Effect of salinity and different nitrogen sources on the activity of antioxidant enzymes and indole alkaloid content in Catharanthus roseus seedlings

Ancient Hulled Wheat: An Antioxidant-Rich Crop for Boron-Contaminated Soils

This study investigated the boron (B) tolerance of four ancient hulled wheat species, examining their morphological, physiological, and antioxidant responses to varying B concentrations and the mitigating effects of exogenous glycine betaine (GB). Results revealed that B initially promoted root and shoot biomass, but higher concentrations induced growth inhibition, mitigated by GB application. B exposure increased total protein content and antioxidant enzyme activities at lower concentrations but decreased them at higher concentrations, indicating oxidative stress. Exogenous GB enhanced antioxidant enzyme activities and proline accumulation, alleviating oxidative damage. These findings suggest varying B tolerance among ancient hulled wheat varieties. GB effectively mitigated B-induced stress by bolstering antioxidant defenses and promoting osmotic adjustment. This highlights the potential of ancient hulled wheat as a genetic resource for developing B-tolerant wheat cultivars.

Optimum concentrations of potassium and zinc for better performance, nutritional, and biochemical quality of hydroponically cultivated Spinacia oleracea Cv. Virofly

In order to evaluate micro and macronutrient balance in vegetable growth, a study on greenness, yield, nutritional value, as well as biochemical status in spinach, has been conducted in a greenhouse, utilising the different concentrations of zinc (Zn) and potassium (K) in the nutrient solution. So, three concentrations of Zn (0.22, 5, and 10 mg L- 1) and K (39, 78, and 117 mg L- 1) were applied to hydroponically grown spinach (Spinacia oleracea cv. Virofly) through a factorial experiment based on a randomized complete design with three replications. The results showed that along with increasing concentrations of Zn and K in a nutrient solution, chlorophyll index and plant performance were increased although Zn showed more influence than K. The maximum plant yield was observed at 117 mg L- 1 of K in combination with both concentrations of Zn (5 and 10 mg L- 1). Along with an increase in Zn and K concentrations, the amount of nutrients including Na, Fe, Cu, Ca, Mn, and Mg decreased compared to the control level of Zn and K in nutrient solution except for Zn and K, which increased due to the Zn and K, respectively. Increased levels of Zn and K caused to decrease in malondialdehyde (MDA) content by 51% and 34%, respectively. Hydrogen peroxide (H2O2) was decreased also by 29% and 14% at 10 and 117 mg L- 1 concentration of Zn and K while higher levels of Zn and K in the nutrient solution, increased protein content by 1.4 and 1.2 folded compared to the control plants. The maximum activity of superoxide dismutase (SOD) was recorded in spinach treated with 10 mg L- 1 of Zn in combination independent to the K concentrations. The activity of ascorbate peroxidase (APX) was also affected by Zn as it showed up to 2.1 folded increment at 10 mg L- 1 Zn compared to the 0.22 mg L- 1 concentration. In general, an increase in Zn and K concentration in the nutrient solution decreased the absorption of measured nutrients except for Zn and K in spinach leaves. The effect of increased levels of Zn was more obvious than that of potassium in qualitative and biochemical traits of spinach specially at 5 mg L- 1 concentration. These findings suggest that supplementing hydroponic nutrient solutions with 5 mg L- 1 Zn in combination with 78 mg L- 1 K can lead to the better quality and tolerance of the plant, offering a promising strategy to enhance crop productivity and nutritional value in hydroponically cultivated spinach.

Extreme temperatures elicit the accumulation of cardiac glycoside and their genin units in Calotropis procera by altering the expression of transcripts involved in its biosynthesis

Calotropis procera (Aiton) W.T. Aiton is a medicinal plant belonging to the family Apocynaceae as a core source of natural cardenolides. Cardiac glycosides (CGs) are steroid derivatives reported to have the ability to regulate cancer cell survival and death through multiple signaling pathways. Earlier stage-specific and wound-responsive accumulation of CGs and their genin units have already been reported. Recent cumulative evidences have implicated stress and defense response signaling in the production of secondary metabolite in plants. In this report, seasonal accumulation of CGs and its genin units have been explored along with their profiling under control vs stress conditions with a significant accumulation using LC-MS/MS. The study showed that Calotropis procera plants efficiently accumulate CGs and genin units in both winter and summer beside rainy season, as well as under thermal and salinity stress. Among the three cardenolides, the calotropagenin was accumulated more than coroglaucigenin and uzarigenin whereas CGs like calotropin, frugoside, uscharidin, uscharin, and asclepin were significantly accumulated in response to heat, cold and NaCl. Comparatively for hormonal treatments like methyl jasmonate and salicylic acid, targeted metabsolites showed upto twofold accumulation. Gene expression analysis of CG biosynthetic genes also validated the accumulation pattern of the targeted metabolite. This targeted metabolites accumulation enhances plant tolerance to adverse conditions. Gene expression analysis supports this strategy, emphasizing the plant's effective stress management. These findings significantly contribute to our understanding of how plants adapt to stress through the accumulation of metabolites, thereby enhancing their tolerance to challenging environmental conditions.

Soil Salinization and Ancient Hulled Wheat: A Study on Antioxidant Defense Mechanisms

Soil salinization, which is second only to soil erosion in terms of soil degradation, significantly hinders crop growth and development, leading to reduced yields. This study investigated the enzymatic and non-enzymatic antioxidant defense mechanisms of four ancient hulled wheat species under salt stress, with and without exogenous glycine betaine (0.5 mM). We aimed to assess the salt tolerance of these species and their potential for cultivation in saline/sodic soils. Our findings indicate that sodium and potassium chloride concentrations exceeding 100 mM induce significant stress in hulled wheat. However, combined salt stress (sodium and potassium chloride) reduced this stress by approximately 20-30%. Furthermore, exogenous glycine betaine supplementation almost completely alleviated the negative effects of salt stress, particularly in Triticum boeoticum. This species exhibited a remarkable ability to restore normal growth functions under these conditions. Our results suggest that ancient hulled wheat, especially T. boeoticum, may be a promising candidate for cultivation in sodium-saline soils. By supplementing with potassium fertilizers in addition to nitrogen, plants can effectively control salt influx into their cells and maintain intracellular K+/Na+ balance, thereby mitigating the adverse effects of salinity stress. This approach has the potential to increase crop yields and enhance food security in saline environments.

Genome-Wide Comprehensive Analysis of the Nitrogen Metabolism Toolbox Reveals Its Evolution and Abiotic Stress Responsiveness in Rice (Oryza sativa L.)

Nitrogen metabolism (NM) plays an essential role in response to abiotic stresses for plants. Enzyme activities have been extensively studied for nitrogen metabolism-associated pathways, but the knowledge of nitrogen metabolism-associated genes involved in stress response is still limited, especially for rice. In this study, we performed the genome-wide characterization of the genes putatively involved in nitrogen metabolism. A total of 1110 potential genes were obtained to be involved in nitrogen metabolism from eight species (Arabidopsis thaliana (L.) Heynh., Glycine max (L.) Merr., Brassica napus L., Triticum aestivum L., Sorghum bicolor L., Zea mays L., Oryza sativa L. and Amborella trichopoda Baill.), especially 104 genes in rice. The comparative phylogenetic analysis of the superfamily revealed the complicated divergence of different NM genes. The expression analysis among different tissues in rice indicates the NM genes showed diverse functions in the pathway of nitrogen absorption and assimilation. Distinct expression patterns of NM genes were observed in rice under drought stress, heat stress, and salt stress, indicating that the NM genes play a curial role in response to abiotic stress. Most NM genes showed a down-regulated pattern under heat stress, while complicated expression patterns were observed for different genes under salt stress and drought stress. The function of four representative NM genes (OsGS2, OsGLU, OsGDH2, and OsAMT1;1) was further validated by using qRT-PCR analysis to confirm their responses to these abiotic stresses. Based on the predicted transcription factor binding sites (TFBSs), we built a co-expression regulatory network containing transcription factors (TFs) and NM genes, of which the constructed ERF and Dof genes may act as the core genes to respond to abiotic stresses. This study provides novel sights to the interaction between nitrogen metabolism and the response to abiotic stresses.

Roles of Calcium Signaling in Gene Expression and Photosynthetic Acclimatization of Solanum lycopersicum Micro-Tom (MT) after Mechanical Damage

A momentary increase in cytoplasmic Ca²⁺ generates an oscillation responsible for the activation of proteins, such as calmodulin and kinases, which interact with reactive oxygen species (ROS) for the transmission of a stress signal. This study investigated the influence of variations in calcium concentrations on plant defense signaling and photosynthetic acclimatization after mechanical damage. Solanum lycopersicum Micro-Tom was grown with 0, 2 and 4 mM Ca²⁺, with and without mechanical damage. The expression of stress genes was evaluated, along with levels of antioxidant enzymes, hydrogen peroxide, lipid peroxidation, histochemistry, photosynthesis and dry mass of organs. The ROS production generated by mechanical damage was further enhanced by calcium-free conditions due to the inactivation of the oxygen evolution complex, contributing to an increase in reactive species. The results indicated that ROS affected mechanical damage signaling because calcium-free plants exhibited high levels of H₂O₂ and enhanced expression of kinase and RBOH1 genes, necessary conditions for an efficient response to stress. We conclude that the plants without calcium supply recognized mechanical damage but did not survive. The highest expression of the RBOH1 gene and the accumulation of H₂O₂ in these plants signaled cell death. Plants grown in the presence of calcium showed higher expression of SlCaM2 and control of H₂O₂ concentration, thus overcoming the stress caused by mechanical damage, with photosynthetic acclimatization and without damage to dry mass production.

Transcriptional regulation mechanism of wheat varieties with different nitrogen use efficiencies in response to nitrogen deficiency stress

Background

As one of the microelements, nitrogen play essential roles in cereal production. Although the use of chemical fertilizers has significantly improved the yield of wheat, it has also caused increasingly adverse environmental pollution. Revealing the molecular mechanism manipulating wheat nitrogen use efficiency (NUE), and cultivating wheat germplasms with high nitrogen use efficiency has become important goals for wheat researchers. In this study, we investigated the physiological and transcriptional differences of three wheat cultivars with different NUE under low nitrogen stress.

Results

The results showed that, under low nitrogen conditions, the activities of nitrogen metabolism-related enzymes (GS, NR, GDH), antioxidant enzymes (SOD, POD, CAT) and soluble protein contents of ZM366 (high NUE cultivar) were higher than those of JD8 (low NUE cultivar). The hybrid cultivar of ZM366 and JD8 showed mid-parent or over-parent heterosis. Transcriptome analysis revealed that ‘alanine, aspartate and glutamate metabolism’, ‘terpenoid backbone biosynthesis’ and ‘vitamin B6 metabolism’ pathways play key roles in nitrogen use efficiency in wheat. The significant enhancement of the ‘Calvin cycle’ and ‘photorespiration’ in ZM366 contributed to its higher level of carbon metabolism under low nitrogen stress, which is an important attribute differs from the other two varieties. In addition, the activation of ABA signal transduction and biosynthesis pathways also helps to maintain NUE under low- nitrogen conditions. Moreover, bHLH transcription factors were also found to play a positive role in wheat NUE.

Conclusions

In conclusion, these results enriched our knowledge of the mechanism of wheat NUE, and provided a theoretical basis for improving wheat NUE and breeding new cultivars.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08948-0.

Effects of Exogenous Potassium (K+) Application on the Antioxidant Enzymes Activities in Leaves of Tamarix ramosissima under NaCl Stress

Saline soil is a worldwide distributed resource that seriously harms plants’ growth and development. NaCl is the most widely distributed salt in saline soil. As a typical representative of halophytes, Tamarix ramosissima Lcdcb (T. ramosissima) is commonly grown in salinized soil, and halophytes have different abilities to retain more K+ under salt stress conditions. Halophytes can adapt to different salt environments by improving the scavenging activity of reactive oxygen species (ROS) by absorbing and transporting potassium (K+). In this study, electron microscope observation, hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents determination, primary antioxidant enzyme activity determination and transcriptome sequencing analysis were carried out on the leaves of T. ramosissima under NaCl stress at 0 h, 48 h and 168 h. The results showed that H2O2 and MDA contents increased in the 200 mM NaCl + 10 mM KCl and 200 mM NaCl groups, but the content increased the most in the 200 mM NaCl group at 168 h. In addition, the leaves of T. ramosissima in the 200 mM NaCl + 10 mM KCl group had the most salt secretion, and its superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities were all higher than those of the 200 mM NaCl group and significantly higher than those of the control group. According to the results of transcriptome sequencing, it was found that the expression of 39 genes related to antioxidant enzyme activity changed significantly at the transcriptional level. Among them, 15 genes related to antioxidant enzyme activities were upregulated, and 24 genes related to antioxidant enzyme activities were downregulated in the leaves of T. ramosissima when exogenous potassium (K+) was applied under NaCl stress for 48 h; when exogenous potassium (K+) was used for 168 h under NaCl stress, 21 antioxidant enzyme activity-related genes were upregulated, and 18 antioxidant enzyme activity-related genes were downregulated in T. ramosissima leaves. Based on the changes of expression levels at different treatment times, 10 key candidates differentially expressed genes (DEGs) (Unigene0050462, Unigene0014843, Unigene0046159, Unigene0046160, Unigene0008032, Unigene0048033, Unigene0004890, Unigene0015109, Unigene0020552 and Unigene0048538) for antioxidant enzyme activities were further screened. They played an important role in applying exogenous potassium (K+) for 48 h and 168 h to the leaves of T. ramosissima in response to NaCl stress. Their expression levels were dominated by upregulation, which enhanced the activity of antioxidant enzymes, and helped T. ramosissima mitigate NaCl poison and resist NaCl stress. Particularly, Unigene0048538 in glutathione S-transferase (GST) activity had the largest log2 fold-change in the comparison groups of 200 mM NaCl-48 h vs. 200 mM NaCl + 10 mM KCl-48 h and 200 mM NaCl-168 h vs. 200 mM NaCl + 10 mM KCl-168 h. Its expression level was upregulated and played an important role in NaCl toxicity. At the same time, the results of the phylogenetic tree analysis showed that Unigene0048538 had the closest genetic distance to Prunus persica in the evolutionary relationship. In summary, with the increase of exogenous potassium (K+) application time under NaCl stress, T. ramosissima can resist high NaCl stress by enhancing antioxidant enzymes’ activity and maintaining the growth of T. ramosissima. Still, it is not enough to completely eliminate NaCl poison. This study provides a theoretical basis for the molecular mechanism of salt tolerance and K+ mitigation of NaCl poison by the representative halophyte T. ramosissima in response to NaCl stress.

Trehalose: a promising osmo-protectant against salinity stress-physiological and molecular mechanisms and future prospective

Salt stress is one of the leading threats to crop growth and productivity across the globe. Salt stress induces serious alterations in plant physiological, metabolic, biochemical functioning and it also disturbs antioxidant activities, cellular membranes, photosynthetic performance, nutrient uptake and plant water uptake and resulting in a significant reduction in growth and production. The application of osmoprotectants is considered as an important strategy to induce salt tolerance in plants. Trehalose (Tre) has emerged an excellent osmolyte to induce salinity tolerance and it got considerable attention in recent times. Under salinity stress, Tre helps to maintain the membrane integrity, and improves plant water relations, nutrient uptake and reduces the electrolyte leakage and lipid per-oxidation. Tre also improves gas exchange characteristics, protects the photosynthetic apparatus from salinity induced oxidative damages and brings ultra-structure changes in the plant body to induce salinity tolerance. Moreover, Tre also improves antioxidant activities and expression of stress responsive proteins and genes and confers salt tolerance in plants. Additionally, Tre is also involved in signaling association with signaling molecules and phytohormones and resultantly improved the plant performance under salt stress. Thus, it is interesting to understand the role of Tre in mediating the salinity tolerance in plants. Therefore, in this review we have summarized the different physiological and molecular roles of Tre to induce salt tolerance in plants. Moreover, we have also provided the information on Tre cross-talk with various osmolytes and hormones, and its role in stress responsive genes and antioxidant activities. Lastly, we also shed light on research gaps that need to be addressed in future studies. Therefore, this review will help the scientists to learn more about the Tre in changing climate conditions and it will also provide new insights to insights that could be used to develop salinity tolerance in plants.

Calcium in Photosynthetic Restoration and Growth of Annona emarginata after Mechanical Damage

Calcium, an essential element with structural function in the cell wall and plasma membrane, in addition to being a secondary messenger, is responsible for the regulation of physiological processes in plant development and responses to biotic and abiotic stresses. This study investigated the effects of calcium variation on photosynthetic performance, growth, and enzymatic antioxidant defense system in A. emarginata subjected to mechanical damage. The experimental design was in 6 × 5 factorial randomized blocks. A. emarginata plants were submitted to the six treatments: plants grown in solution with 0 mM Ca2+ without mechanical damage, 0 mM Ca2+ with mechanical damage, 2 mM Ca2+ without mechanical damage, 2 mM Ca2+ with mechanical damage, 4 mM Ca2+ without mechanical damage, and 4 mM Ca2+ with mechanical damage, as well as five evaluation periods at 0, 15, 30, 60, and 90 days after mechanical damage. The fluorescence of chlorophyll a, gas exchange, total dry mass, quantitative growth, and lipid peroxidation was studied. It is concluded that the A. emarginata plants showed better performance in restoration after mechanical damage in the presence of Ca2+ and was more sensitive in the absence of the mineral. Cultivation of the species with 2 mM Ca2+ in complete nutrient solution was sufficient to guarantee the efficiency of the enzymatic antioxidant defense system, and photosynthetic restoration of plants subjected to mechanical damage.

Enhancement of Vindoline and Catharanthine Accumulation, Antioxidant Enzymes Activities, and Gene Expression Levels in Catharanthus roseus Leaves by Chitooligosaccharides Elicitation

Catharanthus roseus (L.) G. Don is a plant belonging to the genus Catharanthus of the Apocynaceae family. It contains more than one hundred alkaloids, of which some exhibit significant pharmacological activities. Chitooligosaccharides are the only basic aminooligosaccharides with positively charged cations in nature, which can regulate plant growth and antioxidant properties. In this study, the leaves of Catharanthus roseus were sprayed with chitooligosaccharides of different molecular weights (1 kDa, 2 kDa, 3 kDa) and different concentrations (0.01 μg/mL, 0.1 μg/mL, 1 μg/mL and 10 μg/mL). The fresh weights of its root, stem and leaf were all improved after chitooligosaccharides treatments. More importantly, the chitooligosaccharides elicitor strongly stimulated the accumulation of vindoline and catharanthine in the leaves, especially with the treatment of 0.1 μg/mL 3 kDa chitooligosaccharides, the contents of them were increased by 60.68% and 141.54%, respectively. Furthermore, as the defensive responses, antioxidant enzymes activities (catalase, glutathione reductase, ascorbate peroxidase, peroxidase and superoxide dismutase) were enhanced under chitooligosaccharides treatments. To further elucidate the underlying mechanism, qRT-PCR was used to investigate the genes expression levels of secologanin synthase (SLS), strictosidine synthase (STR), strictosidine glucosidase (SGD), tabersonine 16-hydroxylase (T16H), desacetoxyvindoline-4-hydroxylase (D4H), deacetylvindoline-4-O-acetyltransferase (DAT), peroxidase 1 (PRX1) and octadecanoid-responsive Catharanthus AP2-domain protein 3 (ORCA3). All the genes were significantly up-regulated after chitooligosaccharides treatments, and the transcription abundance of ORCA3, SLS, STR, DAT and PRX1 reached a maximal level with 0.1 μg/mL 3 kDa chitooligosaccharides treatment. All these results suggest that spraying Catharanthus roseus leaves with chitooligosaccharides, especially 0.1 μg/mL of 3 kDa chitooligosaccharides, may effectively improve the pharmaceutical value of Catharanthus roseus.

Nitrogen form differently modulates growth, metabolite profile, and antioxidant and nitrogen metabolism activities in roots of Spartina alterniflora in response to increasing salinity

Sodium tolerance and nitrogen-source preferences are two of the most fascinating and ecologically important areas in plant physiology. Spartina alterniflora is a highly salt-tolerant species and appears to prefer ammonium (NH₄⁺) over nitrate (NO₃^-) as an inorganic N source, presenting a suite of aboveground physiological and biochemical mechanisms that allows growth in saline environments. Here, we tested the interactive effects of salinity (0, 200, 500 mM NaCl) and nitrogen source (NO₃^-, NH₄⁺, NH₄NO₃) on some physiological and biochemical parameters of S. alterniflora at the root level. After three months of treatments, plants were harvested to determine root growth parameters and total amino acids, proline, total soluble sugars, sucrose, and root enzyme activity. The control (0 mM NaCl) had the highest root growth rate in the medium containing only ammonium and the lowest in the medium containing only nitrate. Except for NO₃^--fed plants, the 200 mM NaCl treatment generally had less root growth than the control. Under high salinity, NH₄⁺-fed plants had better root growth than NO₃^--fed plants. In the absence of salinity, NH₄⁺-fed plants had higher superoxide dismutase, ascorbate peroxidase, glutathione reductase, and guaiacol peroxidase activities than NO₃^--fed plants. Salinity generally promoted the activity of the principal antioxidant enzymes, more so in NH₄⁺-fed plants. Nitrogen metabolism was characterized by higher constitutive levels of glutamate dehydrogenase (GDH) activity under ammonia nutrition, accompanied by elevated total amino acids levels in roots. The advantage of ammonium nutrition for S. alterniflora under salinity was connected to high amino acid accumulation and antioxidant enzyme activities, together with low H₂O₂ concentration and increased GDH activity. Ammonium improved root performance of S. alterniflora, especially under saline conditions, and may improve root antioxidant capacity and N-assimilating enzyme activities, and adjust osmotically to salinity by accumulating amino acids.

Discernment of grape rootstocks base on their response to salt stress using selected characteristics in combination with chemometric tools

In the present study, first, the 19 parameters of 21 grapevine rootstocks under salinity were measured. Then chemometrics methods including principal component analysis (PCA) and quadratic discriminant analysis (QDA) were used to select the most significant and responsible characteristics for discrimination of grapevine rootstocks. For QDA, the 19 parameters were arranged in 4 sets. The first set includes total phenolic content, total flavonoid content, total anthocyanin content, and free radicals scavenging activity showed 88.10% correct classification. The second set (phenylalanine ammonia-lyase, superoxide dismutase, ascorbate peroxidase, and catalase activity) had 94.64% correct classification. Na⁺, K⁺, K⁺/Na⁺, electrolyte leakage, and malondialdehyde content parameters were in the third set and had 89.29% correct discrimination. The best discrimination was obtained by the fourth set, including total carbohydrate content, total protein content, proline, glycine-betaine, chlorophyll a, and chlorophyll b characteristics with 100% correct discrimination.

Diversity in Chemical Structures and Biological Properties of Plant Alkaloids

Phytochemicals belonging to the group of alkaloids are signature specialized metabolites endowed with countless biological activities. Plants are armored with these naturally produced nitrogenous compounds to combat numerous challenging environmental stress conditions. Traditional and modern healthcare systems have harnessed the potential of these organic compounds for the treatment of many ailments. Various chemical entities (functional groups) attached to the central moiety are responsible for their diverse range of biological properties. The development of the characterization of these plant metabolites and the enzymes involved in their biosynthesis is of an utmost priority to deliver enhanced advantages in terms of biological properties and productivity. Further, the incorporation of whole/partial metabolic pathways in the heterologous system and/or the overexpression of biosynthetic steps in homologous systems have both become alternative and lucrative methods over chemical synthesis in recent times. Moreover, in-depth research on alkaloid biosynthetic pathways has revealed numerous chemical modifications that occur during alkaloidal conversions. These chemical reactions involve glycosylation, acylation, reduction, oxidation, and methylation steps, and they are usually responsible for conferring the biological activities possessed by alkaloids. In this review, we aim to discuss the alkaloidal group of plant specialized metabolites and their brief classification covering major categories. We also emphasize the diversity in the basic structures of plant alkaloids arising through enzymatically catalyzed structural modifications in certain plant species, as well as their emerging diverse biological activities. The role of alkaloids in plant defense and their mechanisms of action are also briefly discussed. Moreover, the commercial utilization of plant alkaloids in the marketplace displaying various applications has been enumerated.

Drought and salinity: A comparison of their effects on the ammonium-preferring species Spartina alterniflora

Drought and salinity are the most serious environmental factors affecting crop productivity worldwide; hence, it is important to select and develop both salt- and drought-tolerant crops. The perennial smooth cordgrass Spartina alterniflora Loisel is unusual in that it is highly salt-tolerant and seems to prefer ammonium (NH₄ ⁺ ) over nitrate (NO₃ ^- ) as an inorganic N source. In this study, we determined whether Spartina's unique preference for NH₄ ⁺ enhances performance under salt and drought stress. Greenhouse experiments were conducted to compare the interactive effects of N source, salinity, and low water availability on plant performance (growth and antioxidant metabolism). Drought significantly reduced growth and photosynthetic activity in S. alterniflora, more so with NH₄ ⁺ than NO₃ ^- ; in contrast, NH₄ ⁺ enhanced growth under high salinity. The increased tolerance of S. alterniflora to salt stress in the presence of NH₄ ⁺ was linked to a high level of antioxidant enzyme activity, combined with low MDA content, EL, and H₂ O₂ production. In contrast, drought stress negated the growth advantages for S. alterniflora exposed to salt stress in the presence of NH₄ ⁺ . The susceptibility of S. alterniflora to drought was partly due to reduced antioxidant enzyme activities, thereby reducing the defense against the oxidative damages induced by osmotic stress. In conclusion, in contrast to salt stress, drought stress negates the beneficial effects of ammonium as an N source in the C₄ plant Spartina alterniflora.

Chitosan nanoparticles effectively combat salinity stress by enhancing antioxidant activity and alkaloid biosynthesis in Catharanthus roseus (L.) G. Don

Chitosan nanoparticles (CSNPs) are non-toxic and biodegradable stimulants of growth and secondary metabolite production, which offer new routes to combat plant stress. Salinity is a common and significant abiotic stress that adversely affects plant growth and development. The possible benefits of CSNPs in salt stress mitigation have not yet been reported in Catharanthus roseus, an important source of anticancer alkaloids. Plants were exposed to 150 mM NaCl as a salt stress treatment, while CSNPs were applied as a foliar spray at 1% concentration. Plant growth was considerably impaired under salt stress conditions; however, CSNPs treatment significantly reversed this effect. Specifically, CSNPs retarded chlorophyll reduction and induced activities of catalase, ascorbate peroxidase, and glutathione reductase. Thus, CSNPs alleviated the oxidative stress, indicated by lower levels of malondialdehyde and H₂O₂, thereby enabling membrane function retention and enhancing salt tolerance. Higher alkaloid accumulation was observed in salt-stressed plants following CSNP spraying than in controls. Interestingly, the expression levels of mitogen-activated protein kinases (MAPK3), geissoschizine synthase (GS), and octadecanoid-derivative responsive AP2-domain (ORCA3) genes were significantly elevated in salt-stressed plants sprayed with CSNPs. Overall, CSNP treatment overcame the deleterious effects of salinity in C. roseus by activating the antioxidant defense system, which helps to scavenge reactive oxygen species, and inducing expression of MAPK3, GS, and ORCA3 genes, thus, leading to higher alkaloid accumulation and better protection against salinity stress.

Evaluation of microalgae polysaccharides as biostimulants of tomato plant defense using metabolomics and biochemical approaches

Microalgal polysaccharides (PSs) may be an effective elicitor agent that can efficiently protect plants against biotic stresses. In this study, wee investigates, the effect of PS obtained from microalgae and cyanobacteria (D. salina MS002, P. tricorontum MS023, Porphyridium sp. MS081, Desmodesmus sp., D. salina MS067 and A. platensis MS001) on the biochemical and metabolomics markers linked to defense pathways in tomato plants. The phenylalanine ammonia lyase (PAL), chitinase, 1,3-beta-glucanase and peroxidase (POX) activities have been improved in tomato plants leaves treated by polysaccharides extracted from P. triocnutum (238.26%); Desmodesmus sp. (19.95%); P. triocnutum (137.50%) and Porphyridium sp. (47.28%) respectively. For proteins, polyphenols and H2O2, the maximum effect was induced by D. salina 067 (55.01%), Porphyridium sp. (3.97%) and A. platensis (35.08%) respectively. On the other hand, Gas Chromatography-mass spectrometry (GC-MS) metabolomics analysis showed that PSs induced the modification of metabolite profile involved in the wax construction of tomato leaves, such as fatty acids, alkanes, alkenes and phytosterol. PS treatments improved the accumulation of fatty acids C16:3, C18:2 and C18:3 released from the membrane lipids as precursors of oxylipin biosynthesis which are signaling molecules of plant defense. In addition, PS treatment induced the accumulation of C18:0 and Azelaic acid which is a regulator of salicylic acid-dependent systemic acquired resistance. However, molecular and metabolic studies can determine more precisely the mode of action of microalgal polysaccharides as biostimulants/elicitors plant defense.

Effects of Nutrient Fertility on Growth and Alkaloidal Content in Mitragyna speciosa (Kratom)

Leaves harvested from the Southeast Asian tree Mitragyna speciosa (kratom) have a history of use as a traditional ethnobotanical source of medicine to combat fatigue, improve work productivity, and to reduce opioid-related withdrawal symptoms. Kratom leaves contain an array of alkaloids thought to be responsible for the bioactivity reported by users. Interest in the consumptive effects of kratom has led to its recent popularity and use in North America, Western Europe, and Australia. Although the chemistry and pharmacology of select kratom alkaloids are understood, studies have not examined the influence of production environment on growth and alkaloidal content. To directly address this need, 68 kratom trees were vegetatively propagated from a single mother stock to reduce genetic variability and subjected to four varying fertilizer application rates. Leaves were analyzed for chlorophyll concentration, biomass, and alkaloidal content to understand the physiological response of the plant. While increasing rates of fertilizer promoted greater plant growth, relationships with alkaloidal content within leaves were highly variable. Fertility rate had little influence on the concentration of mitragynine, paynantheine, speciociliatine, mitraphylline, and corynoxine per leaf dry mass. 7-Hydroxymitragynine was below the lower limit of quantification in all the analyzed leaf samples. Low to medium rates of fertilizer, however, maximized concentrations of speciogynine, corynantheidine, and isocorynantheidine per leaf dry mass, suggesting a promotion of nitrogen allocation for secondary metabolism occurred for these select alkaloids. Strong correlations (r 2 = 0.86) between extracted leaf chlorophyll and rapid, non-destructive chlorophyll evaluation (SPAD) response allowed for development of a reliable linear model that can be used to diagnose nutrient deficiencies and allow for timely adjustment of fertilization programs to more accurately manage kratom cultivation efforts. Results from this study provide a greater understanding of the concentration and synthesis of nine bioactive alkaloids in fresh kratom leaves and provide foundational information for kratom cultivation and production.

Phytochemicals Derived from Catharanthus roseus and Their Health Benefits

Catharanthus roseus (C. roseus) is an important medicinal plant distributed in many countries. It has attracted increasing attention due to it being shown to possess a range of phytochemicals with various biological activities such as antioxidant, antibacterial, antifungal, antidiabetic and anticancer properties. Remarkably, vinblastine and vincristine isolated from this plant were the first plant-derived anticancer agents deployed for clinical use. Recently, new isolated indole alkaloids from this plant including catharoseumine, 14′,15′-didehydrocyclovinblastine, 17-deacetoxycyclovinblastine and 17-deacetoxyvinamidine effectively inhibited human cancer cell lines in vitro. Moreover, vindoline, vindolidine, vindolicine and vindolinine isolated from C. roseus leaf exhibited in vitro antidiabetic property. These findings strongly indicate that this plant is still a promising source of bioactive compounds, which should be further investigated. This paper provides an overview of the traditional use and phytochemical profiles of C. roseus, and summarises updated techniques of the preparation of dried material, extraction and isolation of bioactive compounds from this plant. In addition, purported health benefits of the extracts and bioactive compounds derived from this plant were also addressed to support their potential as therapeutic agents.

Different carbon sources and their concentrations change alkaloid production and gene expression in Catharanthus roseus shoots in vitro

To compare the effects of different carbon sources on physiological aspects, especially medicinal alkaloid biosynthesis and related gene expression in Catharantus roseus (L.) G.Don, we employed sucrose and sorbitol with two concentrations (87.64 mM, the equimolar concentration of sucrose in MS basal medium, and 150 mM) on the plant's shoots in vitro in presence of 100 μM methyl jasmonate. The production of plant alkaloids including vincristine, vinblastine, ajmalicine, vindoline and catharantine and their biosynthetic and regulatory gene expression was measured. Both treatments had incremental effects on alkaloid production, upregulated the mitogen-activated protein kinase3 (MAPK3) and a downstream responsive transcription factor, ORCA3, which resulted in elevated transcript contents of the important genes in terpenoid indol alkaloids biosynthetic pathway including peroxidase1 (PRX1), geissoschizine synthase (GS), strictosidine synthase (STR) and deacetylvindoline acetyltransferase (DAT). Defensive responses such as antioxidant enzymes (catalase, peroxidase and superoxide dismutase) activities and non-enzymatic metabolites (total phenolics, flavonoids and carotenoids) contents increased under both treatments but the effects of sorbitol were stronger. Reduced fresh weight and chlorophylls contents, increased malondialdehyde (MDA) and carotenoid contents were shown after a week under all employed treatments. It seems that replacement of sucrose with sorbitol and also, increased concentrations of both carbon sources via increasing osmotic pressure make stressful conditions for the plant especially in longer times.

Mechanisms underlying silicon-dependent metal tolerance in the marine diatom Phaeodactylum tricornutum

Anthropogenic activities have significantly changed the stoichiometry and concentrations of nutrients in coastal waters. Silicon (Si) has become a potential limiting nutrient due to disproportionate nitrogen, phosphorus, and silicate inputs into these areas. The disrupted nutrient ratios can cause changes to metal sensitivity and accumulation in marine diatoms, an important group of eukaryotic phytoplankton that requires silicon for growth. In this study, we examined the effects of Si availability on the metal sensitivity in the diatom P. tricornutum. We found that Si starvation dramatically compromised its cadmium, copper, and lead tolerances. Interestingly, multiple lines of evidence indicated that Si-enriched cells had higher metal adsorption and influx rates than Si-starved cells. Yet Si-enriched cells also had a greater ability to respond to and counteract metal toxicity via elevated expression of membrane and vacuolar metal transporters and greater antioxidant activities which scavenge reactive oxygen species created by metal stress.

Nitrogen Enhances Salt Tolerance by Modulating the Antioxidant Defense System and Osmoregulation Substance Content in Gossypium hirsutum

Increasing soil salinity suppresses both productivity and fiber quality of cotton, thus, an appropriate management approach needs to be developed to lessen the detrimental effect of salinity stress. This study assessed two cotton genotypes with different salt sensitivities to investigate the possible role of nitrogen supplementation at the seedling stage. Salt stress induced by sodium chloride (NaCl, 200 mmol·L-1) decreased the growth traits and dry mass production of both genotypes. Nitrogen supplementation increased the plant water status, photosynthetic pigment synthesis, and gas exchange attributes. Addition of nitrogen to the saline media significantly decreased the generation of lethal oxidative stress biomarkers such as hydrogen peroxide, lipid peroxidation, and electrolyte leakage ratio. The activity of the antioxidant defense system was upregulated in both saline and non-saline growth media as a result of nitrogen application. Furthermore, nitrogen supplementation enhanced the accumulation of osmolytes, such as soluble sugars, soluble proteins, and free amino acids. This established the beneficial role of nitrogen by retaining additional osmolality to uphold the relative water content and protect the photosynthetic apparatus, particularly in the salt-sensitive genotype. In summary, nitrogen application may represent a potential strategy to overcome the salinity-mediated impairment of cotton to some extent.

Exogenous indole acetic acid alleviates Cd toxicity in tea (Camellia sinensis)

Cadmium (Cd), a toxic heavy metal, restrains the growth and development of plants and threatens global food safety. Many studies on the alleviation of heavy metal toxicity by exogenous phytohormones have emerged, but reports on tea (Camellia sinensis) are still scarce. In this study, the effects of indole acetic acid (IAA) (2 μM and 10 μM) on Cd uptake and on the physiological and biochemical characteristics of the 'Xiangfeicui' tea cultivar were investigated for the first time. The order of Cd accumulation in tea seedlings was root > stem > mature leaf > tender leaf. Under Cd stress (30 mg kg^-1), photosynthetic pigment levels, antioxidant enzyme activity, root vigor, root IAA content, and the levels of most metabolites (including caffeine, soluble sugar, total amino acids, some amino acid components, and most catechins) were significantly reduced, while levels of malondialdehyde, proline, epicatechin, and some amino acids increased. We therefore propose that by reducing Cd accumulation, exogenous IAA can lessen the adverse effects of Cd on the physiology and biochemistry of tea seedlings, promoting the growth of healthier tea plants.

Nitrogen alleviates salinity toxicity in Solanum lycopersicum seedlings by regulating ROS homeostasis

The present study was aimed to investigate adaptation in physiology and biochemistry of Solanum lycopersicum seedlings under NaCl (NaCl₀; 0.0 g NaCl kg^-1 sand, NaCl₁; 0.3 g NaCl/kg sand and NaCl₂; 0.5 g NaCl/kg sand) stress, simultaneously supplemented with different (deprived; 0 mg/kg sand, LN; 105 mg/kg sand, MN; 210 mg/kg sand and HN; 270 mg/kg sand) levels of nitrogen (N). NaCl at both doses caused significant loss in growth, K⁺ content, K⁺/Na⁺ ratio, total chlorophyll and photosynthetic oxygen evolution. Further, N supplementation influences growth of test seedlings, that attained maximum growth in HN followed by MN, LN and deprived N conditions. N at HN level significantly declined Na⁺ accumulation in the cell and enhanced level of K⁺. NaCl treatment enhanced level of oxidative stress biomarkers: superoxide radical (O₂^•-), hydrogen peroxide (H₂O₂), MDA equivalents contents and electrolyte leakage in leaf as well as root despite enhanced activity of SOD, POD, CAT and GST, and enzymes participating in the ascorbate-glutathione cycle (AsA-GSH cycle) viz. APX, DHAR and GR. At the same time, higher contents of total AsA (AsA + DHA) and total GSH (GSH + GSSG), and maintained ratios of AsA/DHA and GSH/GSSG in HN fed seedlings were observed. Overall, the results suggest that HN supplementation was able in alleviating NaCl induced toxicity in test seedlings which was mainly due to the up-regulation of the AsA-GSH cycle, K⁺ and K⁺/Na⁺ ratio, which resulted into better growth performance of HN fed seedlings under NaCl stress while reverse was noticed for LN and deprive N conditions.

Stress and defense responses in plant secondary metabolites production

In the growth condition(s) of plants, numerous secondary metabolites (SMs) are produced by them to serve variety of cellular functions essential for physiological processes, and recent increasing evidences have implicated stress and defense response signaling in their production. The type and concentration(s) of secondary molecule(s) produced by a plant are determined by the species, genotype, physiology, developmental stage and environmental factors during growth. This suggests the physiological adaptive responses employed by various plant taxonomic groups in coping with the stress and defensive stimuli. The past recent decades had witnessed renewed interest to study abiotic factors that influence secondary metabolism during in vitro and in vivo growth of plants. Application of molecular biology tools and techniques are facilitating understanding the signaling processes and pathways involved in the SMs production at subcellular, cellular, organ and whole plant systems during in vivo and in vitro growth, with application in metabolic engineering of biosynthetic pathways intermediates.

Transcriptome sequencing revealed molecular mechanisms underlying tolerance of Suaeda salsa to saline stress

The halophyte Suaeda salsa displayed strong resistance to salinity. Up to date, molecular mechanisms underlying tolerance of S. salsa to salinity have not been well understood. In the present study, S. salsa seedlings were treated with 30‰ salinity and then leaves and roots were subjected to Illumina sequencing. Compared with the control, 68,599 and 77,250 unigenes were significantly differentially expressed in leaves and roots in saline treatment, respectively. KEGG enrichment analyses indicated that photosynthesis process, carbohydrate, lipid and amino acid metabolisms were all downregulated in saline treatment, which should inhibit growth of S. salsa. Expression levels of Na+/H+ exchanger, V-H+ ATPase, choline monooxygenase, potassium and chloride channels were upregulated in saline treatment, which could relieve reduce over-accumulation of Na+ and Cl-. Fe-SOD, glutathione, L-ascorbate and flavonoids function as antioxidants in plants. Genes in relation to them were all upregulated, suggesting that S. salsa initiated various antioxidant mechanisms to tolerate high salinity. Besides, plant hormones, especially auxin, ethylene and jasmonic acid signaling transduction pathways were all upregulated in response to saline treatment, which were important to gene regulations of ion transportation and antioxidation. These changes might comprehensively contribute to tolerance of S. salsa to salinity. Overall, the present study provided new insights to understand the mechanisms underlying tolerance to salinity in halophytes.

Antioxidant enzyme activity and growth responses of Huangguogan citrus cultivar to nitrogen supplementation

This study examined the physiological effects of different amounts of nitrogen (N) supplementation (0 to 2.72 kg/year) on the citrus cultivar Huangguogan (Citrus reticulata × Citrus sinensis). Root activity, chlorophyll content, and fruit quality were measured, and the activities of the antioxidant enzymes superoxide dismutase (SOD), guaiacol peroxidase (POD), and catalase (CAT), and the contents of malondialdehyde (MDA) and soluble protein in root, leaf, and fruit tissues were examined at different developmental stages. Root activity, chlorophyll content, fruit quality, antioxidant enzyme activity, MDA content, and soluble protein content increased in plants treated with an appropriate amount of N. Both excessive N and N deficiency decreased the content of MDA and the activities of antioxidant enzymes. Application of 1.36-1.81 kg N/year is suggested for citrus fertilization and the lower end of this range is recommended for minimizing environmental impact and production cost.

Nitrogen in the defense system of Annona emarginata (Schltdl.) H. Rainer

The concentration of nitrogen can generate different strategies in plants in response to stress. In this study, we investigated how nitrogen concentration interferes with the defense system of Annona emarginata. Low concentrations of nitrogen increased the allocation of photosynthetic resources to carbon metabolism, resulting in an increase in the synthesis of volatile substances involved in signaling and defense that contributed to antioxidant enzymes in overcoming stress. The availability of nitrogen at 5.62 mM concentration might have helped to induce increased resistance in the plants because at this concentration, signaling substances and defense substances (monoterpenes and sesquiterpenes) were observed. Plants cultivated with the highest nitrate concentration displaced energy for the reduction of this ion, likely forming nitric oxide, a signaling molecule. This condition, together with the decrease in carbon skeletons, may have contributed to the lower synthesis of volatile substances of the specialized metabolism that are also involved with signaling. Varying the nitrogen in Annona emarginata cultivation revealed that depending on the concentration, volatile substances show higher or lower synthesis and participation in the system of signaling and defense in the plant. These results may suggest that volatile substances participate in resistance to pests and diseases, which is a necessary condition for Annona emarginata to be preferentially used as rootstock for Annona x atemoya.

Dynamic responses of Haloxylon ammodendron to various degrees of simulated drought stress

Haloxylon ammodendron, a C4 perennial, succulent and xero-halophytic shrub, is highly resistant to harsh environments, therefore, exploring the stress resistance mechanism will be beneficial for the use of xerophytes to prevent desertification. To determine osmotic adjustment (OA) and antioxidase functions under simulated drought stress, 8-week-old seedlings were treated with sorbitol solutions to maintain osmotic potentials (Ψs) at a control and -0.5 and -1.0 MPa. Under -0.5 MPa osmotic stress, H. ammodendron stably maintained the water content of assimilating branches, a result that was not significantly different from the result of the control group. Moreover, the Ψs decreased significantly, which helped plants absorb water efficiently from the environment, as H. ammodendron accumulated massive osmotic regulators in its assimilating branches to adjust shoot Ψs. Specifically, the contribution of Na⁺ to shoot Ψs was up to 45%, and Na⁺ became the main osmotic regulator of OA. During the treatments, the content and contribution of K⁺ remained stable. However, the total contribution of three organic osmotic regulators (free proline, betaine and soluble sugar) was only 20%, and betaine was the main organic osmotic regulator, accounting for approximately 15% of the 20% contribution. Moreover, H. ammodendron seedlings presented strong antioxidases, especially when there was a high activity level of superoxide dismutase, and with an increase in treatment time and degree of osmotic stress, the activity of peroxidase and catalase increased significantly. Substantial accumulation of osmotic adjustment substances was an important strategy for H. ammodendron to cope with simulated drought stress, in particular, H. ammodendron absorbed much Na⁺ and transported Na⁺ into the assimilating branch for OA. The scavenging of reactive oxygen species by antioxidases was another adaptation strategy for H. ammodendron to adapt to simulated drought stress.

iTRAQ-Based Quantitative Proteome Revealed Metabolic Changes in Winter Turnip Rape (Brassica rapa L.) under Cold Stress

Winter turnip rape (Brassica rapa L.) is a large-scale winter-only oil crop cultivated in Northwest China. However, its cold-resistant molecular mechanism remains inadequate. Studying the cold adaptation mechanisms of winter turnip rape based on the proteomic technique of isobaric tags for relative and absolute quantification (iTRAQ) offers a solution to this problem. Under cold stress (−4 °C for eight hours), 51 and 94 differently accumulated proteins (DAPs) in Longyou 7 (cold-tolerant) and Tianyou 4 (cold-sensitive) were identified, respectively. These DAPs were classified into 38 gene ontology (GO) term categories, such as metabolic process, cellular process, catalytic activity, and binding. The 142 DAPs identified between the two cold-stressed cultivars were classified into 40 GO terms, including cellular process, metabolic process, cell, catalytic activity, and binding. Kyoto Encyclopedia of Genes and Genomes enrichment analysis indicated that the DAPs participated in 10 pathways. The abundance of most protein functions in ribosomes, carbon metabolism, photosynthesis, and energy metabolism including the citrate cycle, pentose phosphate pathway, and glyoxylate and dicarboxylate metabolism decreased, and the proteins that participate in photosynthesis–antenna and isoflavonoid biosynthesis increased in cold-stressed Longyou 7 compared with those in cold-stressed Tianyou 4. The expression pattern of genes encoding the 10 significant DAPs was consistent with the iTRAQ data. This study provides new information on the proteomic differences between the leaves of Longyou 7 and Tianyou 4 plants and explains the possible molecular mechanisms of cold-stress adaptation in B. rapa.

Modulation of antioxidative defense expression and osmolyte content by co-application of 24-epibrassinolide and salicylic acid in Pb exposed Indian mustard plants

The study focuses on potential of combined pre-soaking treatment of 24-Epibrassinolide (EBL) and Salicylic acid (SA) in alleviating Pb phytotoxicity in Brassica juncea L. plants. The seeds after treatment with combination of both the hormones were sown in mixture of soil, sand and manure (3:1:1) and were exposed to Pb concentrations (0.25mM, 0.50mM and 0.75mM). After 30 days of growth, the plants were harvested and processed, for quantification of various metabolites. It was found that pre-sowing of seeds in combination of EBL and SA, mitigated the adverse effects of metal stress by modulating antioxidative defense response and enhanced osmolyte contents. Dry matter content and heavy metal tolerance index were enhanced in response to co-application of EBL and SA. The levels of superoxide anions, hydrogen peroxide and malondialdehyde were lowered by the combined treatment of hormones. Enhancement in activities of guaiacol peroxidase, catalase, glutathione reductase and glutathione-s-transferase were recorded. Contents of glutathione, tocopherol and ascorbic acid were also enhanced in response to co-application of both hormones. Expression of POD, CAT, GR and GST1 genes were up-regulated whereas SOD gene was observed to be down-regulated. Contents of proline, trehalose and glycine betaine were also reported to be elevated as a result of treatment with EBL+SA. The results suggest that co-application of EBL+SA may play an imperative role in improving the antioxidative defense expression of B. juncea plants to combat the oxidative stress generated by Pb toxicity.

Physiological characteristics, dry matter, and active component accumulation patterns of Changium smyrnioides in response to a light intensity gradient

CONTEXT

Changium smyrnioides Wolff (Apiaceae) is an endangered medicinal plant with numerous pharmacological uses.

OBJECTIVE

To investigate the effect of light intensity levels on the growth and accumulation of secondary metabolites of C. smyrnioides, cultivated seedlings were subjected to different relative light intensities via sun-shading.

MATERIALS AND METHODS

Changium smyrnioides seedlings were subjected to five irradiance treatments (100, 60.54, 44.84, 31.39, and 10.56% sunlight) in glasshouse for 9 months. Enzymatic and non-enzymatic antioxidants with spectrophotometric method, photosynthetic parameters with Li-6400XT, dry matter accumulation and active component contents in the root with spectrophotometric and HPLC method were analyzed.

RESULTS

With an increase in relative light intensity levels, activities of enzymatic and non-enzymatic antioxidants, and malondialdehyde (MDA) contents were increased overall, while net photosynthetic rate (P_n) and dry matter accumulation patter first increased and then declined. The highest net photosynthetic rate (30.68 μmol/m²·s) and dry root weight (5.07 g) were achieved under 60.54% sunlight. Lower relative light intensity levels stimulated the accumulation levels of bioactive compounds in the roots so that the highest contents of mannitol (1.35%) and choline (405.58 μg/g) were recorded under 31.39% sunlight, and the highest polysaccharide content (10.80%) were achieved under 44.84% sunlight. With a decrease in the relative light intensity levels, the water-soluble component content increased first and then decreased.

DISCUSSION AND CONCLUSION

The results revealed that 31.39-60.54% sunlight serve as appropriate relative light intensity conditions for cultivated C. smyrnioides.

Drought stress obliterates the preference for ammonium as an N source in the C4 plant Spartina alterniflora

The C₄ grass Spartina alterniflora is known for its unique salt tolerance and strong preference for ammonium (NH₄⁺) as a nitrogen (N) source. We here examined whether Spartina's unique preference for NH₄⁺ results in improved performance under drought stress. Manipulative greenhouse experiments were carried out to measure the effects of variable water availability and inorganic N sources on plant performance (growth, photosynthesis, antioxidant, and N metabolism). Drought strongly reduced leaf number and area, plant fresh and dry weight, and photosynthetic activity on all N sources, but the reduction was most pronounced on NH₄⁺. Indeed, the growth advantage seen on NH₄⁺ in the absence of drought, producing nearly double the biomass compared to growth on NO₃^-, was entirely obliterated under both intermediate and severe drought conditions (50 and 25% field capacity, respectively). Both fresh and dry weight became indistinguishable among N sources under drought. Major markers of the antioxidant capacity of the plant, the activities of the enzymes superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase, showed higher constitutive levels on NH₄⁺. Catalase and glutathione reductase were specifically upregulated in NH₄⁺-fed plants with increasing drought stress. This upregulation, however, failed to protect the plants from drought stress. Nitrogen metabolism was characterized by lower constitutive levels of glutamine synthetase in NH₄⁺-fed plants, and a rise in glutamate dehydrogenase (GDH) activity under drought, accompanied by elevated proline levels in leaves. Our results support postulates on the important role of GDH induction, and its involvement in the synthesis of compatible solutes, under abiotic stress. We show that, despite this metabolic shift, S. alterniflora's sensitivity to drought does not benefit from growth on NH₄⁺ and that the imposition of drought stress equalizes all N-source-related growth differences observed under non-drought conditions.

Approaches in modulating proline metabolism in plants for salt and drought stress tolerance: Phytohormones, mineral nutrients and transgenics

Major abiotic stress factors such as salt and drought adversely affect important physiological processes and biochemical mechanisms and cause severe loss in crop productivity worldwide. Plants develop various strategies to stand healthy against these stress factors. The accumulation of proline (Pro) is one of the striking metabolic responses of plants to salt and drought stress. Pro biosynthesis and signalling contribute to the redox balance of cell under normal and stressful conditions. However, literature is meager on the sustainable strategies potentially fit for modulating Pro biosynthesis and production in stressed plants. Considering the recent literature, this paper in its first part overviews Pro biosynthesis and transport in plants and also briefly highlights the significance of Pro in plant responses to salt and drought stress. Secondly, this paper discusses mechanisms underlying the regulation of Pro metabolism in salt and drought-exposed plant via phytohormones, mineral nutrients and transgenic approaches. The outcome of the studies may give new opportunities in modulating Pro metabolism for improving plant tolerance to salt and drought stress and benefit sustainable agriculture.

Effects of epiphytic algae on biomass and physiology of Myriophyllum spicatum L. with the increase of nitrogen and phosphorus availability in the water body

The disappearance of submerged vascular macrophytes in shallow eutrophic lakes is a common phenomenon in the world. To explore the mechanism of the decline in submerged macrophyte abundance due to the growth of epiphytic algae along a nutrient gradient in eutrophic water, a 2 × 3 factorial experiment was performed over 4 weeks with the submerged macrophyte (Myriophyllum spicatum L.) by determining the plant's biomass and some physiological indexes, such as chlorophyll (Chl) content, malondialdehyde (MDA) content, and superoxide dismutase (SOD) activity in the leaves of M. spicatum L. on days 7, 14, 21, and 28, which are based on three groups of nitrogen and phosphorus levels in the water body (N-P [mg L^-1]: NP1 0.5-0.05, NP2 2.5-0.25, NP3 4.5-0.45) and two levels of epiphytic algae (the epiphytic algae group and the control group). Epiphytic algal biomass was also assayed. The results indicated that epiphytic algal biomass remarkably enhanced in the course of the experiment with elevated levels of nitrogen and phosphorus in the water. Under the same level of nutrient condition, plants' biomass accumulation and Chl content were higher in the control group than that in the epiphytic algae group, respectively, while MDA content and SOD activity in the former were lower than that in the latter. The influences of epiphytic algae on the biomass accumulation and Chl content and MDA content became greater and greater with elevated levels of nutrients. In general, in this experiment, water nutrients promoted the growth of both epiphytic algae and submerged plants, while the growth of epiphytic algae hindered submerged macrophytes' growth by reducing Chl content and promoting peroxidation of membrane lipids in plants.

Elevated CO2 affects secondary metabolites in Robinia pseudoacacia L. seedlings in Cd- and Pb-contaminated soils

Secondary metabolites play important roles in plant interactions with the environment. The co-occurrence of heavy metal contamination of soils and rising atmospheric CO2 has important effects on plant. It is important to explore the ways in which production of plant secondary metabolites is affected by heavy metals under elevated atmospheric CO2. We examined the effects of elevated CO2 on secondary metabolite contents in Robinia pseudoacacia seedlings grown in Cd- and lead (Pb)-contaminated soils. The increase in secondary metabolites was greater under Cd + Pb exposure than under exposure to individual metals regardless of elevated CO2 with the exception of condensed tannins in leaves and total alkaloids in stems. Except for phenolic compounds and condensed tannins, elevated CO2 was associated with increased secondary metabolite contents in leaves and stems of plants exposed to Cd, Pb, and Cd + Pb compared to plants exposed to ambient CO2 + metals. Changes in saponins in leaves and alkaloids in stems were greater than changes in the other secondary metabolites. Significant interactive effects of CO2, Cd, and Pb on secondary metabolites were observed. Saponins in leaves and alkaloids in stems were more sensitive than other secondary metabolites to elevated CO2 + Cd + Pb. Elevated CO2 could modulate plant protection and defense mechanisms in R. pseudoacacia seedlings exposed to heavy metals by altering the production of secondary metabolites. The increased Cd and Pb uptake under elevated CO2 suggested that R. pseudoacacia may be used in the phytoremediation of heavy metal-contaminated soils under global environmental scenarios.

Beneficial behavior of nitric oxide in copper-treated medicinal plants

Despite numerous reports implicating nitric oxide (NO) in the environmental-stress responses of plants, the specific metabolic and ionic mechanisms of NO-mediated adaptation to metal stress remain unclear. Here, the impacts of copper (Cu) and NO donor (SNP, 50μM) alone or in combination on the well-known medicinal plant Catharanthus roseus L. were investigated. Our results showed that Cu markedly increased Cu(2+) accumulation, decreased NO production, and disrupted mineral equilibrium and proton pumps, thereby stimulating a burst of ROS; in addition, SNP ameliorates the negative toxicity of Cu, and cPTIO reverses this action. Furthermore, the accumulations of ROS and NO resulted in reciprocal changes. Interestingly, nearly all of the investigated amino acids and the total phenolic content in the roots were promoted by the SNP treatment but were depleted by the Cu+SNP treatment, which is consistent with the self-evident increases in phenylalanine ammonia-lyase activity and total soluble phenol content induced by SNP. Unexpectedly, leaf vincristine and vinblastine as well as the total alkaloid content (ca. 1.5-fold) were decreased by Cu but markedly increased by SNP (+38% and +49% of the control levels). This study provides the first evidence of the beneficial behavior of NO, rather than other compounds, in depleting Cu toxicity by regulating mineral absorption, reestablishing ATPase activities, and stimulating secondary metabolites.

Supplemental exogenous NPK application alters biochemical processes to improve yield and drought tolerance in wheat (Triticum aestivum L.)

The recent food security issues, combined with the threats from climate change, demand future farming systems to be more precise and accurate to fulfill the ever increasing global food requirements. The role of nutrients such as nitrogen (N), phosphorous (P), and potassium (K) in stimulating plant growth and development is well established; however, little is known about their function, if applied in combination, in improving crop yields under environmental stresses like drought. The aim of this study was to evaluate the effects of combined foliar spray of supplemental NPK (NPKc) on physiological and biochemical mechanisms that enhance the drought tolerance potential of wheat for improved yield. Foliar NPKc markedly influenced the accumulation of osmoprotectants and activity of both nitrogen assimilation and antioxidant enzymes. It significantly improved the concentration of proline (66 %), total soluble sugars (37 %), and total soluble proteins (10 %) and enhanced the activity of nitrate reductase, nitrite reductase, catalase, and peroxidase by 47, 45, 19, and 8 %, respectively, with respect to no spray under water-deficit conditions which, in turn, improve the yield and yield components. The accumulation of osmolytes and activity of antioxidant machinery were more pronounced in drought tolerant (Bhakkar-02) than sensitive genotype (Shafaq-06).

NH4+ protects tomato plants against Pseudomonas syringae by activation of systemic acquired acclimation

NH4 (+) nutrition provokes mild toxicity by enhancing H2O2 accumulation, which acts as a signal activating systemic acquired acclimation (SAA). Until now, induced resistance mechanisms in response to an abiotic stimulus and related to SAA were only reported for exposure to a subsequent abiotic stress. Herein, the first evidence is provided that this acclimation to an abiotic stimulus induces resistance to later pathogen infection, since NH4 (+) nutrition (N-NH4 (+))-induced resistance (NH4 (+)-IR) against Pseudomonas syringae pv tomato DC3000 (Pst) in tomato plants was demonstrated. N-NH4 (+) plants displayed basal H2O2, abscisic acid (ABA), and putrescine (Put) accumulation. H2O2 accumulation acted as a signal to induce ABA-dependent signalling pathways required to prevent NH4 (+) toxicity. This acclimatory event provoked an increase in resistance against later pathogen infection. N-NH4 (+) plants displayed basal stomatal closure produced by H2O2 derived from enhanced CuAO and rboh1 activity that may reduce the entry of bacteria into the mesophyll, diminishing the disease symptoms as well as strongly inducing the oxidative burst upon Pst infection, favouring NH4 (+)-IR. Experiments with inhibitors of Put accumulation and the ABA-deficient mutant flacca demonstrated that Put and ABA downstream signalling pathways are required to complete NH4 (+)-IR. The metabolic profile revealed that infected N-NH4 (+) plants showed greater ferulic acid accumulation compared with control plants. Although classical salicylic acid (SA)-dependent responses against biotrophic pathogens were not found, the important role of Put in the resistance of tomato against Pst was demonstrated. Moreover, this work revealed the cross-talk between abiotic stress acclimation (NH4 (+) nutrition) and resistance to subsequent Pst infection.

Physiological and biochemical parameters for evaluation and clustering of rice cultivars differing in salt tolerance at seedling stage

Salinity tolerance levels and physiological changes were evaluated for twelve rice cultivars, including four white rice and eight black glutinous rice cultivars, during their seedling stage in response to salinity stress at 100 mM NaCl. All the rice cultivars evaluated showed an apparent decrease in growth characteristics and chlorophyll accumulation under salinity stress. By contrast an increase in proline, hydrogen peroxide, peroxidase (POX) activity and anthocyanins were observed for all cultivars. The K(+)/Na(+) ratios evaluated for all rice cultivars were noted to be highly correlated with the salinity scores thus indicating that the K(+)/Na(+) ratio serves as a reliable indicator of salt stress tolerance in rice. Principal component analysis (PCA) based on physiological salt tolerance indexes could clearly distinguish rice cultivars into 4 salt tolerance clusters. Noteworthy, in comparison to the salt-sensitive ones, rice cultivars that possessed higher degrees of salt tolerance displayed more enhanced activity of catalase (CAT), a smaller increase in anthocyanin, hydrogen peroxide and proline content but a smaller drop in the K(+)/Na(+) ratio and chlorophyll accumulation.

Salicylic acid alters antioxidant and phenolics metabolism in Catharanthus roseus grown under salinity stress

BACKGROUND

Salicylic acid (SA) acts as a potential non-enzymatic antioxidant and a plant growth regulator, which plays a major role in regulating various plant physiological mechanisms. The effects of salicylic acid (SA; 0.05 mM) on physiological parameters, antioxidative capacity and phenolic metabolism, lignin, alkaloid accumulation in salt stressed Catharanthus roseus were investigated.

MATERIALS AND METHODS

Catharanthus roseus seeds were grown for two months in a glass house at 27-30°C in sunlight, and then divided into four different groups and transplanted with each group with the following solutions for one month: group I (non-saline control), group II, 100 mM NaCl, group III, 0.05 mM SA, group IV, 100 mM NaCl+0.05 mM SA and to determine the physiological parameters (DW, FW, WC), chlorophyll contents, carotenoid contents, lipid peroxidation, phenolics, lignin, alkaloid and enzymatic assays in each leaf pairs and roots.

RESULTS

SA exhibited growth-promoting property, which correlated with the increase of dry weight, water content, photosynthetic pigments and soluble proteins. SA has additive effect on the significant increase in phenylalanine ammonia-lyase (PAL) activity, which is followed by an increase in total soluble phenolics and lignin contents in all leaf pairs and root of C. roseus. SA enhances malondialdehyde content in all leaf pairs and root. The antioxidant enzymes (catalase, glutathione reductase, glutathione-S-tranferase, superoxide dismutase, peroxidase) as well as alkaloid accumulation increased in all treatments over that of non-saline control but the magnitude of increase was found more in root. Further, the magnitude of increase of alkaloid accumulation was significantly higher in 100 mM NaCl, but highly significant was found in presence of 0.05 mM SA and intermediate in presence of both 0.05 mM SA+100 mM NaCl.

CONCLUSION

We concluded that applied SA to salt stress, antioxidant and phenolic metabolism, and alkaloid accumulation were significantly altered and the extent of alteration varied between the SA and salt stress.

The improved resistance to high salinity induced by trehalose is associated with ionic regulation and osmotic adjustment in Catharanthus roseus

The effects of exogenous trehalose (Tre) on salt tolerance of pharmaceutical plant Catharanthus roseus and the physiological mechanisms were both investigated in this study. The results showed that the supplement of Tre in saline condition (250 mM NaCl) largely alleviated the inhibitory effects of salinity on plant growth, namely biomass accumulation and total leaf area per plant. In this saline condition, the decreased level of relative water content (RWC) and photosynthetic rate were also greatly rescued by exogenous Tre. This improved performance of plants under high salinity induced by Tre could be partly ascribed to its ability to decrease accumulation of sodium, and increase potassium in leaves. The exogenous Tre led to high levels of fructose, glucose, sucrose and Tre inside the salt-stressed plants during whole the three-week treatment. The major free amino acids such as proline, arginine, threonine and glutamate were also largely elevated in the first two-week course of treatment with Tre in saline solution. It was proposed here that Tre might act as signal to make the salt-stressed plants actively increase internal compatible solutes, including soluble sugars and free amino acids, to control water loss, leaf gas exchange and ionic flow at the onset of salt stress. The application of Tre in saline condition also promoted the accumulation of alkaloids. The regulatory role of Tre in improving salt tolerance was optimal with an exogenous concentration of 10 mM Tre. Larger concentrations of Tre were supra-optimum and adversely affected plant growth.

Analysis of alkaloids from different chemical groups by different liquid chromatography methods

Alkaloids are biologically active compounds widely used as pharmaceuticals and synthesised as secondary methabolites in plants. Many of these compounds are strongly toxic. Therefore, they are often subject of scientific interests and analysis. Since alkaloids — basic compounds appear in aqueous solutions as ionized and unionized forms, they are difficult for chromatographic separation for peak tailing, poor systems efficiency, poor separation and poor column-to-column reproducibility. For this reason it is necessity searching of more suitable chromatographic systems for analysis of the compounds. In this article we present an overview on the separation of selected alkaloids from different chemical groups by liquid chromatography thus indicating the range of useful methods now available for alkaloid analysis. Different selectivity, system efficiency and peaks shape may be achieved in different LC methods separations by use of alternative stationary phases: silica, alumina, chemically bonded stationary phases, cation exchange phases, or by varying nonaqueous or aqueous mobile phase (containing different modifier, different buffers at different pH, ion-pairing or silanol blocker reagents). Developments in TLC (NP and RP systems), HPLC (NP, RP, HILIC, ion-exchange) are presented and the advantages of each method for alkaloids analysis are discussed.

Physiological responses of Egeriadensa to high ammonium concentration and nitrogen deficiency

High ammonia (i.e. the total of NH(3) and NH(4)(+)) concentration or nitrogen deficiency in water can exert stress on growth and health of many aquatic plants. To investigate the physiological impacts of high ammonia-N (NH(4)Cl) concentration and nitrogen deficiency on plant physiology, apical shoots of submerged macrophyte Egeriadensa were first treated with five levels of nitrogen: 0, 1, 10, 30, 60 mg L(-1) ammonia-N (NH(4)Cl) for 5d. After having explored the stress range of ammonia-N, its effect on E. densa was further examined at three levels of ammonium (0, 1, 30 mg L(-1) ammonia-N) and at six exposure times (0, 1, 2, 3, 5 and 7d). In testing the concentration-dependent stress, the increase of ammonia-N reduced the amounts of total chlorophyll (chl a and b), soluble proteins and soluble carbohydrates, but increased the activity levels of malondialdehyde (MDA), superoxide dismutase (SOD), catalase and peroxidase in E. densa. In the N-free medium, total chlorophyll, soluble proteins, soluble carbohydrates and the activities of SOD and peroxidase in E. densa decreased significantly compared with the control (1 mg L(-1) ammonia-N). When comparing the ammonia-N impacts over time, the plants showed a declining trend in total chlorophyll, soluble proteins and soluble carbohydrates, but an rising trend in MDA, SOD, peroxidase and catalase in 30 mg L(-1) ammonia-N over 7d. Compared with the control, the N-free medium significantly decreased the amounts of total chlorophyll, soluble proteins, soluble carbohydrates, SOD and peroxidase in E. densa over time. Our study indicates that high ammonium (ammonia-N ≥ 10 mg L(-1)) affects the growth of E. densa through inducing oxidative stress and inhibiting photosynthesis, and nitrogen deficiency can also induce an abiotic stress condition for the E. densa growth by reducing photosynthetic pigments, soluble proteins, soluble carbohydrates, and the activity of antioxidant enzymes.

Cumulative effect of nitrogen and sulphur on Brassica juncea L. genotypes under NaCl stress

In the present study, N and S assimilation, antioxidant enzymes activity, and yield were studied in N and S-treated plants of Brassica juncea (L.) Czern. & Coss. (cvs. Chuutki and Radha) under salt stress. The treatments were given as follows: (1) NaCl(90) mM+N(0)S(0) mg kg(-1) sand (control), (2) NaCl(90) mM+N(60)S(0) mg kg(-1) sand, (3) NaCl(90) mM+N(60)S(20) mg kg(-1) sand, (4) NaCl(90) mM+N(60)S(40) mg kg(-1) sand, and (5) NaCl(90) mM+N(60)S(60) mg kg(-1) sand. The combined application of N (60 mg kg(-1) sand) and S (40 mg kg(-1) sand) proved beneficial in alleviating the adverse effect of salt stress on growth attributes (shoot length plant(-1), fresh weight plant(-1), dry weight plant(-1), and area leaf(-1)), physio-biochemical parameters (carbonic anhydrase activity, total chlorophyll, adenosine triphosphate-sulphurylase activity, leaf N, K and Na content, K/Na ratio, activity of nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase, catalase, superoxide dismutase, ascorbate peroxidase and glutathione reductase, and content of glutathione and ascorbate), and yield attributes (pods plant(-1), seeds pod(-1), and seed yield plant(-1)). Therefore, it is concluded that combined application of N and S induced the physiological and biochemical mechanisms of Brassica. The stimulation of antioxidant enzymes activity and its synergy with N and S assimilation may be one of the important mechanisms that help the plants to tolerate the salinity stress and resulted in an improved yield.