Phloem Tissue and Sieve Elements in Algae, Mosses and Ferns

Behnke, H.–Dietmar

doi:10.1007/978-1-4684-8658-2_6

Cited by 14 publications

(5 citation statements)

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“…Whether the stem of Physcomitrella gametophore also has food-conducting cells is as yet unknown. Nevertheless, endohydric mosses like Physcomitrella often also possess specialized food-conducting cells, and these cells have been interpreted to resemble phloem sieve cells ( Behnke, 1975 ; Behnke and Sjolund, 2012 ). These food-conducting cells, also referred to as leptoids ( Hébant, 1970 , 1975 ; Behnke, 1975 ), are considered analogs of sieve elements ( Ligrone et al, 2000 ), and have been postulated to form a symplasmic conduit for the movement of sucrose in the gametophore ( Reinhart and Thomas, 1981 ; Raven, 2003 ).…”

Section: Introductionmentioning

confidence: 99%

“…Nevertheless, endohydric mosses like Physcomitrella often also possess specialized food-conducting cells, and these cells have been interpreted to resemble phloem sieve cells ( Behnke, 1975 ; Behnke and Sjolund, 2012 ). These food-conducting cells, also referred to as leptoids ( Hébant, 1970 , 1975 ; Behnke, 1975 ), are considered analogs of sieve elements ( Ligrone et al, 2000 ), and have been postulated to form a symplasmic conduit for the movement of sucrose in the gametophore ( Reinhart and Thomas, 1981 ; Raven, 2003 ). Intriguingly, the Physcomitrella genome harbors orthologs of H + -coupled sucrose uptake transporters (SUTs) ( Kühn and Grof, 2010 ; Reinders et al, 2012a ), and given that the mode of photosynthate transport in mosses is likely to be symplasmic ( Raven, 2003 ), it has been argued that the SUTs in moss gametophores in fact act to recover sucrose leaked into the apoplasm ( Reinders et al, 2014 ).…”

Section: Introductionmentioning

confidence: 99%

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Alternate Modes of Photosynthate Transport in the Alternating Generations of Physcomitrella patens

Regmi

Gaxiola

2017

Front. Plant Sci.

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Physcomitrella patens has emerged as a model moss system to investigate the evolution of various plant characters in early land plant lineages. Yet, there is merely a disparate body of ultrastructural and physiological evidence from other mosses to draw inferences about the modes of photosynthate transport in the alternating generations of Physcomitrella. We performed a series of ultrastructural, fluorescent tracing, physiological, and immunohistochemical experiments to elucidate a coherent model of photosynthate transport in this moss. Our ultrastructural observations revealed that Physcomitrella is an endohydric moss with water-conducting and putative food-conducting cells in the gametophytic stem and leaves. Movement of fluorescent tracer 5(6)-carboxyfluorescein diacetate revealed that the mode of transport in the gametophytic generation is symplasmic and is mediated by plasmodesmata, while there is a diffusion barrier composed of transfer cells that separates the photoautotrophic gametophyte from the nutritionally dependent heterotrophic sporophyte. We posited that, analogous to what is found in apoplasmically phloem loading higher plants, the primary photosynthate sucrose, is actively imported into the transfer cells by sucrose/H+ symporters (SUTs) that are, in turn, powered by P-type ATPases, and that the transfer cells harbor an ATP-conserving Sucrose Synthase (SUS) pathway. Supporting our hypothesis was the finding that a protonophore (2,4-dinitrophenol) and a SUT-specific inhibitor (diethyl pyrocarbonate) reduced the uptake of radiolabeled sucrose into the sporangia. In situ immunolocalization of P-type ATPase, Sucrose Synthase, and Proton Pyrophosphatase – all key components of the SUS pathway – showed that these proteins were prominently localized in the transfer cells, providing further evidence consistent with our argument.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Alternate Modes of Photosynthate Transport in the Alternating Generations of Physcomitrella patens

Regmi

Gaxiola

2017

Front. Plant Sci.

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“…LEPTOIDS are cells in bryophytes which are structurally specialized for generally short-distance transport of photoassimilates (Eschrich andSteiner, 1967, 1968;Hebant, 1970Hebant, , 1977. Although the general characteristics of leptoids have been summarized recently (Behnke, 1975;Hebant, 1977), there remains much to be understood about such features as the presence and nature of "pore" contents, the structure and frequency of plasmodesmata, and the chemistry of the so-called "nacreous" wall. This is the second in a series of papers from this laboratory dealing with the structure of leptoids in the gametophore of polytrichaceous mosses.…”

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confidence: 99%

Cell Wall Chemistry and Fine Structure in Leptoids of Dendroligotrichum (Bryophyta): The End Wall

Scheirer

1978

American J of Botany

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Leptoids (sieve elements) of Dendroligotrichum are characterized by a highly oblique end wall which is composed of cellulose (birefringent; IKI‐H2SO4‐positive), polyuronides (toluidine blue‐positive), pectins (hydroxylamine‐positive) and natural aldehydes (silver hexamine and silver proteinate‐positive). Cytochemically the end wall appears identical to the unevenly thickened lateral wall. Electron cytochemical localization of aldehydes with silver proteinate reveals two distinct wall layers in comparison to the 3‐layered lateral wall. Plasmodesmata are present in the end wall with a frequency of 15‐20 per μm2. A characteristic feature of end wall plasmodesmata is an expanded median cavity which is 0.12‐0.15 μm in diameter. Frequently an electron‐dense substance, whose chemical nature and origin are unknown, occludes the plasmodesmata.

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“…Differences between leptoids and primitive sieve elements are small (Htbant, 1977: 63;Scheirer, 1980: 299) and it is unlikely that any structural differences exist to distinguish them especially considering the most advanced types found in the gametophyte of the Polytrichales. The term 'sieve element of bryophytes' has been suggested to emphasize this essential similarity (Behnke, 1975). In Aglaophyton the cells of this zone are very similar to leptoids in having an S-shaped oblique end wall.…”

Section: The Nature Of the Conducting Strand In Aglaophttoxmentioning

confidence: 99%

Aglaophyton major, a non-vascular land-plant from the Devonian Rhynie Chert

Edwards

1986

Botanical Journal of the Linnean Society

121

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EDWARDS, D. S., 1986. Aglaophyton major, a non‐vascular land‐plant from the Devonian Rhynie Chert. The genus Aglaophyton is described to accommodate the plant formerly known as Rhynia major, re‐examined using new material and techniques. The plant, which is a sporophyte, is suggested to have been shorter than originally supposed and to have formed extensive stands of decumbent axes. These features, with information on the angle of dichotomous branching and the frequency of sporangia, are incorporated into a new reconstruction of the plant. The conducting strand within the axes consists of three zones, a central region of thin‐walled cells, a middle region of thick‐walled cells and an outer region of thin‐walled cells. There is no indication of differential wall thickenings in the cells of any of these zones and the strand is interpreted in terms of a bryophytic conducting strand, the inner two regions being comparable to hydroids and the outer region comparable to the leptoids found in polytrichaceous moss gametophytes and sporophyles. The plant thus exhibits characters intermediate between tracheophytes and some mosses and cannot be considered a member of either group; at the present time it is not assigned to a higher category. A rediagnosis of Rhynia gwynne‐vaughanii, based on published results and new data, is also included.

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Phloem Tissue and Sieve Elements in Algae, Mosses and Ferns

Cited by 14 publications

References 20 publications

Alternate Modes of Photosynthate Transport in the Alternating Generations of Physcomitrella patens

Alternate Modes of Photosynthate Transport in the Alternating Generations of Physcomitrella patens

Cell Wall Chemistry and Fine Structure in Leptoids of Dendroligotrichum (Bryophyta): The End Wall

Aglaophyton major, a non-vascular land-plant from the Devonian Rhynie Chert

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