidative stress of Capsicum annuum under drought stress

Abstract: Drought-stressed plants accumulate cyclitols such as myo-inositol, pinitol, quercitol in the cytosol. These solutes (compatible solutes) protect plants from stress effects. Synthetic myo-inositol was used in the investigation of drought stress tolerance in pepper plants. Hydrogen peroxide (H2O2), membrane damage, ascorbate peroxidase (AP), catalase (CAT), proline and calcium increased in plants under drought conditions. Water status, calcium level, glutathione reductase activities increased in myo-inositol treated Capsicum annuum L. (pepper) under drought stress. Exogenous myo-inositol significantly decreased H2O2, membrane damage and proline levels and AP (except for 5 µM) and CAT activity, compared with untreated plants. Myo-inositol can play a role as effective as proline in signal transduction and in regulating concentrations of reactive oxygen species within tolerable ranges and in maintaining cell turgor by binding water molecules. Myo-inositol may become a useful instrument to eliminate the negative effects of drought environments.

Effects of 24-epibrassinolide and the synthetic brassinosteroid mimic on chili pepper under drought

Abstract: Drought is major stress that severely reduces plant growth and productivity. To improve drought tolerance, an exogenous brassinosteroids (BRs) has been used effectively in the field condition. However, the application of BRs is expensive due to the scarcity of natural BRs and the multistep synthesis of BRs. In an attempt to reduce the cost, 7,8-dihydro-8α-20-hydroxyecdysone (DHECD) has been proposed to function as an imitation of 24-epibrassinolide (EBR). In this study, chili pepper plants (Capsicum annuum L. var. frutescens (L.) Kuntze) were sprayed with DHECD, EBR at 1 µM or distilled water (control). Plants were subjected to severe water stress (25% pot water capacity) for 5 days and their physiological effects and yield were investigated. The result showed that the applications of DHECD and EBR before the beginning of water stress could improve leaf water status determined by relative water content in plants grown under drought condition. The electrolyte leakage, lipid peroxidation level, and H2O2 production were significantly declined, while the accumulations of proline and total soluble sugar were increased in the treated plants. Moreover, the net photosynthesis (PN) was elevated due to the increases of stomatal conductance (gs) and intercellular CO2 concentration (Ci) after BR pretreatments under drought. In addition, applications of DHECD and EBR maintained all chlorophyll fluorescence parameters; Fv/Fm, Fv′/Fm′, ΦPSII, qP, and ETR, to remain the photosynthesis. As a result, shoot biomass, fruit yield and capsaicin level were considerably enhanced in the treated plants. DHECD showed better performance to maintain membrane integrity; however, EBR had more effect on the osmotic maintenance. The result also showed that pretreatment with BRs had little or no effect on well-watered plants. The study concluded that DHECD and EBR alleviated the impact of drought on physiological responses and consequently minimized yield loss.

Mitigating effect of nano-zerovalent iron, iron sulfate and EDTA against oxidative stress induced by chromium in Helianthus annuus L.

Abstract: Due to its wide industrial application, chromium (Cr) is known to be a critical environmental pollutant. Contamination of water and agricultural soil by Cr inhibits crop productivity and their physiological and biochemical processes. The objective of the current work was to investigate the effects of appropriate reducing agents such as EDTA, iron sulfate (Fe2+), and zerovalent nano iron (Fe0 nanoparticles) on growth and physiology of sunflower plants under Cr(VI) stress. Results showed that the Cr uptake increased by increasing the amount of EDTA, leading to a significant reduction in morphological and physiological parameters except for MDA and H2O2 contents. Treatment with Fe0 nanoparticles and Fe2+ reduced Cr concentration in root and shoot, increased root and shoot dry weight, plastid pigments (chlorophyll and carotenoids) and proline contents; however, the level of MDA and H2O2 decreased significantly. All parameters were affected by Fe2+ during the first week of sampling; however, Fe0 nanoparticles affected all traits until the end of the third sampling stage. A statistically significant and positive correlation was found between root Cr concentration and MDA and H2O2 seedlings treated with EDTA, Fe2+, and Fe0 grown under Cr stress. From the result of this study, it can be concluded that sunflower has the potential for accumulation of Cr as a heavy metal, and treatment with Fe0 nanoparticles to prevent Cr uptake is more effective than other employed treatments.

Interaction of boron and aluminum on the physiological characteristics of rape (Brassica napus L.) seedlings

Abstract: It has been reported that aluminum (Al) toxicity is a major limiting factor for plant growth and production on acidic soils. Boron (B) is indispensable micronutrient for normal growth of higher plants, and its addition could alleviate Al toxicity. The rape seedlings were grown under three B (0.25, 25 and 500 μM) and two Al concentrations [0 (−Al) and 100 μM (+Al) as AlCl3·6H2O]. The results indicated that Al stress severely hampered root elongation and root activity at 0.25 μM B while the normal (25 μM) and excess (500 μM) B improved the biomass of rape seedlings under Al exposure. Additionally, normal and excess B treatment reduced accumulation of Al in the roots and leaves under Al toxicity, which was also confirmed by hematoxylin with light staining. This indicates that both normal and excess B could alleviate Al toxicity. Furthermore, it also decreased the contents of malondialdehyde and soluble protein under Al toxicity. Likewise, superoxide dismutase activity (SOD) improved by 97.82 and 131.96% in the roots, and 168 and 119.88% in the leaves at 25 and 500 µM B, respectively, while the peroxidase and catalase activities dropped as a result of Al stress. The study results demonstrated that appropriate B application is necessary to avoid the harmful consequences of Al toxicity in rape seedlings.

Multivariate analysis on the distribution of elements in plants

Abstract: The present review accentuates the elemental composition of plants as investigated by various researchers utilizing sophisticated techniques. Plants contain plethora of elements which extend their benefits to humans both in terms of medicine as well as nutrition. Therefore, there is a need to explore the elemental composition of plants to investigate their nutraceutical importance. In this review, the elemental data was analyzed using different multivariate techniques. The average values of elements used in this review are sodium (Na) (241.1 µg/g dw), magnesium (Mg) (1202.4 µg/g dw), aluminum (Al) (159.6 µg/g dw), silicon (Si) (133.7 µg/g dw), phosphorus (P) (1947 µg/g dw), sulfur (S) (1483.1 µg/g dw), chloride (Cl) (624.5 µg/g dw), potassium (K) (3008.5 µg/g dw), calcium (Ca) (1663.1 µg/g dw) and iron (Fe) (143.6 µg/g dw) respectively. Maximum accumulation of Na, K, Ca, Mg, Fe, P and S occurs in Poaceae, Lamiaceae, Lauraceae, Sapotaceae, Apiaceae, Pedaliaceae and Brassicaceae, respectively.

Cold stress induces biochemical changes, fatty acid profile, antioxidant system and gene expression in Capsella bursa pastoris L.

Abstract: In the present study, we analysed the response of 30 day old seedlings of Capsella bursa-pastoris to cold stress (CS) Seeds of C bursa-pastoris were grown at 25 °C for 1 month and then exposed to low temperature of 10 °C Plant tissues were collected at different time points (24, 48, 72, 96 and 120 h) and assayed for change in osmoprotectants, fatty acid composition of membrane system and antioxidant enzymes We also analysed the gene expression of important stress related transcription factors (TF) such as, LEA (Late embryogenesis abundant) and DREB (Dehydration responsive element binding) A significant increase in the levels of several osmoprotectants such as proline (Pro), glycine betaine (GB), free amino acids, total proteins, total soluble sugars and trehalose was observed CS increased membrane fluidity by changing the ratio of saturated and unsaturated fatty acids in membranes which in turn resulted in significant ion leakage CS in C bursa-pastoris led to a significant decrease in photosynthetic pigments and ultimately altered the overall growth and biomass Similarly, significant changes in antioxidant enzymes were observed, POD (peroxidase), CAT (cataalase), SOD (superoxide dismutase) and GR (glutathione reductase) increased significantly while as APX (ascorbate peroxidase) declined in response to CS We assessed the transcriptional expression using qRT-PCR of these antioxidant genes coordinated with their enzyme activities Additionally, in C bursa-pastoris cold inducible genes encoding DREB and LEA (protein also got upregulated under CS) The present study suggests that C bursa-pastoris responded to CS efficiently by changing its different metabolic pathways, antioxidant system, fatty acid composition and gene expression

Insights into fluoride-induced oxidative stress and antioxidant defences in plants

Abstract: Fluoride is a common pollutant which occurs in various environmental matrices considered as one of the most phytotoxic pollutants. It is essential to the living organisms in trace quantities but at its higher concentration it becomes poisonous. Excess amount of fluoride in environment not only exerts its toxic effects on human beings and animals but also on plants. Toxicological impacts of fluoride on plants have been largely debated due to reduction of growth parameters, inhibition of metabolic activities and decreased photosynthetic activity. The signs of fluoride impacts on plants may be severe, acute or chronic and toxicity of fluoride depends on dose, frequency of exposure, duration and genotype of plant. This article overviews understanding of transport, uptake and fluoride accumulation in plants and provide insights into the fluoride-induced oxidative stress and regulatory mechanisms to cope up with it. The main objective of this article is to prospect new research avenues to unravel the mechanisms explaining fluoride toxicity in various plant species.