Cortical Cylinder Research Articles

Phytoremediation of petroleum hydrocarbons-contaminated soil using Desmodium incanum DC., Fabaceae

Abstract The current research aimed to investigate both the tolerance and the phytoremediation potential of Desmodium incanum DC. on petroleum-contaminated soil. There were analyzed D. incanum seeds germination, surviving, growth and development cultivated at different contaminants concentrations as well as the pollutant degradation rate by gas chromatography and rhizosphere community. The experiment was carried out on a greenhouse containing non-contaminated soil (NCS), vegetated contaminated soil (VCS) and non-vegetated contaminated soil (NVCS) at the following petroleum concentrations (petroleum per of dry soil): 50 g kg-1 and 100 g kg-1. The experiments were performed during 90 days. The germination was more evident as it was observed higher petroleum concentrations. After 90 days, the surviving rate of the both groups 100%, and the soil samples were extracted and analyzed by gas chromatography. The VCS (100 g kg-1) group growth was reduced when compared to the NVCS (100 g kg-1). The petroleum influenced the morph anatomy and development of the plant. Significant increases in the total area, cortical and central cylinder of the roots in the contamination presence. The plant provided the development of larger amounts of microorganisms in the rhizosphere zone, and higher petroleum compounds degradation, confirming their potential phytoremediation for soils contaminated by petroleum.

Anatomy and Lignin Characterisation of Twigs in the Chaparral Shrub Rhamnus Californica

Characterisation of anatomical properties and analysis of lignin content and monomer composition were performed on twigs of the shrub Rhamnus californica L. in order to highlight their role in the adaptive strategies of this species in Mediterranean-type ecosystems. Our results showed that R. californica twigs develop a thick cuticle accompanied by several layers of subepidermal cells with suberised walls aiming to save water. The xylem is characterised by anatomical and chemical traits ensuring safety of water transport and preventing permanent damage through the enhancement of mechanical strength, also favoured by the lignification of pith cell walls. Moreover, the accumulation of phenolic compounds in the cortical cylinder is a strategy to protect against herbivory and to screen against high levels of radiation. Our overall analysis suggests that R. californica has evolved a strategy of shoot development that allows it to cope with the multiple environmental stresses found in Mediterraneantype ecosystems, among which summer drought and grazing play a major role especially for the survival of seedlings and young plants.

Mercury uptake, distribution and DNA affinity in durum wheat ( Triticum durum Desf.) plants

Mercury uptake, distribution and translocation mechanisms in plants of Triticum durum were studied after treatments with 203Hg(NO 3) 2 (mercuric nitrate). Results show that the highest mercury levels are observed in the roots or in the leaves depending on the way by which mercury was subministrated to the plants (i.e. by water or air, respectively). Autoradiographic experiments on histological sections show that mercury is preferentially bound to the cell walls of the outer layers of the root cortical cylinder; moreover, labeling is also observed in the outer layer of the central cylinder and in the parenchyma cell nuclei. In the leaf, mercury is incorporated on epidermal and stomatal cell walls and on parenchyma cell nuclei. DNA extracted from 203Hg-treated leaves was analyzed in Cs 2SO 4 gradients and it was observed that mercury is preferentially linked to certain DNA families.

MORPHOLOGY, DISTRIBUTION, AND HISTOCHEMISTRY OF SECRETORY STRUCTURES IN VEGETATIVE ORGANS OF SANTOLINA LEUCANTHA BERTOL. (ASTERACEAE)

In the vegetative organs of Santolina leucantha Bertol. (Anthemideae), two distinct types of secretory structures are present: Internal secretory ducts and external glandular trichomes. The ducts are variable in morphology and location, depending on the organ in which they are present. The trichomes, however, show the same structure everywhere. In the roots, there are also scattered cells rich in secretion that are distributed in the periphery of the cortical cylinder. The histochemical analysis of the secretion reveals the presence in all the vegetative organs of many important secondary compounds. Vegetative secretory structures are similar to those in the capitulum we have described in a previous paper.

Growth, in-vivo extensibility and tissue tension in mung bean seedlings subjected to water stress

The effect of a mild water stress on growth, in-vivo extensibility and tissue tension in hypocotyls of mung bean ( Phaseolus aureus L. cv. Berkin) seedlings was investigated. The subapical (growing) regions of the hypocotyls were marked and the seedlings transferred to distilled water or polyethyleneglycol solutions of an osmotic pressure of 0 to −30 bar. Growth of the marked regions was measured over the next 8 h. In-vivo extensibility was measured with a custom-built constant-stress extensiometer by stretching of living tissue (creep test). Tissue tension was estimated by measuring the rate of expansion of the peeled cortical cylinder in distilled water and by measuring the amount of contraction of the peeled epidermis on isolation. The plastic in-vivo extensibility was not significantly impaired by water stress, while a slight decrease in elastic extensibility was observed. The rate of expansion of the peeled cortical cylinder was increased in the water stressed seedlings. The epidermis lost its ability to contact on isolation owing to the imposed water stress. These changes in tissue tension were completely reversible upon rewatering of the seedlings. It is concluded that mild water stress inhibits growth by reducing the water potential of the cells. There is also a concomitant reduction of tissue tension.

Interaction between cortical cylinder and epidermis during auxin-mediated growth in pea internodes

The interaction between cortical cylinder (cortex plus vascular tissue) and epidermis during auxin (indole-3-acetic acid, IAA)-induced growth of third internode sections from red light-grown pea seedlings ( Pisum sativum L. cv. Alaska) was investigated. A quantitative comparison of the relative effects of IAA on growth of intact and peeled sections showed that intact segments are nearly 20-fold more sensitive to IAA than peeled cortical cylinders. Tissue tension, determined with the ‘split section test’, was constant during IAA-induced growth of intact sections. Peeled sections also displayed a small amount of tissue tension, which was likewise independent of IAA. The incorporation of myo-[2- 3H(N)]inositol ([ 3H]Ins) into non-cellulosic polysaccharides in the cell walls was stimulated by IAA in both the cortical cylinder and the epidermis by + 70% and + 55%, respectively, after 4 h. A mich higher amount of incorporation was detectable in the epidermis than in the cortical cylinder on a unit weight basis. During a 4-h growth period in IAA the cortical cylinder lost about 50 μg of its initial dry weight per section whereas the epidermis increased in dry weight by about + 24 μg. We conclude that during IAA-induced long-term growth the cortical cylinder (1) provides the driving force for organ growth, (2) responds to IAA by an increase in matrix cell wall synthesis and (3) releases material, some of which is transferred to the attached epidermal cells.

Growth, in Vivo Extensibility, and Tissue Tension in Developing Pea Internodes

The relationship between growth, in vivo extensibility, and tissue tension in the first 3 internodes of 5, 6, and 7 day-old pea plants (Pisum sativum L. cv Alaska), grown under continuous red light was investigated. The upper 15 millimeters of each internode was marked with ink and its elongation growth measured over the next subsequent 8 hours. In vivo extensibility was measured by stretching living tissue at constant force (creep test) in a custom-built extensiometer. Tissue tension was determined by (a) measuring the rate of expansion of the isolated cortical cylinder after adding water and the amount of contraction of the epidermis after peeling, and (b) by use of the ;split section test.' A good correlation between rate of elongation growth, in vivo extensibility, and tissue tension was established. The epidermis peeled from the growing third internode of 7 day-old plants and measured immediately showed a plastic extensibility (E(pl) twice that of peels from nongrowing excised sections. This high E(pl)-value was lost on incubation of the sections in distilled water, and was subsequently restored by incubating the sections in auxin (indole-3-acetic acid). We conclude that the in situ growth of the internodes is a function of tissue-tension, which provides the driving force of organ growth, and the extensibility (E(pl) of the outer epidermal wall, which is in the growing plant in a ;loosened' state. We furthermore suggest that in the intact plant auxin is causally involved in the wall loosening process in the epidermis.

Differential Effect of Auxin on in Vivo Extensibility of Cortical Cylinder and Epidermis in Pea Internodes

The effect of auxin indole-3-acetic acid (IAA) on growth and in vivo extensibility of third internode sections from red light grown pea seedlings (Pisum sativum L. cv Alaska) and the isolated tissues (cortex plus vascular tissue = cortical cylinder, and epidermis) was investigated. Living tissue was stretched at constant force (creep test) in a custom-built extensiometer. In the intact section, IAA-induced increase in total (E(tot)), elastic (E(el)), and plastic (E(pl)) extensibility is closely related to the growth rate. The extensibility of the cortical cylinder, measured immediately after peeling of intact sections incubated for 4 hours in IAA, is not increased by IAA. Epidermal strips, peeled from growing sections incubated in IAA, show a E(pl) increase, which is correlated to the growth rate of the intact segments. The isolated cortical cylinder expands in water; IAA has only a small growth-promoting effect. The extensibility of the cortical cylinder is not increased by IAA. Epidermal strips contract about 10% on isolation. When incubated in IAA, they do not elongate, but respond with an E(pl) increase. The amount of expansion of the cortical cylinder and contraction of the epidermis (tissue tension), measured immediately following excision and peeling, stays constant during IAA-induced growth of intact sections. The results support the hypothesis that IAA induces growth of the intact section by causing an E(pl) increase of the outer epidermal wall. The driving force comes from the expansion of the cortical cylinder which is under constant compression in the intact section.

Rapid auxin-induced stimulation of cell wall synthesis in pea internodes

The effect of auxin (indole-3-acetic acid; IAA) on growth and incorporation of myo-[2-(3)H(N)]inositol ([(3)H]Ins) into noncellulosic polysaccharides in the cell walls of third internode sections from red light-grown pea seedlings (Pisum sativum L. cv. Alaska) was investigated. Intact sections were incubated on [(3)H]Ins for 4 hr to permit uptake of the tracer and then IAA was added. Growth started after a lag phase of 15 min under these conditions. The sections were removed from the tracer and separated into epidermis and cortical cylinder (cortex plus vascular tissue). In the epidermis, IAA-induced stimulation of [(3)H]Ins incorporation started after a lag of 15 min. The amount of incorporation was 15% higher after 30 min and 24% higher after 2 hr than in the control. In the cortical cylinder, IAA-induced stimulation of [(3)H]Ins incorporation started only approximately 1 hr after adding IAA. The ionophore monensin (20 muM) inhibited the IAA-induced growth by 95%. Under these conditions, the IAA-induced stimulation of [(3)H]Ins incorporation and the IAA-induced increase in in vivo extensibility of the sections was almost completely inhibited, although oxygen uptake was unaffected. We suggest that wall synthesis (as represented by [(3)H]Ins incorporation) and wall loosening (increase in in vivo extensibility) are related processes. The results support the hypothesis that IAA induces growth by rapid stimulation of cell wall synthesis in the growth-limiting epidermal cell layer.

A quantitative study of the projection area of the central and the paracentral visual field in area 17 of the cat. I. The precision of the topography.

1. In the course of long oblique penetrations through the postlateral gyrus a variation in the position of the receptive fields (RF-scatter) of single cells recorded extracellularly is observed. This is superimposed on the continuous topological representation of the retina. Spezifying the RF-positions by the azimuthal and elevation coordinates of their geometrical centers, the standard deviation (SD) of the mean RF-positions of cells recorded in 200 mum long horizontal sections of cortex is calculated and the total radial scatter of RF-positions (Sanderson, 1971) as defined: (see article) is determined. The radial scatter is found to have its smallest value (1 degree visual angle (v.a.)) in the projection area of the functional center of the area centralis increasing to 3-4 degrees v.a. at 10 degrees eccentricity. 2. The mean RF-diameter as defined: (see article) is centrally 0.7 degrees v.a. increasing to 2.6 degrees v.a. at 10 degrees eccentricity. The ratio of the largest RF-diameter to the smallest RF-diameter is between 7-9 and remains almost constant over the central 10 degrees of the projection area. The magnification factor (M) as defined: mm Cortex/degree v.a. is centrally 2.3, decreasing paracentrally to 0.6. 3. The cells in area 17 whose RFs have the same direction in the visual field constitute the spatial subunit of the retinocortical projection. The diameter of the spatial subunit is calculated as: (see article). The spatial subunit functionally represents, therefore, that part of the visual field whose location and area is calculated by averaging over the RFs of the individuals of its cell population. It is found that the cells belonging to a spatial subunit are distributed within a cortical cylinder of 2.6-2.8 mm in diameter, the peak of the distribution coinciding with the central axis of the cylinder. 4. Within the projection area of the central 10 degrees of the retina in area 17 the spatial subunits have the same diameter. This suggests that each retinal ganglion cell is functionally connected with an equal number of cells in area 17 irrespective of its position within the retina and that, therefore, the retinocortical projection is organized on the basis of a stereotyped schema if a basic spatial relationship is concerned.

A quantitative study of the projection area of the central and the paracentral visual field in area 17 of the cat. II. The spatial organization of the orientation domain.

Cells in cat's area 17 respond optimally if elongated contrasts are presented at a certain angle or orientation with respect to the retina, or to the visual field, respectively (Hubel and Wiesel, 1962). The preferred orientation and the range of orientation sensitivity of cells in close proximity to one another have been determined in order to investigate the spatial arrangement of the orientation domain in area 17. 1. A slight overrepresentation of vertical and horizontal orientations is seen in cells with complex receptive fields, whereas in cells with simple fields all orientations are represented to an equal degree. The orientation selectivity, defined as the halfwidth of tuning curves constructed from the cells response to a moving stimulus, is less than 60 degrees in more than 80% of all cells investigated, and is on the average 20-30 degrees smaller in cells with simple than in cells with complex receptive fields. 2. In 80% of all cases considered the difference in the preferred orientation between two cells less than 200 mum horizontally distant in area 17 is less than 30 degrees, which is of the order of an individual cells orientation selectivity. Each cell, therefore, will respond to some extent to that orientation which is preferred by the cells in the immediate surroundings. 3. Sequential changes in the preferred orientation between cells successively recorded are observed as the postlateral gyrus is explored from anterior to posterior and from medial to lateral. On these general trends a random variation in the preferred orientation between neighbouring cells of the order of 5-10 degrees is superimposed. One orientation sequence (180 degrees) occupies 700-1200 mum, so that on the average a change in the preferred orientation of the order of 10 degrees is complete after 50 mum distance in the cortex measured parallel to the pial surface. Assuming that 18 different orientations (+/- 5 degrees) functionally represent one complete orientation sequence it is found that 'all' orientations are functionally represented by the cells contained in a cortical cylinder of 300-700 mum in diameter. 4. Cells having the same preferred orientation are grouped together in cortical regions which appear in crossection as a band or a spot. These regions have been termed iso-orientation bands or spots. The diameter of the spots and the small diameter of the bands do not exceed 100 mum. Taking an average orientation selectivity of 40 degrees for cells vertically aligned in area 17 it is calculated that cells situated 100 mum to either side of an iso-orientation band or around an iso-orientation spot still respond with 50% of the discharge to their own optimal orientation ...