Graphical Abstract Highlights d MemBright allows for bright and specific staining of EVs d The zebrafish embryo allows tracking of tumor EVs at high spatiotemporal resolution d Circulating tumor EVs are mostly taken up by endothelial cells and patrolling macrophages d Zebrafish melanoma EVs favor metastatic outgrowth in zebrafish embryos
Cancer extracellular vesicles (EVs) shuttle at distance and fertilize pre-metastatic niches facilitating subsequent seeding by tumor cells. However, the link between EV secretion mechanisms and their capacity to form pre-metastatic niches remains obscure. Using mouse models, we show that GTPases of the Ral family control, through the phospholipase D1, multi-vesicular bodies homeostasis and tune the biogenesis and secretion of pro-metastatic EVs. Importantly, EVs from RalA or RalB depleted cells have limited organotropic capacities in vivoand are less efficient in promoting metastasis. RalA and RalB reduce the EV levels of the adhesion molecule MCAM/CD146, which favors EV-mediated metastasis by allowing EVs targeting to the lungs. Finally, RalA, RalB, and MCAM/CD146, are factors of poor prognosis in breast cancer patients. Altogether, our study identifies RalGTPases as central molecules linking the mechanisms of EVs secretion and cargo loading to their capacity to disseminate and induce pre-metastatic niches in a CD146-dependent manner.
Aims The flow of electric current in the root-soil system relates to the pathways of water and solutes, its characterization provides information on the root architecture and functioning. We developed a current source density approach with the goal of non-invasively image the current pathways in the root-soil system. Methods A current flow is applied from the plant stem to the soil, the proposed geoelectrical approach images the resulting distribution and intensity of the electric current in the root-soil system. The numerical inversion procedure underlying the approach was tested in numer
Abstract. The investigation of plant roots is inherently difficult and often neglected.
Being out of sight, roots are often out of mind. Nevertheless, roots play a key role
in the exchange of mass and energy between soil and the atmosphere, in addition to
the many practical applications in agriculture. In this paper, we propose a
method for roots imaging based on the joint use of two electrical
noninvasive methods: electrical resistivity tomography (ERT) and
mise-à-la-masse (MALM). The approach is based on the key assumption that the
plant root system acts as an electrically conductive body, so that injecting
electrical current into the plant stem will ultimately result in the injection
of current into the subsoil through the root system, and particularly through
the root terminations via hair roots. Evidence from field data, showing that
voltage distribution is very different whether current is injected into the
tree stem or in the ground, strongly supports this hypothesis. The proposed
procedure involves a stepwise inversion of both ERT and MALM data that
ultimately leads to the identification of electrical resistivity (ER)
distribution and of the current injection root distribution in the
three-dimensional soil space. This, in turn, is a proxy to the active (hair)
root density in the ground. We tested the proposed procedure on synthetic
data and, more importantly, on field data collected in a vineyard, where the
estimated depth of the root zone proved to be in agreement with literature on
similar crops. The proposed noninvasive approach is a step forward towards a
better quantification of root structure and functioning.
We added induced polarization to the concept of classical resistivity to map in-situ root systems in soil. 2. Both TDIP and SIP are applicable for identifying root polarization. 3. High resolution images showed a correlation between root location and complex resistivity anomalies under semi-controlled conditions. 4. Using a frequency band provided useful information for locating coarse roots.
Abstract. This paper presents a time-lapse application of
electrical methods (electrical resistivity tomography, ERT; and
mise-à-la-masse, MALM) for monitoring plant roots and their activity
(root water uptake) during a controlled infiltration experiment. The use of
non-invasive geophysical monitoring is of increasing interest as these
techniques provide time-lapse imaging of processes that otherwise can only
be measured at few specific spatial locations. The experiment here described was conducted in a vineyard in Bordeaux (France) and was focused on the
behaviour of two neighbouring grapevines. The joint application of ERT and
MALM has several advantages. While ERT in time-lapse mode is sensitive to
changes in soil electrical resistivity and thus to the factors controlling
it (mainly soil water content, in this context), MALM uses DC current
injected into a tree stem to image where the plant root system is in effective
electrical contact with the soil at locations that are likely to be the same
where root water uptake (RWU) takes place. Thus, ERT and MALM provide
complementary information about the root structure and activity. The
experiment shows that the region of likely electrical current sources
produced by MALM does not change significantly during the infiltration time
in spite of the strong changes of electrical resistivity caused by changes
in soil water content. Ultimately, the interpretation of the current source
distribution strengthened the hypothesis of using current as a proxy for
root detection. This fact, together with the evidence that current injection
in the soil and in the stem produces totally different voltage patterns,
corroborates the idea that this application of MALM highlights the active
root density in the soil. When considering the electrical resistivity
changes (as measured by ERT) inside the stationary volume of active roots
delineated by MALM, the overall tendency is towards a resistivity increase
during irrigation time, which can be linked to a decrease in soil water
content caused by root water uptake. On the contrary, when considering the
soil volume outside the MALM-derived root water uptake region, the
electrical resistivity tends to decrease as an effect of soil water content
increase caused by the infiltration. The use of a simplified infiltration
model confirms at least qualitatively this behaviour. The monitoring results
are particularly promising, and the method can be applied to a variety of
scales including the laboratory scale where direct evidence of root
structure and root water uptake can help corroborate the approach. Once
fully validated, the joint use of MALM and ERT can be used as a valuable
tool to study the activity of roots under a wide variety of field
conditions.
Tree rooting strategies are driven by external and internal factors such as climate conditions (rain frequency, wind direction), soil structure and crop type. In order to ensure water efficiency for irrigated crops, it is essential to know how each crop adapts its rooting strategy. We couple Mise-a-la-masse (MALM) with Electrical Resistivity Tomography (ERT) for investigating orange tree roots undergoing different irrigation strategies (Partial Root-zone Drying – or PRD - versus Full Irrigation). This is a totally novel approach giving an overall picture of roots structure and functioning in the subsoil. Our results show clear differences of rooting extent between different irrigation strategies, and identify privileged direction of root development due to distinct RWU patterns. These results are corroborated also by seasonal monitoring of evapotranspiration (ET) and soil water content (SWC), which exhibit very large differences in the soil water distribution in space and time for the trees undergoing different irrigation schedules.
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