Effects of Kinetin on the Permeability of Allium cepa Cells

Abstract

Permeability changes of Allium cepa cells were studied by a plasmometric method. Onion epidermis was floated in phosphate buffer solution with kinetin (2.5 milligrams/liter), or buffer without kinetin as a control, for 10 hours. The treated and control tissues were then transferred to one of the following four permeants: thiourea, urea, maloamide, dimethylurea.Kinetin treatment increased the permeability of onion epidermal cells to (14); further, the half-time for tritiated water efflux in both cylinders of carrot root tissue and of pelargonium stem pith is influenced by kinetin (6). This paper is a report of a study of kinetin effects on the permeability of onion epidermal cell membrane to four nonelectrolytes. MATERIALS AND METHODSThe inner epidermis of onion (Alliumn cepa) bulb scale was used. Epidermal tissue was cut into 12-x 15-mm strips. After floating the tissue on buffer solution for 10 hr in the dark at room temperature with or without kinetin, it was then transferred into a perfusion chamber. The flow of permeating solution through the chamber was kept constant by gravity.The phosphate buffer solution (2.5 mm, pH 6) for pretreatment contained 1 % sucrose with 2.5 mg/liter kinetin. The same buffer solution, less kinetin, was used for the pretreatment of the control tissue. All chemicals used were practical grade from Fisher Scientific Products, except kinetin (Calbiochem), and 1, 3-dimethylurea (Eastman Kodak).Permeability determinations were made by the plasmometric method (12,21). After transferring the tissue to the perfusion chamber with buffer solution, the chamber was covered with a glass slip sealed with Vaseline and placed on the stage of a microscope. The permeating solutions were 1 M thiourea, 1 M urea, 0.9 M malonamide, and 0.8 M 1, 3-dimethylurea. For the experiments with urea and malonamide, the hypertonic solutions were introduced directly into the chamber containing pretreated tissues. The solutions, at first. caused plasmolysis of the cells. As the permeants entered the cell, the protoplast expanded. The deplasmolysis is assumed to result from a permeation of the "plasmolyticum" into the treated cell. For experiments with the other two compounds (thiourea, dimethylurea) pretreated tissues were first plasmolyzed with 1 M mannitol and were then subjected to each of the permeants for observation of deplasmolysis. As the permeant was introduced into the perfusion chamber, a time lapse camera mounted on the microscope photographed the onion cells at given intervals.The camera was equipped with an auxiliary lens system to photograph a watch, automatically recording the time for each frame.Cells nearly cylindrical in shape were selected for study. The lengths of the protoplasts were measured on the photographic negative by means of a low magnification dissecting microscope and an eyepiece micrometer. This was done as soon as the protoplast was perfectly plasmolyzed, at which time both ends were clearly rounded off. Measurements were made for each frame, and the time was recorded.Usi...

Short-term effects of cytokinins on the lipid fatty acids of green leaves

“…This effect may be important in regard to cellular membrane systems. An influence of cytokinins on membrane penneability has been described (7,13,17,18) and control of permeation processes by their action on membrane metabolism has been reported (18, 19).…”

Kinetin Increases Water Permeability of Phosphatidylcholine Lipid Bilayers

“…For example, in the dimyristoylphosphatidylcholine liposome experiments reported in Figure 6, even a I mM kinetin solution would have a kinetin-to-phospholipid ratio of 0.2. It would be difficult to compare the effective kinetinto-phospholipid ratio reported here with kinetin concentrations reported in other experiments using, for example, beet root tissue (23), sunflower cotyledons (14), or onion epidermis cells (9). Since kinetin likely partitions into the hydrophobic membrane, we propose that the molarity of kinetin in the bathing solution is not as important as the total amount of kinetin exposed to the surface phospholipids.…”

“…Various cytokinins have been shown to affect phosphate absorption with beet root discs (23) and potato tubers (13), uptake of monovalent cations by sunflower cotyledons (14), increased permeability to thiourea and urea with onion epidermis (9), alterations in respiration rates for whole cells as well as plant organelles (19), and changes in net water movement (17) with carrot cylinders (12) and radish cotyledons (3). By their very nature, use of complex natural plant tissues makes these experiments difficult to interpret.…”

“…The reported studies of kinetinaltered membrane processes have involved complex natural membranes (3, 9, 12-14, 17, 19, 23) and therefore the specific nature of the hormone-membrane interaction remains obscured. It is assumed that, if cytokinins do affect membranes, they must do so by directly altering a membrane protein (9,10,19 (4). The initial absorbance change rate, AA/At, which is known to be proportional to the liposome volume change (2,4,5,7,25), was determined for each experiment.…”

Effects of Kinetin and Root Tip Removal on Exudation and Potassium (Rubidium) Transport in Roots of Honey Locust

“…They were washed with running tap H20 for 10 min, and then soaked in 1% (v/v) sodium hypochlorite for 30 min and thoroughly rinsed with deionized H20. The seeds were planted in vermiculite, 5 Six days after planting (4 days in vermiculite and 2 days in culture solution), the seedlings had a single primary root, 7 to 8 cm long and about 0.8 mm in diameter, with no lateral roots. The modified Johnson solution was then replaced with aerated root was excised and 5 mm of the sides near the cut end were coated with lanolin-paraffin (95:5).…”