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Developmental Biology and Induction of Phi Thickenings by Abiotic Stress in Roots of the Brassicaceae.

ABSTRACT: Phi thickenings are specialized bands of secondary wall deposited around radial walls of root cortical cells. These structures have been reported in various species from the Brassicaceae, including Brassica oleracea, where previous reports using hydroponics indicated that they can be induced by exposure to salt. Using roots grown on agar plates, we show that both salt and sucrose can induce the formation of phi thickenings in a diverse range of species within the Brassicaceae. Within the genus Brassica, both B. oleracea and B. napus demonstrated the formation of phi thickenings, but in a strongly cultivar-specific manner. Confocal microscopy of phi thickenings showed that they form a complex network of reinforcement surrounding the inner root cortex, and that a delicate, reticulate network of secondary wall deposition can also variously form on the inner face of the cortical cell layer with phi thickenings adjacent to the endodermal layer. Results presented here indicate that phi thickenings can be induced in response to salt and water stress and that wide variation occurs in these responses even within the same species.

SUBMITTER: Aleamotu'a M

PROVIDER: S-EPMC6027303 | biostudies-literature | 2018 Jun

REPOSITORIES: biostudies-literature

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Developmental Biology and Induction of Phi Thickenings by Abiotic Stress in Roots of the Brassicaceae.

Aleamotu'a Maketalena M Tai Yu-Ting YT McCurdy David W DW Collings David A DA

Plants (Basel, Switzerland) 20180619 2

Phi thickenings are specialized bands of secondary wall deposited around radial walls of root cortical cells. These structures have been reported in various species from the Brassicaceae, including <i>Brassica oleracea</i>, where previous reports using hydroponics indicated that they can be induced by exposure to salt. Using roots grown on agar plates, we show that both salt and sucrose can induce the formation of phi thickenings in a diverse range of species within the Brassicaceae. Within the ...[more]

PMID: 29921823

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Project description:Background and aimsRoot absorptive characteristics rely on the presence of apoplastic barriers. However, little is known about the establishment of these barriers within a complex root system, particularly in a major portion of them - the lateral roots. In Zea mays L., the exodermis differentiates under the influence of growth conditions. Therefore, the species presents a suitable model to elucidate the cross-talk among environmental conditions, branching pattern and the maturation of barriers within a complex root system involved in the definition of the plant-soil interface. The study describes the extent to which lateral roots differentiate apoplastic barriers in response to changeable environmental conditions.MethodsThe branching, permeability of the outer cell layers and differentiation of the endo- and exodermis were studied in primary roots and various laterals under different types of stress of agronomic importance (salinity, heavy metal toxicity, hypoxia, etc.). Histochemical methods, image analysis and apoplastic tracer assays were utilized.Key resultsThe results show that the impact of growth conditions on the differentiation of both the endodermis and exodermis is modulated according to the type/diameter of the root. Fine laterals clearly represent that portion of a complex root system with a less advanced state of barrier differentiation, but with substantial ability to modify exodermis differentiation in response to environmental conditions. In addition, some degree of autonomy in exodermal establishment of Casparian bands (CBs) vs. suberin lamellae (SLs) was observed, as the absence of lignified exodermal CBs did not always fit with the lack of SLs.ConclusionsThis study highlights the importance of lateral roots, and provides a first look into the developmental variations of apoplastic barriers within a complex root system. It emphasizes that branching and differentiation of barriers in fine laterals may substantially modulate the root system-rhizosphere interaction.

Project description:The prophage-encoded Shiga toxin is a major virulence factor in Stx-producing Escherichia coli (STEC). Toxin production and phage production are linked and occur after induction of the RecA-dependent SOS response. However, food-related stress and Stx-prophage induction have not been studied at the single-cell level. This study investigated the effects of abiotic environmental stress on stx expression by single-cell quantification of gene expression in STEC O104:H4 Δstx2::gfp::ampr In addition, the effect of stress on production of phage particles was determined. The lethality of stressors, including heat, HCl, lactic acid, hydrogen peroxide, and high hydrostatic pressure, was selected to reduce cell counts by 1 to 2 log CFU/ml. The integrity of the bacterial membrane after exposure to stress was measured by propidium iodide (PI). The fluorescent signals of green fluorescent protein (GFP) and PI were quantified by flow cytometry. The mechanism of prophage induction by stress was evaluated by relative gene expression of recA and cell morphology. Acid (pH < 3.5) and H2O2 (2.5 mM) induced the expression of stx2 in about 18% and 3% of the population, respectively. The mechanism of prophage induction by acid differs from that of induction by H2O2 H2O2 induction but not acid induction corresponded to production of infectious phage particles, upregulation of recA, and cell filamentation. Pressure (200 MPa) or heat did not induce the Stx2-encoding prophage (Stx2-prophage). Overall, the quantification method developed in this study allowed investigation of prophage induction and physiological properties at the single-cell level. H2O2 and acids mediate different pathways to induce Stx2-prophage.IMPORTANCE Induction of the Stx-prophage in STEC results in production of phage particles and Stx and thus relates to virulence as well as the transduction of virulence genes. This study developed a method for a detection of the induction of Stx-prophages at the single-cell level; membrane permeability and an indication of SOS response to environmental stress were additionally assessed. H2O2 and mitomycin C induced expression of the prophage and activated a SOS response. In contrast, HCl and lactic acid induced the Stx-prophage but not the SOS response. The lifestyle of STEC exposes the organism to intestinal and extraintestinal environments that impose oxidative and acid stress. A more thorough understanding of the influence of food processing-related stressors on Stx-prophage expression thus facilitates control of STEC in food systems by minimizing prophage induction during food production and storage.

Dataset Information

Developmental Biology and Induction of Phi Thickenings by Abiotic Stress in Roots of the Brassicaceae.

Publications

Developmental Biology and Induction of Phi Thickenings by Abiotic Stress in Roots of the Brassicaceae.

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