Aspects of Sieve Element Ontogeny and Structure in Smilax rotundifolia

Ervin, Edward L.; Evert, Ray F.

doi:10.1086/336389

Cited by 23 publications

(7 citation statements)

References 10 publications

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“…This is consistent with earlier investigations on the phloem of large numbers of taxa (Cheadle & Esau, 1958 ;Zahur, 1959 ;Wilson, 1965 ;Karnik, 1981 ;Outer, 1983Outer, , 1986Outer, , 1993Esau & Cheadle, 1984). However, a few reports have indicated the absence of companion cells in the protophloem of both roots and shoots of some angiosperms (Schneider, 1955 ;Parthasarathy, 1966 ;Ervin & Evert, 1967 ;Esau & Gill, 1973 ;Eleftheriou, 1996). Reports of the absence of companion cells in some dicot taxa considered to be primitive and of their only occasional occurrence in the genus Pyrus have not been substantiated by further studies (Esau, 1969).…”

Section: supporting

confidence: 90%

Companion cells in the secondary phloem of Indian dicotyledonous species: a quantitative study

2000

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Companion cells in the secondary phloem of 125 Indian dicotyledonous species belonging to 43 families were examined by light microscopy. Four types of companion cell were identified : E-, S-and L-types which were equal in length, shorter, or longer, respectively, than the associated sieve tube element ; and R-type, in which two or more companion cells in a vertical row were associated with the sieve tube element. The commonest was the Etype and the rarest was the L-type. E-type companion cells were most frequently found associated with short sieve tube elements (50-250 µm) which had a high frequency of simple sieve plates, considered phylogenetically advanced. R-type companion cells were most frequently associated with long sieve tube elements ( 400 µm) with a high frequency of compound sieve plates, considered phylogenetically the least advanced. A strong positive correlation was found between the average number of companion cells associated with a sieve tube element and the lengths of the sieve tube elements. There was also a strong negative correlation between the average number of companion cells associated with a sieve tube element and companion cell lengths.

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Section: supporting

confidence: 90%

Companion cells in the secondary phloem of Indian dicotyledonous species: a quantitative study

2000

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“…For the meristematic zone, phloem unloading is confined to PSEs, some of which were accompanied by CCs similar to other monocot stems (e.g. Ervin and Evert, 1967). If the PSEs were symplasmically isolated, as found for PSEs in stems of P. vulgaris (Wood et al, 1998), then Suc will exit PSE lumens across their plasma membrane.…”

Section: Functions Of Sugar Transporters Where Apoplasmic Unloading Mmentioning

confidence: 89%

Sucrose Transporter Localization and Function in Phloem Unloading in Developing Stems

et al. 2016

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How sucrose transporters (SUTs) regulate phloem unloading in monocot stems is poorly understood and particularly so for species storing high Suc concentrations. To this end, Sorghum bicolor SUTs SbSUT1 and SbSUT5 were characterized by determining their transport properties heterologously expressed in yeast or Xenopus laevis oocytes, and their in planta cellular and subcellular localization. The plasma membrane-localized SbSUT1 and SbSUT5 exhibited a strong selectivity for Suc and high Suc affinities in X. laevis oocytes at pH 5-SbSUT1, 6.3 6 0.7 mM, and SbSUT5, 2.4 6 0.5 mM Suc. The Suc affinity of SbSUT1 was dependent on membrane potential and pH. In contrast, SbSUT5 Suc affinity was independent of membrane potential and pH but supported high transport rates at neutral pH. Suc transport by the tonoplast localized SbSUT4 could not be detected using yeast or X. laevis oocytes. Across internode development, SUTs, other than SbSUT4, were immunolocalized to sieve elements, while for elongating and recently elongated internodes, SUTs also were detected in storage parenchyma cells. We conclude that apoplasmic Suc unloading from de-energized protophloem sieve elements in meristematic zones may be mediated by reversal of SbSUT1 and/or by uniporting SWEETs. Storage parenchyma localized SbSUT1 and SbSUT5 may accumulate Suc from the stem apoplasms of elongating and recently elongated internodes, whereas SbSUT4 may function to release Suc from vacuoles. Transiting from an apoplasmic to symplasmic unloading pathway as the stem matures, SbSUT1 and SbSUT5 increasingly function in Suc retrieval into metaphloem sieve elements to maintain a high turgor to drive symplasmic unloading by bulk flow.In most herbaceous crop plants, photoassimilates fixed in source leaves are loaded into the collection phloem as Suc, which is translocated through the transport phloem by a pressure flow mechanism to supply carbon substrate for sink growth and/or storage (Münch, 1930). A portion of the translocated Suc is unloaded along the transport phloem linking collection phloem of leaf minor veins with release phloem in terminal sinks, such as shoot/root apices and developing tubers, fruits, and seeds. While there is a growing mechanistic understanding of phloem unloading into terminal sinks, unloading from the transport phloem has attracted less attention. This status particularly applies to stems of monocot species that accumulate Suc to high concentrations such as sugarcane (Saccharum officinarum) and sweet Sorghum (Slewinski, 2012;Grof et al., 2014), in which stem storage is the predominant sink, limited by its capacity to accumulate Suc (Watt et al., 2013).Transport phloem of monocot stems traverses their intercalary meristems, located immediately above the basal node of each elongating internode, cell elongation and mature zones. Hence, Suc unloaded from the transport phloem supports stem growth (cell division and expansion) and storage (elongating and mature zones; Milne et al., 2015). Apoplasmic phloem unloading into the intercalary meristem ...

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“…Because PSEs lose their nucleus, they cannot divide to keep pace with the growth of the neighboring cells. Therefore, they become increasingly elongated until they become inactive in transport and eventually obliterated (Erwin and Evert, 1967; Eleftheriou and Tsekos, 1982; Furuta et al, 2014). In the elongation zone of the root, solutes are transferred laterally from the metaphloem SEs (MSEs) to the PSEs, allowing phloem continuity between source and sink tissues (Stadler et al, 2005; Winter et al, 1992).…”

Section: Introductionmentioning

confidence: 99%

Phloem unloading in Arabidopsis roots is convective and regulated by the phloem-pole pericycle

Ross‐Elliott

Jensen

Haaning

et al. 2017

eLife

209

210

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In plants, a complex mixture of solutes and macromolecules is transported by the phloem. Here, we examined how solutes and macromolecules are separated when they exit the phloem during the unloading process. We used a combination of approaches (non-invasive imaging, 3D-electron microscopy, and mathematical modelling) to show that phloem unloading of solutes in Arabidopsis roots occurs through plasmodesmata by a combination of mass flow and diffusion (convective phloem unloading). During unloading, solutes and proteins are diverted into the phloem-pole pericycle, a tissue connected to the protophloem by a unique class of ‘funnel plasmodesmata’. While solutes are unloaded without restriction, large proteins are released through funnel plasmodesmata in discrete pulses, a phenomenon we refer to as ‘batch unloading’. Unlike solutes, these proteins remain restricted to the phloem-pole pericycle. Our data demonstrate a major role for the phloem-pole pericycle in regulating phloem unloading in roots.DOI: http://dx.doi.org/10.7554/eLife.24125.001

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Aspects of Sieve Element Ontogeny and Structure in Smilax rotundifolia

Cited by 23 publications

References 10 publications

Companion cells in the secondary phloem of Indian dicotyledonous species: a quantitative study

Companion cells in the secondary phloem of Indian dicotyledonous species: a quantitative study

Sucrose Transporter Localization and Function in Phloem Unloading in Developing Stems

Phloem unloading in Arabidopsis roots is convective and regulated by the phloem-pole pericycle

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