scholarly journals Sieve tube structural variation in Austrobaileya scandens and its significance for lianescence

2021 ◽  
Author(s):  
Juan M Losada ◽  
Zhe He ◽  
Noel Michele Holbrook
Keyword(s):  
Structural Variation ◽  
Vascular System ◽  
Light And Electron Microscopy ◽  
Sieve Tube ◽  
Phloem Transport ◽  
Sieve Plate ◽  
Geometrical Properties ◽  
Mechanical Constraints ◽  
Vascular Elements ◽  
Sieve Plates

Lianas are characterized by large leaf areas and slender stems, a combination of features that require an efficient vascular system. The only extant member of the Austrobaileyaceae, is an endemic twining liana of the tropical Australian forests with well-known xylem hydraulic traits. However, the vascular phloem continuum through aerial organs remains understudied. We analyzed the structure of phloem conduits across leaf veins and stems of A. scandens, combining topological data obtained through light and electron microscopy, with current models of phloem transport. Leaves displayed a low xylem to phloem ratio compared with leaves of other angiosperms, with vascular elements invariant in diameter along the midrib, but tapered across vein hierarchies. Sieve plate pore radii were extremely small: 0.08μm in minor veins, increasing to 0.12μm in the petiole and only to 0.20μm at the base of the stem, tens of meters away. Searcher branches contained tube shaped phloem conduits with a pectin-rich wall, whereas twining stems displayed sieve elements with tangential connections that displayed a greater fraction of the tubes populated with an astonishing number of sieve plates. Hydraulic segmentation of the leaves in Austrobaileyaceae correlate with vesseless leaves that benefit photoassimilate export through volumetric scaling of the sieve tube elements. Yet, compared with canopy dominant trees, the geometrical properties of the sieve tube in twining stems, restrict considerably energy distribution in the sub-canopy layers, potentially favoring the allocation of assimilates toward the elongating branches. Thus, the conductive xylem of twining stems contrasts with a poorly conductive phloem that meets the mechanical constraints of lianescence.

scholarly journals Sieve tube structural variation in Austrobaileya scandens and its significance for lianescence

2021 ◽  
Author(s):  
Juan Losada ◽  
Zhe He ◽  
Noel Holbrook
Keyword(s):  
Resource Allocation ◽  
Hydraulic Resistance ◽  
Structural Variation ◽  
Vascular System ◽  
Sieve Tube ◽  
Sink Strength ◽  
Sieve Plate ◽  
Vascular Elements ◽  
Microscopy Analysis ◽  
Sieve Plates

Lianas combine large leaf areas with slender stems, features that require an efficient vascular system. The only extant member of the Austrobaileyaceae is an endemic twining liana of the tropical Australian forests with well-known xylem hydraulics, but the vascular phloem continuum aboveground remains understudied. Microscopy analysis across leaf veins and stems of A. scandens revealed a low foliar xylem to phloem ratio, with isodiametric vascular elements along the midrib, but tapered across vein orders. Small sieve plate pore radii increased from 0.08 µm in minor veins to 0.12 µm in the petiole, but only to 0.20 µm at the stem base, tens of meters away. In searcher branches, phloem conduits contained a pectin-rich wall and simple plates, whereas in twinning stems, conduits connected through highly-angled-densely populated sieve plates. Twisted and elongated stems of A. scandens display a high hydraulic resistance of phloem conduits, which decreases from leaves to stems, efficiently delivering photoassimilate from sources under Münch predictions. Sink strength of a continuously growing canopy might be stronger than in self-supporting understory plants, favoring resource allocation to aerial organs in angiosperms that colonized the vertical niche.

scholarly journals Anatomical features of conductive tissues of soybeans that prevent the penetration of pathogenic agents of bacterial blight into seeds

2021 ◽  
Vol 188 (4) ◽  
pp. 25-34
Author(s):  
S.V. Zelentsov ◽  
◽  
G.M. Saenko ◽  
E.V. Moshnenko ◽  
◽  
...  
Keyword(s):  
Bacterial Blight ◽  
Pathogenic Bacteria ◽  
Vascular System ◽  
Sieve Tube ◽  
Soybean Seeds ◽  
Oil Crops ◽  
Russian Research Institute ◽  
Sieve Plates ◽  
Soybean Leaves ◽  
Pathogenic Agents

The ways of penetration of pathogenic bacteria from the infected vegetative parts of plants into soybean seeds remain practically unexplored. It is widely believed that soybean seeds are infected through the vascular system from already infected areas of the vegetative parts. The aim of the present research was to study the possibility of penetration of pathogens of bacterial blight into soybean seeds through the conductive tissues of plants. The studies were carried out in 2019–2021 in V.S. Pustovoit All-Russian Research Institute of Oil Crops on plants and seeds of soybean variety Vilana. It was found that the size of stomatal slots in soybean leaves is 8–12 µm. This ensures free penetration of bacteria with a diameter of 1.3–1.7 µm into the leaf mesophyll. The pore sizes of the sieve plates of the phloem range from 0.4–0.7 to 0.8–1.6 µm, depending on the age of the plants. The largest pores of the phloem sieve plates are comparable to the diameters of pathogenic bacteria. However, a large number of transverse sieve plates located in the vessels of the phloem every 0.05–0.1 mm will filter and partially retain bacteria in each sieve tube along the path of cell sap in the phloem. Therefore, the pathogenic bacteria passing through the entire phloem from leaves infected with bacteriosis up to pods is physically unlikely. In pods, the vascular system ends in the area of attachment of the placenta to the seed hilum. In the hilum, there are no conductive tissues, and the further flow of water and nutrients into the seed is carried out diffusely through the plasmodesma of cell walls. It was found that the anatomical structure of the soybean phloem prevents the free movement of pathogenic bacteria along the conductive system directly into the inner tissues of the seeds. Therefore, the hypothesis of infection of soybean seeds with pathogens of bacterial blight through the conducting system of the plant should be considered untenable

Vascular System of the Stem of the Wheat Plant .II. Development

1972 ◽  
Vol 20 (1) ◽  
pp. 65 ◽  
Author(s):  
JW Patrick
Keyword(s):  
Vascular System ◽  
Wheat Plant ◽  
Sieve Tube ◽  
Triticum Aestivum L ◽  
Leaf Primordia ◽  
Vascular Differentiation ◽  
Vascular Elements ◽  
A Site ◽  
Further Development ◽  
Main Tiller

The sequence of vascular differentiation in the shoot of the main tiller of Triticum aestivum L. was reconstructed from seriai transverse sections of shoot apices made at various stages of development. The pattern of initiation and development of the pro- cambial strands was confirmed. The provascular bundles of the pith plexus arose independently and developed acropetally from the base of the future node. Early dif- ferentiation of proto-phloem and -xylem in the main procambial strands proceeded bidirectionally up the leaf primordia and down the stem from a site of initiation isolated from other differentiated vascular elements. Further development was basipetal from the tip of the primordia, and the rate of differentiation of the sieve elements was sufficient to maintain phloem continuity across the intercalary meristems of the laminae, sheaths, and internodes. Within the developing nodes sieve tube differentiation in the cross-linking strands lagged behind that of the leaf traces they interconnected, and this may influence the movement of photoassimilate from a recently expanded leaf to the apex.

Sieve tube elements in the stem of Neptunia oleracea Lour

1968 ◽  
Vol 16 (3) ◽  
pp. 433 ◽  
Author(s):  
JJ Shah ◽  
MR James
Keyword(s):  
Aquatic Plant ◽  
Sieve Tube ◽  
Sieve Plate ◽  
Callose Deposition ◽  
Nuclear Disintegration ◽  
Full Development ◽  
Companion Cells ◽  
Sieve Plates ◽  
Structural Aspects ◽  
Sieve Tube Element

Some structural aspects of the phloem of Neptunia oleracea, an aquatic plant, are reported. The sieve tube elements on an average are 190μ long and 13μ wide and have compound sieve plates at varying degrees of inclination. The developing sieve tube element has a single large spindle-shaped slime body, which presumably has an outer membrane. The slime body undergoes dispersal before or after full development of the sieve plate, but often nuclear degeneration occurs first. Distinct slime plugs are absent. Plastids and other granular bodies are attached to many of the strands, which are less than 0.5μ in diameter. During the process of nuclear disintegration the nuclear membrane is indistinct, and extruded nucleolus is not observed. Sieve areas and connections are comparatively few in number, and the sieve areas and wall connections as well as the sieve plates show scanty callose deposition. Plastids are abundant in the sieve tube elements, especially near the sieve plates. The companion cells of two consecutive sieve tube elements are placed on alternate sides and hence their longitudinal continuity is not always maintained. Companion cells do not exceed the length of the sieve tube element.

Studies on the Phloem Sealing Mechanism in Ricinus Fruit Stalks

1983 ◽  
Vol 10 (6) ◽  
pp. 561 ◽  
Author(s):  
J Kallarackal ◽  
JA Milburn
Keyword(s):  
Electron Microscopy ◽  
Sieve Tube ◽  
Sieve Plate ◽  
Tube System ◽  
Phloem Sap ◽  
Starch Grains ◽  
P Protein ◽  
Sieve Tubes ◽  
Sealing Mechanism ◽  
Sieve Plates

Fruit stalks of R. communis were made to exude phloem sap by repeated slicing at intervals of a few minutes. Samples 1 mm thick from the fruit stalks were fixed for electron microscopy. Samples were also fixed and processed for electron microscopy from previously intact (non-exuding) fruit stalks. Examination of the sieve tubes from these two different samples showed predominantly open sieve-plate pores in the exuding fruit stalk. The sieve plates of the non-exuding fruit stalk showed occlusion of the sieve-plate pores by P-protein. The starch grains from the broken plastids also had characteristic distributions. The implications of these observations are discussed in relation to comprehending the mechanism by which sieve-plate pores become choked, and so sealing the sieve-tube system as a result of injury.

scholarly journals THE FINE STRUCTURE AND DEVELOPMENT OF THE COMPANION CELL OF THE PHLOEM OF ACER PSEUDOPLATANUS

1965 ◽  
Vol 24 (1) ◽  
pp. 117-128 ◽  
Author(s):  
F. B. P. Wooding ◽  
D. H. Northcote
Keyword(s):  
Endoplasmic Reticulum ◽  
Sieve Tube ◽  
Acer Pseudoplatanus ◽  
Sieve Plate ◽  
Wheat Grain ◽  
Companion Cell ◽  
Large Nucleus ◽  
Cell Organelles ◽  
Phloem Tissue ◽  
Aleurone Cells

At maturity the companion cell of the phloem of the sycamore Acer pseudoplatanus has a large nucleus, simple plastids closely sheathed with rough endoplasmic reticulum, and numerous mitochondria. The cytoplasm contains numerous ribosomes, resulting in a very electron-opaque cytoplasm after permanganate fixation. Bodies similar to the spherosomes of Frey-Wyssling et al. (4) are collected in clusters and these also contain bodies of an unidentified nature similar to those found by Buttrose (1) in the aleurone cells of the wheat grain. The pores through the wall between the companion cell and sieve tube are complex and develop from a single plasmodesma. Eight to fifteen plasmodesmata on the companion cell side communicate individually with a cavity in the centre of the wall which is linked to the sieve tube by a single pore about twice the diameter of an individual plasmodesma. This pore is lined with material of an electron opacity equivalent to that of material bounding the sieve plate pores. The development of the cell organelles, the possible role played in the phloem tissue by the companion cell, and the function of the complex pores contained in its wall are discussed.

Vascular system of the floret of Alopecurus carolinianus (Gramineae)

1987 ◽  
Vol 65 (12) ◽  
pp. 2592-2600 ◽  
Author(s):  
Thompson Demetrio Pizzolato
Keyword(s):  
Vascular System ◽  
Sieve Tube ◽  
Sieve Element ◽  
Sieve Elements

The interconnecting vascular system of the floret of Alopecurus carolinianus Walter begins as a single, collateral bundle, which enters the rachilla and becomes reorganized into a diarch pattern while ascending between the glumes. During a pronounced posterior enlargement, the rachilla bundle becomes connected with the median and four lateral bundles of the lemma. Above the trace to the lemma median, elements of a xylem discontinuity surrounded by those of a sieve-element plexus form in the rachilla bundle. Higher, a trace consisting of elements of the xylem discontinuity and the plexus enters the anterior and the posterior stamen. Two bundles, the lowest portion of the pistil vasculature, rise eccentrically from the xylem discontinuity and sieve-element plexus at the level of the stamen traces. The bundles condense into one which rotates counterclockwise and connects with the anterior sieve tube of the pistil. The xylem discontinuity of the bundle now in the pistil begins to diminish, and the sieve elements fan out to the sides and posterior of the xylem discontinuity. From the sieve elements one or two posterolaterals emerge toward the styles. The bundle of diffuse sieve elements in a semicircle behind the diminishing xylem discontinuity is now the placental bundle of the pistil. After its xylem discontinuity and then its sieve elements fade out, the placental bundle merges with the ovule at the chalaza.

Further theoretical analysis of concentration–pressure–flux waves in phloem transport systems

1978 ◽  
Vol 56 (8) ◽  
pp. 1086-1090 ◽  
Author(s):  
Jack M. Ferrier
Keyword(s):  
Hydrostatic Pressure ◽  
Water Flux ◽  
Sieve Tube ◽  
Phloem Transport ◽  
Time Dependent ◽  
Transport Systems ◽  
Flux Variation ◽  
Complex Interactions ◽  
Theoretical Results ◽  
Sugar Source

Theoretical results show that waves involving complex interactions between osmotic pressure, hydrostatic pressure, and fluxes of water and solute can occur in any phloem transport system surrounded by a semipermeable membrane. These results show that such waves can travel from sugar sink to sugar source as well as from sugar source to sugar sink. The time-dependent sugar concentration variation is shown to be caused largely by the time-dependent variation of the gradient of mass flow velocity in the sieve tube which is produced by the time-dependent variation of water flux across the membrane. This water flux variation is produced by a slight phase difference between osmotic and hydrostatic pressure variation. It is proposed that this phenomenon be called the concentration–pressure–flux (CPJ) wave.

scholarly journals THE FINE STRUCTURE OF DIFFERENTIATING SIEVE TUBE ELEMENTS

1965 ◽  
Vol 25 (1) ◽  
pp. 79-95 ◽  
Author(s):  
G. Benjamin Bouck ◽  
James Cronshaw
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Fine Structure ◽  
Fibrous Material ◽  
Sieve Tube ◽  
Longitudinal Direction ◽  
Sieve Plate ◽  
Wall Surface ◽  
Developmental Sequences ◽  
Tubular Form

The developmental sequences leading to the formation of mature sieve tube elements were studied in pea plants by electron microscopy. From this study it has been found that the peripheral layer of cytoplasm in the mature element is composed of flattened cisternae which are apparently derived from a tubular form of endoplasmic reticulum (ER) and possibly the nuclear envelope. These flattened cisternae, designated in this report as sieve tube reticula, are attached perpendicularly to the wall surface and are oriented in a predominantly longitudinal direction. Cisternae of the sieve tube reticulum are frequently associated with the slime in mature elements, and tubular ER may be associated with slimelike material in the developing sieve tube element. During differentiation mitochondria become reduced in size and chloroplasts either fail to develop stroma and grana lamellae or lose them early in development. In agreement with other workers it is found that the sieve plate pores appear to be plugged with a finely fibrous material, presumably "slime." Nacreous wall formation is well established before reorganization of cytoplasmic components. Microtubules are prevalent during these early stages, but are lost as the element matures.

Seasonal Changes in Callose Levels and Fluorescein Translocation in the Phloem of Vitis Vinifera L.

IAWA Journal ◽  
1991 ◽  
Vol 12 (3) ◽  
pp. 223-234 ◽  
Author(s):  
Roni Aloni ◽  
Carol A. Peterson
Keyword(s):  
Vitis Vinifera ◽  
Sieve Tube ◽  
Growing Season ◽  
Early Spring ◽  
Vitis Vinifera L ◽  
First Year ◽  
Secondary Phloem ◽  
Radial Gradient ◽  
Sieve Tubes ◽  
Sieve Plates

The secondary phloem of Vitis vinifera L. is characterised by a radial gradient of sieve tube diameters. Sieve tubes maturing early in the growing season have the largest diameters; those maturing late in the season have the smallest. In early spring, masses of winter dormancy callose are gradually digested in a polar radial pattern, proceeding outwards from the cambium. The fluorescent dye, fluorescein, was used to detect translocation in sieve tubes. During spring, dye translocation was first observed in the wider sieve tubes produced near the end of the previous year and wh ich had reduced amounts of callose. But translocation was not observed in the very narrow sieve tubes formed at the end of the year although they were the first to be callose free. The reactivated sieve tubes functioned for about one month. New sieve tubes differentiated three weeks after dormancy callose breakdown and started to function about one week later, so that the transition of translocation activity from the sieve tubes of the previous year to those of the current year is relatively rapid. The sieve tubes formed toward the end of the growing season (but not the narrowest ones formed at the very end of the season) function during parts of two successive seasons, while the sieve tubes forrned early in the season usually function during the first year only. Callose amounts increase gradually during summer in both the old and new sieve tubes and become relatively heavy in the old ones. At this developmental stage, translocation occurs through young sieve plates with relatively high callose deposits.

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