Salt-adaptive strategies in oil seed crop Ricinus communis early seedlings (cotyledon vs. true leaf) revealed from proteomics analysis

Comprehensive LC-MS/MS analysis of nitrogen-related plant metabolites

We have developed and validated a novel LC-MS/MS method for simultaneously analyzing amino acids, biogenic amines, and their acetylated and methylated derivatives in plants. This method involves a one-step extraction of 2-5 mg of lyophilized plant material followed by fractionation of different biogenic amine forms, and exploits an efficient combination of hydrophilic interaction liquid chromatography (HILIC), reversed phase (RP) chromatography with pre-column derivatization, and tandem mass spectrometry (MS). This approach enables high-throughput processing of plant samples, significantly reducing the time needed for analysis and its cost. We also present a new synthetic route for deuterium-labeled polyamines. The LC-MS/MS method was rigorously validated by quantifying levels of nitrogen-related metabolites in seedlings of seven plant species, including Arabidopsis, maize, and barley, all of which are commonly used model organisms in plant science research. Our results revealed substantial variations in the abundance of these metabolites between species, developmental stages, and growth conditions, particularly for the acetylated and methylated derivatives and the various polyamine fractions. However, the biological relevance of these plant metabolites is currently unclear. Overall, this work contributes significantly to plant science by providing a powerful analytical tool and setting the stage for future investigations into the functions of these nitrogen-related metabolites in plants.

Castor (Ricinus communis L.) differential cell cycle and metabolism reactivation, germinability, and seedling performance under NaCl and PEG osmoticum: Stress tolerance related to genotype-preestablished superoxide dismutase activity

Castor (Ricinus communis) is a relevant industrial oilseed feedstock for many industrial applications, being globally mainly cultivated by smallholder farmers in semiarid areas, where abiotic stresses predominate. Therefore, susceptible to generating reactive oxygen species (ROS) and subsequent oxidative stress, compromising cell metabolism upon seed imbibition and germination, seedling and crop establishment, and yield. The present study evaluated the consequences of water restriction by Polyethylene glycol (PEG) and Sodium chloride (NaCl) on cell cycle and metabolism reactivation on germinability, seedling growth, and vigor parameters in 2 commercial castor genotypes (Nordestina and Paraguaçu). PEG water restriction inhibited germination completely at -0.23 MPa or higher, presumably due to reduced oxygen availability. The restrictive effects of NaCl saline stress on germination were observed only from -0.46 MPa onwards, affecting dry mass accumulation and the production of normal seedlings. In general, superoxide dismutase (SOD) activity increased in NaCl -0.23 MPa, whereas its modulation during the onset of imbibition (24h) seemed to depend on its initial levels in dry seeds in a genotype-specific manner, therefore, resulting in the higher stress tolerance of Nordestina compared to Paraguaçu. Overall, results show that Castor germination and seedling development are more sensitive to the restrictive effects of PEG than NaCl at similar osmotic potentials, contributing to a better understanding of the responses to water restriction stresses by different Castor genotypes. Ultimately, SOD may constitute a potential marker for characterizing castor genotypes in stressful situations during germination, early seedling, and crop establishment, and a target for breeding for Castor-improved stress tolerance.

Response of sugar metabolism in the cotyledons and roots of Ricinus communis subjected to salt stress

Ricinus communis is an important oilseed crop worldwide and is also considered one of the best potential plants for salt-affected soil improvement in northeast China. However, little is known about photosynthesis and carbohydrate metabolism in this plant, nor the distribution of carbohydrates in cotyledons and roots under salinity stress. In the present study, seedling growth, gas exchange parameters (P_N , E, g_s and C_i ), carbohydrate (fructose, sucrose, glucose, soluble sugar and starch) metabolism and related enzymes and genes were measured in Ricinus plants. Under salt stress, P_N of cotyledons decreased significantly (P < 0.05), resulting in weak photosynthetic capacity. Furthermore, salt stress increased sucrose and glucose content in cotyledons, but decreased soluble sugar and starch content. However, sucrose increased and starch decreased in roots. This may be correlated with the increasing sugar metabolism under salinity, including notable changes in sugar-related enzyme activities (SPS, SuSy, α-amylase and β-amylase) and gene expression of RcINV, RcSUS, RcAmY, RcBAM and RcGBE1. The results suggest that salinity reduces photosynthesis of cotyledons, alters carbohydrate allocation between cotyledons and roots and also promotes starch utilization in cotyledons and starch biosynthesis in roots, leading to a functional imbalance between cotyledons and roots. Together, these findings provide insights into the crucial role of sugar metabolism in improving salt-tolerance of Ricinus during the early seedling growth stage.

The Developmental Delay of Seedlings With Cotyledons Only Confers Stress Tolerance to Suaeda aralocaspica (Chenopodiaceae) by Unique Performance on Morphology, Physiology, and Gene Expression

Cotyledons play an important role in seedling establishment, although they may just exist for a short time and become senescent upon the emergence of euphylla. So far, the detailed function of cotyledons has not been well understood. Suaeda aralocaspica is an annual halophyte distributed in cold deserts; its cotyledons could exist for a longer time, even last until maturity, and they must exert a unique function in seedling development. Therefore, in this study, we conducted a series of experiments to investigate the morphological and physiological performances of cotyledons under salt stress at different developmental stages. The results showed that the cotyledons kept growing slowly to maintain the normal physiological activities of seedlings by balancing phytohormone levels, accumulating osmoprotectants and antioxidants, and scavenging reactive oxygen species (ROS). Salt stress activated the expression of osmoprotectant-related genes and enhanced the accumulation of related primary metabolites. Furthermore, differentially expressed transcriptional profiles of the cotyledons were also analyzed by cDNA-AFLP to gain an understanding of cotyledons in response to development and salt stress, and the results revealed a progressive increase in the expression level of development-related genes, which accounted for a majority of the total tested TDFs. Meanwhile, key photosynthetic and important salt stress-related genes also actively responded. All these performances suggest that "big cotyledons" are experiencing a delayed but active developmental process, by which S. aralocaspica may survive the harsh condition of the seedling stage.

Untargeted LC-MS-based metabolomics revealed specific metabolic changes in cotyledons and roots of Ricinus communis during early seedling establishment under salt stress

Early seedling development is one of the most crucial period of the plant's life cycle, which is highly susceptible to adverse environmental conditions, especially those impose by salt stress. Castor plant (Ricinus communis) is a famous non-edible oilseed and salt-resistant crop worldwide. However, the specific metabolic responses in the cotyledons and roots of this species during seedling establishment under salt stress are still not clearly understood. In the present study, 16 d castor seedlings were treated with 150 mM NaCl for 6 d, and the metabolite profiling of cotyledons and roots was conducted using liquid chromatography (LC) combined with electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). The Principal Component Analysis (PCA) results showed that the metabolites were great differed in cotyledons and roots under salt stress. There were 38 differential metabolites, mainly including fatty acid, nucleic acid and organic acids in the cotyledons, but only 19 differential metabolites, mainly including fatty acid and organic acids in the roots under such condition. Furthermore, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed that flavone and flavonol biosynthesis, pantothenate and CoA biosynthesis, citrate cycle and carotenoid biosynthesis were the common metabolic pathways in response to salt stress in the two organs. Salt stress caused metabolite process alteration mainly on carbon and nitrogen metabolisms, and the carbon allocation from root to cotyledon was increased. Additionally, changes of amino acids and nucleic acids profiles were only found in the cotyledons, and the roots could enhance the activity of antioxidant enzyme systems to scavenge ROS under salinity. In conclusion, the present research provides an improved understanding on specific physiological changes in the cotyledons in castor early seedlings, and explores their interaction under salt stress.

Anatomical changes in stem and root of soybean plants submitted to salt stress

The soybean is a legume that is widely cultivated in many countries due to the high levels of protein and oil contained in its seed, and is used for human and animal nutrition. However, salinity affects more than 800 million hectares worldwide, limiting global agricultural production. The aim of this research was to evaluate the structural behaviour of the roots and stems under progressive salt stress, detailing the possible anatomical modifications to these organs in soybean plants during this stress. The plants were randomized into five treatments (0, 50, 100, 150 and 200 mm NaCl). All the root regions studied and exposed to 100 mm Na+ exhibited increases in the epidermis and endodermis and formation of lysogenic aerenchyma with increasing salinity, revealing the protective roles of these structures in reducing Na+ influx. In the stem, increases in the cortex and pith in the first internode subject to 100 mm Na+ suggest anatomical responses that aim to minimize oxidative stress. Soybean plants subjected to progressive salt stress (>50 mm Na+ ) avoided cavitation and loss of function linked to vessel elements, reducing the metaxylem in all the root and stem regions analysed. Finally, our results confirm anatomical changes to the roots and stems.

Laying Diet Supplementation with Ricinus communis L. leaves and Evaluation of Productive Performance and Potential Modulation of Antioxidative Status

This study evaluated the antioxidant capacity of Ricinus communis L. (RC) leaves and powder when used as a feed additive for laying hens. Results showed that the total phenolic content of the aqueous leaf extract of Ricinus communis L. (RCE) was 48.39 mg gallic acid equivalent (GAE) per gram dry weight (DW). The flavonoid content was 9.76 mg quercetin dihydrate equivalent (QE)/g DW. Ferrous chelating activity was approximately 56.2% with an RCE concentration of 1 mg/mL; the highest chelating activity was 91.2% with 4 mg/mL extract. The reducing power of 1 mg/mL RC was 1.17 times better than 1 mg/mL butylated hydroxytoluene (BHT). The Trolox equivalent antioxidant capacity (TEAC) value of 12.5 mg/mL RCE was equivalent to 3.09 mg/mL Trolox. RCE (10 mg/mL) had a lipid oxidative inhibition capacity of 35.3%. A total of 80 ISA brown laying hens at twenty-nine weeks of age were randomly allocated into the control or 1 of 3 treatment groups; the latter received 0.5%, 1% or 2% of RC, respectively, for 12 weeks. Results showed that the RC supplementation improved the feed conversion rate and 0.5% RC generated the best results. Additionally, the egg yolk score was significantly increased in all RC-supplemented groups. Moreover, there was no significant difference in serum characteristics between the treatment groups. Serum antioxidant enzyme activity showed that superoxide dismutase (SOD) activity increased in the RC-supplemented groups relative to the control but was not significantly different. mRNA expression levels of the antioxidant regulatory genes GCLC, GST, HO-1, SOD1, and SOD2 were significantly increased with 2% RC supplementation. In summary, RC is a suitable feed additive for laying hens and the addition of 0.5% RC leaf powder resulted in the greatest benefits.

Changes and Associations of Genomic Transcription and Histone Methylation with Salt Stress in Castor Bean

Soil salinity is a major source of abiotic plant stress, adversely affecting plant growth, development and productivity. Although the physiological and molecular mechanisms that underlie plant responses to salt stress are becoming increasingly understood, epigenetic modifications, such as histone methylations and their potential regulation of the transcription of masked genes at the genome level in response to salt stress, remain largely unclear. Castor bean, an important nonedible oil crop, has evolved the capacity to grow under salt stress. Here, based on high-throughput RNA-seq and ChIP-seq data, we systematically investigated changes in genomic transcription and histone methylation using typical histone H3 lysine 4 trimethylation (H3K4me3) and histone H3 tri-methylated lysine 27 (H3K27me3) markers in castor bean leaves subjected to salt stress. The results showed that gain or loss of histone methylation was closely associated with activated or repressed gene expression, though variations in both transcriptome and histone methylation modifications were relatively narrow in response to salt stress. Diverse salt responsive genes and switched histone methylation sites were identified in this study. In particular, we found for the first time that the transcription of the key salt-response regulator RADIALIS-LIKE SANT (RSM1), a MYB-related transcription factor involved in ABA(abscisic acid)-mediated salt stress signaling, was potentially regulated by bivalent H3K4me3-H3K27me3 modifications. Combining phenotypic variations with transcriptional and epigenetic changes, we provide a comprehensive profile for understanding histone modification, genomic transcription and their associations in response to salt stress in plants.

Responses of GABA shunt coupled with carbon and nitrogen metabolism in poplar under NaCl and CdCl2 stresses

The γ-aminobutyric acid (GABA) shunt is closely associated with plant tolerance; however, little is known about its mechanism. This study aimed to decipher the responses of the GABA shunt and related carbon-nitrogen metabolism in poplar seedlings (Populus alba × Populus glandulosa) treated with different NaCl and CdCl₂ concentrations for 30 h. The results showed that the activities of glutamate decarboxylase (GAD) and GABA-transaminase (GABA-T) were activated, as well as α-ketoglutarate dehydrogenase (α-KGDH) and succinate dehydrogenase (SDH) activities were enhanced by NaCl and CdCl₂ stresses, except for SDH under CdCl₂ stress. Meanwhile, the expression levels of GADs, GABA-Ts SDHs, succinyl-CoA ligases (SCSs), and succinic acid aldehyde dehydrogenases (SSADHs) were also increased. Notably, significant increases in the key components of GABA shunt, Glu and GABA, were observed under both stresses. Soluble sugars and free amino acids were enhanced, whereas citrate, malate and succinate were almost inhibited by both NaCl and CdCl₂ stresses except that citrate was not changed or just increased by 50-mM NaCl stress. Thus, these results suggested that the carbon-nitrogen balance could be altered by activating the GABA shunt when main TCA-cycle intermediates were inhibited under NaCl and CdCl₂ stresses. This study can enhance the understanding about the functions of the GABA shunt in woody plants under abiotic stresses and may be applied to the genetic improvement of trees for phytoremediation.

Physiological and Proteomic Analyses Reveal Adaptive Mechanisms of Ryegrass (Annual vs. Perennial) Seedlings to Salt Stress

Ryegrass has a relatively high salt tolerance and is considered to be a promising species for both foraging and turf purposes in salt-affected soils in China. While annual ryegrass and perennial ryegrass are two different species, they have similar genomes. However, little is known about their physiological and molecular response mechanisms to salinity stress. Here, biomass, chlorophyll fluorescence, and inorganic ion and organic solute content were measured. 2-DE-based proteomic technology was then used to identify the differentially expressed proteins in the salt-treated seedlings. The results showed that salt stress reduced growth and photosynthesis in the seedlings of both species, but much more so in annual ryegrass. With increasing salinity, the Na+ concentration increased while the K+ concentration decreased in both species, and the sugars and proline increased as the primary organic solutes used to cope with osmotic stress. Additionally, proteomic analysis revealed 33 and 37 differentially expressed proteins in annual and perennial ryegrass, respectively. Most of the identified proteins were involved in carbohydrate and energy metabolism, photosynthesis, genetic information processes, amino acid metabolism, stress defense, and protein synthesis and folding. The results suggest that the two-ryegrass species had different physiological and proteomic responses. These findings can provide new insights into physiological mechanisms by which ryegrass species respond to salt stress.

A proteomic and biochemical investigation on the effects of sulfadiazine in Arabidopsis thaliana

Animal manure or bio-solids used as fertilizers are the main routes of antibiotic exposure in the agricultural land, which can have immense detrimental effects on plants. Sulfadiazine (SDZ), belonging to the class of sulfonamides, is one of the most detected antibiotics in the agricultural soil. In this study, the effect of SDZ on the growth, changes in antioxidant metabolite content and enzyme activities related to oxidative stress were analysed. Moreover, the proteome alterations in Arabidopsis thaliana roots in response to SDZ was examined by means of a combined iTRAQ-LC-MS/MS quantitative proteomics approach. A dose-dependent decrease in leaf biomass and root length was evidenced in response to SDZ. Increased malondialdehyde content at higher concentration (2 μM) of SDZ indicated increased lipid peroxidation and suggest the induction of oxidative stress. Glutathione levels were significantly higher compared to control, whereas there was no increase in ascorbate content or the enzyme activities of glutathione metabolism, even at higher concentrations. In total, 48 differentially abundant proteins related to stress/stimuli response followed by transcription and translation, metabolism, transport and other functions were identified. Several proteins related to oxidative, dehydration, salinity and heavy metal stresses were represented. Upregulation of peroxidases was validated with total peroxidase activity. Pathway analysis provided an indication of increased phenylpropanoid biosynthesis. Probable molecular mechanisms altered in response to SDZ are highlighted.