Root Endodermis Research Articles

The tertiary endodermis in barley roots: Fine structure in relation to radial transport of ions and water

The presence of numerous pits containing plasmodesmata in the inner tangential wall of the tertiary endodermis in barley roots is demonstrated by electron microscopy. The pit floor is covered by a thin layer of material which is continuous with and resembles the tertiary wall. The plasmodesmatal pore is constricted at its ends so that the plasmalemma lining the pore is appressed to the desmotubule. The frequency of plasmodesmata and their cross-sectional area is estimated, and phosphate and water fluxes through them are calculated on the assumption that they represent the only communication between the cortex and the vascular tissue. The pressure gradient across the ends of the plasmodesmata necessary to support the observed water flux is calculated for limiting cases of the pore radius and the viscosity of the fluid passing through the pore.

On the Differentiation of Casparian Dots of the Endodermis in the Crown Roots of Rice Plant

Observations with ordinary microscope show that the casparian dots differentiate at the very near parts from the root tips as typical small dots on the radial wall of the endodermis (Fig. 1). The phenomena of bandplasmolysis induced with alcohol reagent is also confirmed (Fig. 2). Further studies with electron microscopy reveal that the morphogenetical process of casparian dots is carried on at the radial wall from its very initiation to the quite differentiated state (Fig. 7, 8, 9, and 10). This fact is something contrary with the suggestion described by Van Fleet16) on observation genus Smilax. The casparian dots, which are not distinguishable with ordinary microscope in the basal part of root, were confirmed to be covered under thickened secondary wall (Fig. 14, 16). The electron micrographs (Fig. 12, 13) also clear up that the partial plasmamembrane of the endodermal cell unify itself together with the casparian dots. This fact no doubt will give the morphological evidence to the unique phenomena of bandplasmolysis through casparian dots of endodermal cells.

On the Cell Wall Thickening of the Endodermis in the Crown Roots of Rice Plants

Different roots grown under different conditions of cultivations have shown conspicuous morphological difference in the thickness of the inner tangential and radial walls of the endodermal cells. The degree of the thickness was greater in those roots grown in upland condition than those grown in the submerged one. The thickness of the cell walls of the endodermal cells shows sensitive reaction to the change of the soil conditions during the growing period. In a word, the thickness of the cell walls of the endodermal layer can be induced greatly to a state of typical U or C shape in appearance of transversal views. This phenomena are closely correlated to the soil water conditions. Further observations of the endodermal cells reveal the following morphological features; first, the existence of cytoplasm and nuclei in any stage of the development and second, numerous small pits in the thickened inner tangential, radial and transversal walls. The degree of thickness, in usual, is correlated to the orientation of the tissue elements of the stele and sometimes the passage cells were found opposite to the protoxylem elments. The differences in thickness of the endodermal layer in the roots which keep close correlation to the soil water condition, together with sorne typical characteristics shown in the cells of this layer may have endowed quite specialized function in regard to the physiological mode of water utilization by the roots of rice plants grown in paddy fields.

On the Meristematic State of the Endodermis in the Crown Roots of Rice Plants

Three tiers of initials are usually separated in the apical meristem of the crown root tips in rice plants (Fig. 1). The cortical-epidermal initials which lie opposite the tip of the plerome are a common origin giving rise to the epidermis, exodermis and cortex. The innermost layer of cells in the cortex is the endodermis. From the observation of the longitudinal and transversal sections of the root tips under the ordinary microscope, the following phenomena are cleared up. The cortical-epidermal initials divide periclinally and the inner daughter cell is the first endodermal cell (Fig. 1). The endodermal layer which extend from the first endodermal cell to the endodermal cells setting to vacuolate remains meristematic ones. Within certain limits 150-180 μ from the cortical-epidermal initials, the three types of mitosis namely, periclinal, transversal and anticlinal divisions can be evidently found (Fig. 2, 3, 4, 5 and 6). Only the periclinal division of the endodermal cells among the three types of divisions gives rise to the cortical cells. The number of the embryonal cells corresponding to the region mentioned above can be estimated at more than 10 (Fig. 8). Beyond the limits of such region the periclinal division in the endodermal layer cease, while the other two types of division are found in low frequency until begining to vacuolate. It seems that these three types of division keep close relationship among them in distributing the new cells surrounding the stele of the root. About 1100-1200 μ back from the cortical-epidermal initials, vacuolation of the endodermal cells begin and successively elongation of the cell wall take place in parallel to the root axis. The specific staining characters of nuclei and nucleoli with Azure B (Fig. 10) superior to neighbouring cortical cells in this stage suggest that the endodermal cells still have high physiological activity.

THE PATHOGENICITY OF PRATYLENCHUS PENETRANS TO CELERY

Celery seedlings, grown aseptically in silica sand with plant nutrients, were inoculated with surface-sterilized specimens of the root lesion nematode Pratylenchus penetrans (Cobb, 1917) Filip. & Stek., 1941. The reactions of invaded roots were studied microscopically. The epidermis, cortex, and endodermis of young celery roots showed different degrees of discoloration after invasion of P. penetrans, with the endodermis most severely affected. Pratylenchus penetrans was a primary parasite and pathogen of celery.

Anatomical Variations of Root Tissues during the Growing Season of Naked Barley and Wheat Plants

This observations were carried out during 1954 to 1955 to gain a preliminary fundamental information to study the anatomical effects of various external conditions to the root tissues of barley and wheat plants. Both crown and seminal rooots of naked barley and wheat undergo extensive anatomical change during their growing season ; i. e., development of thickening and lignin reaction of cell membrane in endodermis, pericycle and stele parenchyma of crown and seminal roots, occurrence of thickened cell membrane inouter and inner cortex of crown root, occurrence of collapsed space in central portion of crown root, and deformation, splitting and disappearance of epidermal cell layer of seminal root. These changes were most severe during the early March and the early April. However, the degree of these changes was differ with species or cultivated locations ; for instance, the thickening of cell membrane as described above was more conspicious in naked barley than in wheat (see Fig. 1), and also more in OITA barley than in NAGASAKI and KAGOSHIMA ones (See Table 1).

Some Effects of Zinc Deficiency on the Anatomy of the Tomato

1. Tomato seedlings of the Rutgers variety were grown with drip-culture solutions in which the concentration of zinc was varied: 0.05 (controls), 0.005, 0.0005 p.p.m., and no zinc at all. At harvest, 1 month from the beginning of the experiment, their growth was proportional to the amount of zinc received. The low-zinc and minus-zinc plants showed definite symptoms of zinc deficiency. One plant from each series was selected for histological study. 2. Extreme zinc deficiency resulted in a reduction or, in the total absence of zinc, a complete cessation of meristematic activity in the root tips and cambium, in necrosis of leaf tissue, and in the precocious maturation of tissues. This was particularly apparent in the root tips, where both xylem and endodermis matured just a short distance from the promeristem. In the roots of minus-zinc plants small but definite tumors, similar to those formed on roots exposed to low concentrations of certain growth-regulating substances, developed a short distance behind th...

Observations on the root anatomy of the genus Aletris.

Summary (1) Aletris is a liliaceous genus with both American and Asiatic species, all of which possess a rhizome bearing tough, wiry, adventitious roots. (2) The roots are characterized by the peculiar nature of the surface-layer, all the cells being elongated radially and forming a closely-set system of papillae. (3) The root endodermis is composed of elongated cells with pointed ends similar to prosenchymatous fibres. These develop extremely heavy thickenings of lignocellulose. (4) There are a few isolated passage-cells in the young root, but they develop the tertiary condition a short distance behind the root-tip. (5) In old roots all the tissues external to the endodermis are frequently exfoliated. (6) The metaxylem vessels in Aletris farinosa possess scalariform perforations between the vessel segments. (7) There is evidence that in the various species of Aletris there is a series of transitional stages from the scalariform perforation to the ring type. (8) An examination of herbarium material suggests that the root anatomy may be of value in differentiating between the various species.

Origin of Leaf, and Adventitious and Secondary Roots of Ceratopteris thalictroides

1. In Ceratopteris thalictroides the leaf initial develops from the outside portion of the segment of the apical cell of the main axis. 2. The initial of the first adventitious root at the node develops from a hypodermal cell derived from the cell immediately below the leaf initial. Later roots may develop from cells derived from the leaf initial. These roots are also hypodermal in origin. 3. The secondary root develops from a layer occupying the position of the endodermis in the primary root.

THE‐ TOXIC ACTION OF COAL GAS UPON PLANTS

Summary. Further experiments upon the effect upon the plant of atmospheres contaminated with coal gas, lend support to the view that this effect is mainly produced as a result of the mobility of unsaturated fatty substances in the plant walls in the presence of unsaturated gaseous hydrocarbons present in the coal gas. Unsaturated fatty acids appear to be normal constituents of the meristem wall and in the presence of these unsaturated gaseous hydrocarbons they migrate towards the plant surface leaving the meristem walls more permeable. As a result, premature vacuolation and extension of the cells of the meristem take place. A failure of the primary endodermis in root and etiolated stem, owing to the absence of the fat impregnated Casparian strip, is frequently associated with this greater mobility of the unsaturated fatty acids. The normal green stem is indifferent to traces of coal gas because the fatty substances leave the meristem walls and accumulate in the surface wall at a very early stage of development. The development of the cork phellogen in the stem of Sambucus is briefly traced, and the effect of coal gas upon this stem at different developmental stages is described. The effects described are best interpreted on the assumption that at a very early stage of their formation, the cork cells cut off from the phellogen are very susceptible to the presence of coal gas. At this stage these cells become distended with water, and the fatty acids diffusing from the protoplast, fail to remain in and on the walls so that no suberin lamella is formed. These results are entirely in accordance with the effects of coal gas upon the differentiating cells of the apical meristem cf etiolated stem or root and can be explained by the greater mobility of unsaturated fatty acids in the presence of the gaseous unsaturated hydrocarbons present in the coal gas. The experimental results are also in accord with those ot earlier investigators. They suggest that coal gas will not be toxic to cork enveloped tissues except in the case of leakage from buried gas mains around the root systems of the plant; entry of pathogenic organisms will then be facilitated by che proliferated, unsuberised tissue formed from the cork phellogen. The proliferated tissue formed from the cork phellogen in these experiments with coal gas appears to be suggestive in connection with the aerenchyma formed upon plant surfaces immersed in stagnant water.