Structure of plastids of a variegated Betula pubescens mutant

The patterns of variegation in the leaves of Betula pubescens only become evident in the mature leaves. However, the young plastids are also abnormal and pigment analysis does not suggest that the deformation of the plastids is caused by carotenoid deficiency. In mature leaves the mutant plastids are badly deformed. Among the most typical defects are an amoeboid form and the budding of peripheral reticular parts from the mutant plastids. These budding parts can easily be mistaken for mitochondria, but a closer inspection reveals differences in their tubular structures. These buds should therefore only be considered a special type of abnormal plastid.

Some Observations on the Actions of Steroids on the Metaplasia of the Amoeba, Naegleria Gruberi

1. The age of the culture of Naegleria gruberi, i.e. the time since the last subculture, is of little importance in determining the numbers of cells which turn flagellate when placed in the extremely dilute buffer solutions used. 2. Between 17° and 21° C. there is a very great decrease in the time which the amoebae require in order to become flagellate when placed in buffer solution. 3. There is no evidence that the amoeba, as such, differentiates between solutions of KC1 or NaCl. On the other hand, the flagellate form is somewhat more reactive to KC1 than to NaCl, and fewer flagellates are found in KC1 solutions. 4. The metaplasia is affected by the presence of steroids in the medium. 5. The more interesting actions of the steroids tested may be summarized as follows. At high concentrations, progesterone and deoxycorticosterone, when applied to the amoeba, prevent the change to the flagellate form. When applied to the flagellate, progesterone has little action, but deoxycorticosterone encourages the return to the amoeboid form, especially in the presence of K+. In lower concentrations both steroids favour the change from amoeba to flagellate and also from flagellate to amoeba. Other steroids have characteristic effects. 6. While the dose/response curves indicate qualitatively different effects of concentration of progesterone and deoxycorticosterone they only show quantitatively different effects with oestradiol and androsterone. 7. Progesterone acts on amoebae at concentrations which are comparable with those at which it acts in the human body. 8. When both progesterone and oestradiol are applied together at concentrations which suppress the flagellate form the effects are additive. The same applies to mixtures of testosterone and oestradiol. An activating concentration of progesterone has not yet been tested in combination with an inhibiting dose of oestradiol.

Further Observations on the ‘Metaplasia’ of an Amoeba, Naegleria gruberi

The development of flagella by Naegleria gruberi, which occurs when a culture of organisms in the amoeboid form is treated with distilled water, has been shown (Willmer, 1956) to be a phenomenon probably related more to the ionic balance between the organism and its external environment than to the simple movement of water in and out of the cell in response to total osmotic changes. From Text-fig. 1 it may be seen that with respect to the response of the amoeba to different concentrations of the various salts investigated there are for each salt two somewhat critical concentrations. In the case of NaCl solutions in distilled water these turning points occur at about 30 mM. and 1 mM., and in the case of KCl solutions at about 50 mM. and 6 mM. Above the higher of these concentrations in each case the organisms always assume the amoeboid form, and below the lower they become flagellate at least as frequently as they do in distilled water.

Factors Which Influence the Acquisition of Flagella by the Amoeba, Naegleria Gruberi

1. When placed in distilled water Naegleria gruberi changes from an amoeboid organism, with little evidence of polarity, to a highly polarized free-swimming flagellate. The details of this metamorphosis are described. The change is reversible. 2. Alteration of osmotic pressure is not in itself the direct cause of the metamorphosis, though the loss of certain ions is clearly important. 3. The metamorphosis is favoured by the presence of low concentrations (less than M/80) of sodium bicarbonate, sodium lactate and sodium phosphate. 4. The flagellate form probably occurs most frequently in conditions of neutrality; but, in the presence of phosphate, acid conditions tend to be more favourable to the flagellate form, while in the presence of bicarbonate the optimum pH is nearer pH 8.0. 5. The metamorphosis to the flagellate form is suppressed by a variety of agents including lithium salts, magnesium chloride and the sulphate ion under some conditions. These all act at concentrations which leave the amoeboid form in full activity. In some cases their action is decreased by the presence of bicarbonate in the medium.

Phase Contrast and Electron Microscope Studies of the Appearance and Behaviour of the White Cells of Normal Human Blood

1. The phase-contrast microscope has been used to study form and movement of human leucocytes and blood platelets in three types of preparation; (a) warm sealed blood drops, (b) warm sealed films of leucocytes adhering to coverslips after incubation of blood drops at 37° C. for 30 minutes or more, and (c) warm sealed films of blood platelets obtained by similarly incubating drops of saline suspensions of these cells. Similar preparations to (b) and (c) were obtained on formvar films and studied in the electron microscope. Phagocytosis was studied in all the above preparations after adding suspensions of collodion particles or of Staphylococcus albus. 2. The neutrophils were the most versatile cells seen in the above preparations. The amoeboid forms were the most mobile and phagocytic. Another form showed rapidly waving processes which gradually spread into a flat membrane on the glass. lattened immobile neutrophils were still capable of phagocytosis. Bacteria which adhered to the cell surface moved over it towards the thicker central region of the cell where ingestion occurred. 3. Eosinophils showed a mobile amoeboid form and flattened forms which were often very bizarre in shape. They did not phagocytose readily. 4. Monocytes showed slowly moving amoeboid forms or forms with ruffle-like membranes around the cell. They were phagocytic. 5. Lymphocytes were capable of amoeboid movement but did not flatten on glass and were not phagocytic. 6. Blood platelets showed dendritic and flattened forms. Bacteria or collodion particles adhered to the surfaces of the latter and travelled over them, clustering at their thicker centres.