THE FORMATION OF 'H-PIECES' IN THE WALLS OF ULOTHRIX AND HORMIDIUM

Transcription

1 THE FORMATION OF 'H-PIECES' IN THE WALLS OF ULOTHRIX AND HORMIDIUM BY FRANK W. JANE University College, Eondon AND N. WOODHEAD University College of North Wales (With 3 figures in the text) THERE would appear to be little information upon any marked thickening in the walls of vegetative cells of Ulothrix and Hormidium, or of the formation of H-pieces, comparable with those found in species of Microspora. West (1916) hints at their occurrence in Ulothrix zonata (cf. his Fig. 181) in connexion with aplanospore formation, while Fig. 53 F and G of West & Fritsch (1927) clearly indicate that they have been observed in Ulothrix aequalis, both during aplanospore development and in the liberation of macrozoospores. Smith (1933) goes so far as to state, 'All genera referred to the Ulotrichaceae have a cell-wall that is not composed of overlapping H-pieces', but this statement is probably a lapsus calami, for he implies as well that H-pieces occur in Binuclearia and Radiofilum, both of which genera he includes in this family. It is well known that the cell membrane of some Chlorophyceae consists of inner and outer parts; and sometimes includes a bounding cuticle. West (1916) states that most species of Ulothrix overwinter as short filaments with thick transverse and lateral walls, and that when active cell division starts, these old,.thick walls are burst apart as the cells divide. Piercy (1917), in her investigation of Hormidium, concluded that splitting of the filaments was due to separation at the middle lamella, and implied that this layer may increase considerably prior to separation of adjacent cells, and even extend along the longitudinal walls from cell to cell. She also noted the presence of a cuticle in H. flaccidum, and deduced from inconclusive tests that this layer was mucilaginous, or at least that it became so, and not cutinized. Investigations of earlier workers on the separation of cells in this genus are referred to in her paper. In the late winter of 1940 collections of Ulothrix zonata, from the River Ogwen, near Bangor, yielded some filaments in which the septa between adjacent cells were occasionally thickened, and sometimes laterally swollen, to a remarkable degree (Fig. i): these thickenings immediately suggested a condition comparable to that obtaining in the walls of some species of Microspora, and probably to the somewhat elaborate walls of Cladophora. Each cell was surrounded by an inner

2 184 FRANK W. JANE and N. WOODHEAD wall (Fig. I D, F, iw), in which stratification was often visible, while an outer layer of wall was often continuous along the filament (Fig. i F, ow) and across.the septa (Fig. i D, ow): as far as could be ascertained there was a continuous, delicate pellicle external to the outer wall. The H-shaped swellings might have been produced either by the outer wall in the region of the septum, or by a swelling of the middle lamellae, the swelling being accompanied by lateral expansion which caused the walls to bulge in this region. Sco/e for A,B,C&.D Sco/e fot ES(F Fig. 1. Ulothrix zonata (Web. et Mohr) Kuntz; pieces of filaments showing swollen cell walls. A and B were drawn from living material, C and D from material treated with ruthenium red, E from material stained in Congo red, F from material treated similarly to E, then mounted in dilute glycerine. Ku, inner wall; ow, outer wall. These swellings, which will be referred to as plugs, were subjected to microchemical tests. With Schultze's solution there was a doubt as to whether the plugs were very faintly coloured or not, but the test could certainly not be regarded as affording conclusive proof that they were composed of cellulose. Similarly the application of iodine followed by sulphuric acid led to a faint violet coloration, but this test likewise could hardly be regarded as conclusive. When immersed in ruthenium red the plugs sometimes assumed a very faint pink tinge after a lengthy period, and this may perhaps be regarded as indicative of the presence of traces

3 'I H-pieces in the walls of Ulothrix and Hormidium 185 of pectin in these structures; again, however, it was impossible to regard this test as conclusive, and it may be added that the contents of adjacent cells were coloured by the dye. After treatment with 6 % aqueous potash, both cold and warm, the. plugs appeared as highly refractive bodies, without any trace of stratification. When filaments were treated overnight with alcoholic potash, and subsequently tested for cellulose with iodine and sulphuric acid, a positive reaction was obtained in the plugs. Even after this potash treatment, however, no positive reaction for pectin was obtained with ruthenium red. These results indicate that there is a 'cuticle' or pellicle of a fatty nature bounding the filaments, and inhibiting the penetration of reagents into the walls; it might be expected that treatment with potash would render such a layer more easily penetrable. It may be added that filaments were allowed to soak in 5 % hydrochloric acid overnight and then washed in water for 3 hr.: after this treatment it was possible to obtain a blue coloration of the plugs with methylene blue, a coloration which could not be obtained without such preliminary acid treatment. These tests lead to the conclusion that the plugs are greatly swollen regions of the outer layers of the cell wall, and are not derived from a thickening of the middle lamella. At times (Fig. i C, D, E, F), the inner wall adjacent to the plugs is easily seen, this inner wall showing stratification. Material of Ulothrix sonata was collected from the same locality in early May 1941; in this, very few swollen plugs were encountered, but the inner and outer layers of the wall the former only, stratified could easily be seen in the region of the septum. The presence of a pellicle of fatty material was indicated by positive reactions with Sudan blue and Sudan black. This pellicle varied somewhat in thickness; in parts it was well defined and continuous, elsewhere thinner; and sometimes not evenly distributed. Outside the pellicle was a thin layer of mucilage (Fig. 2 A). Filaments which had been allowed to dry out on a slide often had a moniliform appearance (Fig. 2 B), produced by the septa contracting to a greater degree than the cells themselves; it is concluded that the outer layers of the wall are more watery (probably more mucilaginous) than the inner wall, and shrink more upon drying, because they lose a greater amount of water. There is no trace of pectin in these outer layers (tested with ruthenium red). It is inferred that the outer layers (outer wall) are different, chemically, from the inner wall; they may well represent an intermediate stage in the degradation of cellulose to mucilage.^ It is doubtful if the plugs or H-pieces were in this condition; their highly refractive appearance after treatment in potash seems to militate against such an assumption. The presence of a thin layer of mucilage outside the pellicle is of interest; it is difficult to visualize the change of a fatty material, and the pellicle is undoubtedly of a fatty nature, into mucilage; equally, it does not seem likely that mucilage, formed from the outer surface of the outer wall, could pass through the impervious pellicle. It seems probable that the outer layers of the wall become mucilaginous before the formation of the fatty pellicle just within their boundary. ^ There is a resemblance between these plugs and the cell structure at cell disjunction in certain species oi Spirogyra, cf. Fritsch (1935).

4 i86 FRANK W. JANE and N. WOODHEAD There was no evidence that the swollen plugs functioned as separation disks, for the filaments did not seem to be more liable to break in such regions than elsewhere. The formation of such plugs is apparently rare in Ulothrix, for it is difficult to beheve that they would not have been recorded, were it otherwise. It is, perhaps, not unreasonable to regard the condition as pathological, and it may be noted that the plugs occurred soon after the weather had been exceptionally cold for a protracted period. During the early months of 1941, plugs of an appearance similar to those just described were found in a few filaments of a Hormidium collected in a pool at Criccieth. We refer the plant to Hormidium flacddum. Unfortunately so little ow IW m p m p 5PJU, Fig. 2. Ulothrix zonata (Web. et Mohr) Kuntz; A, part of a living filament; B, part of a filament which has been dried out on slide, iw, inner wall; m, mucilage; ow, outer wall; p, pellicle. material was available that it was not possible to carry out any microchemical tests, but our observations leave little doubt that the plugs are similar in nature and origin to those described above in Ulothrix zonata. In the Hormidium, however, they are directly concerned with fragmentation of the filaments (Fig. 3 D, E, F) and become more extensive than those of Ulothrix, so that eventually the whole of the cell wall becomes thickened, at times more or less uniformly. Weak zones are developed approximately in the middle of the cell wall (Fig. 3 F, w); here the outer wall eventually breaks and usually becomes hinged back on itself, liberating the cell still enclosed in the inner wall. The cells so liberated proceed to divide and to form new filaments (Fig. 3 D, E, F). It may be that elongation of the cell is responsible for the rupture of the outer wall. In some instances remains of the pellicle could be made out in the region of the septum (Fig. 3 A, B, D, E), but elsewhere, and especially in the cells of the

5 Fig. 3. Hormidium ref. flaccidum (Ktintz) A. Br. A-F, parts of one filament showing ' H-pieces' and fragmentation. The scale of A and B is slightly greater than that shown for the remainder. Note beginnings of swellings at jc in A and F. iw, inner wall; ow, outer wall; p, pellicle; w, zone of weakness.

6 i88 FRANK W. JANE and N. WOODHEAD newer filaments, no stratification of the wall, or even distinction between inner and outer wall layers, could be seen. This is due, at least in part, to the thinness of the walls, but perhaps also to the outer wall and pellicle not having developed. The Hormidium, like the Ulothrix, was collected soon after a period of exceptionally cold weather, and it is possible that the marked development of the outer wall was conditioned by these abnormal conditions. SUMMARY 1. Peculiar.swellings of the septum and adjacent walls are described for Ulothrix zonata and Hormidium ref. flaccidum. 2. In the Ulothrix the wall consists of inner and outer portions, the latter bounded by a pellicle of a fatty nature. 3. Microchemical tests on the Ulothrix indicated that the swellings were produced by the outer cell wall. This is probably true of the Hormidium. 4. In the Hormidium these thickenings serve as a means of fragmentation of the filament, but in the Ulothrix no evidence exists that the filaments break more readily in the region of the thickened walls than elsewhere. REFERENCES FRITSCH, F. E. (1935). Structure and Reproduction of the Atgae, vol. I. Cambridge. PIERCY, A. (1917). The structure and mode of life of a form of Hormidium flaccidum A. Braun. Ann. Bot. 31, SMITH, G. M. (1933). Freshwater Algae of the United States. New York. WEST, G. S. (1916). Algae, vol. i. Cambridge. WEST, G. S. & FRITSCH, F. E. (1927). A Treatise on the British Freshwater Algae. Cambridge.

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