Drought and Subsequent Soil Flooding Affect the Growth and Metabolism of Savoy Cabbage

An important factor of current climate change is water availability, with both droughts and flooding becoming more frequent. Effects of individual stresses on plant traits are well studied, although less is known about the impacts of sequences of different stresses. We used savoy cabbage to study the consequences of control conditions (well-watered) versus continuous drought versus drought followed by soil flooding and a potential recovery phase on shoot growth and leaf metabolism. Under continuous drought, plants produced less than half of the shoot biomass compared to controls, but had a >20% higher water use efficiency. In the soil flooding treatment, plants exhibited the poorest growth performance, particularly after the “recovery” phase. The carbon-to-nitrogen ratio was at least twice as high, whereas amino acid concentrations were lowest in leaves of controls compared to stressed plants. Some glucosinolates, characteristic metabolites of Brassicales, showed lower concentrations, especially in plants of the flooding treatment. Stress-specific investment into different amino acids, many of them acting as osmolytes, as well as glucosinolates, indicate that these metabolites play distinct roles in the responses of plants to different water availability conditions. To reduce losses in crop production, we need to understand plant responses to dynamic climate change scenarios.     

Microscopic investigation of pollen morphology of Brassicaceae from Central Punjab‐Pakistan

The intention of the current study is to provide an account on the palynological features of Brassicaceae from Central Punjab‐Pakistan as a basis for future studies. Different morpho‐palynological characteristics both qualitative and quantitative were analyzed during this research which includes shape of pollen, diameter of pollen, P/E ratio, exine sculpturing, thickness of exine, type of pollen, shape and size of lumens, and thickness of murus. Taxonomic keys were also constructed based on pollen morphological characters for correct identification of species. This study aims to provide detailed information of pollen diversity and their exine structure based on both qualitative and quantitative characters by using Light microscopy and Scanning electron microscopy. Shape of pollen is mostly prolate, but some species also have sub‐prolate to spheroidal prolate types. Exine ornamentation in most species was reticulate, whereas micro reticulate (one species) and coarsely reticulate (one species) exine also observed in some pollen. All the pollen mentioned in this study have tricolpate apertures. Variation found in thickness of exine and other characters proved to be helpful at generic and specific level. The results reinforced the significance of pollen morphological features of family Brassicaceae and aid for valuable taxonomic tool in plant systematics.     

Glucosinolate preservation in stored Brassicaceae seed meals

Limited profitability restricts expanded U.S. production of Brassicaceae oilseed crops despite their positive rotational benefits and capacity to provide biodiesel feedstocks. Improved profitability is possible if the seed meals remaining after oil removal are commercialized as biopesticides. Our objective was to determine storage stability of the precursor pesticidal compounds called glucosinolates within Brassica napus, Brassica juncea, and Sinapis alba seed meals. The seed meals were stored at temperatures of −20, 4, and 25 °C in paper bags, polyethylene containers, or under vacuum for 30 months after purging in a N₂ atmosphere. Glucosinolate concentrations measured every 6 months using HPLC-MS decreased only in meal samples stored at 4 °C, and to the greatest extent in samples stored within paper bags. Relative humidity averaged 80% at this temperature, thus promoting visually obvious fungal growth. Glucosinolate preservation within stored seed meals is possible for 30 months and possibly much longer providing the seed meals are protected from exposure to moisture conditions that promote microbial growth.     

Microsatellite Loci in the Gypsophyte Lepidium subulatum (Brassicaceae), and Transferability to Other Lepidieae

Polymorphic microsatellite markers were developed for the Ibero-North African, strict gypsophyte Lepidium subulatum to unravel the effects of habitat fragmentation in levels of genetic diversity, genetic structure and gene flow among its populations. Using 454 pyrosequencing 12 microsatellite loci including di- and tri-nucleotide repeats were characterized in L. subulatum. They amplified a total of 80 alleles (2–12 alleles per locus) in a sample of 35 individuals of L. subulatum, showing relatively high levels of genetic diversity, H_O = 0.645, H_E = 0.627. Cross-species transferability of all 12 loci was successful for the Iberian endemics Lepidium cardamines, Lepidium stylatum, and the widespread, Lepidium graminifolium and one species each of two related genera, Cardaria draba and Coronopus didymus. These microsatellite primers will be useful to investigate genetic diversity, population structure and to address conservation genetics in species of Lepidium.     

Sulfur-Containing Secondary Metabolites from Arabidopsis thaliana and other Brassicaceae with Function in Plant Immunity

Biosynthesis of antimicrobial secondary metabolites in response to microbial infection is one of the features of the plant immune system. Particular classes of plant secondary metabolites involved in plant defence are often produced only by species belonging to certain phylogenetic clades. Brassicaceae plants have evolved the ability to synthesise a wide range of sulfur-containing secondary metabolites, including glucosinolates and indole-type phytoalexins. A subset of these compounds is produced by the model plant Arabidopsis thaliana. Genetic tools available for this species enabled verification of immune functions of glucosinolates and camalexin (A. thaliana phytoalexin), as well as characterisation of their respective biosynthetic pathways. Current knowledge of the biosynthesis of Brassicaceae sulfur-containing metabolites suggests that the key event in the evolution of these compounds is the acquisition of biochemical mechanisms originating from detoxification pathways into secondary metabolite biosynthesis. Moreover, it is likely that glucosinolates and Brassicaceae phytoalexins, traditionally considered as separate groups of compounds, have a common evolutionary origin and are interconnected on the biosynthetic level. This suggests that the diversity of Brassicaceae sulfur-containing phytochemicals reflect phylogenetic clade-specific branches of an ancient biosynthetic pathway.     

1-Cyano-2-Hydroxy-3-Butene, A Phytotoxin From Crambe (Crambe abyssinica) Seedmeal

Crambe (Crambe abyssinica) seedmeal was found to suppress seedling emergence and biomass accumulation when added to a sandy loam soil containing wheat (Triticum aestivum Cardinal) and hemp sesbania (Sesbania exahata) seeds. Hexane, CH₂Cl₂, MeOH, and water extracts of the seedmeal were prepared and bioassayed against wheat and velvetleaf (Abutilon theophrasti) radicle elongation. The CH₂Cl₂ extract was the most inhibitory, while the other extracts inhibited the bioassay species only slightly (MeOH) or not at all (hexane, water). Fractionation of the CH₂Cl₂ extract identified the major phytotoxin as l-cyano-2-hydroxy-3-butene (CHB), comprising 96.1% of the active CH₂Cl₂ fraction. Radicle elongation of wheat and velvetleaf were inhibited by CHB with I₅₀ values of 2.1 × 10^–4 M for wheat and 2.7 × l0^–3 M for velvetleaf.     

Allelochemicals Isolated from Tissues of the Invasive Weed Garlic Mustard (Alliaria petiolata)

Garlic mustard (Alliaria petiolata) is a naturalized Eurasian species that has invaded woodlands and degraded habitats in the eastern United States and Canada. Several phytotoxic hydrolysis products of glucosinolates, principally allyl isothiocyanate (AITC) and benzyl isothiocyanate (BzITC), were isolated from dichloromethane extracts of garlic mustard tissues. AITC and BzITC were much more phytotoxic to wheat (Triticum aestivum) than their respective parent glucosinolates sinigrin and glucotropaeolin. However, garden cress (Lepidium sativum) growth was inhibited to a greater degree by glucotropaeolin than BzITC, possibly due to conversion to BzITC by endogenous myrosinase. Sinigrin and glucotropaeolin were not detected in leaf/stem tissues harvested at the initiation of flowering, but were present in leaves and stems harvested in the autumn. Sinigrin levels in roots were similar for both sampling dates, but autumn-harvested roots contained glucotropaeolin at levels over three times higher than spring-harvested roots. The dominance of garlic mustard in forest ecosystems may be attributable in part to release of these phytotoxins, especially from root tissues.     

Rhizopus and Fusarium are Selected as Dominant Fungal Genera in Rhizospheres of Brassicaceae

We isolated several strains of Rhizopus and Fusarium spp. as dominant fungi in the rhizospheres of Brassicaceae plants. The Fusarium isolates showed a higher tolerance of the antifungal constituents of "mustard oil," which originates from the glucosinolates that are characteristic secondary metabolites of the Brassicaceae, than other Fusarium isolates from non-Brassicaceae plants. In contrast, the Rhizopus isolates showed a high tolerance regardless of their source. Myrosinase activity was found in Bn-R-1-1 (Rhizopus sp.) isolated from the rhizoplane of Brassica napus and Ls-F-in-4-1 (Fusarium sp.) isolated from a surface-disinfected root of Lepidium sativum (Brassicaceae). Ls-F-in-4-1 was the Fusarium most tolerant of the Brassicaceae antifungal constituents. These results suggest that fungi in the rhizospheres of Brassicaceae plants may be selected because of secondary metabolites exuded from the roots of host plants.     

Changes in the dry matter,sugar, plant fibre and lignin contents of swede,rape and kale roots in response to turnip root fly (Delia floralis) larval damage

Plants from two genotypes of swede (Brassica napus var napobrassica), kale (B oleracea var. acephala) and rape (B napus var napus) were each inoculated at the three to four true leaf stage with 10 eggs of the turnip root fly, Delia floralis. After 8 weeks the damage caused by the resultant larvae significantly reduced the weight of leaves, stems and roots compared with uninoculated plants, with the greatest reduction (26–46%) being found in the roots. Dry matter content, which did not differ between either crop type or cultivar, was unaffected by larval damage. Ethanol-soluble sugar content was reduced in all cases by larval damage, but only significantly in one rape and one swede cultivar. The effect of D floralis damage on the concentrations of individual sugars (glucose, fructose and sucrose) was crop type and cultivar dependent. The neutral detergent fibre and lignin contents of the undamaged swede roots were significantly lower than in either the undamaged kale or rape cultivars studied. In all crop types the neutral detergent fibre and lignin content significantly increased following D floralis damage. The six Brassica genotypes studied fell into two groups on the basis of host status for D floralis. The two kale cultivars and the forage rape Hobson were considered poor hosts for D floralis, with low percent age pupation (38–41%) and low pupae weight (12.5–14.4 mg). The two swedes and the oilseed rape Ariana were considered good host for D floralis, with both higher percentage pupation (51–59%) and pupae weights (19.8–20.0 mg). The possible relationships between the root composition of undamaged and attacked roots, and D floralis resistance are discussed.