scholarly journals Sucrose Concentration Gradients along the Post-Phloem Transport Pathway in the Maternal Tissues of Developing Wheat Grains

1995 ◽  
Vol 109 (2) ◽  
pp. 587-592 ◽  
Author(s):  
D. B. Fisher ◽  
N. Wang
Keyword(s):  
Sucrose Concentration ◽  
Phloem Transport ◽  
Concentration Gradients ◽  
Transport Pathway ◽  
Wheat Grains

The position of regenerating cambia: auxin/sucrose ratio and the gradient induction hypothesis

1978 ◽  
Vol 203 (1151) ◽  
pp. 153-176 ◽  
Keyword(s):  
Control System ◽  
Induction Hypothesis ◽  
Sucrose Concentration ◽  
Vascular Differentiation ◽  
Concentration Gradients ◽  
Published Evidence ◽  
Different Types ◽  
Source And Sink ◽  
Positional Control

To account for the positions in which vascular cambia regenerate in wound callus, a gradient induction hypothesis was proposed in 1961 in terms of gradients in ‘some factor as yet unknown’. It now seems likely that the gradient is based on morphogen diffusion between source and sink on opposite sides of existing cambia, with morphogen diffusing into the adjoining wound callus. It is specifically proposed that there are two morphogens, auxin diffusing centrifugally and sucrose diffusing centripetally. The cambium then regenerates along a path where the ratio of auxin to sucrose concentration is similar to that at the original cambium, and its orientation (as regards xylem and phloem formation) is determined by the direction of the gradient in this ratio. These proposals are supported by published evidence on auxin and sucrose concentration gradients across the cambium, and on their sources, movements, and known effects on vascular differentiation. Simulations of the proposed positional control system predict patterns of cambial regeneration and orientation corresponding to those observed in four different types of would and graft.

Sucrose Concentration Gradients in Wheat Leaves1

Crop Science ◽  
1980 ◽  
Vol 20 (1) ◽  
pp. 95 ◽  
Author(s):  
H. J. Lee ◽  
D. A. Ashley ◽  
R. H. Brown
Keyword(s):  
Sucrose Concentration ◽  
Concentration Gradients

scholarly journals Structural basis of Ca2+-dependent activation and lipid transport by a TMEM16 scramblase

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Maria E Falzone ◽  
Jan Rheinberger ◽  
Byoung-Cheol Lee ◽  
Thasin Peyear ◽  
Linda Sasset ◽  
...  
Keyword(s):  
Plasma Membranes ◽  
Structural Basis ◽  
Concentration Gradients ◽  
Transport Pathway ◽  
Outer Leaflet ◽  
Extracellular Signaling ◽  
Cryo Electron Microscopy ◽  
Cytosolic Domains ◽  
Controlling Processes ◽  
Lipid Nanodiscs

The lipid distribution of plasma membranes of eukaryotic cells is asymmetric and phospholipid scramblases disrupt this asymmetry by mediating the rapid, nonselective transport of lipids down their concentration gradients. As a result, phosphatidylserine is exposed to the outer leaflet of membrane, an important step in extracellular signaling networks controlling processes such as apoptosis, blood coagulation, membrane fusion and repair. Several TMEM16 family members have been identified as Ca2+-activated scramblases, but the mechanisms underlying their Ca2+-dependent gating and their effects on the surrounding lipid bilayer remain poorly understood. Here, we describe three high-resolution cryo-electron microscopy structures of a fungal scramblase from Aspergillus fumigatus, afTMEM16, reconstituted in lipid nanodiscs. These structures reveal that Ca2+-dependent activation of the scramblase entails global rearrangement of the transmembrane and cytosolic domains. These structures, together with functional experiments, suggest that activation of the protein thins the membrane near the transport pathway to facilitate rapid transbilayer lipid movement.

scholarly journals Phloem transport limitation in Huanglongbing affected sweet orange is dependent on phloem-limited bacteria and callose

2021 ◽  
Author(s):  
Stacey Welker ◽  
Myrtho Pierre ◽  
James Patrick Santiago ◽  
Manjul Dutt ◽  
Christopher Vincent ◽  
...  
Keyword(s):  
Genetic Material ◽  
Sugar Transport ◽  
Phloem Transport ◽  
Microbial Infection ◽  
Transport Pathway ◽  
Callose Deposition ◽  
Citrus Production ◽  
Candidatus Liberibacter ◽  
Phloem Translocation ◽  
Translocation Speed

Huanglongbing (HLB), caused by Candidatus Liberibacter asiaticus (CLas), is a phloem-limited disease which disrupts citrus production in affected areas. In HLB-affected plants, phloem sieve plate pores accumulate callose, and leaf carbohydrate export is reduced. However, whether HLB causes a reduction in carbohydrate phloem translocation speed, and the quantitative relationships among callose, CLas population, and phloem translocation are still unknown. In this work, a procedure was developed to concurrently measure sugar transport, callose deposition, and relative pathogen population at different locations throughout the stem. Increasing quantities of CLas genetic material were positively correlated with quantity and density of callose deposits, and negatively correlated with phloem translocation speed. Callose deposit quantity was site- and rootstock dependent, and were negatively correlated with phloem translocation speed, suggesting a localized relationship. Remarkably, callose accumulation and phloem translocation disruption in the scion was dependent on rootstock genotype. Regression results suggested that the interaction of Ct values and number of phloem callose depositions, but not their size or density, explained the effects on translocation speed. Sucrose, starch, and sink 14C label allocation data support the interpretation of a transport pathway limitation by CLas infection. This work shows that the interaction of local accumulation of callose and CLas affect phloem transport. Further, the extent of this accumulation is attenuated by the rootstock and provides important information about the disease mechanism of phloem-inhabiting bacteria. Together, these results constitute the first example of a demonstrated transport limitation of phloem function by a microbial infection.

scholarly journals Maternal Inositol Status and Neural Tube Defects: A Role for the Human Yolk Sac in Embryonic Inositol Delivery?

2020 ◽  
Author(s):  
Stephen W D'Souza ◽  
Andrew J Copp ◽  
Nicholas D E Greene ◽  
Jocelyn D Glazier
Keyword(s):  
Neural Tube ◽  
Normal Development ◽  
Important Determinant ◽  
Recurrence Risk ◽  
Concentration Gradients ◽  
Transport Pathway ◽  
Human Pregnancy ◽  
Periconceptional Period ◽  
Uptake Mechanisms

ABSTRACT Supplementation with myo-inositol during the periconceptional period of pregnancy may ameliorate the recurrence risk of having a fetus affected by a neural tube defect (NTD; e.g., spina bifida). This could be of particular importance in providing a means for preventing NTDs that are unresponsive to folic acid. This review highlights the characteristics of inositol and describes the role of myo-inositol in the prevention of NTDs in rodent studies and the evidence for its efficacy in reducing NTD risk in human pregnancy. The possible reduction in NTD risk by maternal myo-inositol implies functional and developmentally important maternal–embryonic inositol interrelationships and also suggests that embryonic uptake of myo-inositol is crucial for embryonic development. The establishment of active myo-inositol cellular uptake mechanisms in the embryonic stages of human pregnancy, when the neural tube is closing, is likely to be an important determinant of normal development. We draw attention to the generation of materno-fetal inositol concentration gradients and relationships, and outline a transport pathway by which myo-inositol may be delivered to the early developing human embryo. These considerations provide novel insights into the mechanisms that may underpin inositol's ability to confer embryonic developmental benefit.

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