What determines the composition of the phloem sap? Is there any selectivity filter for macromolecules entering the phloem sieve elements?

2020 ◽  
Vol 151 ◽  
pp. 284-291
Author(s):  
Varsha Garg ◽  
Christina Kühn
Keyword(s):  
Selectivity Filter ◽  
Phloem Sap ◽  
Sieve Elements

Proteins in the sieve element-companion cell complexes: their detection, localization and possible functions

2000 ◽  
Vol 27 (6) ◽  
pp. 489 ◽  
Author(s):  
Hiroaki Hayashi ◽  
Akari Fukuda ◽  
Nobuo Suzui ◽  
Shu Fujimaki
Keyword(s):  
Sieve Tube ◽  
Soluble Proteins ◽  
Sieve Element ◽  
Tissue Extract ◽  
Companion Cell ◽  
Phloem Sap ◽  
Sieve Elements ◽  
Cell Complexes ◽  
Companion Cells ◽  
Sieve Tubes

Many kinds of proteins have been found in the sieve element–companion cell complexes by the analyses of phloem sap and microscopic observations. The cDNAs, which encode some of these sieve-tube proteins, have already been cloned. As mature sieve elements lack nuclei and most ribosomes, sieve-tube proteins have been hypothesized to be synthesized in the companion cells and then transported to the lumina of the functional sieve tubes through the plasmodesmata connecting the companion cells and sieve elements. Soluble proteins present in the sieve tubes can be collected by several techniques, such as incision or the aphid technique. The composition of the proteins in the phloem sap is unique compared with that of tissue extract, suggesting these proteins have important roles for the development and functions of sieve tubes.

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.

Freeze-Fracture Studies of Membranes in Developing Sieve Elements in a Plant Tissue Culture

1980 ◽  
Vol 38 ◽  
pp. 636-637
Author(s):  
R. D. Sjolund ◽  
C. Y. Shih
Keyword(s):  
Plant Tissue ◽  
Cultured Cells ◽  
Freeze Fracture ◽  
Tissue Cultures ◽  
Sieve Elements ◽  
Intact Plants ◽  
Plant Tissue Cultures ◽  
Whole Plants ◽  
Energy Dependent ◽  
Similar Elements

The differentiation of phloem in plant tissue cultures offers a unique opportunity to study the development and structure of sieve elements in a manner that avoids the injury responses associated with the processing of similar elements in intact plants. Short segments of sieve elements formed in tissue cultures can be fixed intact while the longer strands occuring in whole plants must be cut into shorter lengths before processing. While iyuch controversy surrounds the question of phloem function in tissue cultures , sieve elements formed in these cultured cells are structurally similar to those of Intact plants. We are particullarly Interested In the structure of the plasma membrane and the peripheral ER in these cells because of their possible role in the energy-dependent active transport of sucrose into the sieve elements.

scholarly journals Recycling of Solanum Sucrose Transporters Expressed in Yeast, Tobacco, and in Mature Phloem Sieve Elements

2010 ◽  
Vol 3 (6) ◽  
pp. 1064-1074 ◽  
Author(s):  
Johannes Liesche ◽  
Hong-Xia He ◽  
Bernhard Grimm ◽  
Alexander Schulz ◽  
Christina Kühn
Keyword(s):  
Sieve Elements ◽  
Sucrose Transporters

Sodium ions do not stabilize the selectivity filter of a potassium channel

2021 ◽  
pp. 167091
Author(s):  
Kitty Hendriks ◽  
Carl Öster ◽  
Chaowei Shi ◽  
Han Sun ◽  
Adam Lange
Keyword(s):  
Potassium Channel ◽  
Selectivity Filter ◽  
Sodium Ions

Ion–peptide interactions between alkali metal ions and a termini-protected dipeptide: modeling a portion of the selectivity filter in K+ channels

2019 ◽  
Vol 21 (2) ◽  
pp. 561-571 ◽  
Author(s):  
Shun-ichi Ishiuchi ◽  
Yuta Sasaki ◽  
James M. Lisy ◽  
Masaaki Fujii
Keyword(s):  
Alkali Metal ◽  
Metal Ions ◽  
Selectivity Filter ◽  
Alkali Metal Ions ◽  
K Channels ◽  
Peptide Interactions

Differentiating K+ and Na+ binding patterns in peptide sequences.

Nondispersive Protein Bodies in Sieve Elements: A Survey and Review of their Origin, Distribution and Taxonomic Significance

IAWA Journal ◽  
1991 ◽  
Vol 12 (2) ◽  
pp. 143-175 ◽  
Author(s):  
H.-Dietmar Behnke
Keyword(s):  
Electron Microscope ◽  
Protein Bodies ◽  
Evolutionary Trends ◽  
Taxonomic Significance ◽  
Additional Species ◽  
Sieve Elements ◽  
P Protein ◽  
Taxonomic Range ◽  
Characteristic Features

Nondispersive protein bodies present in the sieve elements in addition to dispersive P-protein are characteristic features of many woody dicotyledons; their origin may be nuclear or cytoplasmic. While nuclear nondispersive protein bodies are found in only two families, the Boraginaceae and Myristicaceae, bodies of cytoplasmic origin are present in 39 of the more than 350 families screened. These results were obtained from 228 dicotyledons studied with the electron microscope and data of additional species from the literature. The terminology, origin, form and distribution of nondispersive protein bodies are discussed. Their ultrastructural composition is described as being predominantly spindle-shaped, compound- spherical, rod-shaped and rosette-like. Based on the data accumulated from over 450 species (of about 3000 screened) it is evident that their taxonomic range is confined to a few dicotyledon superorders. Compound-spherical nondispersive protein bodies are characteristic of most of the Malvanae/Violanae; spindle-shaped forms are restricted to the Fabaceae (Rutanae). Rosanae-Proteanae-Myrtanae and the Magnolianae are the only other superorders that contain nondispersive protein bodies in several of their families. Evolutionary trends and possible taxonomic consequences implied in this distribution are discussed.

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