Summary
The growth and development of root systems is influenced by mechanical properties of the substrate in which the plants grow. Mechanical impedance, such as by compacted soil, can reduce root ...elongation and limit crop productivity.
To understand better the mechanisms involved in plant root responses to mechanical impedance stress, we investigated changes in the root transcriptome and hormone signalling responses of Arabidopsis to artificial root barrier systems in vitro.
We demonstrate that upon encountering a barrier, reduced Arabidopsis root growth and a characteristic ‘step‐like’ growth pattern is due to a reduction in cell elongation associated with changes in signalling gene expression. Data from RNA‐sequencing combined with reporter line and mutant studies identified essential roles for reactive oxygen species, ethylene and auxin signalling during the barrier response.
We propose a model in which early responses to mechanical impedance include reactive oxygen signalling integrated with ethylene and auxin responses to mediate root growth changes. Inhibition of ethylene responses allows improved growth in response to root impedance, an observation that may inform future crop breeding programmes.
See also the Commentary on this article by Del Bianco & Kepinski 231: 8–10.
The interaction between auxin and cytokinin is important in many aspects of plant development. Experimental measurements of both auxin and cytokinin concentration and reporter gene expression clearly ...show the coexistence of auxin and cytokinin concentration patterning in Arabidopsis root development. However, in the context of crosstalk among auxin, cytokinin, and ethylene, little is known about how auxin and cytokinin concentration patterns simultaneously emerge and how they regulate each other in the Arabidopsis root. This work utilizes a wide range of experimental observations to propose a mechanism for simultaneous patterning of auxin and cytokinin concentrations. In addition to revealing the regulatory relationships between auxin and cytokinin, this mechanism shows that ethylene signaling is an important factor in achieving simultaneous auxin and cytokinin patterning, while also predicting other experimental observations. Combining the mechanism with a realistic in silico root model reproduces experimental observations of both auxin and cytokinin patterning. Predictions made by the mechanism can be compared with a variety of experimental observations, including those obtained by our group and other independent experiments reported by other groups. Examples of these predictions include patterning of auxin biosynthesis rate, changes in PIN1 and PIN2 patterns in pin3,4,7 mutants, changes in cytokinin patterning in the pls mutant, PLS patterning, and various trends in different mutants. This research reveals a plausible mechanism for simultaneous patterning of auxin and cytokinin concentrations in Arabidopsis root development and suggests a key role for ethylene pattern integration.
Using a wide range of experimental observations, this study proposes a mechanism for simultaneous patterning of auxin and cytokinin concentrations. This mechanism reveals that ethylene signaling is important in achieving simultaneous auxin and cytokinin patterning, while also predicting other experimental observations. These results illustrate the importance of hormonal crosstalk in patterning auxin, cytokinin, and ethylene concentrations in the Arabidopsis root.
The mechanisms behind the regulation of root development under a lack of water (osmotic stress) is a critical subject for plant biology and global agriculture. Previously osmotic stress has been ...shown to inhibit root growth via an abscisic acid (ABA)-mediated reduction in auxin transport, independent of ethylene signalling. This thesis examines the impact of osmotic stress on critical developmental signals: auxin, ABA, and reactive oxygen species (ROS) minutes after encountering osmotic stress and following a longer stress period of 24 hours. The roles of these signals in the root were analysed via loss-of-function mutants, gene expression analysis, and bioimaging in concert with exogenous chemical treatment. Auxin, ABA, and ROS (represented by level of oxidation) levels were all found to rapidly increase within 10 minutes of osmotic stress leading to downstream responses. ROS and ABA appear to have a strong positive feedback relationship that can develop with minutes. Under the longer stress period of 24 hours, auxin responses were found to decrease while both ROS and ABA responses were shown to increase. PIN-mediated auxin transport was shown to play a key role in the reduction of auxin in the root tip following 24-hour osmotic stress treatment. PIN3 and PIN7 gene expression and protein distribution were altered under osmotic stress, associated with a reduction of the auxin maximum at the root tip. ROP2 was found to play a central role in root development under osmotic stress root, along with the decrease of auxin and increase in ABA signalling after 24 hours. It was also shown that several respiratory burst oxidase homologs (RBOHs) play a role in root development under standard conditions as well as under osmotic stress. PERK4 and RBOHC likely play a key role in ROS production under ABA-mediated osmotic stress response, with the loss-of-function of PERK4 significantly improving root growth under osmotic stress.
Similarities to human subacute sclerosing panencephalitis (SSPE) were revealed in a study of the brains of ferrets inoculated with a cell associated measles virus originally isolated from an SSPE ...patient. The similarities were greatest in animals that showed neurological signs 3-4 months after inoculation and had high titers of neutralizing antibodies against measles virus. These included dense core particles, nuclear bodies, alterations of basement membranes of small blood vessels, plasma cells, distorted myelin, and rod-like structures in some nuclei. Other abnormalities seen were Hirano bodies, tubular aggregates in cisternae of endoplasmic reticulum and clusters of cytoplasmic tubules. No cells containing viral inclusion bodies were observed by electron microscopy but cell cultures of the brains of these animals always yielded abundant measles virus nucleocapsids in typical SSPE multinucleated syncytia. These findings suggest that the ferret is a suitable animal model for the study of the pathogenesis of SSPE.
The Mental Deficiencies Jervis, George A.
The Annals of the American Academy of Political and Social Science,
03/1953, Letnik:
286, Številka:
1
Journal Article
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