Antioxidants, free radicals, storage proteins, puroindolines, and proteolytic activities in bread wheat (Triticum aestivum) seeds during accelerated aging

Comparative seed longevity under genebank storage and artificial ageing: a case study in heteromorphic wheat wild relatives

Seed longevity is a complex trait that depends on numerous factors. It varies among species and populations, and within different seed morphs produced by the same plant. Little is known about variation in longevity in different seed morphs or the physiological and molecular basis of these differences. We evaluated the longevity and oxidative stress status in heteromorphic seeds aged in two different storage conditions. We compared controlled ageing tests (seed storage at 45°C and 60% relative humidity; a method of accelerated ageing used to estimate longevity in genebank conditions) with storage in a genebank for up to 40 years (-18°C and 8% seed moisture content). We employed as study species two wild wheats characterized by seed heteromorphism: Aegilops tauschii and Triticum monococcum subsp. aegilopoides. We estimated the ROS content and the expression of genes coding for enzymes related to the H₂ O₂ scavenging pathway. Results confirmed that seed longevity varies between different seed morphs. Different storage environments resulted in different longevity and survival curves. ROS levels, even if with variable patterns, were higher in several aged seed lots. We observed consistency in the expression of two genes (GSR and CAT) related to ROS scavenging in the late phase of pre-germinative metabolism. Differences in seed longevity between morphs were observed for the first time under genebank conditions. Our results suggest also that controlled ageing tests should be used with caution to infer ranks of longevity under cold storage.

Antioxidant Properties of Pulp, Peel and Seeds of Phlegrean Mandarin (Citrus reticulata Blanco) at Different Stages of Fruit Ripening

In this work, we assess the potential of waste products of Phlegrean mandarin (Citrus reticulata Blanco), namely seeds and peel, to be reutilized as a source of bioactive compounds beneficial for the human diet. Starting from the evidence that the by-products of this specific cultivar are the most powerful sources of antioxidants compared to pulp, we have investigated if and how the bioactive compounds in peel and seeds may be affected by fruit ripening. Three stages of fruit ripening have been considered in our study: unripe fruits = UF, semi-ripe fruits = SRF, ripe fruits = RF. The overall results indicated that RF showed the highest concentration of antioxidants. Among fruit components, peel was the richest in total antioxidant capacity, total polyphenol content, total flavonoids, total chlorophylls and carotenoids, while seeds exhibited the highest concentration of total condensed tannins and ascorbic acid. The liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay indicates the occurrence, in peel extracts, of 28 phenolic compounds, mainly flavonoids (FLs); in seeds, 34 derivatives were present in the first stage (UF), which diminish to 24 during the ripening process. Our data indicated that the content of phytochemicals in citrus strongly varies among the fruit components and depends on the ripening stage. The higher antioxidant activity of peel and seeds, especially in RF, encourage a potential use of by-products of this specific citrus cultivar for industrial or pharmacological applications. However, to maximize the occurrence of desired bioactive compounds, it is important also to consider the ripening stage at which fruits must be collected.

Carotenoid cleavage dioxygenases (HD-CCD1A and B) contribute as strong negative regulators of β-carotene in Indian bread wheat (cv. HD2967)

Wheat (Triticum aestivum L.) is the most common cereal crop that is considered to be deficient in provitamin A carotenoids. Carotenoids are prone to degrade into apocarotenoids by the activity of carotenoid cleavage dioxygenases (CCDs). Hence, in this study, multiple CCDs were cloned from commercial Indian wheat cultivar HD2967 to understand their role in provitamin A carotenoids degradation. The homoeolog specific expression of HD-CCD1 and HD-CCD4 at different grain filling stages revealed the higher expression of transcripts arising from the A and B subgenomes of HD-CCD1. Furthermore, the grain development stages showed a strong negative correlation of HD-CCD1A (r = - 0.969) and B (r = - 0.970) homoeologs expression to that of β-carotene accumulation. It suggested that they could be potentially involved in deciding the turn-over of β-carotene in wheat grain. Three-dimensional (3D) structures for all six homoeologs of HD-CCD1 and HD-CCD4 were predicted using maize VP14 template to gain better insight into their molecular mechanism. Ramachandran plot assessment revealed that ~ 90% of residues are in the most favoured region. Docking studies with various carotenoid substrates revealed the higher affinity of HD-CCD1A and B for β-carotene and β-cryptoxanthin. Bacterial complementation analysis validated the functional role of all six homoeologs with HD-CCD1B showing the highest activity followed by HD-CCD1A for β-carotene degradation. Results of this study provide valuable insights into the characteristics of HD-CCDs in wheat and thereby justifying them (HD-CCD1A and B) as the candidate genes for employing genome editing tools for developing β-carotene enriched wheat grains.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02775-y.

Comparative Studies on Different Citrus Cultivars: A Revaluation of Waste Mandarin Components

Peel, pulp and seed extracts of three mandarin varieties, namely Phlegraean mandarin (Citrus reticulata), Kumquat (Citrus japonica), and Clementine (Citrus clementina) were compared and characterised in terms of photosynthetic pigment content, total polyphenols amount, antioxidant activity and vitamin C to assess the amount of functional compounds for each cultivar. The highest polyphenols content was found in the Phlegraean mandarin, especially in peel and seeds, whereas Kumquat exhibited the highest polyphenols amount in the pulp. The antioxidant activity was higher in the peel of Phlegraean mandarin and clementine compared to Kumquat, which showed the highest value in the pulp. The antioxidant activity peaked in the seeds of Phlegraean mandarin. The vitamin C in the Phlegraean mandarin was the highest in all parts of the fruit, especially in the seeds. Total chlorophyll content was comparable in the peel of different cultivars, in the pulp the highest amount was found in clementine, whereas kumquat seeds showed the greatest values. As regards total carotenoids, peel and pulp of clementine exhibited higher values than the other two cultivars, whereas the kumquat seeds were the richest in carotenoids. Among the analysed cultivars Phlegraean mandarin may be considered the most promising as a source of polyphenols and antioxidants, compared to the clementine and Kumquat, especially for the functional molecules found in the seeds. Moreover, regardless of cultivars this study also highlights important properties in the parts of the fruit generally considered wastes.

Heteromorphic seeds of wheat wild relatives show germination niche differentiation

Crop wild relatives are fundamental genetic resources for crop improvement. Wheat wild relatives often produce heteromorphic seeds that differ in morphological and physiological traits. Several Aegilops and Triticum species possess, within the same spikelet, a dimorphic seed pair, with one seed being larger than the other. A comprehensive analysis is needed to understand which traits are involved in seed dimorphism and if these aspects of variation in dimorphic pairs are functionally related. To this end, dispersal units of Triticum urartu and five Aegilops species were X-rayed and the different seed morphs weighed. Germination tests were carried out on seeds, both dehulled and left in their dispersal units. Controlled ageing tests were performed to detect differences in seed longevity among seed morphs, and the antioxidant profile was assessed in terms of antioxidant compounds equipment and expression of selected antioxidant genes. We used PCA to group seed morphs sharing similar patterns of germination traits, longevity estimates and antioxidant profile. Different seed morphs differed significantly in terms of mass, final germination, germination timing, longevity estimates and antioxidant profile in most of the tested species. Small seeds germinated slower, had lower germination when left in their dispersal units, a higher antioxidant potential and were longer-lived than large seeds. The antioxidant gene expression varied between morphs, with different patterns across species but not clearly reflecting the phenotypic observations. The results highlight different trait trade-offs in dimorphic seeds of Aegilops and T. urartu, affecting their germination phenology and longevity, thereby resulting in recruitment niche differentiation.

Dynamic proteomic changes in soft wheat seeds during accelerated ageing

Previous research demonstrated that soft wheat cultivars have better post-harvest storage tolerance than harder cultivars during accelerated ageing. To better understand this phenomenon, a tandem mass tag-based quantitative proteomic analysis of soft wheat seeds was performed at different storage times during accelerated ageing (germination ratios of 97%, 45%, 28%, and 6%). A total of 1,010 proteins were differentially regulated, of which 519 and 491 were up- and downregulated, respectively. Most of the differentially expressed proteins were predicted to be involved in nutrient reservoir, enzyme activity and regulation, energy and metabolism, and response to stimulus functions, consistent with processes occurring in hard wheat during artificial ageing. Notably, defense-associated proteins including wheatwin-2, pathogenesis-related proteins protecting against fungal invasion, and glutathione S-transferase and glutathione synthetase participating in reactive oxygen species (ROS) detoxification, were upregulated compared to levels in hard wheat during accelerated ageing. These upregulated proteins might be responsible for the superior post-harvest storage-tolerance of soft wheat cultivars during accelerated ageing compared with hard wheat. Although accelerated ageing could not fully mimic natural ageing, our findings provided novel dynamic proteomic insight into soft wheat seeds during seed deterioration.

The Effect of Storage Condition and Duration on the Deterioration of Primed Rice Seeds

Seed priming is a successful practice to improve crop establishment under adverse environment. However, reduced longevity of primed rice (Oryza sativa L.) seeds during storage limited the adoption of this technique. Present study investigated the effect of temperature, relative air humidity (RH) and oxygen on the longevity of primed rice seeds in a range of 60 days storage. In addition, the biochemical and morphological mechanisms associated with deterioration of primed seeds during storage were explored. Three types of priming treated rice seeds and one non-primed control were stored under (1) low temperature-vacuum (LT-V), (2) room temperature-vacuum (RT-V), (3) room temperature-aerobic-low RH (RT-A-LH) and (4) room temperature-aerobic- high RH (RT-A-HH) for 0, 15, 30, 45, and 60 days. The results showed that storage of seeds under different conditions for 15-60 days did not influence the longevity of non-primed rice seeds. Meanwhile, the viability of primed rice seeds did not reduce when stored under LT-V, RT-V, and RT-A-LH, but was significantly reduced under RT-A-HH. Under vacuum condition, the increases of storage temperature (30°C) did not reduce the longevity of primed seeds. Likewise, the oxygen did not influence the longevity of primed rice seeds stored under low RH. Nevertheless, increase of RH significantly reduced the viability of primed seeds stored for 15-60 days. Reduced starch metabolism, the consumption of starch reserves in rice endosperms, the accumulation of malondialdehyde and the decreases of antioxidant enzyme activities might be associated with the deterioration of primed rice seeds during storage. In conclusion, storage of primed seeds under high RH condition beyond 15 days is deteriorative for germination and growth of rice. The primed rice seeds are recommended to store at vacuum or low RH or low temperature condition to ensure good crop establishment.

Distinct expression and function of carotenoid metabolic genes and homoeologs in developing wheat grains

BACKGROUND

β-carotene, the most active provitamin A molecule produced by plants, plays important roles in human nutrition and health. β-carotene does not usually accumulate in the endosperm (i.e. flour) of mature wheat grains, which is a major food source of calories for humans. Therefore, enriching β-carotene accumulation in wheat grain endosperm will enable a sustainable dietary supplementation of provitamin A. Several metabolic genes affecting β-carotene accumulation have already been isolated from wheat, including phytoene synthase 1 (PSY1), lycopene ε-cyclase (LCYe) and carotenoid β-ring hydroxylase1/2 (HYD1/2).

RESULTS

In this work, we cloned and biochemically characterized two carotenoid cleavage dioxygenases (CCDs), CCD1 and CCD4, from wheat. While CCD1 homoeologs cleaved β-apo-8'-carotenal, β-carotene, lutein and zeaxanthin into apocarotenoid products, CCD4 homoeologs were inactive towards these substrates in in vitro assays. When analyzed by real-time qPCR, PSY1, LCYe, HYD1/2 and CCD1/4 homoeologs showed distinct expression patterns in vegetative tissues and sections of developing tetraploid and hexaploid wheat grains, suggesting that carotenoid metabolic genes and homoeologs are differentially regulated at the transcriptional level in wheat.

CONCLUSIONS

The CCD1/4 enzyme activity and the spatial-temporal gene expression data provide critical insights into the specific carotenoid metabolic gene homoeologs that control β-carotene accumulation in wheat grain endosperm, thus establishing the knowledge base for generation of wheat varieties with enhanced β-carotene in the endosperm through breeding and genome editing approaches.

Identification of a member of the catalase multigene family on wheat chromosome 7A associated with flour b* colour and biological significance of allelic variation

Carotenoids (especially lutein) are known to be the pigment source for flour b* colour in bread wheat. Flour b* colour variation is controlled by a quantitative trait locus (QTL) on wheat chromosome 7AL and one gene from the carotenoid pathway, phytoene synthase, was functionally associated with the QTL on 7AL in some, but not all, wheat genotypes. A SNP marker within a sequence similar to catalase (Cat3-A1snp) derived from full-length (FL) cDNA (AK332460), however, was consistently associated with the QTL on 7AL and implicated in regulating hydrogen peroxide (H2O2) to control carotenoid accumulation affecting flour b* colour. The number of catalase genes on chromosome 7AL was investigated in this study to identify which gene may be implicated in flour b* variation and two were identified through interrogation of the draft wheat genome survey sequence consisting of five exons and a further two members having eight exons identified through comparative analysis with the single catalase gene on rice chromosome 6, PCR amplification and sequencing. It was evident that the catalase genes on chromosome 7A had duplicated and diverged during evolution relative to its counterpart on rice chromosome 6. The detection of transcripts in seeds, the co-location with Cat3-A1snp marker and maximised alignment of FL-cDNA (AK332460) with cognate genomic sequence indicated that TaCat3-A1 was the member of the catalase gene family associated with flour b* colour variation. Re-sequencing identified three alleles from three wheat varieties, TaCat3-A1a, TaCat3-A1b and TaCat3-A1c, and their predicted protein identified differences in peroxisomal targeting signal tri-peptide domain in the carboxyl terminal end providing new insights into their potential role in regulating cellular H2O2 that contribute to flour b* colour variation.

Chromosomal location of wheat genes of the carotenoid biosynthetic pathway and evidence for a catalase gene on chromosome 7A functionally associated with flour b* colour variation

Knowledge of molecular and genetic mechanisms controlling wheat grain quality characteristics is significant for improving flour for end-product functionality. Flour b* colour is an important quality trait for breeding wheat varieties to produce grain for specific market requirements. The degree of flour yellowness is due to the accumulation of carotenoids in grain, particularly lutein. Flour b* is under polygenic control and quantitative trait loci (QTL) have frequently been reported on chromosome 7AL. Analysis of carotenoid genes showed that phytoene synthase (PSY) co-located to the QTL on 7AL but other genes at this locus are also thought to contribute flour b* colour variation. This study used the wheat genome survey sequence and identified the chromosomal location of all wheat carotenoid genes, but none other than PSY were located on 7AL and, therefore, other genes may control flour b* colour variation including oxidative genes that degrade carotenoids. An investigation of EST bin mapped to 7AL identified a gene encoding a catalase enzyme (Cat3-A1) that was phylogenetically related to other plant class III enzymes, co-located to the QTL for flour b* colour variation on 7AL in three mapping populations and expressed during seed development. Therefore, Cat3-A1 was functionally associated with flour b* colour variation. Catalase acts upon hydrogen peroxide as a substrate and it was postulated that Cat3-A1 alleles control varying degrees of bleaching action on lutein in developing wheat grain. Markers for Cat3-A1 developed in this study can be used in conjunction with other candidate gene markers including phytoene synthase and lycopene-ε-cylase to develop a molecular signature for selecting lines with specific flour b* colour values in wheat breeding.

Molecular characterisation and the light-dark regulation of carotenoid biosynthesis in sprouts of tartary buckwheat (Fagopyrum tataricum Gaertn.)

Seven partial-length cDNAs and 1 full-length cDNA that were involved in carotenoid biosynthesis and 2 partial-length cDNAs that encoded carotenoid cleavage dioxygenases were first isolated and characterised in 2 tartary buckwheat cultivars (Fagopyrum tataricum Gaertn.), Hokkai T8 and Hokkai T10. They were constitutively expressed at high levels in the leaves and flowers, where carotenoids are mostly distributed. During the seed development of tartary buckwheat, an inverse correlation between transcription level of carotenoid cleavage dioxygenase and carotenoid content was observed. The light-grown sprouts exhibited higher levels of expression of carotenoid biosynthetic genes in T10 and carotenoid content in both T8 and T10 compared to the dark-grown sprouts. The predominant carotenoids in tartary buckwheat were lutein and β-carotene, and very abundant amounts of these carotenoids were found in light-grown sprouts. This study might broaden our understanding of the molecular mechanisms involved in carotenoid biosynthesis and indicates targets for increasing the production of carotenoids in tartary buckwheat.

Intragenic enhancers and suppressors of phytoene desaturase mutations in Chlamydomonas reinhardtii

Photosynthetic organisms synthesize carotenoids for harvesting light energy, photoprotection, and maintaining the structure and function of photosynthetic membranes. A light-sensitive, phytoene-accumulating mutant, pds1-1, was isolated in Chlamydomonas reinhardtii and found to be genetically linked to the phytoene desaturase (PDS) gene. PDS catalyzes the second step in carotenoid biosynthesis—the conversion of phytoene to ζ-carotene. Decreased accumulation of downstream colored carotenoids suggested that the pds1-1 mutant is leaky for PDS activity. A screen for enhancers of the pds1-1 mutation yielded the pds1-2 allele, which completely lacks PDS activity. A second independent null mutant (pds1-3) was identified using DNA insertional mutagenesis. Both null mutants accumulate only phytoene and no other carotenoids. All three phytoene-accumulating mutants exhibited slower growth rates and reduced plating efficiency compared to wild-type cells and white phytoene synthase mutants. Insight into amino acid residues important for PDS activity was obtained through the characterization of intragenic suppressors of pds1-2. The suppressor mutants fell into three classes: revertants of the pds1-1 point mutation, mutations that changed PDS amino acid residue Pro64 to Phe, and mutations that converted PDS residue Lys90 to Met. Characterization of pds1-2 intragenic suppressors coupled with computational structure prediction of PDS suggest that amino acids at positions 90 and 143 are in close contact in the active PDS enzyme and have important roles in its structural stability and/or activity.

Carotenoid biosynthesis genes in rice: structural analysis, genome-wide expression profiling and phylogenetic analysis

Carotenoids, important lipid-soluble antioxidants in photosynthetic tissues, are known to be completely absent in rice endosperm. Many studies, involving transgenic manipulations of carotenoid biosynthesis genes, have been performed to get carotenoid-enriched rice grain. Study of genes involved in their biosynthesis can provide further information regarding the abundance/absence of carotenoids in different tissues. We have identified 16 and 34 carotenoid biosynthesis genes in rice and Populus genomes, respectively. A detailed analysis of the domain structure of carotenoid biosynthesis enzymes in rice, Populus and Arabidopsis has shown that highly conserved catalytic domains, along with other domains, are present in these proteins. Phylogenetic analysis of rice genes with Arabidopsis and other characterized carotenoid biosynthesis genes has revealed that homologous genes exist in these plants, and the duplicated gene copies probably adopt new functions. Expression of rice and Populus genes has been analyzed by full-length cDNA- and EST-based expression profiling. In rice, this analysis was complemented by real-time PCR, microarray and signature-based expression profiling, which reveal that carotenoid biosynthesis genes are highly expressed in light-grown tissues, have differential expression pattern during vegetative/reproductive development and are responsive to stress.

Alternative splicing, activation of cryptic exons and amino acid substitutions in carotenoid biosynthetic genes are associated with lutein accumulation in wheat endosperm

Endosperm carotenoid content in wheat is a primary determinant of flour colour and this affects both the nutritional value of the grain and its utility for different applications. Utilising wheat rice synteny two genes, epsilon-cyclase (epsilon-LCY) and phytoene synthase (Psy-A1), were identified as candidate genes for two of the QTL affecting lutein content in wheat endosperm. Analysis of the sequence changes in epsilon-LCY and Psy-A1 revealed possible causal mechanisms for both QTL. A point mutation in epsilon-LCY results in the substitution of a conserved amino acid in the high lutein allele. This substitution has been observed in high lutein-accumulating species from the Gentiales order. In Psy-A1, a sequence duplication at the end of exon 2 creates a new splice site and causes alternative splicing of the transcript and activation of a cryptic exon, resulting in four different transcripts: a wild-type transcript, two transcripts with early terminations and a transcript that would produce an in-frame, albeit longer protein. Only the wild-type splice variant produced an enzymatically active protein and its mRNA abundance was reduced by titration with the other splice variants. This reduction in wild-type mRNA is argued to result in a reduction in PSY protein and thus carotenoid content in wheat.

Phytic acid prevents oxidative stress in seeds: evidence from a maize (Zea mays L.) low phytic acid mutant

A maize mutant defective in the synthesis of phytic acid during seed maturation was used as a tool to study the consequences of the lack of this important reserve substance on seed survival. Data on germinability, free iron level, free radical relative abundance, protein carbonylation level, damage to DNA, degree of lipid peroxidation, alpha- and gamma-tocopherol amount and antioxidant capacity were recorded on seeds of maize B73 and of an isogenic low phytic acid mutant (lpa1-241), either unaged or incubated for 7 d in accelerated ageing conditions (46 degrees C and 100% relative humidity). The lpa1-241 mutant, compared to wild type (wt), showed a lower germination capacity, which decreased further after accelerated ageing. Whole lpa1-241 mutant kernels contained about 50% more free or weakly bound iron than wt ones and showed a higher content of free radicals, mainly concentrated in embryos; in addition, upon accelerated ageing, lpa1-241 seed proteins were more carbonylated and DNA was more damaged, whereas lipids did not appear to be more peroxidated, but the gamma-tocopherol content was decreased by about 50%. These findings can be interpreted in terms of previously reported but never proven antioxidant activity of phytic acid through iron complexation. Therefore, a novel role in plant seed physiology can be assigned to phytic acid, that is, protection against oxidative stress during the seed's life span. As in maize kernels the greater part of phytic acid (and thus of metal ions) is concentrated in the embryo, its antioxidant action may be of particular relevance in this crop.

Kinetics of carotenoids degradation during the storage of einkorn (Triticum monococcum L. ssp. monococcum) and bread wheat (Triticum aestivum L. ssp. aestivum) flours

To evaluate the effect of storage temperature, the degradation kinetics of carotenoids in wholemeal and white flour of einkorn cv. Monlis and bread wheat cv. Serio, stored at -20, 5, 20, 30, and 38 degrees C, was assessed by normal-phase high-performance liquid chromatography. In Monlis, the carotenoids content (8.1 and 9.8 mg/kg for wholemeal and white flour, respectively) was 8-fold higher than in Serio (1.0 and 1.1 mg/kg). Only lutein and zeaxanthin were detected in bread wheat, while significant quantities of (alpha and beta)-carotene and beta-cryptoxanthin were observed in einkorn. Carotenoids degradation was influenced by temperature and time, following first-order kinetics. The degradation rate was similar in wholemeal and white flour; however, loss of lutein and total carotenoids was faster in Serio than in Monlis. The activation energy E(a) ranged from 35.2 to 52.5 kJ/mol. Temperatures not exceeding 20 degrees C better preserve carotenoids content and are recommended for long-term storage.

Carotenoid accumulation and function in seeds and non-green tissues

Carotenoids are plant pigments that function as antioxidants, hormone precursors, colourants and essential components of the photosynthetic apparatus. Carotenoids accumulate in nearly all types of plastids, not just the chloroplast, and are thus found in most plant organs and tissues, albeit at trace levels in some tissues. In this review we summarise the current knowledge of the carotenoid content of non-green plastids and discuss what is known about the regulation of their biosynthesis in roots, fruits, flowers, tubers and seeds. The emphasis is on food crops as carotenoids are essential components of human diets, primarily as some are precursors of vitamin A. The low carotenoid content of many staple foods, such as cereals, can exacerbate dietary deficiencies. The World Health Organisation has estimated that more than 100 million children are vitamin A-deficient and up to 500,000 of these children become blind each year. Many of these children die within 12 months of going blind. Thus, understanding the regulation of carotenoid accumulation in food crops, especially tubers and cereals, should facilitate improvements to nutritional value with potentially significant health benefits.

Vitamin synthesis in plants: tocopherols and carotenoids

Carotenoids and tocopherols are the two most abundant groups of lipid-soluble antioxidants in chloroplasts. In addition to their many functional roles in photosynthetic organisms, these compounds are also essential components of animal diets, including humans. During the past decade, a near complete set of genes required for the synthesis of both classes of compounds in photosynthetic tissues has been identified, primarily as a result of molecular genetic and biochemical genomics-based approaches in the model organisms Arabidopsis thaliana and Synechocystis sp. PCC6803. Mutant analysis and transgenic studies in these and other systems have provided important insight into the regulation, activities, integration, and evolution of individual enzymes and are already providing a knowledge base for breeding and transgenic approaches to modify the types and levels of these important compounds in agricultural crops.

Patterns of protein oxidation in Arabidopsis seeds and during germination

Increased cellular levels of reactive oxygen species are known to occur during seed development and germination, but the consequences in terms of protein degradation are poorly characterized. In this work, protein carbonylation, which is an irreversible oxidation process leading to a loss of function of the modified proteins, has been analyzed by a proteomic approach during the first stages of Arabidopsis (Arabidopsis thaliana) seed germination. In the dry mature seeds, the legumin-type globulins (12S cruciferins) were the major targets. However, the acidic alpha-cruciferin subunits were carbonylated to a much higher extent than the basic (beta) ones, consistent with a model in which the beta-subunits are buried within the cruciferin molecules and the alpha-subunits are more exposed to the outside. During imbibition, various carbonylated proteins accumulated. This oxidation damage was not evenly distributed among seed proteins and targeted specific proteins as glycolytic enzymes, mitochondrial ATP synthase, chloroplastic ribulose bisphosphate carboxylase large chain, aldose reductase, methionine synthase, translation factors, and several molecular chaperones. Although accumulation of carbonylated proteins is usually considered in the context of aging in a variety of model systems, this was clearly not the case for the Arabidopsis seeds since they germinated at a high rate and yielded vigorous plantlets. The results indicate that the observed specific changes in protein carbonylation patterns are probably required for counteracting and/or utilizing the production of reactive oxygen species caused by recovery of metabolic activity in the germinating seeds.

1H magnetization transfer in hydrated gluten and flour: effects of wheat aging

The interaction of water with flour or gluten in hydrated samples was investigated by proton magnetization transfer measurements. Flour and gluten from both durum and bread wheat seeds, either unaged or artificially aged over different periods of time, were investigated. Measurements were performed at several radio frequency power levels and frequency offsets, and the data were quantitatively modeled by two interacting pools, a liquid (water) and a solid (macromolecules) one. A super-Lorentzian line shape well described the magnetization of the solid pool. Magnetization transfer was found to be more efficient for flour with respect to gluten samples, in agreement with their hydrophilic/hydrophobic behavior. The aging treatment of seeds resulted in a minor degree of interaction between macromolecules and water.