Vascular bundles

Air pollutants may enter plant systems by either a primary or a secondary pathway. The primary pathway is analogous to human inhalation. Figure 8-2 shows the cross section of a leaf. Both of the outer surfaces are covered by a layer of epidermal cells, which help in moisture retention. Between the epidermal layers are the mesophyll cells—the spongy and palisade parenchyma. The leaf has a vascular bundle which carries water, minerals, and carbohydrates throughout the plant. Two important features shown in Fig. 8-2 are the openings in the epidermal layers called stomates, which are controlled by guard cells which can open and close, and air spaces in the interior of the leaf. 

In the peel strong immunological depositions of acetyl esterase were found in epidermis, the small cells of the exocarp and in the oil cavities (Fig. 3 A,B,C). In the mesocarp and endocarp the immunological depositions were more moderate (Fig. 3 D), but strong immunological depositions were found in the vascular bundles, especially in xylem. The immunological depositions in the peel seem to be correlated with cell size or cell age. The small cytoplasma rich cells have a higher content of acetyl esterase. 

In lamella and core the strongest immunological depositions were found in the vascular bundles (Fig. 3 F), whereas acetyl esterase was present in moderate amounts in all other cells. No acetyl esterase was found in the outermost parts of the tissues, cuticula of epidermis, innermost cell layer of endocarp, outer walls of juice vesicles and outer cell layer of lamella. 

It has been postulated that CH4 in the gaseous form or dissolved in water enters into root aerenchyma, which forms by degeneration of cortical cells between the exodermis and the vascular bundle, where the dissolved CH4 is gasified and moves by diffusion from the root aerenchyma through the restrictive transition zone into the aerenchyma of the culm and then... 

Fig. 2 OCT image and microscopy section of a plant, a - OCT image of the leaf from upper side b - microscopic section of the leaf c - OCT image of lower side of the leaf. White bar in the images correspond to 1 mm. Arrows indicate vascular bundles in OCT images and in microscopy sections...

In the early stages, the tissue around the vascular bundles appears semitranslucent, glassy, and water-soaked. As the infection progresses, the vascular ring becomes discolored and the tissue around it degrades and develops a colorless rot with a paste-like consistency. 

Transgenic tomato plants Wound induced vascular bundle-specific expression of P-glucuronidase gene Jacinto et al. (14)... 

S. gftajnintm feeds preferentially from phloem (17). Hydroxamic acids are more concentrated in the vascular bundles of wheat leaves than in other tissues. Moreover, these compounds are not present in... 

The apparent orientation of insect stylets to the vascular bundles caused by hydrogen ion concentrations was first reported by Fife and Frampton ( ). The leafhoppers fed mainly in the phloem tissue, which had a substantially higher pH than the surrounding plant cells. Other discriminating criteria for phloem-feeding insects have been indicated, including carbohydrate concentration (10) and positive hydrostatic pressure (11). 

Special characteristics Small hairs Stems with vascular bundles... 

I Stems with open vascular bundles in a circle, with a cambium cylinder embryo usually with two cotyledons and a terminal plumule flowers mostly pentamerous or tetramerous, of many diverse types from low to high, occasionally trimerous plants of many... 

II Stems with closed, usually scattered vascular bundles embryo usually with one terminal cotyledon and a lateral plumule flower parts mostly in threes, all except the lowest types being of die pentacyclic trimerous condition or a modification of this leaves commonly three-spiral in the lower types and two-ranked in the higher.-.Class Monocotyledoneae... 

Closed Vascular Bundle A vascular bundle in which there is no cambium and consequently no secondary growth. 

The C4 cycle for concentration of carbon dioxide. The C4 plants reduce their rate of photorespiration by using a C02 concentrating mechanism that enables them to avoid the competition from 02. All species of C4 plants have a characteristic internal leaf anatomy in which a single dense layer of dark green cells surrounds the vascular bundles in the leaves. This bundle sheath is surrounded by a loosely packed layer of... 

Measurement of the moisture diffusion coefficient as a function of position in wheat grain was performed [47] the moisture diffusion rate normal to the transverse 1.3 mm section of wheat grain was measured in structural features at a 150 pm resolution. The motion of water was most severely hindered in the endosperm, and water appeared less hindered in the vascular bundles. 

The amount of limonin incorporated into the juice is influenced by a number of juice processing variables. Factors such as the maceration of albedo, central vascular bundle and carpellary membranes, the time of contact between the rag and the juice, and the amount of pulp incorporated into the final juice product are known to influence juice limonin content. The uneven distribution of XIV in the various tissues of the fruit (Table VII) is largely responsible for the effects of processing variables (33). 

Features Root bark thick, greyish-brown outside, transverse section yellowish, vascular bundles in radiating lines. Fracture short and mealy. Very bitter and mucilaginous in taste. 

The anatomy of the tuber is shown diagrammatically in Figure 11.2. Parts that can be distinguished are the skin (periderm) with the lenticels, the eyes, the bud and stem ends, the cortex, the ring of vascular bundles, the perimedullary zone, and the pith with medullary rays which are homologous with the medulla of the stolon.7... 

Accumulation of fructans is enhanced by high light intensity and moderate temperatures. It is reduced by excess nitrogen or insufficient potassium (Soja and Haunold, 1991). Distribution of assimilates initially occurs on the periphery of the stem with subsequent movement inward. The portion of the stem receiving assimilates is dictated by its vascular connections. Radial movement inward is restricted to cells interior to vascular bundles. 

Sedimentation of amyloplasts within the cell has been correlated with the capacity of the plant to perceive gravity. The buoyant mass of amyloplasts present in specialized cells in the center of the root cap and in the stem (depending on the plant species, in the endodermis, the bundle sheath, or in the parenchyma to the inside of the vascular bundle) would allow the amyloplasts to sediment inside the cell, where the cytosol would have a relatively low viscosity. This sedimentation would translate into a signal of an unknown nature, maybe through pressure onto a sensitive part of the cell or acting as a mechano transducer, etc. Whatever the nature of the signal, it eventually results in the asymmetry of the organ and its curvature. The isolation of starchless mutants of Arabidopsis thaliana and Nicotiana sylvestris has made... 

Figure 1-3. Idealized longitudinal section through part of a vascular bundle in a stem, illustrating various anatomical aspects of the xylem and the phloem. New cells forming in the xylem initially contain cytoplasm, which is lost as the cells mature and become conducting. Fiber cells, which occur in the xylem, are usually quite tapered and provide structural support. The nucleated companion cells are metabolically involved with the sieve-tube members of the phloem.

Figure 8-14. Schematic transverse section through a leaf of a C4 plant, indicating a vascular bundle containing xylem (x) and phloem (p) cells, a concentric layer of bundle sheath cells (bs), and the surrounding mesophyll cells (m). Bundle sheath cells of C4 plants appear more conspicuously green than do mesophyll cells because the former generally con tarn more and/or larger chloroplasts (which are granaless in some types of C4 plants).

Weid, M., Ziegler, J. and Kutchan, T.M. (2004) The role of latex and the vascular bundle in morphine biosynthesis in the opium poppy, Papaver somniferum. Proc. Natl. Acad. Sci. USA, 101,13957-4962. 

Errera examined the distribution of alkaloids in plant tissues by histochemistry and found that alkaloids were present in active tissues near the vegetative points, ovule, epidermis and the layer just inside of it, hair, peripheral layers of fruits and seeds, vascular bundle, cork cambium, cork tissues, and latex tube (9). Molisch microscopically investigated 15 kinds of alkaloids as distinguishable crystal forms after treatment with acids or alkaloid reagents, and then histochem-ically examined them in plant tissue and cell sections following treatment with acids or alkaloid reagents (9). Tunmann and Rosenthaler observed histochemi-cally the distribution of alkaloids in tissues and cells of 36 families of plants 10). 

The functional and microcirculatory hepatic unit forms the basis for assessing the hepatic acinus (A. M. Rappaport, 1954). (41-43) The portal vascular bundle, with the terminal branches of the hepatic artery and portal vein diverging fan-shaped after penetrating the lobules, is at the centre of the acinar structure. These vessels represent the central axis for the circular blood supply of the related liver parenchyma. This area is roughly the shape of a rhombus, the outer angles of which are formed by the two central veins of the adjacent lobules while the diagonal... 

Photosynthesis takes place primarily in plant leaves, and little to none occurs in stems, etc. The parts of a typical leaf include the upper and lower epidermis, the mesophyll, the vascular bundle(s) (veins), and the... 

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