ATP-sulfurylase activity,photosynthesis, and shoot dry mass of mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis> L.) cultivars differing in sulfur accumulation capacity

Sulfur (S) is an essential nutrient element required in a large quantity by mustard. S regulates photosynthesis and plant growth through improving nitrogen (N) acquisition. Mustard cultivars Alankar, Varuna, Pusa Jai Kisan, and SS2 differing in S accumulation capacity calculated as sulfate transport index (STI) were tested for ATP-sulfurylase activity, S and N accumulation, photosynthesis, and shoot dry mass (DM) at 30 and 60 d after sowing (DAS). The activity of ATP-sulfurylase, shoot N content, net photosynthetic rate (P _N), leaf area, and shoot DM of the cultivars were in the order: Pusa Jai Kisan>Alankar>Varuna>SS2. ATP-sulfurylase activity was strongly and positively correlated with P _N and shoot DM in all the cultivars. Hence ATP-sulfurylase activity may be used as a physiological trait for augmenting photosynthesis and shoot DM.     

Effects of irradiance on photosynthetic characteristics and growth of <Emphasis Type="Italic">Mosla chinensis</Emphasis> and <Emphasis Type="Italic">M. scabra</Emphasis>

Photosynthetic and growth characteristics of Mosla chinensis and M. scabra were compared at three irradiances similar to shaded forest understory, forest edge, and open land. At 25 % full ambient irradiance, M. chinensis and M. scabra had similar photosynthetic characteristics, but saturation irradiance, compensation irradiance, and apparent quantum yield of M. chinensis were higher than those of M. scabra at full ambient irradiance and 70 % full ambient irradiance. At the same irradiance treatment, specific leaf area and leaf area ratio of M. chinensis were lower than those of M. scabra. Photon-saturated photosynthetic rate and water use efficiency of M. chinensis, however, were not significantly higher than those of M. scabra, and the leaf area and total biomass were lower than those of M. scabra. As a sun-acclimated plant, the not enough high photosynthetic capacity and lower biomass accumulation may cause that M. chinensis has weak capability to extend its population and hence be concomitant in the community.     

Transgenic Indian mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis>) expressing tomato glucanase leads to arrested growth of <Emphasis Type="Italic">Alternaria brassicae</Emphasis>

Brassica juncea is an important oilseed crop of the Indian sub-continent. Yield loss due to fungal disease alternaria leaf spot caused by Alternaria brassicae is a serious problem in cultivation of this crop. Nonavailability of resistance genes within crossable germplasms of Brassica necessitates use of genetic engineering strategies to develop genetic resistance against this pathogen. The pathogenesis related (PR) proteins are group of plant proteins that are toxic to invading fungal pathogens, but are present in plant in trace amount. Thus, overexpression of PR proteins leads to increased resistance to pathogenic fungi in several crops. The PR protein glucanase hydrolyzes a major cell-wall component, glucan, of pathogenic fungi and acts as a plant defense barrier. We report the expression of a class I basic glucanase gene, under the control of CaMV 35S promoter, in Indian mustard and its genetic resistance against alternaria leaf spot. Southern and Northern hybridization confirmed stable integration and expression of the glucanase gene in mustard transgenics. Several independent transgenics were screened in vitro and under poly house conditions for their resistance against Alternaria brassicae. In an in vitro antifungal assay, transgenics arrested hyphal growth of Alternaria brassicae by 15-54%. Under pathogen-challenged conditions in poly house, the transgenics showed restricted number, size and spread of lesions caused by Alternaria brassicae. Also, the onset of disease was delayed in transgenics compared to untransformed parent plants. The results demonstrate potentiality of a PR protein from a heterologous source in developing alternaria leaf spot resistance in Indian mustard.     

Responses of dominant desert species <Emphasis Type="Italic">Artemisia ordosica</Emphasis> and <Emphasis Type="Italic">Salix psammophila</Emphasis> to water stress

Morphology, biomass accumulation and allocation, gas exchange, and chlorophyll fluorescence were compared for one-year-old seedlings of Salix psammophila and Artemisia ordosica, two dominant desert species, in response to two water supplies (equivalent to 315.0 mm for present precipitation in growing season and to 157.5 mm for future decreasing precipitation) during 105 d. For both species, photochemical efficiency of photosystem 2 (F_v/F_m), net photosynthetic rate, transpiration rate, stomatal conductance, biomass accumulation in different organs, tree height, number of leaves, and leaf area were reduced in response to the decrease in water supply. For both species, instantaneous water use efficiency was not affected by the water deficit. However, diurnal patterns of gas exchange and biomass allocation were affected in different ways for the two species, with notably a decrease in specific leaf area and an increase in root : shoot ratio for S. psammophila only. Overall, S. psammophila was more responsive to the decreasing precipitation than A. ordosica.     

Photosynthetic water use efficiency in tree crowns of <Emphasis Type="Italic">Shorea beccariana</Emphasis> and <Emphasis Type="Italic">Dryobalanops aromatica</Emphasis> in a tropical rain forest in Sarawak,East Malaysia

Photosynthetic water use efficiency (PWUE), stomatal conductance (g _s), and water potential were measured at two different positions in the tree crown of two emergent tropical tree species (Shorea beccariana Burck, Dryobalanops aromatica Gaertn. f.). The trees were about 50 m high, in a tropical rain forest in Sarawak, East Malaysia. In both species, g _s at the upper crown position at midday was lower than at the lower crown position, even though both positions were exposed to full sunlight; the difference was greater in S. beccariana. Hydraulic limitation occurs in the upper crown position in both species. A midday depression was observed in the photon saturated photosynthetic rate in both species, especially at the upper crown. However, PWUE was markedly higher in the upper crown than the lower crown at midday, even though no morphological adjustment was observed in the leaves; this difference was greater in S. beccariana.     

Production and genetic characterization of somatic hybrids between leaf mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis>) and broccoli (<Emphasis Type="Italic">Brassica oleracea</Emphasis>)

Inter-specific somatic hybrids of leaf mustard (Brassica juncea) and broccoli (Brassica oleracea) were established to introduce cytoplasmic male sterility (CMS) and Verticillium dahliae Kleb. resistance from broccoli to leaf mustard. Protoplasts isolated from hypocotyls and cotyledons of inbred lines of leaf mustard and broccoli were fused using 40% (w/v) polyethelene glycol and then cultured in modified k8p medium supplemented with 0.2 mg/l 2,4-dichlorophenoxi-acetic acid, 0.5 mg/l 6-benzyladenine (BA), 0.1 mg/l naphthaleneacetic acid (NAA), and 0.1 mg/l kinetin (Kin), and 0.4 M mannitol as osmoticum. At the eight- to ten-cell stage, divided cells were transferred to Kao’s basal medium supplemented with 0.3 M sucrose as carbon source and 0.1% agarose, 2 mg/l BA, 2 mg/l zeatin (ZEA), 1 mg/l NAA, and 0.5 mg/l Kin for callus proliferation. After 35 d, when small calli reached 2–3 mm in diameter, calli were transferred to regeneration medium containing 5 mg/l ZEA and 2 mg/l indole-3-acetic acid. The chromosome numbers of putative somatic hybrids varied from 46 to 54. A total of ten plants showed a 0.5-kb, CMS-specific band, while two regenerated plants showed a missing band similar to that of leaf mustard by polymerase chain reaction amplification using Ogura CMS-specific primers. Hybrid state was confirmed by random amplified polymorphic DNA analysis. Regenerated plants had normal petals and stamens, but only two plants produced pollen and set seed.     

Transgenic Indian mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis>) with resistance to the mustard aphid (<Emphasis Type="Italic">Lipaphis erysimi</Emphasis> Kalt.)

. Wheat germ agglutinin (WGA), the chitin-binding lectin from wheat germ, has been shown to be antimetabolic, antifeedant and insecticidal to the mustard aphid (Lipaphis erysimi. Kalt). A cDNA encoding WGA was transferred to Indian mustard (Brassica juncea cv. RLM-198) through Agrobacterium-mediated transformation. Southern analysis of the transgenics showed the integration of the transgene, while Northern and Western analyses demonstrated that the transgene was expressed in the transgenics. Bioassays using leaf discs showed that feeding on transgenics induced high mortality and significantly reduced fecundity of aphids.     

Influence of insect-infested cotyledons on early seedling growth of Mongolian oak, <Emphasis Type="Italic">Quercus mongolica</Emphasis>

Insect-infested (II) acorns germinated 3 d earlier than the healthy (H) ones. However, germination ratio of II-acorns was strongly decreased compared with H-acorns and there were great differences in activities of amylase. We found an apparently lower net photosynthetic rate and total chlorophyll contents of the first true leaf of II-acorns than of the H-ones. Maximal photochemical efficiency of photosystem 2 (PS2, F_v/F_m) decreased in seedlings germinated from II-acorns than from the H-ones. Infestation of insects, especially for weevil (Curculio spp.) had significantly negative effects on length of taproots, height of plants, dry mass (DM) of roots and the first fully expanded true leaf. Leaf area and total N content of the first true leaf declined due to limitation of resource reserves in cotyledons. Damage of cotyledons caused by weevil accounted much for poor development of seedlings germinated from II-acorns. A mutual relationship between seedling establishment and seed-infesting insects may exist due to high predation on H-acorns by small rodents. An erratum to this article is available at .     

Production of interspecific somatic hybrids between tuber mustard (<Emphasis Type="Italic">Brassica</Emphasis><Emphasis Type="Italic">juncea</Emphasis>) and red cabbage (<Emphasis Type="Italic">Brassica oleracea</Emphasis>)

In the present investigation, the interspecific somatic hybridization between tuber mustard and red cabbage was established in order to introduce valuable genes from red cabbage (Brassica oleracea) into Brassica juncea. Prior to fusion treatment, protoplasts of red cabbage were inactivated with 2 mM iodoacetamide to inhibit cell division. Micro-calluses were obtained at a frequency of 10.3% after approximately 5 weeks culture following protoplast fusion. Some of the fusion-derived calluses possessed red pigmented cells after being transferred to proliferation medium, and they were presumably considered to be somatic hybrid cell lines. Plantlets were regenerated from 12 cell lines, of which nine plantlets exhibited characteristics intermediate of both parents in terms of plant morphology. With the exception of common protein bands featured by two parents, there were unique banding patterns produced in the hybrids by using SDS-PAGE analysis. By chromosome countings, it was showed that they ranged approximately from 2n=30 to 42 in chromosome numbers. Their hybridity were further confirmed by RAPD analysis revealing that genes of both parents were partially incorporated into the hybrids. Positively, all these hybrids were capable of seed-setting. The pod-setting was 4.2 in somatic hybrid H₇ when backcrossed with tuber mustard.     

Transgenic Indian mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis>) plants expressing an <Emphasis Type="Italic">Arabidopsis</Emphasis> phytochelatin synthase (<Emphasis Type="Italic">AtPCS1</Emphasis>) exhibit enhanced As and Cd tolerance

Phytochelatins (PCs) are post-translationally synthesized thiol reactive peptides that play important roles in detoxification of heavy metal and metalloids in plants and other living organisms. The overall goal of this study is to develop transgenic plants with increased tolerance for and accumulation of heavy metals and metalloids from soil by expressing an Arabidopsis thaliana AtPCS1 gene, encoding phytochelatin synthase (PCS), in Indian mustard (Brassica juncea L.). A FLAG-tagged AtPCS1 gDNA, under its native promoter, is expressed in Indian mustard, and transgenic pcs lines have been compared with wild-type plants for tolerance to and accumulation of cadmium (Cd) and arsenic (As). Compared to wild type plants, transgenic plants exhibit significantly higher tolerance to Cd and As. Shoots of Cd-treated pcs plants have significantly higher concentrations of PCs and thiols than those of wild-type plants. Shoots of wild-type plants accumulated significantly more Cd than those of transgenic plants, while accumulation of As in transgenic plants was similar to that in wild type plants. Although phytochelatin synthase improves the ability of Indian mustard to tolerate higher levels of the heavy metal Cd and the metalloid As, it does not increase the accumulation potential of these metals in the above ground tissues of Indian mustard plants.     

Interaction of silicon and cadmium in <Emphasis Type="Italic">Brassica juncea</Emphasis> and <Emphasis Type="Italic">Brassica napus</Emphasis>

The objective of this study was to determine the effect of silicon (Si) and cadmium (Cd) on root and shoot growth and Cd uptake in two hydroponically cultivated Brassica species (B. juncea (L.) Czern. cv. Vitasso and B. napus L. cv. Atlantic). Both species are potentially usable for phytoextraction. Inhibitory effects of Cd on root elongation were diminished by the impact of Si. Primary roots elongation in the presence of Cd + Si compared with Cd was stronger and the number of lateral roots was lower in B. juncea than in B. napus. Cd content per plant was higher in B. napus roots and shoots compared with B. juncea. Suberin lamellae were formed closer to the root apex in Cd + Si than in Cd treated plants and this effect was stronger in B. napus than in B. juncea. Accelerated maturation of endodermis was associated with reduced Cd uptake. Cd decreased the content of chlorophylls and carotenoids in both species, but Si addition positively influenced the content of photosynthetic pigments which was higher in B. napus than in B. juncea. Si enhanced more substantially translocation of Cd into the shoot of B. napus than of B. juncea. Based on our results B. napus seems to be more suitable for Cd phytoextraction than B. juncea because these plants produce more biomass and accumulate higher amount of Cd. The protective effect of Si on Cd treated Brassica plants could be attributed to more extensive development of suberin lamellae in endodermis.     

Antioxidant defense system in leaves of Indian mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis>) and rape (<Emphasis Type="Italic">Brassica napus</Emphasis>) under cadmium stress

Plant species capable of hyper-accumulating heavy metals are of considerable interest for phytoremediation, and differ in their ability to accumulate metals from environment. Using two brassica species (Brassica juncea and Brassica napus), nutrient solution experiments were conducted to study variation in tolerance to cadmium (Cd) toxicity based on (1) lipid peroxidation and (2) changes in antioxidative defense system in leaves of both plants (i.e., superoxide dismutase (SOD EC 1.15.1.1), catalase (CAT EC 1.11.1.6), ascorbate peroxidase (APX EC 1.11.1.11), guaiacol peroxidase (GPX EC 1.11.1.7), glutathione reductase (GR EC 1.6.4.2), levels of phytochelatins (PCs), non-protein thiols (NP-SH), and glutathione. Plants were grown in nutrient solution under controlled environmental conditions, and subjected to increasing concentrations of Cd (0, 10, 25 and 50 μM) for 15 days. Results showed marked differences between both species. Brassica napus under Cd stress exhibited increased level of lipid peroxidation, as was evidenced by the increased malondialdehyde (MDA) content in leaves. However, in Brassica juncea treated plants, MDA content remained unchanged. In Brassica napus, with the exception of GPX, activity levels of some antioxidant enzymes involved in detoxification of reactive oxygen species (ROS), including SOD, CAT, GR, and APX, decreased drastically at high Cd concentrations. By contrast, in leaves of Brassica juncea treated plants, there was either only slight or no change in the activities of the antioxidative enzymes. Analysis of the profile of anionic isoenzymes of GPX revealed qualitative changes occurring during Cd exposure for both species. Moreover, levels of NP-SH and PCs, monitored as metal detoxifying responses, were much increased in leaves of Brassica juncea by increasing Cd supply, but did not change in Brassica napus. These results indicate that Brassica juncea plants possess the greater potential for Cd accumulation and tolerance than Brassica napus.     

Mitochondrial <Emphasis Type="Italic">atpA</Emphasis> gene is altered in a new <Emphasis Type="Italic">orf220</Emphasis>-type cytoplasmic male-sterile line of stem mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis>)

The purpose of this research is to identify the probable mitochondrial factor associated with cytoplasmic male sterility (cms) by comparative analysis of cms and its isogenic maintainer lines in stem mustards. Dramatic variations in the morphology of floral organs were observed in cms stem mustard. Mitochondrial atpA gene was shown to be altered in cms compared with that in its maintainer line, of which mitochondrial atpA gene from its maintainer line was sequenced to encode 507 amino acids. It was indicative of high homology with mitochondrial atpA genes from other species, even as high as 94% in similarity with Oryza sativa in terms of amino acid constituents. However, only 429 amino acids were deduced in cms showing 83% similarity with atpA gene from its maintainer line. Two copies were observed in its maintainer line, but only one was found in cms. Such numerous differences of mitochondrial atpA gene between cms and its maintainer lines may not be the results of evolutionary divergence but the rearrangements of mitochondria. Expression of mitochondrial atpA gene was shown to be down-regulated in cms by using Northern blot. Consequently, mitochondrial ATP synthesis was severely decreased more than one fold in cms stem mustard indicating deficiency in mitochondrial ATP synthesis in this type of cms. Therefore, we deduced that mitochondrial atpA gene altered in cms could be associated with male-sterility in this type of cms. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Jing-Hua Yang and Yan Huai contributed equally to this work.     

A genetic analysis of relative growth rate and underlying components in <Emphasis Type="Italic">Hordeum spontaneum</Emphasis>

Species from productive and unproductive habitats differ inherently in their relative growth rate (RGR) and a wide range of correlated quantitative traits. We investigated the genetic basis of this trait complex, and specifically assessed whether it is under the control of just one or a few genes that can act as master switches by simultaneously affecting a range of traits in the complex. To address this problem, we crossed two Hordeum spontaneum lines originating from two habitats that differ in productivity. The F₃ offspring, in which parental alleles are present in different combinations due to recombination and segregation, was analysed for RGR and its underlying components (leaf area ratio, unit leaf rate, photosynthesis, respiration), as well as a number of other physiological and morphological parameters. For this intra-specific comparison, we found a complex of positively and negatively correlated traits, which was quite similar to what is generally observed across species. A quantitative trait loci (QTL) analysis showed three major and one minor QTL for RGR. Most other variables of the growth-trait complex showed fewer QTLs that were typically scattered over various locations on the genome. Thus, at least in H. spontaneum, we found no evidence for regulation of the trait complex by one or two master switches.Electronic Supplementary Material Supplementary material is available for this article at     

Leaf traits of natural populations of <Emphasis Type="Italic">Adiantum reniforme</Emphasis> var. <Emphasis Type="Italic">sinensis</Emphasis>, endemic to the Three Gorges region in China

Leaf mass per unit area (LMA), carbon and nitrogen contents, leaf construction cost, and photosynthetic capacity (P _max) of Adiantum reniforme var. sinensis, an endangered fern endemic to the Three Gorges region in southwest China, were compared in five populations differing in habitat such as soil moisture and irradiance. The low soil moisture and high irradiance habitat population exhibited significantly higher LMA, area-based leaf construction (CC_A), and carbon content (C_A), but lower leaf nitrogen content per unit dry mass (N_M) than the other habitat populations. The high soil moisture and low irradiance habitat populations had the lowest CC_A, but their cost/benefic ratios of CCA/P _max were similar to the medium soil moisture and irradiance habitat population due to their lower leaf P _max. Hence A. reniforme var. sinensis prefers partially shaded, moist but well-drained, slope habitats. Due to human activities, however, its main habitats now are cliffs or steeply sloped bare rocks with poor and thin soil. The relatively high energy requirements and low photosynthetic capacity in these habitats could limit the capability of the species in extending population or interspecific competition and hence increase its endangerment.     

Growth,biomass production,and assimilatory characters in <Emphasis Type="Italic">Cenchrus ciliaris</Emphasis> L. Under elevated CO<Subscript>2</Subscript> condition

The effect of elevated carbon dioxide (600±50 cm³ m⁻³; C₆₀₀) on growth performance, biomass production, and photosynthesis of Cenchrus ciliaris L. cv. 3108 was studied. This crop responded significantly by plant height, leaf length and width, and biomass production under C₆₀₀. Leaf area index increased triple fold in the crops grown in the open top chamber with C₆₀₀. The biomass production in term of fresh and dry biomass accumulation increased by 134.35 (fresh) and 193.34 (dry) % over the control (C₃₆₀) condition where the crops were grown for 20 d. The rate of photosynthesis and stomatal conductance increased by 24.51 and 46.33 %, respectively, in C₆₀₀ over C₃₆₀ plants. In comparison with C₃₆₀, the rate of transpiration decreased by 6.8 % under C₆₀₀. Long-term exposure (120 d) to C₆₀₀ enhanced photosynthetic water use efficiency by 34 %. Also the contents of chlorophylls a and b significantly increased in C₆₀₀. Thus C. ciliaris grown in C₆₀₀ throughout the crop season may produce more fodder in terms of green biomass.     

Induction and origin of adventitious shoots from chimeras of <Emphasis Type="Italic">Brassica juncea</Emphasis> and <Emphasis Type="Italic">Brassica oleracea</Emphasis>

The chimeras between tuber mustard (Brassica juncea) and red cabbage (B. oleracea) were artificially synthesized in our previous study. Adventitious shoots were induced from nodal segments and leaf discs of TCC (LI-LII-LIII, LI -the outmost layer of shoot apical meristem; LII -the middle layer; LIII -the innermost layer. T = Tuber mustard, C = Red cabbage) chimeras. The origin of the shoots was analyzed by histology and molecular biology. As a result, the frequency of adventitious shoot induction rose with the increase of BA in MS medium in the area of the nodes. However, there was no different induction frequency of adventitious shoots from nodal segment bases in media with different BA concentrations. Most adventitious shoots (clustered shoots) arising from the node area were TTT (Tuber mustard- Tuber mustard- Tuber mustard) and only 4 shoots were chimeras, which indicated that more shoots originated from LI than from LII and LIII. All shoots from nodal segment bases were CCC (Red cabbage-Red cabbage- Red cabbage), indicating that the shoots originated from LII or LII and LIII. There were significant differences in the regeneration rate in the margin of the leaf discs among the three combinations of BA and NAA. Most adventitious shoots from the margin of leaf discs were CCC but 2 out of 70 were chimeras, which indicated that more shoots originated from LII or LII and LIII than from LI. All chimeras obtained by regeneration were different from the original explant donor in type in the present study. The origin of the adventitious shoots varied with the site of origin on the donor plant, and could be multicellular and multihistogenic.     

Effect of cytokinins on shoot regeneration from cotyledon and leaf segment of stem mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis> var. <Emphasis Type="Italic">tsatsai</Emphasis>)

Cotyledon and leaf segments of stem mustard (Brassica juncea var. tsatsai) were cultured on Murashige and Skoog medium supplemented with various concentrations of different cytokinins [6-benzyladenine (BA), N-(2-chloro-4-pyridyl)-n-phenylurea (CPPU), 6-furfurylaminopurine (KT) and thidiazuron (TDZ)] in combinations with different levels of α-naphthalene acetic acid (NAA). The shoot regeneration frequency of cotyledon and leaf segment was dependent on the kinds and concentrations of cytokinins used in the medium, while in most cases cotyledon gave high regeneration frequency than leaf segment. TDZ proved to be the best cytokinin to induce shoot from both cotyledon and leaf segments compared to BA, KT and CPPU. The highest frequency of shoot regeneration was 61.3–67.9 % in cotyledon and 40.7–52.4% in leaf segment respectively when 2.27 or 4.54 μM TDZ was combined with 5.37 μM NAA. Next to TDZ, CPPU was also very suitable to induce shoot formation both in cotyledon and leaf segment. When 1.61 μM CPPU was combined with 2.69 μM NAA, shoot regeneration frequency was 45.0% in cotyledon and 36.4% in leaf segment, respectively. It was also shown that KT and BA affected shoot regeneration from cotyledon and leaf segment, the shoot regeneration was greatly increased when NAA was added together with cytokinins. The efficient and reliable shoot regeneration system was developed in both cotyledon and leaf segments. This regeneration protocol may be applicable to the improvement of this crop by genetic engineering in the future.     

Morphological and genetic characterization of a new cytoplasmic male sterility system (<Emphasis Type="Italic">oxa</Emphasis> CMS) in stem mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis>)

Key message

oxa CMS is a new cytoplasmic male sterility type in Brassica juncea.

Abstract

oxa CMS is a cytoplasmic male sterility (CMS) line that has been widely used in the production and cultivation of stem mustard in the southwestern China. In this study, different CMS-type specific mitochondrial markers were used to confirm that oxa CMS is distinct from the pol CMS, ogu CMS, nap CMS, hau CMS, tour CMS, Moricandia arvensis CMS, orf220-type CMS, etc., that have been previously reported in Brassica crops. Pollen grains of the oxa CMS line are sterile with a self-fertility rate of almost 0% and the sterility strain rate and sterility degree of oxa CMS is 100% due to a specific flower structure and flowering habit. Scanning electron microscopy revealed that most pollen grains in mature anthers of the oxa CMS line are empty, flat and deflated. Semi-thin section further showed that the abortive stage of anther development in oxa CMS is initiated at the late uninucleate stage. Abnormally vacuolated microspores caused male sterility in the oxa CMS line. This cytological study combined with marker-assisted selection showed that oxa CMS is a novel CMS type in stem mustard (Brassica juncea). Interestingly, the abortive stage of oxa CMS is later than those in other CMS types reported in Brassica crops, and there is no negative effect on the oxa CMS line growth period. This study demonstrated that this novel oxa CMS has a unique flower structure with sterile pollen grains at the late uninucleate stage. Our results may help to uncover the mechanism of oxa CMS in Brassica juncea.