Elevating the yield and altering the composition of seed tocopherols (Toc’s) are important to rapeseed breeding and production. However, little is known about the biosynthesis of Toc’s in response to environmental signals. In this study, we investigated the effects of exogenous gibberellin (GA3) and paclobutrazol (PAC) on Toc biosynthesis. We also explored the interactive effects between the two plant growth regulators (PGRs) and other factors, such as PGR treatment duration, genotype, and growing location on the total Toc yield and composition in oilseed rape seed. GA3 significantly enhanced the production of Toc’s and elevated the α-/γ-Toc ratio in a time- and genotype-dependent manner. By contrast, PAC significantly reduced Toc yield. Genotypic differences were observed in the effects of GA3 on Toc yield and composition in the seeds. GA3 significantly increased the Toc yield and α-/γ-Toc ratio in Zheyou-50, a genotype with a low proportion of very long chain fatty acids (VLCFAs). However, GA3 did not significantly influence these parameters in Jiu-Er-13Xi, a genotype with a high VLCFA proportion. The increased Toc yield induced by GA3 was mediated by the upregulation of genes (BnPDS1 and BnVTE1) that catalyze the production of Toc precursors. Therefore, applying GA3 can improve rapeseed quality by increasing Toc yield and improving Toc composition.

Yellow-seeded (YS) rapeseed varieties have attracted considerable interests from cultivators because of their thin seed coat and high seed oil content. However, compared with black-seeded (BS) rapeseed, little is known about the response of YS rapeseed to abiotic stresses. In this study, we characterized the cellular structures of YS varieties and BS varieties and the physiological parameters of the YS and BS seedlings subjected to high-salt and/or high-cadmium conditions. We observed larger and denser (in arrangement) oilbodies in YS than in BS varieties. The BS variety seed coat was much thicker than that of the YS variety because of the existence of a palisade layer where pigments are deposited. Either at the eighth day or 1 month after sowing, YS seedlings showed higher sensitivity to NaCl and/or CdCl2 stress than BS seedlings, as reflected by the length of roots, biomass, and a variety of physiological parameters, including MDA, chlorophyll content, and antioxidant activities. Our results suggested that the more vigorous growth of BS seedlings is likely due to the higher flavonoid content in their vegetative tissues, and the poor performance of YS seedlings under stress treatment (especially with NaCl) could be attributed to its relatively low flavonoid content. Our findings raise some points that need further investigation to obtain an in-depth understanding of the molecular mechanisms involved.

To assess the potential role of salicylic acid (SA) in plants under cadmium (Cd) stress, a study was conducted on three different oilseed rape (Brassica napus) genotypes. Gas exchange parameters, photosynthetic pigments, antioxidant enzymes activities, mineral nutrients concentration, and ultrastructural analysis were carried out for assessment. Interestingly, cadmium treatment reduced gas exchange parameters, photosynthetic pigments, mineral elements [calcium (Ca), magnesium (Mg), and iron] and the activity of catalase (CAT) enzyme. Whereas, a pronounced increase was observed in malondialdehyde content and antioxidant enzymes, cadmium and zinc accumulation. Impressively, SA played its role as an alleviatory agent by reducing the damage to all parameters caused by Cd except internal CO2 concentration which was further decreased by SA. Even more, Cd and SA showed synergistic effects by increasing superoxide dismutase, peroxidases, ascorbate peroxidase, guaiacol peroxidase, glutathione reductase and decreasing CAT. Apart from affecting the enzyme activities of oilseed rape, both Cd and SA had the same inhibitory effects on Ca and Mg concentrations. Damage caused by Cd to chloroplast and other internal organelles were almost rectified by SA. Effective role of SA, in alleviating Cd toxicity, could be attributed to the SA-induced improvement of photosynthetic activities, enhancement of antioxidant enzymes activities, reduction in lipid peroxidation and Cd uptake. These findings reflect the possible role of SA as a potential inhibitor of cadmium toxicity by strengthening the internal immunity in oilseed rape.

Tocopherols (Tocs) are vital scavengers of reactive oxygen species (ROS) and important seed oil quality indicators. Nitrogen (N) is one of the most important fertilizers in promoting biomass and grain yield in crop production. However, the effect of different sources and application rates of N on seed Toc contents in oilseed rape is poorly understood. In this study, pot trials were conducted to evaluate the effect of two sources of N fertilizer (urea and ammonium nitrate). Each source was applied to five oilseed rape genotypes (Zheshuang 72, Jiu-Er-1358, Zheshuang 758, Shiralee, and Pakola) at three different application rates (0.41 g/pot (N1), 0.81 g/pot (N2), and 1.20 g/pot (N3)). Results indicated that urea increased α-, γ-, and total Toc (T-Toc) more than did ammonium nitrate. N3 was proven as the most efficient application rate, which yielded high contents of γ-Toc and T-Toc. Highly significant correlations were observed between Toc isomers, T-Toc, and α-/γ-Toc ratio. These results clearly demonstrate that N sources and application rates significantly affect seed Toc contents in oilseed rape.

Tocopherols are lipophilic molecules, ubiquitously synthesized in all photosynthetic organisms. Being a group of vitamin E compounds, they play an essential role in human nutrition and health. Despite their structural and functional attributes as important antioxidants in plants, it would be misleading to ignore the potential roles of tocopherols beyond their antioxidant properties in planta. Detailed characterization of mutants and transgenic plants, including Arabidopsis (vte1, vte2, vte4, and so on), maize (sxd1) mutants, and transgenic potato and tobacco lines altered in tocopherol biosynthesis and contents, has led to surprising outcomes regarding the additional functions of these molecules. Thus, the aim of this review is to highlight the past and present research findings on tocopherols’ structural, biosynthesis, and functional properties in plants. Special emphasis is given to their suggested functions in planta, such as cell signaling, hormonal interactions, and coordinated response of tocopherols to other antioxidants under abiotic stresses. Moreover, some important questions about possible new functions of tocopherols will be discussed as future prospects to stimulate further research.

To date, little is known about the correlations among the tocopherol (T) and fatty acid (FA) components in rapeseed oils. In the current study, a germplasm collection of landraces from the species Brassica juncea, Brassica rapa, and Brassica napus and a collection of low erucic acid (EA) breeding lines from B. napus were analyzed for FA and T contents. In the groups comprising landraces, the most notable correlation was the significantly positive one between α-T and the sum of C18:1 and C18:2, whereas neither positive correlations were found between α-T and C18:3 nor were positive correlations observed between α-T and very long chain FAs (VLCFA). Hardly any association between γ-T and FA components was observed, indicating the possible function of α-T beyond its antioxidant property. The complexity of correlation between T and FA components in Brassica oils may arise from the role of α-T in the FA metabolism of endoplasmic reticulum (ER).

Arabidopsis seeds accumulate considerable fatty acids (FA/s) from embryo until maturity. The environmental stimuli and the regulatory factors that determine FA accumulation, however, remain unclear. In this study, we investigated the role of DELLAs, the negative regulatory factors in the gibberellin transduction pathway, in seed oil formation in Arabidopsis. Seed morphology, weight-per-thousand seeds, oil content, and FA composition were compared among the seeds of the DELLAga1-3 rga-t2 rgl2-1 (triple), ga1-3 rga-t2 rgl1-1rgl2-1 (quadruple), ga1-3 gai-t6 rga-t2 rgl1-1 rgl 2-1 (penta), and wild type (WT), Landsberg erecta (Ler). Significant differences between the WT and the penta mutant for the above traits were observed. Compared with WT, the penta seeds were characterized by a decrease of 22 % seed oil in term of μg/mg, an increment of 10 % seed oil in term of FA/seed, and an alteration of FA composition. In general, the dynamics of FA accumulation in the penta and WT developing seeds (2–16 days after anthesis, DAA) were not obviously different. However, there was higher FA accumulation in penta seeds from 6 DAA compared with WT. RNA gel blotting indicated that the fatty acid desaturase genes were expressed in seeds as well as in leaves. The different transcript levels of the genes between the penta mutant and WT unveiled a part of the reasons accounting for the differences observed. To our knowledge, this is the first report on the effect of DELLAs on the dynamic process of seed oil formation of a flowering plant.

Seed oil production in oilseed rape is greatly affected by the temperature during seed maturation. However, the molecular mechanism of the interaction between genotype and temperature in seed maturation remains largely unknown. We developed two near-isogenic lines (NIL-9 and NIL-1), differing mainly at a QTL region influencing oil content on Brassica napus chromosome C2 (qOC.C2.2) under high temperature during seed maturation. The NILs were treated under different temperatures in a growth chamber after flowering. RNA from developing seeds was extracted on the 25th day after flowering (DAF), and transcriptomes were determined by microarray analysis. Statistical analysis indicated that genotype, temperature, and the interaction between genotype and temperature (G × T) all significantly affected the expression of the genes in the 25 DAF seeds, resulting in 4,982, 19,111, and 839 differentially expressed unisequences, respectively. NIL-9 had higher seed oil content than NIL-1 under all of the temperatures in the experiments, especially at high temperatures. A total of 39 genes, among which six are located at qOC.C2.2, were differentially expressed among the NILs regardless of temperature, indicating the core genetic divergence that was unaffected by temperature. Increasing the temperature caused a reduction in seed oil content that was accompanied by the downregulation of a number of genes associated with red light response, photosynthesis, response to gibberellic acid stimulus, and translational elongation, as well as several genes of importance in the lipid metabolism pathway. These results contribute to our knowledge of the molecular nature of QTLs and the interaction between genotype and temperature.

Knowledge about the genes implicated in lipid biosynthesis acquired from the model plant Arabidopsis is useful in understanding the formation of seed oil in Brassica oilseeds. In this paper, we report the screening of polymorphic markers at the loci putative for the seed oil formation between two geographically different genotypes: the Chinese cultivar Ningyou-7 and the European cultivar Tapidor. These primer pairs (150) were designed based on 75 Brassica genes that were Arabidopsis orthologues implicated in the oil formation. A total of 52 out of the 150 primer pairs associated with 47 of the 75 genes showed polymorphisms between the two genotypes. The type of polymorphisms that could be detected on capillary electrophoresis images and their respective visual futures are described. Further, we selected 34 polymorphic markers to scan allelic variations and found rich DNA polymorphisms among the 54 Brassica oilseed cultivars. On the average, each primer pair resulted in 5.6 alleles at the region that was covered. The correlation between the alleles and seed quality traits revealed that the alleles of BnFAD7 were related to the variation of linolenic acid (C18:3) contents among the cultivars. The allele FAD7-ics11170 (3/4)-b that was significantly correlated with high linolenic acid content can be used as an efficient marker for the selection of breeding materials with high linolenic acid content.

The genomic era provides new perspectives in understanding polyploidy evolution, mostly on the genome-wide scale. In this paper, we show the sequence and expression divergence between the homologous ALCATRAZ (ALC) loci in Brassica napus, responsible for silique dehiscence. We cloned two homologous ALC loci, namely BnaC.ALC.a and BnaA.ALC.a in B. napus. Driven by the 35S promoter, both the loci complemented to the alc mutation of Arabidopsis thaliana, yet only the expression of BnaC.ALC.a was detectable in the siliques of B. napus. Sequence alignment indicated that BnaC.ALC.a and BolC.ALC.a, or BnaA.ALC.a and BraA.ALC.a, possess a high level of similarity. The understanding of the sequence and expression divergence among homologous loci of a gene is of due importance for an effective gene manipulation and TILLING (or ECOTILLING) analysis for the allelic DNA variation at a given locus.

The oilseed rape plant’s transition from the vegetative to the reproductive stage is important to its yield. This transition is controlled by a large group of flowering time genes that respond to environmental and endogenous cues. The role of jasmonates in flowering is almost unknown in Brassicaceae, even in the genus Arabidopsis. In this paper, the clear effect of exogenous methyl jasmonate (MeJA) on the flowering time, floral organ morphology, and transcript levels of a group of genes implicated in floral development is shown. In controlled greenhouse experiments, we found that the effect of MeJA depended on both plant genotype and jasmonate dosage. MeJA promoted maximum flowering when it was applied to the cultivars of early flowering types of oilseed rape, such as cultivars Mei-Jian and Fu-You 4. In addition, a concentration of 100 μM resulted in the most number of early open flowers, in comparison with the results obtained for concentrations of 50 and 80 μM. Furthermore, the application of high concentrations of MeJA (100 μM) also produced various kinds of abnormal flowers. Our results demonstrated that the combined actions of the floral identity genes, specifically BnAP1, BnAP2, BnAP3, BnAG1, and BnPI3, as reflected by their respective relative transcript levels, were responsible for causing the different kinds of flower abnormalities previously undescribed in oilseed rape. We expect our assay to be an enriching addition to the body of work that attempts to understand the signaling function of jasmonates in the floral inductive pathway.

Because of its prolific growth, oilseed rape (Brassica napus L.) can be grown advantageously for phytoremediation of the lands contaminated by industrial wastes. Therefore, toxic effect of cadmium on the germination of oilseed rape, the capability of plants for cadmium phytoextraction, and the effect of exogenous application of plant growth regulators to mitigate phytotoxicity of cadmium were investigated. For the lab study of seedlings at early stage, seeds were grown on filter papers soaked in different solutions of Cd2+ (0, 10, 50, 100, 200 and 400 μM). In greenhouse study, seedlings were grown in soil for 8 weeks, transferred to hydroponic pots for another 6 weeks growth, and then treated with plant growth regulators and cadmium. Four plant growth regulators viz. jasmonic acid (12.5 μM), abscisic acid (10 μM), gibberellin (50 μM) and salicylic acid (50 μM); and three levels of Cd2+ (0, 50 and 100 μM) were applied. Data indicated that lower concentration of Cd2+ (10 μM) promoted the root growth, whereas the severe stresses (200 or 400 μM) had negative effect on the establishment of germinating seedlings. Plants treated with any of the tested plant growth regulators alleviated cadmium toxicity symptoms, which were reflected by more fresh weight, less malondialdehyde concentration in leaves and lower antioxidant enzyme activities. The application of abscisic acid to the plants cultivated in the medium containing 100 μM Cd2+ resulted in significantly lower plant internal cadmium accumulation.

The variation among Chinese genotypes of Brassica napus L. for seed tocopherols content and their analysis using gas chromatography has not been comprehensively reported till to date. In the present study, the tocopherol contents of four Chinese genotypes of Brassica napus L., namely, Gaoyou 605, Zhejiang 619, Zheshuang 758, and Zheshuang 72, were evaluated using three modified sample preparation protocols (P1, P2, and P3) for tocopherol extraction. These methods were distinguished as follows. Protocol one (P1) included the evaporation of solvent after extraction without silylation. Protocol two (P2) followed the direct supernatant collection after overnight extraction without drying and silylation. Protocol three (P3) included trimethylsilylation with N, O-bis(trimethylsilyl) trifluoroacetamide. Genotypic comparison of tocopherol and its isoforms revealed that Gaoyou 605 was dominant over the other genotypes with (140.5±10.5), (316.2± 9.2), and (559.1± 24.3) μg g−1 of seed meal α-, γ-, and total (T-) tocopherol, respectively, and a 0.44±0.04 α- to γ-tocopherol ratio. The comparison of the sample preparation protocols, on the other hand, suggests that P3 is the most suitable method for the tocopherol extraction from Brassica oilseeds and for the analysis of tocopherols using gas chromatography flame ionization detector (GC-FID). Trimethylsilylation is the key step differentiating P3 from P1 and P2. Variations detected in tocopherol contents among the Chinese rapeseed (B. napus) genotypes signify the need to quantify a wide range of rapeseed germplasm for seed tocopherol dynamics in short and crop improvement in long.

The transition of a plant from vegetative to reproductive stage is controlled by a large group of genes, which respond to environmental and endogenous stimuli. Application of methyl jasmonate (MeJA) and gibberellins (GA3) to oilseed plants (Brassica napus L.) interrupts the delicate endogenous balance and results in various floral organ abnormalities. Exogenous MeJA or GA3 influences the transcriptome at the initial flowering stage in Arabidopsis, but the corresponding changes of transcriptome in floral tissues of oilseed rape remain unknown. In this study, cDNA-amplified fragment length polymorphism (cDNA-AFLP) was analyzed to identify genes whose expression was modulated by application of MeJA and GA3 to flower buds. A total of 2 787 cDNA fragments were counted using 64 primer pair combinations, and bands larger than 50 bp were compared among four treatments, namely, water control, MeJA (50 μmol L−1), MeJA (100 μmol L−1), and GA3 (50 μmol L−1). Overall, 168 transcript-derived fragments (TDFs) were differentially expressed among the treatments. The expression pattern of some TDFs was confirmed by semi-quantitative RT-PCR analysis, and a group of 106 differentially displayed TDFs was cloned and sequenced. Homologs of Arabidopsis genes were identified and classified into 12 functional categories. A total of 34, 39, and 24 TDFs were responsive to GA3, MeJA, and both GA3 and MeJA, respectively. This finding indicated that cross-talk between these two hormones may be involved in regulating flower development. This study provides potential target genes for manipulation in terms of flowering time and floral organ initiation, important agronomic traits of oilseed rape.

•The removal of DELLA repression resulted in earlier leaf senescence, whereas the enhancement of DELLA proteins retarded leaf senescence.•The removal or enhancement of DELLA proteins led to up- or downregulation of SAG12 and SAG29 during leaf senescence in the respective mutants.•The Q-DELLA/ga1-3 senescent leaves contained more sugar, but less chlorophyll and fatty acids than those of ga1-3 and WT.•Both absolute and relative contents of C18:3 in Q-DELLA/ga1-3 senescent leaves were lower than those in WT and ga1-3 leaves.•GA signaling upregulated certain genes on various hormone pathways, implicating its role upstream of these hormones in leaf senescence regulation.Leaf senescence is an integrated response of leaf cells to developmental age and various internal and environmental signals. However, the role of gibberellins (GA) in leaf senescence is not clear. In the current study, we investigated the effect of DELLA on leaf senescence. Compared with the wild type (WT), leaf senescence occurred earlier in the mutant ga1-3 gai-t6 rga-t2 rgl1-1 rgl2-1 (abbreviated as Q-DELLA/ga1-3) whose DELLA repression was removed, whereas leaf senescence was retarded in the mutant ga1-3 whose GA biosynthesis was blocked and whose DELLA proteins accumulated abnormally. During leaf senescence, SAG12 and SAG29 were upregulated in Q-DELLA/ga1-3 and downregulated in ga1-3 plants. The Q-DELLA/ga1-3 senescent leaves contained more sugar but less chlorophyll and fatty acids (FAs) than those of ga1-3 and WT. Both absolute and relative contents of C18:3 in Q-DELLA/ga1-3 senescent leaves were lower compared with those of the WT and ga1-3 leaves. The genes regulating FA β-oxidation in Q-DELLA/ga1-3, such as KAT2, LACS6, LACS7, ACX1, ACX2 and MAP2, were significantly upregulated. The removal of DELLA repression highly upregulated certain genes on various hormone pathways, suggesting that GA signaling acts upstream of the jasmonic acid, salicylic acid, and ethylene pathways in regulating leaf senescence.