Triacontanol modulates photosynthesis and osmoprotectants in canola (Brassica napus L.) under saline stress

Abstract

An experiment was conducted to assess the effect of pre-sowing seed treatment with triacontanol (TRIA) in canola (Brassica napus L.) cultivar (RBN-3060) under saline stress. Canola seeds were soaked in three levels of TRIA (0, 0.5, and 1 mg L^?1) for 12 hours. Three levels of salt stress (0, 100, and 150 mM NaCl) in full strength Hoagland's nutrient solution were applied to 56-days-old plants. Salt stress caused a significant reduction in growth, gas exchange, photochemical quenching (qP), and shoot and root K⁺ contents, while increased leaf glycine betaine, free proline, and shoot Na⁺ contents. Pre-sowing seed treatment with TRIA increased shoot fresh weight, number of seeds per plant, photosynthetic rate, transpiration rate, ratio of chlorophyll a/b, qP, electron transport rate, shoot and root K⁺ contents, and free proline and glycine betaine contents of canola plants at various TRIA levels under nonsaline or saline conditions.     

Genome-wide association study for frost tolerance in canola (Brassica napus L.) under field conditions

Journal of Plant Biochemistry and Biotechnology - Canola growers in the North Central Region of the United States and Canada are highly concerned about possible early frost. Plants can be killed...     

BnFAD2、BnFAD3和BnFATB基因的共干扰对油菜种子脂肪酸组分的影响

甘蓝型油菜是一种重要的油料作物,为了改良其种子脂肪酸组分,提升其经济价值,本研究分析了油菜种子发育时期脂肪酸合成积累模式及BnFAD2、BnFAD3、BnFATB基因的表达规律,认为这3个基因在种子发育中后期(授粉后25d起)的高效表达对油酸合成积累有着重要影响。通过Napin启动子诱导对油菜植株中BnFAD2、BnFAD3、BnFATB基因进行RNAi共干扰抑制,以达到提升油酸含量的目的。试验结果表明,转基因油菜种子中BnFAD2、BnFAD3、BnFATB基因的表达受到强烈抑制,种子中油酸含量由66.76%提升至82.98%,且油脂合成的相关基因同步出现表达上调。     

Phytohormone production and colonization of canola (Brassica napus L.) roots by Pseudomonas fluorescens 6-8 under gnotobiotic conditions

Pseudomonas fluorescens 6-8, a rhizosphere isolate previously shown to enhance root elongation of canola ( Brassica napus L.), was characterized for its ability to produce indole-3-acetic acid and cytokinins in pure culture and in the rhizosphere of canola under gnotobiotic conditions in comparison with the cytokinin-producing strain P. fluorescens G20-18 and its mutant CNT2. Strain 6-8 produced isopentenyl adenosine, zeatin riboside, and dihydroxyzeatin riboside at levels similar to those of G20-18, but only very low concentrations of indole-3-acetic acid. In a gnotobiotic assay canola inoculated with 6-8 and G20-18 had higher concentrations of isopentenyl adenosine and zeatin riboside in the rhizosphere and greater root length than the noninoculated control. The ability of strain 6-8 to colonize canola roots was assessed following transformation with the green fluorescent protein and inoculation onto canola seed in a gnotobiotic assay. Higher populations of strain 6-8 were observed on the proximal region of the root closest to the seed than on the mid and distal portions 9?days after seed inoculation. The ability of P. fluorescens 6-8 to produce cytokinins, colonize the roots of canola seedlings, and enhance root elongation may contribute to its ability to survive in the rhizosphere and may benefit seedling growth.     

Water use dynamics of dryland canola (Brassica napus L.) grown on contrasting soils under elevated CO2

Plant and Soil - Increasing atmospheric carbon dioxide concentration ([CO2]) stimulates the leaf-level (intrinsic) water use efficiency (iWUE), which may mitigate the adverse effects of drought by...     

Diversity of root-associated bacteria associated with field-grown canola (Brassica napus L.) and wheat (Triticum aestivum L.)

Little is known about the composition and diversity of the bacterial community associated with plant roots. The purpose of this study was to investigate the diversity of bacteria associated with the roots of canola plants grown at three field locations in Saskatchewan, Canada. Over 300 rhizoplane and 220 endophytic bacteria were randomly selected from agar-solidified trypticase soy broth, and identified using fatty acid methyl ester (FAME) profiles. Based on FAME profiles, 18 bacterial genera were identified with a similarity index >0.3, but 73% of the identified isolates belonged to four genera: Bacillus (29%), Flavobacterium (12%), Micrococcus (20%) and Rathayibacter (12%). The endophytic community had a lower Shannon-Weaver diversity index (1.35) compared to the rhizoplane (2.15), and a higher proportion of Bacillus, Flavobacterium, Micrococcus and Rathayibacter genera compared to rhizoplane populations. Genera identified in the endophytic isolates were also found in the rhizoplane isolates. Furthermore, principal component analysis indicated three clusters of bacteria regardless of their site of origin, i.e., rhizoplane or endophytic. In addition, the rhizoplane communities of canola and wheat grown at the same site differed significantly. These results indicate that diverse groups of bacteria are associated with field-grown plants and that endophytes are a subset of the rhizoplane community.     

Synergistic effects of drought and ascorbic acid on growth,mineral nutrients and oxidative defense system in canola (Brassica napus L.) plants

A study was conducted to find out the role of ascorbic acid (AsA) in modulating growth and different physio-biochemical attributes of canola plants under well-watered as well as water-deficit conditions. Drought stress imposed on 60 % field capacity significantly decreased the shoot and root fresh and dry weights, leaf chlorophyll contents, shoot and root P, root K⁺, and activity of CAT enzyme, while increased chlorophyll a/b contents, MDA, NPQ, leaf total phenolics, free proline and GB contents in both canola cultivars. Foliar-applied varying levels (50, 100 and 150 mg L^?1) of AsA enhanced shoot and root fresh and root dry weights, qN, NPQ, shoot and root P, AsA as well as the activity of POD enzyme particularly under drought stress conditions. Of both canola cultivars, cv. Dunkeld was higher in shoot fresh weights, ETR and F _v /F _m, MDA, proline and GB contents, and POD activity, however, cv. Cyclone in total phenolics and qN under well-watered and water-deficit conditions. Overall, the foliar-applied AsA had a positive effect, though not marked, on salt sensitive cv. Cyclone in terms of improved growth and other attributes, whereas exogenously applied AsA had a non-significant effect on relatively salt tolerant cv. Dunkeld.     

Genetic and physical mapping of flowering time loci in canola (Brassica napus L.)

We identified quantitative trait loci (QTL) underlying variation for flowering time in a doubled haploid (DH) population of vernalisation—responsive canola (Brassica napus L.) cultivars Skipton and Ag-Spectrum and aligned them with physical map positions of predicted flowering genes from the Brassica rapa genome. Significant genetic variation in flowering time and response to vernalisation were observed among the DH lines from Skipton/Ag-Spectrum. A molecular linkage map was generated comprising 674 simple sequence repeat, sequence-related amplified polymorphism, sequence characterised amplified region, Diversity Array Technology, and candidate gene based markers loci. QTL analysis indicated that flowering time is a complex trait and is controlled by at least 20 loci, localised on ten different chromosomes. These loci each accounted for between 2.4 and 28.6 % of the total genotypic variation for first flowering and response to vernalisation. However, identification of consistent QTL was found to be dependant upon growing environments. We compared the locations of QTL with the physical positions of predicted flowering time genes located on the sequenced genome of B. rapa. Some QTL associated with flowering time on A02, A03, A07, and C06 may represent homologues of known flowering time genes in Arabidopsis; VERNALISATION INSENSITIVE 3, APETALA1, CAULIFLOWER, FLOWERING LOCUS C, FLOWERING LOCUS T, CURLY LEAF, SHORT VEGETATIVE PHASE, GA3 OXIDASE, and LEAFY. Identification of the chromosomal location and effect of the genes influencing flowering time may hasten the development of canola varieties having an optimal time for flowering in target environments such as for low rainfall areas, via marker-assisted selection.     

Chelate-assisted phytoextraction using canola (Brassica napus L.) in outdoors pot and lysimeter experiments

Phytoextraction is an emerging technology for non-destructive remediation of heavy metal-polluted soils. This study was conducted to test chelate-assisted phytoextraction of Cu, Pb and Zn using EDTA and canola (Brassica napus L. cv. Petranova) on a moderately polluted industrial soil (loamy sand) in the sub-continental climate of Eastern Austria. The effects of the rate (up to 2.1 g kg^–1 soil) and mode (single versus split) of EDTA application on the biomass, water contents and metal concentrations in shoots and roots were investigated along with changes of metal lability in soil and leaching from the root zone in parallel outdoors pot and lysimeter experiments. Labile (1 M NH₄NO₃-extractable) metal concentrations in soil increased considerably upon application of EDTA, indicating enhanced phytoavailability. However, this was also associated with enormously increased metal concentrations in the leachates collected below the root zone. Enhanced metal labilities and leachate concentrations persisted for more than 1 year after harvest. Metal lability was more enhanced by EDTA in rhizosphere relative to bulk soil, indicating interactions of EDTA with root activities. Shoot biomass and water contents of canola were virtually unaffected by EDTA, revealing that canola can tolerate excessive metal concentrations in soil pore water. Metal concentrations in shoots were increased considerably, but were insufficient to obtain reasonable extraction rates. Split applications were generally more effective than the same amounts of EDTA added at once. Metal concentrations in roots decreased after each application of EDTA, possibly indicating metal removal from roots by free protonated EDTA, but increased again within several days. As the application of chelate-assisted phytoextraction is limited by the risk of groundwater pollution, further work should focus on natural, continuous phytoextraction technologies.     

Identification and characterization of CBL and CIPK gene families in canola (Brassica napus L.)

Background

Canola (Brassica napus L.) is one of the most important oil-producing crops in China and worldwide. The yield and quality of canola is frequently threatened by environmental stresses including drought, cold and high salinity. Calcium is a ubiquitous intracellular secondary messenger in plants. Calcineurin B-like proteins (CBLs) are Ca²⁺ sensors and regulate a group of Ser/Thr protein kinases called CBL-interacting protein kinases (CIPKs). Although the CBL-CIPK network has been demonstrated to play crucial roles in plant development and responses to various environmental stresses in Arabidopsis, little is known about their function in canola.

Results

In the present study, we identified seven CBL and 23 CIPK genes from canola by database mining and cloning of cDNA sequences of six CBLs and 17 CIPKs. Phylogenetic analysis of CBL and CIPK gene families across a variety of species suggested genome duplication and diversification. The subcellular localization of three BnaCBLs and two BnaCIPKs were determined using green fluorescence protein (GFP) as the reporter. We also demonstrated interactions between six BnaCBLs and 17 BnaCIPKs using yeast two-hybrid assay, and a subset of interactions were further confirmed by bimolecular fluorescence complementation (BiFC). Furthermore, the expression levels of six selected BnaCBL and 12 BnaCIPK genes in response to salt, drought, cold, heat, ABA, methyl viologen (MV) and low potassium were examined by quantitative RT-PCR and these CBL or CIPK genes were found to respond to multiple stimuli, suggesting that the canola CBL-CIPK network may be a point of convergence for several different signaling pathways. We also performed a comparison of interaction patterns and expression profiles of CBL and CIPK in Arabidospsis, canola and rice, to examine the differences between orthologs, highlighting the importance of studying CBL-CIPK in canola as a prerequisite for improvement of this crop.

Conclusions

Our findings indicate that CBL and CIPK family members may form a dynamic complex to respond to different abiotic or hormone signaling. Our comparative analyses of the CBL-CIPK network between canola, Arabidopsis and rice highlight functional differences and the necessity to study CBL-CIPK gene functions in canola. Our data constitute a valuable resource for CBL and CPK genomics.     

Confirmation of QTL controlling seed yield in spring canola (Brassica napus L.) hybrids

Allelic effects observed in QTL discovery experiments must be confirmed to be useful in subsequent breeding efforts. Two QTL affecting seed yield of spring hybrid canola (Brassica napus L.) were previously identified in two populations of inbred backcross lines (IBLs) containing germplasm introgressed from a winter cultivar. The effects of favorable alleles at these QTL were retested by crossing two selected IBLs (M5 and M31) to three spring canola lines having different genetic backgrounds. Doubled haploid (DH) lines derived from each F₁ were genotyped with RFLP markers flanking the QTL and grouped into the four possible QTL genotypes. For the first field experiment, DH lines derived by crossing the M5 line to one spring line were crossed to two female testers and evaluated as individual testcross progenies in one environment. QTL genotypes had large variances and were not significantly different. A second field experiment was conducted using the DH lines from the first experiment and two other sets of DH lines derived from the M31 line crossed to two different spring canola lines. Individual lines within each QTL genotype of each set were bulked and crossed to the same testers used in Experiment 1. Bulked hybrid seeds of each QTL genotype were planted in a split-split plot randomized block design and 12 replicates. QTL genotypes had smaller variances in this experiment, and the effects of one QTL were confirmed in some genetic backgrounds. These results suggest that bulking of QTL genotypes and use of an appropriate experimental design with many replicates are needed to detect small differences between QTL genotypes.     

Isolation and characterization of ACC deaminase-producing fluorescent pseudomonads, to alleviate salinity stress on canola (Brassica napus L.) growth

Salinity stress is of great importance in arid and semi-arid areas of the world due to its impact in reducing crop yield. Under salinity stress, the amount of 1-aminocyclopropane-1-carboxylate (ACC), a precursor for ethylene production in plants, increases. Here, we conducted research under the hypothesis that isolated ACC deaminase-producing Pseudomonas fluorescens and Pseudomonas putida can alleviate the stressful effects of salinity on canola (Brassica napus L.) growth. The experiments were conducted in the Soil and Water Research Institute, Tehran, Iran. Seven experimental stages were conducted to isolate and characterize ACC deaminase-producing Pseudomonas fluorescens strains and to determine factors enhancing their growth and, consequently, their effects on the germination of canola seeds. Under salinity stress, in 14% of the isolates, ACC deaminase activity was observed, indicating that they were able to utilize ACC as the sole N-source. Bacterial strains differed in their ability to synthesize auxin and hydrogen cyanide compounds, as well as in their ACC deaminase activity. Under salinity stress, the rate of germinating seeds inoculated with the strains of ACC deaminase-producing Pseudomonas fluorescens and Pseudomonas putida, and seedling growth was significantly higher. These results indicate the significance of soil biological activities, including the activities of plant growth-promoting bacteria, in the alleviation of soil stresses such as salinity on plant growth.     

Extent and structure of linkage disequilibrium in canola quality winter rapeseed (Brassica napus L.)

Linkage disequilibrium was investigated in canola quality winter rapeseed to analyze (1) the prospects for whole-genome association analyses and (2) the impact of the recent breeding history of rapeseed on linkage disequilibrium. A total of 845 mapped AFLP markers with allele frequencies ≥0.1 were used for the analysis of linkage disequilibrium in a population of 85 canola quality winter rapeseed genotypes. A low overall level of linkage disequilibrium was found with a mean r ² of only 0.027 over all 356,590 possible marker pairs. At a significance threshold of P = 2.8 × 10⁻⁷, which was derived by a Bonferroni correction from a global α-level of 0.1, only 0.78% of the marker pairs were in significant linkage disequilibrium. Among physically linked marker pairs, the level of linkage disequilibrium was about five times higher with more than 10% of marker pairs in significant linkage disequilibrium. Linkage disequilibrium decayed rapidly with distance between linked markers with high levels of linkage disequilibrium extending only for about 2 cM. Owing to the rapid decay of linkage disequilibrium with distance association analyses in canola quality rapeseed will have a significantly higher resolution than QTL analyses in segregating populations by interval mapping, but much larger number of markers will be necessary to cover the whole genome. A major impact of the recent breeding history of rapeseed on linkage disequilibrium could not be observed.     

The effect of abscisic acid on the growth and storage of germinating rape (Brassica napus L.) seed dried following selection on the basis of a newly-emerged radicle

Abscisic acid at 1 × 10^–4M concentration controlled the progress of the emerging radicle from germinating rape seeds and apparently restricted it to the dehydration tolerant phase. ABA treatment during germination followed by washing reduced the deleterious effects of drying the seeds following selection based on a newly-emerged radicle. Furthermore, the longevity of these low-moisture-content germinating seeds at a range of temperatures was improved by the ABA treatment. The viability of the treated seeds stored at –20°C was maintained for up to 100 days.     

Preliminary studies on the effects of 4-chlorophenoxyacetic acid on the senescence and dehiscence of pods in oil seed rape (Brassica napus L.)

The auxin 4-chlorophenoxyacetic acid (4-CPA) has been found to delay the maturation and dehiscence of the pods of oil seed rape. Dipping pods in solutions of 500 gl^–1, 4-CPA, 36 and 39 days after anthesis delayed significantly the autolysis of the thin-walled parenchyma of the dehiscence zones, the senescence of the pod walls and the loss of water from the pod walls and seeds. Increases in both the fresh and dry weights of both pod walls and seeds were recorded in the treated pods as compared with controls.     

Genetic control of linolenic acid concentration in seed oil of rapeseed (Brassica napus L.)

Summary Results from a diallel mating of two rapeseed lines with distinctly different linolenic acid concentration show that this trait is mainly under control of nuclear genes of the embryo. However, significant differences in reciprocal F₁, BC₁ and BC₂ indicate maternal control, which is realized by interaction between maternal genotype and nuclear genes of the embryo. Additionally, temperature exerts considerable influence on the degree of maternal control. Since no reciprocal differences are detectable in F₂, cytoplasmic factors seem not to be involved in the inheritance of linolenic acid concentration. Hypotheses on the physiological nature of maternal control of this trait are discussed.     

Effects of sowing time and plant age on critical nitrogen concentrations in canola (Brassica napus L.)

Critical concentrations of NO₃-N in fresh petiole tissue and total N in the dried lamina were determined for the youngest mature leaf (YML) of field-grown canola. For dry matter yield of canola sown on 4 May, critical NO₃-N concentration in the YML petiole at the rosette stage (RS) was 1.46 mg/g fresh wt. At the flower-buds-visible stage (BV) it was 0.45 mg/g fresh wt. For seed yield the values were 1.72 and 0.53 mg/g fresh wt. Critical total N concentration in the YML lamina for dry matter yield were 69 mg/g dry wt. at RS and 57 at BV. For seed yield they were 71 and 59 mg/g dry wt. Critical NO₃-N concentrations in the YML petiole of canola sown on 30 May were reduced by 50%; critical total-N concentrations in the YML lamina were not reduced to the same extent. Despite the reductions in critical N concentrations in the YML, critical N fertilizer rates for vegetative growth and seed yield were unaffected by sowing date or plant growth stage.     

Gene transfer between canola (Brassica napus L. and B. campestris L.) and related weed species

Brassica species are particularly receptive to gene transformation techniques. There now exists canola genotypes with transgenic herbicide resistance for glyphosate, imidazolinone, sulfonylurea and glufosinate herbicides. The main concern of introducing such herbicide resistance into commercial agriculture is the introgression of the engineered gene to related weed species. The potential of gene transfer between canola (Brassica napus and B. campestris) and related weed species was determined by hand pollination under controlled greenhouse conditions. Canola was used as both male and female parent in crosses to the related weed species collected in the Inland Northwest region of the United States. Weed species used included: field mustard (B. rapa), wild mustard (S. arvensis) and black mustard (B. nigra). Biological and cytological aspects necessary for successful hybrid seed production were investigated including: pollen germination on the stigma; pollen tube growth down the style; attraction of pollen tubes to the ovule; ovule fertilisation; embryo and endosperm developmental stages. Pollen germination was observed in all 25 hybrid combinations. Pollen tubes were found in the ovary of over 80% of combinations. About 30% of the hybrid combinations developed to the heart stage of embryo development or further. In an additional study involving transgenic glufosinate herbicide resistant B. napus and field mustard it was found that hybrids occurred with relatively high frequency, hybrids exhibited glufosinate herbicide resistance and a small proportion of hybrids produced self fertile seeds. These fertile plants were found to backcross to either canola or weed parent.     

Interaction of salicylic acid and ethylene and their effects on some physiological and biochemical parameters in canola plants (Brassica napus L.)

Environmental stresses, such as cold, heat, salinity, and drought, induce ethylene production and oxidative stress and cause damage in plants. On the other hand, studies have shown that salicylic acid (SA) induced resistance to environmental stresses in plants. In this research, the effects of ethylene on chlorophyll (Chl), carotenoid (Car), anthocyanin, flavonoids, ascorbic acid, dehydroascorbic acid, total ascorbate, lipid peroxidation, and ethylene production in leaves of canola pretreated with SA were studied. The plants were grown in pots until they have four leaves. Leaves were sprayed for two days with three different concentrations of SA (0, 0.5, and 1 mM). The plants were treated for three days with three concentrations of ethylene (0, 50, and 100 ppm). At the end of the ethylene treatments, all examined parameters were measured. The results showed that the ethylene treatments induced lipid peroxidation, while SA mitigated this effect. The ethylene treatment lowered significantly Chl and Car contents and anthocyanin accumulation, but SA alleviated these effects. SA induced an increase in ascorbic acid content in canola plants after the ethylene treatments. Therefore, we concluded that SA played an important role in the alleviation of damages caused by stress conditions.