scholarly journals Testing the Münch hypothesis of long distance phloem transport in plants

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Michael Knoblauch ◽  
Jan Knoblauch ◽  
Daniel L Mullendore ◽  
Jessica A Savage ◽  
Benjamin A Babst ◽  
...  
Keyword(s):  
Strong Support ◽  
Sieve Tube ◽  
Phloem Transport ◽  
Plant Tissues ◽  
Long Distance ◽  
Pressure Flow ◽  
Long Distance Transport ◽  
Sieve Tubes ◽  
Distance Transport ◽  
Source And Sink

Long distance transport in plants occurs in sieve tubes of the phloem. The pressure flow hypothesis introduced by Ernst Münch in 1930 describes a mechanism of osmotically generated pressure differentials that are supposed to drive the movement of sugars and other solutes in the phloem, but this hypothesis has long faced major challenges. The key issue is whether the conductance of sieve tubes, including sieve plate pores, is sufficient to allow pressure flow. We show that with increasing distance between source and sink, sieve tube conductivity and turgor increases dramatically in Ipomoea nil. Our results provide strong support for the Münch hypothesis, while providing new tools for the investigation of one of the least understood plant tissues.

PLASMODESMAL MODIFICATIONS AND DISTRIBUTION OF TOSPO VIRUS IN POTATO AND TOMATO

1999 ◽  
Vol 47 (4) ◽  
pp. 245-250 ◽  
Author(s):  
Ishwar D. Garg ◽  
S.M. Paul Khurana
Keyword(s):  
Long Distance ◽  
Phloem Tissue ◽  
Cortical Cells ◽  
Electron Dense Material ◽  
Phloem Parenchyma ◽  
Long Distance Transport ◽  
Infected Tomato ◽  
Sieve Tubes ◽  
The One ◽  
Distance Transport

The tospovirus isolate on tomato was found to be systemic while the one on potato was non-systemic. The virus was present in all the tissues except xylem vessels in tomato, while it was often found only in the cortical cells of potato stems. Virions were detected in all cells of phloem tissue in tomato, while none were present in the case of potato. Plasmodesmata were present between phloem parenchyma and the phloem sieve tubes in infected tomato but none were present in infected potato. There were pronounced plasmodesmal changes in response to infection in tomato. These included dissolution of the desmotubule (central rod-like structure), making the plasmodesmata pore-like structures with a diameter of ca. 45 nm, which contained electron-dense material, presumably ribonucleoprotein of the virus. No such changes were found in infected potato. These results of comparative studies suggested that the virus was non-systemic in potato due to its non-loading into the phloem and consequently lacked long distance transport.

scholarly journals Defenses against Virus and Vector: A Phloem-Biological Perspective on RTM- and SLI1-Mediated Resistance to Potyviruses and Aphids

Viruses ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 129 ◽  
Author(s):  
Karen J. Kloth ◽  
Richard Kormelink
Keyword(s):  
Virus Transmission ◽  
Phloem Transport ◽  
Long Distance ◽  
Functional Connection ◽  
Phloem Sap ◽  
Biological Perspective ◽  
Long Distance Transport ◽  
Underlying Mechanisms ◽  
Phloem Feeding ◽  
Distance Transport

Combining plant resistance against virus and vector presents an attractive approach to reduce virus transmission and virus proliferation in crops. Restricted Tobacco-etch virus Movement (RTM) genes confer resistance to potyviruses by limiting their long-distance transport. Recently, a close homologue of one of the RTM genes, SLI1, has been discovered but this gene instead confers resistance to Myzus persicae aphids, a vector of potyviruses. The functional connection between resistance to potyviruses and aphids, raises the question whether plants have a basic defense system in the phloem against biotic intruders. This paper provides an overview on restricted potyvirus phloem transport and restricted aphid phloem feeding and their possible interplay, followed by a discussion on various ways in which viruses and aphids gain access to the phloem sap. From a phloem-biological perspective, hypotheses are proposed on the underlying mechanisms of RTM- and SLI1-mediated resistance, and their possible efficacy to defend against systemic viruses and phloem-feeding vectors.

A study of phloem sieve element structure using electron, fluorescent, and confocal microscopy

1991 ◽  
Vol 49 ◽  
pp. 202-203
Author(s):  
Richard D. Sjolund ◽  
Chi Wang
Keyword(s):  
Cell Walls ◽  
Higher Plants ◽  
Post Injury ◽  
Long Distance ◽  
Callose Deposition ◽  
Sieve Elements ◽  
Long Distance Transport ◽  
P Protein ◽  
Sieve Tubes ◽  
Distance Transport

Phloem sieve elements are the cells responsible for the long distance transport of nutrients, primarily sugars and amino acids, in higher plants. The translocation of nutrients in these cells, joined together to form long sieve tubes, is dependent on the development of high hydrostatic pressures (20 bars or higher). The dissection of plant tissues containing these phloem cells which is necessary for microscopic study usually results in the cutting of the sieve elements and a resultant loss of phloem contents due to the explosive release of the hydrostatic pressure. Wound-sealing mechanisms involving P-protein filaments and callose deposition in the cell walls rapidly seal off wound sites and prevent the loss of translocates, especially in Angiosperms. As a result, most electron microscope images of sieve elements obtained from plant organs reveal post-injury structure following wounding.

scholarly journals Role of ureides in source-to-sink transport of photoassimilates in non-fixing soybean

2020 ◽  
Vol 71 (15) ◽  
pp. 4495-4511 ◽  
Author(s):  
Sandi Win Thu ◽  
Ming-Zhu Lu ◽  
Amanda M Carter ◽  
Ray Collier ◽  
Anthony Gandin ◽  
...  
Keyword(s):  
Transgenic Plants ◽  
Phloem Transport ◽  
Transport Processes ◽  
Long Distance ◽  
Long Distance Transport ◽  
Source To Sink ◽  
Cellular Import ◽  
Soybean Plants ◽  
Distance Transport

Abstract Nitrogen (N)-fixing soybean plants use the ureides allantoin and allantoic acid as major long-distance transport forms of N, but in non-fixing, non-nodulated plants amino acids mainly serve in source-to-sink N allocation. However, some ureides are still synthesized in roots of non-fixing soybean, and our study addresses the role of ureide transport processes in those plants. In previous work, legume ureide permeases (UPSs) were identified that are involved in cellular import of allantoin and allantoic acid. Here, UPS1 from common bean was expressed in the soybean phloem, which resulted in enhanced source-to-sink transport of ureides in the transgenic plants. This was accompanied by increased ureide synthesis and elevated allantoin and allantoic acid root-to-sink transport. Interestingly, amino acid assimilation, xylem transport, and phloem partitioning to sinks were also strongly up-regulated. In addition, photosynthesis and sucrose phloem transport were improved in the transgenic plants. These combined changes in source physiology and assimilate partitioning resulted in increased vegetative growth and improved seed numbers. Overall, the results support that ureide transport processes in non-fixing plants affect source N and carbon acquisition and assimilation as well as source-to-sink translocation of N and carbon assimilates with consequences for plant growth and seed development.

The Fine Structure of Phloem Cells

1985 ◽  
Vol 43 ◽  
pp. 632-635
Author(s):  
James Cronshaw
Keyword(s):  
Structural Studies ◽  
High Concentration ◽  
Long Distance ◽  
Phloem Tissue ◽  
Sieve Elements ◽  
Long Distance Transport ◽  
P Protein ◽  
Companion Cells ◽  
Electron Microscopical ◽  
Distance Transport

Long distance transport in plants takes place in phloem tissue which has characteristic cells, the sieve elements. At maturity these cells have sieve areas in their end walls with specialized perforations. They are associated with companion cells, parenchyma cells, and in some species, with transfer cells. The protoplast of the functioning sieve element contains a high concentration of sugar, and consequently a high hydrostatic pressure, which makes it extremely difficult to fix mature sieve elements for electron microscopical observation without the formation of surge artifacts. Despite many structural studies which have attempted to prevent surge artifacts, several features of mature sieve elements, such as the distribution of P-protein and the nature of the contents of the sieve area pores, remain controversial.

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