Transfer Cells: Novel Cell Types with Unique Wall Ingrowth Architecture Designed for Optimized Nutrient Transport

In Arabidopsis, polarized deposition of wall ingrowths in phloem parenchyma (PP) transfer cells (TCs) occurs adjacent to cells of the sieve element/companion cell (SE/CC) complex. However, the spatial relationships between these different cell types in minor veins, where phloem loading occurs, are poorly understood. PP TC development and wall ingrowth localization were compared to other phloem cells in leaves of Col-0 and the transgenic lines AtSUC2::AtSTP9-GFP and AtSWEET11::AtSWEET11-GFP that identify CCs and PP respectively. The development of PP TCs in minor veins, indicated by deposition of wall ingrowths, proceeded basipetally in leaves. However, not all PP develop ingrowths and higher levels of wall ingrowth deposition occur in abaxial- compared to adaxial-positioned PP TCs. Furthermore, the deposition of wall ingrowths was exclusively initiated on and preferentially covered the PP TC/SE interface, rather than the PP TC/CC interface, and only occurred in PP cells that were adjacent to SEs. Collectively, these results demonstrate the dominant impact of SEs on wall ingrowth deposition in PP TCs and suggest the existence of two sub-types of PP cells in leaf minor veins. Compared to PP cells, PP TCs showed more abundant accumulation of AtSWEET11-GFP, indicating functional differences in phloem loading between PP and PP TCs.

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Ontogeny of phloem transfer cells in Hieracium floribundum

Canadian Journal of Botany ◽

10.1139/b75-303 ◽

1975 ◽

Vol 53 (23) ◽

pp. 2745-2758 ◽

Cited By ~ 8

Author(s):

R. L. Peterson ◽

E. C. Yeung

Keyword(s):

Cell Types ◽

Transfer Cells ◽

Vascular Cambium ◽

Secondary Phloem ◽

Sieve Elements ◽

Wall Ingrowths ◽

Wall Ingrowth ◽

Companion Cells ◽

Parenchyma Cells ◽

Cambium Activity

The primary phloem system in the rhizome of Hieracium floribundum has transfer cells that have developed from companion cells and parenchyma cells, which are adjacent to sieve elements. In both cell types changes occur in the cytoplasmic organelles at the time of wall ingrowth formation. Dicytosomes and polyribosomes become more numerous and 'boundary formations' and other multivesiculated structures appear. Few microtubules were found in the cytoplasm at this time. After the wall ingrowths become obvious, the transfer cells develop numerous mitochondria and an enlarged nucleus. The phloem transfer cells become vacuolated with age and the wall ingrowths become less numerous. This may be associated with a change in the translocation pattern in the phloem after the inception of vascular cambium activity. Parenchyma cells in the secondary phloem usually become rather vacuolated and develop few wall ingrowths.

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Unraveling the puzzle of phloem parenchyma transfer cell wall ingrowth

Journal of Experimental Botany ◽

10.1093/jxb/eraa311 ◽

2020 ◽

Vol 71 (16) ◽

pp. 4617-4620 ◽

Cited By ~ 1

Author(s):

Tyler J McCubbin ◽

David M Braun

Keyword(s):

Cell Wall ◽

Phloem Loading ◽

Transfer Cells ◽

Transfer Cell ◽

Phloem Parenchyma ◽

Wall Ingrowth ◽

Experimental Botany

This article comments on: Wei X, Nguyen ST, Collings DA, McCurdy DW. 2020. Sucrose regulates wall ingrowth deposition in phloem parenchyma transfer cells in Arabidopsis via affecting phloem loading activity. Journal of Experimental Botany 71, 4690–4702.

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