Post-Sieve Element Transport of Sucrose in Developing Seeds

1995 ◽  
Vol 22 (4) ◽  
pp. 681 ◽  
Author(s):  
JW Patrick ◽  
CE Offler
Keyword(s):  
Plasma Membranes ◽  
Grain Legumes ◽  
Experimental Models ◽  
Sieve Element ◽  
Assimilate Transport ◽  
Sucrose Transport ◽  
Cell Complexes ◽  
Developing Seeds ◽  
Element Transport ◽  
Energy Dependent

Developing seeds of cereals and grain legumes have proven to be useful experimental models to examine post-sieve element assimilate transport in sink tissues. Morphologically, these seeds offer well-defined sinks in which the processes of sucrose import plus efflux and influx plus metabolism may be examined independently. In all cases, sucrose is delivered through the phloem to the maternal seed tissues. Unloading from the sieve element-companion cell complexes is symplastic. Subsequently, sucrose moves through a symplastic route to cells responsible for sucrose efflux to the seed apoplast. The efflux cells are located at, or near, the maternal/filial interface. Sucrose is retrieved from the seed apoplast by the outermost cell layers of the filial tissues. Subsequent transfer of sucrose to the sites of storage in the filial tissues is confined principally to a symplastic route. Sucrose efflux from the maternal tissues appears to be passive in cereals and energy dependent in grain legumes, possibly through a sucrose/proton antiport system. Sucrose influx across the plasma membranes of the filial cells is energy dependent and, for grain legumes, is energy coupled through a sucrose/proton symporter. Studies on the control of post-sieve element transport of sucrose have focused largely on the membrane transport steps. The role of phytohormones as modulators of sucrose transport is uncertain in grain legumes, efflux from the maternal cells could be regulated by rates of sucrose utilisation in the filial tissues through a turgor homeostat mechanism located in the efflux cells.

Genotypic differences in seed growth rates of Phaseolus vulgaris L. II. Factors contributing to cotyledon sink activity and sink size

2000 ◽  
Vol 27 (2) ◽  
pp. 119 ◽  
Author(s):  
Mechthild Tegeder ◽  
Melinda Thomas ◽  
Louise Hetherington ◽  
Xin-Ding Wang ◽  
Christina E. Offler ◽  
...  
Keyword(s):  
Growth Rates ◽  
Membrane Surface ◽  
Genotypic Variation ◽  
Microsomal Protein ◽  
Sucrose Transport ◽  
Cell Complexes ◽  
Dermal Cell ◽  
Seed Growth ◽  
Cultivar Variation ◽  
Plasma Membrane Surface

A previous study [Thomas et al. (2000) Aust. J. Plant Physiol. 27, 109–118] showed that genotypic dif-ferences in seed growth rates of Phaseolus vulgaris L. cultivars was accounted for by variation in dry matter flux and seed size. Bulk cotyledon saps contained identical concentrations of sucrose across cultivars suggesting that geno-typic variation in capacities for sucrose transport and metabolism are equally matched. Cotyledon sucrose transport, monitored as in vitro uptake of [14C]sucrose, exhibited genotypic variation and this was abolished by para-chloromercuribenzene- sulfonate. Eadie–Hofstee transformations of concentration-dependent [14C]sucrose uptake showed that genotypic variation in sucrose flux resulted from differences in maximal transporter activity. Maximal sucrose fluxes and levels of transcript and microsomal protein for the sucrose/H+ symporter and H+-ATPase were positively correlated. In contrast, sucrose binding protein transcript and microsomal protein levels correlated negatively with sucrose fluxes. In all cultivars, a sucrose/H+ symporter and H+-ATPase were co-localised to plasma membranes of the dermal cell complexes. Total plasma membrane surface areas of the dermal cell complexes and total volume of storage parenchyma cells correlated with cultivar variation in seed growth rates. Differences in cell number and size accounted for cultivar variation in total plasma membrane surface area of the dermal cell complexes and total storage parenchyma cell volume.

scholarly journals Comprehensive hormone profiling of the developing seeds of four grain legumes

2013 ◽  
Vol 32 (12) ◽  
pp. 1939-1952 ◽  
Author(s):  
Susan M. H. Slater ◽  
Hai Ying Yuan ◽  
Monika M. Lulsdorf ◽  
Albert Vandenberg ◽  
L. Irina Zaharia ◽  
...  
Keyword(s):  
Grain Legumes ◽  
Developing Seeds ◽  
Hormone Profiling

scholarly journals Experimental membranous nephropathy redux

2005 ◽  
Vol 289 (4) ◽  
pp. F660-F671 ◽  
Author(s):  
Andrey V. Cybulsky ◽  
Richard J. Quigg ◽  
David J. Salant
Keyword(s):  
Signaling Pathways ◽  
Complement Activation ◽  
Membranous Nephropathy ◽  
Plasma Membranes ◽  
Stress Proteins ◽  
Experimental Models ◽  
Slit Diaphragm ◽  
Glomerular Epithelial Cell ◽  
Substantial Progress ◽  
Key Steps

Membranous nephropathy (MN) is a common cause of nephrotic syndrome in adults. Active and passive Heymann nephritis (HN) in rats are valuable experimental models because their features so closely resemble human MN. In HN, subepithelial immune deposits form in situ as a result of circulating antibodies. Complement activation leads to assembly of C5b-9 on glomerular epithelial cell (GEC) plasma membranes and is essential for sublethal GEC injury and the onset of proteinuria. This review revisits HN and focuses on areas of substantial progress in recent years. The response of the GEC to sublethal C5b-9 attack is not simply due to disruption of the plasma membrane but is due to the activation of specific signaling pathways. These include activation of protein kinases, phospholipases, cyclooxygenases, transcription factors, growth factors, NADPH oxidase, stress proteins, proteinases, and others. Ultimately, these signals impact on cell metabolic pathways and the structure/function of lipids and key proteins in the cytoskeleton and slit-diaphragm. Some signals affect GEC adversely. Thus C5b-9 induces partial dissolution of the actin cytoskeleton. There is a decline in nephrin expression, reduction in F-actin-bound nephrin, and loss of slit-diaphragm integrity. Other signals, such as endoplasmic reticulum stress, may limit complement-induced injury, or promote recovery. The extent of complement activation and GEC injury is dependent, in part, on complement-regulatory proteins, which act at early or late steps within the complement cascade. Identification of key steps in complement activation, the cellular signaling pathways, and the targets will facilitate therapeutic intervention in reversing GEC injury in human MN.

scholarly journals Thrombocytopoiesis--analysis by membrane tracer and freeze-fracture studies on fresh human and cultured mouse megakaryocytes.

1984 ◽  
Vol 99 (2) ◽  
pp. 390-402 ◽  
Author(s):  
D Zucker-Franklin ◽  
S Petursson
Keyword(s):  
Plasma Membrane ◽  
Plasma Membranes ◽  
Freeze Fracture ◽  
Precursor Cell ◽  
Membrane Domains ◽  
Thin Sections ◽  
Energy Dependent ◽  
First Time ◽  
Later Phase ◽  
Peripheral Cytoplasm

The origin of platelets (Pt) from megakaryocytes (MK) is beyond question, but the mechanism whereby Pts are released from the precursor cell is still debated. A widely-held theory claims that the MK plasma membrane invaginates to form demarcation membranes (DMS), which delineate Pt territories. Accordingly, Pts would be derived mostly from the periphery of the MK, and the MK and Pt plasma membranes would have to be virtually identical. Since, on morphologic grounds, this theory is untenable, several aspects of thrombocytopoiesis were reexamined with the help of membrane tracer and freeze-fracture analyses of freshly-collected human and cultured mouse MK. To our surprise, freeze-cleavage of the MK plasma membrane revealed that the vast majority of intramembranous particles (IMP) remained associated with the protoplasmic leaflet (P face), whereas the partition coefficient of IMPs of the platelet membrane was the reverse. This is the first time that any difference between MK and Pt membranes has been determined. Replicas of freeze-fractured MK that were in the process of thrombocytopoiesis revealed an additional novel phenomenon, i.e., numerous areas of membrane discontinuity that appeared to be related to Pt discharge. When such areas were small, the IMP were lined up along the margin of the crevice. At a later phase, a labyrinth of fenestrations was observed. Thin sections of MK at various stages of differentiation showed that Pt territories were fully demarcated before connections of the DMS with the surface could be found. Therefore, the Pt envelope is probably not derived from invaginations of the MK plasma membrane. When living, MK were incubated with cationic ferritin or peroxidase at 37 degrees C, the tracers entered into the DMS but did not delineate all membranes with which the DMS was in continuity, suggesting the existence of distinctive membrane domains. Interiorization of tracer was not energy-dependent, but arrested at low temperatures. At 4 degrees C the DMS remained empty, unless there was evidence that Pts had been released. In such instances, the tracers outlined infoldings of peripheral cytoplasm that was devoid of organelles. Thus, the majority of Pts seem to originate from the interior of the MK, and the surface membranes of the two cells differ in origin and structure. The observations do not only throw new light on the process of thrombocytopoiesis, but also strengthen the possibility that MKs and Pts may be subject to different stimuli.

Source physiology and assimilate transport: the interaction of sucrose metabolism, starch storage and phloem export in source leaves and the effects on sugar status in phloem

2000 ◽  
Vol 27 (6) ◽  
pp. 497 ◽  
Author(s):  
Ewald Komor
Keyword(s):  
Genetic Manipulation ◽  
Sieve Tube ◽  
Phloem Loading ◽  
Assimilate Transport ◽  
Vascular Bundles ◽  
Ambient Conditions ◽  
Sucrose Transport ◽  
Carbon Export ◽  
Export Rate ◽  
Long Day

Phloem loading of sucrose is decisive for the speed of mass flow, because sucrose is the dominant solutein the sieve tube sap of nearly all plant species. The export rate of carbon is linearly correlated to the concentration of sucrose in green leaves. Saturation of export was not observed, because surplus of assimilates is converted to starch, a process which is regulated by the sucrose level in the cytosol. Consequently, an increase of sucrose synthesis by overexpression of SPS did not enhance carbon export (at least under normal ambient conditions). Saturation of sucrose export could be observed only in experimental systems, where sucrose was fed directly to the phloem (e.g. in Ricinus seedling) or where constraints on transport activity were imposed by genetic manipulation either on the transporters (e.g. in sucrose transporter antisense plants) or on the path of sucrose (e.g. in plants trans ormed with TMV movement protein, or by incubation in salts). The balance between carbon storage and carbon export is subject to adaptation to meet growth requirements under special circumstances. For example, in a starch-deficient mutant, the day time export rate is nearly doubled compared to wild type plants. Furthermore, plants under short day illumination greatly accelerated starch storage compared to plants under long day illumination (a modulation which persists even a few days after a shift to long day conditions). Plants with a higher assimilation rate due to elevated ambient CO2 increase the nightly carbon export rate, whereas the export rate in day time rate appeared to work at its upper limit. The overall efficiency of sucrose export and incorporation into biomass is ca 0.65, which is close to the theoretical value of 0.75. Sucrose transport along the phloem strands is modulated according to the input at the source, but the individual phloem strands show also partial coordination with respect to sucrose concentrations (as revealed by NMR-imaging), especially obvious after physical interruption of some vascular bundles.

Transport of nutrients into developing seeds: a review of physiological mechanisms

1992 ◽  
Vol 2 (2) ◽  
pp. 59-73 ◽  
Author(s):  
P. Wolswinkel
Keyword(s):  
Seed Coat ◽  
Storage Proteins ◽  
Nutrient Transport ◽  
Assimilate Transport ◽  
Sink Strength ◽  
High Concentration ◽  
Precocious Germination ◽  
Developing Seeds ◽  
Empty Seed ◽  
Taxonomic Groups

AbstractAfter synthesis in the vegetative parts of the plant, assimilates are translocated to fruits through xylem and phloem. Research on factors controlling nutrient transport into developing seeds via the phloem has been stimulated by the development of the empty seed coat technique.There is a consensus that as assimilates are transported from maternal tissues to filial tissues they are delivered to the extracellular space (the apoplast) separating the two generations, prior to uptake from the apoplast into the tissues of the embryo or endosperm. The empty seed coat technique has been used for the study of several aspects of nutrient transport into seeds, e.g. metabolic control and turgorsensitive transport. The osmotic environment of seed tissues has a strong effect on assimilate transport into empty seeds. Several lines of evidence suggest that one of the main ‘secrets’ of the high sink strength of developing seeds, at least in many taxonomic groups of dicotyledons, is that the sink end of the phloem pathway is ‘bathed’ in an apoplast solution with a high concentration of osmotically active solutes. Data on maize do not fit this pattern. A turgor homeostat mechanism may help to maintain high solute concentrations in the seed apoplast. The apoplast environment of seed tissues may also stimulate synthesis of storage proteins and be involved in the prevention of precocious germination. In addition to the osmotic environment, other factors influencing sink strength are discussed. Some aspects of solute transformation during transport through seed tissues are described.

Plasma membrane localization of the type I H+-PPase AVP1 in sieve element–companion cell complexes from Arabidopsis thaliana

Plant Science ◽  
2011 ◽  
Vol 181 (1) ◽  
pp. 23-30 ◽  
Author(s):  
Julio Paez-Valencia ◽  
Araceli Patron-Soberano ◽  
Alejandra Rodriguez-Leviz ◽  
Jonathan Sanchez-Lares ◽  
Concepcion Sanchez-Gomez ◽  
...  
Keyword(s):  
Arabidopsis Thaliana ◽  
Plasma Membrane ◽  
Sieve Element ◽  
Membrane Localization ◽  
Type I ◽  
Companion Cell ◽  
Cell Complexes ◽  
Plasma Membrane Localization

Post-sieve element transport of photoassimilates in sink regions

1996 ◽  
Vol 47 (Special_Issue) ◽  
pp. 1165-1177 ◽  
Author(s):  
J.W. Patrick ◽  
C.E. Offler
Keyword(s):  
Sieve Element ◽  
Element Transport
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