Differential metabolite profiles and salinity tolerance between two genetically related brown-seeded and yellow-seeded Brassica carinata lines

Brassica Species in Phytoextractions: Real Potentials and Challenges

The genus Brassica is recognized for including species with phytoaccumulation potential and a large amount of research has been carried out in this area under a variety of conditions, from laboratory experiments to field trials, with spiked or naturally contaminated soils, using one- or multi-element contaminated soil, generating various and sometimes contradictory results with limited practical applications. To date, the actual field potential of Brassica species and the feasibility of a complete phytoextraction process have not been fully evaluated. Therefore, the aim of this study was to summarize the results of the experiments that have been performed with a view to analyzing real potentials and limitations. The reduced biomass and low metal mobility in the soil have been addressed by the development of chemically or biologically assisted phytoremediation technologies, the use of soil amendments, and the application of crop management strategies. Certain issues, such as the fate of harvested biomass or the performance of species in multi-metal-contaminated soils, remain to be solved by future research. Potential improvements to current experimental settings include testing species grown to full maturity, using a greater amount of soil in experiments, conducting more trials under real field conditions, developing improved crop management systems, and optimizing solutions for harvested biomass disposal.

A. Mohamed I, Wang Z, Khatab A, Sherif A, Ahmad H, Khan MN, Hassan HM, Elrewainy IM, Kuai J, Zhou G, Wang B. Antioxidative and Metabolic Contribution to Salinity Stress Responses in Two Rapeseed Cultivars during the Early Seedling Stage

Measuring metabolite patterns and antioxidant ability is vital to understanding the physiological and molecular responses of plants under salinity. A morphological analysis of five rapeseed cultivars showed that Yangyou 9 and Zhongshuang 11 were the most salt-tolerant and -sensitive, respectively. In Yangyou 9, the reactive oxygen species (ROS) level and malondialdehyde (MDA) content were minimized by the activation of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) for scavenging of over-accumulated ROS under salinity stress. Furthermore, Yangyou 9 showed a significantly higher positive correlation with photosynthetic pigments, osmolyte accumulation, and an adjusted Na⁺/K⁺ ratio to improve salt tolerance compared to Zhongshuang 11. Out of 332 compounds identified in the metabolic profile, 225 metabolites were filtrated according to p < 0.05, and 47 metabolites responded to salt stress within tolerant and sensitive cultivars during the studied time, whereas 16 and 9 metabolic compounds accumulated during 12 and 24 h, respectively, in Yangyou 9 after being sown in salt treatment, including fatty acids, amino acids, and flavonoids. These metabolites are relevant to metabolic pathways (amino acid, sucrose, flavonoid metabolism, and tricarboxylic acid cycle (TCA), which accumulated as a response to salinity stress. Thus, Yangyou 9, as a tolerant cultivar, showed improved antioxidant enzyme activity and higher metabolite accumulation, which enhances its tolerance against salinity. This work aids in elucidating the essential cellular metabolic changes in response to salt stress in rapeseed cultivars during seed germination. Meanwhile, the identified metabolites can act as biomarkers to characterize plant performance in breeding programs under salt stress. This comprehensive study of the metabolomics and antioxidant activities of Brassica napus L. during the early seedling stage is of great reference value for plant breeders to develop salt-tolerant rapeseed cultivars.

Roles for Plant Mitochondrial Alternative Oxidase Under Normoxia, Hypoxia, and Reoxygenation Conditions

Alternative oxidase (AOX) is a non-energy conserving terminal oxidase in the plant mitochondrial electron transport chain (ETC) that has a lower affinity for oxygen than does cytochrome (cyt) oxidase. To investigate the role(s) of AOX under different oxygen conditions, wild-type (WT) Nicotiana tabacum plants were compared with AOX knockdown and overexpression plants under normoxia, hypoxia (near-anoxia), and during a reoxygenation period following hypoxia. Paradoxically, under all the conditions tested, the AOX amount across plant lines correlated positively with leaf energy status (ATP/ADP ratio). Under normoxia, AOX was important to maintain respiratory carbon flow, to prevent the mitochondrial generation of superoxide and nitric oxide (NO), to control lipid peroxidation and protein S-nitrosylation, and possibly to reduce the inhibition of cyt oxidase by NO. Under hypoxia, AOX was again important in preventing superoxide generation and lipid peroxidation, but now contributed positively to NO amount. This may indicate an ability of AOX to generate NO under hypoxia, similar to the nitrite reductase activity of cyt oxidase under hypoxia. Alternatively, it may indicate that AOX activity simply reduces the amount of superoxide scavenging of NO, by reducing the availability of superoxide. The amount of inactivation of mitochondrial aconitase during hypoxia was also dependent upon AOX amount, perhaps through its effects on NO amount, and this influenced carbon flow under hypoxia. Finally, AOX was particularly important in preventing nitro-oxidative stress during the reoxygenation period, thereby contributing positively to the recovery of energy status following hypoxia. Overall, the results suggest that AOX plays a beneficial role in low oxygen metabolism, despite its lower affinity for oxygen than cytochrome oxidase.

Chloride and sulfate salinity differently affect biomass, mineral nutrient composition and expression of sulfate transport and assimilation genes in Brassica rapa

BACKGROUND AND AIMS

It remains uncertain whether a higher toxicity of either NaCl or Na2SO4 in plants is due to an altered toxicity of sodium or a different toxicity of the anions. The aim of this study was to determine the contributions of sodium and the two anions to the different toxicities of chloride and sulfate salinity. The effects of the different salts on physiological parameters, mineral nutrient composition and expression of genes of sulfate transport and assimilation were studied.

METHODS

Seedlings of Brassica rapa L. have been exposed to NaCl, Na2SO4, KCl and K2SO4 to assess the potential synergistic effect of the anions with the toxic cation sodium, as well as their separate toxicities if accompanied by the non-toxic cation potassium. Biomass production, stomatal resistance and Fv/fm were measured to determine differences in ionic and osmotic stress caused by the salts. Anion content (HPLC), mineral nutrient composition (ICP-AES) and gene expression of sulfate transporters and sulfur assimilatory enzymes (real-time qPCR) were analyzed.

RESULTS

Na2SO4 impeded growth to a higher extent than NaCl and was the only salt to decrease Fv/fm. K2SO4 reduced plant growth more than NaCl. Analysis of mineral nutrient contents of plant tissue revealed that differences in sodium accumulation could not explain the increased toxicity of sulfate over chloride salts. Shoot contents of calcium, manganese and phosphorus were decreased more strongly by exposure to Na2SO4 than by NaCl. The expression levels of genes encoding proteins for sulfate transport and assimilation were differently affected by the different salts. While gene expression of primary sulfate uptake at roots was down-regulated upon exposure to sulfate salts, presumably to prevent an excessive uptake, genes encoding for the vacuolar sulfate transporter Sultr4;1 were upregulated. Gene expression of ATP sulfurylase was hardly affected by salinity in shoot and roots, the transcript level of 5'-adenylylsulfate reductase (APR) was decreased upon exposure to sulfate salts in roots. Sulfite reductase was decreased in the shoot by all salts similarly and remained unaffected in roots.

CONCLUSIONS

The higher toxicity of Na2SO4 over NaCl in B. rapa seemed to be due to an increased toxicity of sulfate over chloride, as indicated by the higher toxicity of K2SO4 over KCl. Thus, toxicity of sodium was not promoted by sulfate. The observed stronger negative effect on the tissue contents of calcium, manganese and phosphorus could contribute to the increased toxicity of sulfate over chloride. The upregulation of Sultr4;1 and 4;2 under sulfate salinity might lead to a detrimental efflux of stored sulfate from the vacuole into the cytosol and the chloroplasts. It remains unclear why expression of Sultr4;1 and 4;2 was upregulated. A possible explanation is a control of the gene expression of these transporters by the sulfate gradient across the tonoplast.

Integrating transcriptomics and metabolomics to characterise the response of Astragalus membranaceus Bge. var. mongolicus (Bge.) to progressive drought stress

BACKGROUND

Astragalus membranaceus Bge. var. mongolicus (Bge.) Hsiao (A. mongolicus) is an important traditional Chinese herb that is cultivated on a large scale in northwestern China. Understanding plant responses to drought has important effects on ecological environment recovery and local economic development. Here, we combined transcriptomics (Illumina Hiseq 2000) and metabolomics ((1)H-NMR) to investigate how the roots of two-year-old A. mongolicus responded to 14 days of progressive drought stress.

RESULTS

The dried soil reduced the relative water content (RWC) of the leaves and biomass, induced the differential expression of a large fraction of the transcriptome and significantly altered the metabolic processes. PCA analysis demonstrated that the sucrose, proline, and malate metabolites contributed greatly to the separation. Strikingly, proline was increased by almost 60-fold under severe stress compared to the control. Some backbone pathways, including glycolysis, tricarboxylic acid (TCA) cycle, glutamate-mediated proline biosynthesis, aspartate family metabolism and starch and sucrose metabolism, were significantly affected by drought. An integrated analysis of the interaction between key genes and the altered metabolites involved in these pathways was performed.

CONCLUSIONS

Our findings demonstrated that the expression of drought-responsive genes showed a strong stress-dose dependency. Analysis of backbone pathways of the transcriptome and metabolome revealed specific genotypic responses to different levels of drought. The variation in molecular strategies to the drought may play an important role in how A. mongolicus and other legume crops adapt to drought stress.

Fast responses of metabolites in Vicia faba L. to moderate NaCl stress

Salt stress impairs global agricultural crop production by reducing vegetative growth and yield. Despite this importance, a number of gaps exist in our knowledge about very early metabolic responses that ensue minutes after plants experience salt stress. Surprisingly, this early phase remains almost as a black box. Therefore, systematic studies focussing on very early plant physiological responses to salt stress (in this case NaCl) may enhance our understanding on strategies to develop crop plants with a better performance under saline conditions. In the present study, hydroponically grown Vicia faba L. plants were exposed to 90 min of NaCl stress, whereby every 15 min samples were taken for analyzing short-term physiologic responses. Gas chromatography-mass spectrometry-based metabolite profiles were analysed by calculating a principal component analysis followed by multiple contrast tests. Follow-up experiments were run to analyze downstream effects of the metabolic changes on the physiological level. The novelty of this study is the demonstration of complex stress-induced metabolic changes at the very beginning of a moderate salt stress in V. faba, information that are very scant for this early stage. This study reports for the first that the proline analogue trans-4-hydroxy-L-proline, known to inhibit cell elongation, was increasingly synthesized after NaCl-stress initiation. Leaf metabolites associated with the generation or scavenging of reactive oxygen species (ROS) were affected in leaves that showed a synchronized increase in ROS formation. A reduced glutamine synthetase activity indicated that disturbances in the nitrogen assimilation occur earlier than it was previously thought under salt stress.

Interactive association between biopolymers and biofunctions in carinata seeds as energy feedstock and their coproducts (carinata meal) from biofuel and bio-oil processing before and after biodegradation: current advanced molecular spectroscopic investigations

Recent advances in biofuel and bio-oil processing technology require huge supplies of energy feedstocks for processing. Very recently, new carinata seeds have been developed as energy feedstocks for biofuel and bio-oil production. The processing results in a large amount of coproducts, which are carinata meal. To date, there is no systematic study on interactive association between biopolymers and biofunctions in carinata seed as energy feedstocks for biofuel and bioethanol processing and their processing coproducts (carinata meal). Molecular spectroscopy with synchrotron and globar sources is a rapid and noninvasive analytical technique and is able to investigate molecular structure conformation in relation to biopolymer functions and bioavailability. However, to date, these techniques are seldom used in biofuel and bioethanol processing in other research laboratories. This paper aims to provide research progress and updates with molecular spectroscopy on the energy feedstock (carinata seed) and coproducts (carinata meal) from biofuel and bioethanol processing and show how to use these molecular techniques to study the interactive association between biopolymers and biofunctions in the energy feedstocks and their coproducts (carinata meal) from biofuel and bio-oil processing before and after biodegradation.