EFFECT OF GROWTH IN ACID MEDIA ON THE MORPHOLOGY, HYDROGEN-ION CONCENTRATION, VISCOSITY, AND PERMEABILITY OF WATER HYACINTH AND FROGBIT ROOT CELLS

Abstract

Roots of water hyacinth (Eichhornia crassipes (Mart.) Soims.) and frogbit (Hydrocharis morsus-ranae L.) when grown In solution cultures adjusted to pH 3.5, 4.0, 5.0, 6.0, and 6.5 did not suffer decidedly adverse, direct effects from hydrogen ions except at extreme acidities represented by a pH value of less than 4. During cool weather the plants were able to grow at a somewhat higher concentration of hydrogen ions than was possible in the warm summer months. The boundary between good growth and toxicity was a narrow one. Extreme acidity, short of the critical point, inhibited the growth of the roots by decreasing cell division and cell elongation. In the roots investigated, cell division at pH 3.5 was reduced to one-half of the rate at pH 5.0 and this reduction accounted for three-quarters of the inhibition in the growth of the roots. When grown in a highly acid medium, root cells acquired a resistance to the hydrogen ions. Water hyacinth meristem cells from the highly acid media exhibited a pronounced resistance to hydrochloric acid. It is suggested that this increased resistance is due to the cells having acquired a greater impermeability to the acids. Determination of the pH of expressed root juices revealed that, although all of the saps were decidedly less acid than were the media in which the plants were grown, roots grown in an extremely acid medium had a slightly more acid sap than those grown in a less acid one. A comparison of rates of streaming and the action of protoplasts during plasmolysis indicated that extreme acidity in the growth medium increased the viscosity of the cytoplasm of root cells. No significant difference was noted in the osmotic pressure of the root cells from the different cultures. The absolute permeability of frogbit root hairs to thiourea, as calculated from the formula [Formula: see text], did not vary significantly from.0012 millimoles per square centimeter of surface per hour per molar concentration difference for plants grown within the range of pH 3.6 to pH 6.0.