Abstract
Plasmodesmata are small channels that connect plant cells. While recent technological advances have facilitated analysis of the ultrastructure of these channels, there are limitations to efficiently addressing their presence over an entire cellular interface. Here, we highlight the value of serial block electron microscopy for this purpose. We developed a computational pipeline to study plasmodesmata distributions and detect the presence/absence of plasmodesmata clusters, or pit fields, at the phloem unloading interfaces of Arabidopsis (Arabidopsis thaliana) roots. Pit fields were visualized and quantified. As the wall environment of plasmodesmata is highly specialized, we also designed a tool to extract the thickness of the extracellular matrix at and outside of plasmodesmata positions. We detected and quantified clear wall thinning around plasmodesmata with differences between genotypes, including the recently published plm-2 sphingolipid mutant. Our tools open avenues for quantitative approaches in the analysis of symplastic trafficking.
Highlights
Plasmodesmata are small channels that connect plant cells
The data sets from Yan et al (2019) employed here cover an area encompassing the cells around the protophloem of Arabidopsis roots
Taking advantage of the spatial information on PD contained in the SB-Electron microscopy (EM) data sets, we studied their distribution at selected interfaces
Summary
Plasmodesmata are small channels that connect plant cells. While recent technological advances have facilitated analysis of the ultrastructure of these channels, there are limitations to efficiently addressing their presence over an entire cellular interface. SB-EM technology has been successfully employed to study PD, demonstrating defects in sieve pore (a modified form of PD) structure and distribution (Dettmer et al, 2014) and allowing the quantification of PD densities at the interfaces of the sieve element (SE; Ross-Elliott et al, 2017) and at the endodermal (EN) face of phloem pole pericycle (PPP) cells (Yan et al, 2019) Both SE and PPP cells are key players in the process of phloem unloading, largely mediated by PD (for review, see Truernit, 2017). Important parameters, such as the specific distributions of PD and the cell wall environment of the pores, despite being contained in these data sets, have so far been ignored
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