THE ARRANGEMENT AND ACTION OF MATERIAL IN THE PLASMATIC LAYERS AND CELL-WALLS

OF PLANTS.

BY DR. D. T. MACDOUGAL.

(Read April 25, 1924.)

The purpose of the present paper is to present some collated information on the arrangement of colloidal material in the plasmatic layers and walls of the plant cell which are to be taken in account in measurements of permeability, and to present some results of the action of constructed, dead, and living cells in absorption and endosmosis.

Permeability is used in this and previous publications to denote the condition of the colloidal meshwork of the wall and plasmatic layers, which may vary in active cells so that only water and the more mobile ions may pass through when permeability is least and the largest molecular particles go through when it is greatest.1

The composition and arrangement of materials in the plasmatic layer and the cell-wall has been discussed in previous papers but it is necessary for the sake of clearness to recapitulate the principal facts and to illustrate the matter with Fig. 1. The wall has a semirigid skeleton of cellulose fibers which are capable of but slight changes of volume or of deformation with water content. The spaces in the external part of this meshwork are occupied by pectins or pectates and the inner part of the meshwork nearest the plasmatic mass contains other liquefiable pentosans, such as mannosans and glucosans, while some lipins or phosphatides occur.

The plasmatic mass is made up of amino-acid chains, pentosans and phosphatides, lipo-proteins, glycolipins, etc., the concentration in the bounding layer of the protoplasm being denoted by the closer spacing of the symbols used for the main components.

'MacDougal, D. T., Permeability and the Increase in Volume of Living and of Artificial Cells," Proc. Amer. Phil. Soc., 72, 1, 1923.

One of the first and most important features of the structure described is its incessant variation in composition. The wall which is at first largely composed of liquefiable pentosans progressively includes a larger proportion of the anhydrides as the wall becomes denser and more rigid. Later pectin compounds appear and the maturity of the wall brings it to a condition in which almost any of the salts or organic compounds of the cell as well as fat-soluble substances may pass through the coarser and fixed meshwork. The outer part may undergo secondary changes by which it becomes water proof in total reversal of the effect of the previous alterations. PLASMATIC LAYER

た

CELL WALL

FIG. 1. Diagram of the arrangement of material in the plasmatic layer and cell-wall. Cellulose. Pectin. | Mucilages. Proteins. Fatty substances.

The plasmatic mass at first high in proteinaceous material and in fatty substances progressively acquires a larger proportion of pentosans or mucilages, with inevitable alterations of reaction to substances included in the vacuole and entering the cell from the medium.

In addition to these changes which come rapidly in short-lived absorbing cells or root-hairs, this complex membrane is highly unstable as to its composition. The displacements which may occur as a result of the various types of adsorption may result in the loss

FIG. 2.

Colloidal cell in operation. (a) Capsule infiltrated and coated with material as in Fig. 1; (d) immersion liquid; (n) filling funnel; (o) outlet; (e) receiver; (1) liquid delivered as result of endosmose.

of various bases such as potassium and sodium, or the leakage of carbohydrates and amino compounds from the liquid or meshwork of the cell, as has been described by True and his colleagues.

In view of these facts it is obvious that the permeability phenomena observed in such strict and durable membranes as those of

collodion and of parchment subtend but a narrow angle in any comprehensive view of the operations which attend the passage of electrolytes for example through the enormously complex and continuously variable permeable layers of the cell. Referring again to the diagram (Fig. 1), it is to be noted that this is illustrative of a cell which presents a free surface to the medium. The union of two cells presents an arrangement in which this is doubled, the pectinized layer forming the middle part of the wall and the passage of an ion from one cell to another is attended by all of the adsorptive action of two plasmatic layers, which would never be exactly identical in the two protoplasts.

The model of a "constructed cell" used in these experiments consisting of a cellulose extraction thimble infiltrated and coated with materials represented in the living cell differed from previous description only in certain mechanical features. Its setting is illustrated by Fig. 2. By the omission or addition of substances an analysis may be made as to the parts played by the separate components of the permeable layers. The action of the cell as thus modified may be taken in terms of endosmose, measurements of resistance of immersion liquids or cell contents, or by titrations.

The following points are to be noted in the interpretation of the results which follow: first, that as the permeability of the cell lessens the rate of endosmose with any given concentration of sugar as cellcontents will rise within the limits of these experiments; second, that the relative action of the common bases on the meshwork of colloids in modifying permeability rests upon the total action of these bases on the included substances: this action may include several types of adsorption, and third, that the cell-contents generally of 20 per cent. solution of cane sugar had an osmotic potential of about 15 atmospheres, common in plant cells, while that of the external or immersion liquids was much less than I atmosphere.

Confirmation of the principal conclusions as to the relative action of similar neutral salts of the common bases has been made. Such action runs generally parallel to the ionic mobilities of the bases which is a straight line function of the charges they carry. Other factors, the effects of which are still being measured, are doubtless to be taken into account. The relative action of these bases is modified by the

common ions in an order determined by the balance found between the charge on the anion and that on the kation. Thus the common anions SO, < C1 < NO, exert a retarding effect, lessening the action of the kations on colloids in an increasing series as given. This action is in conformity with the hydration effects on agar as measured in 1921, as repeated in Table I.; and may be taken to apply within a certain range of effects in which swelling in various degrees results from hydration. Abrupt alterations of effect ensue when the concentrations rise to a point where total neutralization and aggregation of the colloid is brought about.2

TABLE I.

HYDRATION OF AGAR IN SULPHATES AND NITRATES.
(Increases in percentage of volume.)

The retarding effects of anions on common bases in permeability effects with young roots were found by Kahho to form the following series,3

Citrate Sulphate < Tartrate < C1 < NO3 < Br < I.

Raber obtained the series below with salts of sodium,*

SCN <I< Br < NO, < CI < Acetate < Sulphate

3

< Tartrate < Phosphate < Citrate.

In my own experiments similar permeability effects were obtained with sodium salts in complete cells and with others from

* See Freundlich, H., “Capillarchemie," 2te Aufl., pp. 572 ff., 1922. MacDougal, D. T., "The Action of Bases and Salts on Biocolloids and Cellmasses," Proc. Amer. Phil. Soc., 70, 15, 1921.

3

Kahho, H., “Ein Beitrag zur Permeabilität des Pflanzenplasmas für Neutralsalze," Biochem. Ztschrft., 123, 284, 1921.

Raber, O., "Permeability of the Cell to Electrolytes," Botan. Gazette, 75, 298, 1923.