The effect of various alkylguanidines on ion absorption and energy metabolism in oat (Avena sadva cv. Goodfileld) roots has been investigated. Of several alkylguanidines tested, octylguanidine was the most effective inhibitor of both K+ and Clr absorption by excised roots. At 225 JM octylguanidine, the transport of both ions was inhibited within 60 seconds and to a similar extent. Octylguanidine inhibited mitochondrial oxidative phosphorylation and mitochondrial adenosine 5'-triphosphatase (ATPase Inhibition by octylguanidine of K+ and Cl-absorption by excised oat roots may be due to an inhibition of either the plasma membrane ATPase or mitochondrial oxidative phosphorylation. The isolated plasma membrane did not appear to be permeable to octylguanidine since the plasma membrane ATPase was inhibited only after treating the membrane with Triton. This result indicates that the primary site of action of octylguanidine in excised root is more likely to be the plasma membrane ATPase than mitochondrial oxidative phosphorylation.A variety of guanidine derivatives have been used clinically for the treatment of several human abnormalities including diabetes, malaria, botulism, and hypertension. The mode of action of the substituted guanidines is uncertain, but they are known to interfere with mitochondrial metabolism including ATP formation (2-5, 13, 14, 17, 19) and the energized transport of Na+ and K+ (9). They also competitively inhibit K+ transport in yeast (18) and block the Na+ channel in nerve and muscle membranes (10). K+ absorption by roots of barley was inhibited by octylguanidine (8).Guanidine is a strong organic base with a pKa of about 12.5.At physiologic pH, all but a small fraction of the guanidine molecules exist as positively charged species, i.e. L NH NH2 Alkylation of guanidine increases its inhibitory effect on energy transfer reactions of mitochondria (19). Since the alkyl side chain renders guanidine more lipophyllic, positively charged alkylguanidines may interact with the phospholipids of membranes (21, 22). However, a negative site or region of a protein, buried within the lipid, could be the target for the alkylguanidines (17).The basis for alkylguanidine inhibition of K+ absorption in plants has been investigated. In particular, we examined the effect of octylguanidine on energy transfer reactions of mitochondria and the plasma membrane of oat roots. MATERIALS AND METHODSAbsorption Experiments. Roots from dark-grown 5-day old oat seedlings (A vena sativa L. cv. Goodfield) were used. Seeds were placed in rows between layers of cheesecloth and grown hydroponically over I mm CaSO4 for 5 days as described (12). Absorption of K+ and CF-were determined with 86Rb and 36C1, respectively (I 1). Seedlings were removed from the cheesecloth screen and their roots cut into 1-cm segments. Segments from three roots (90-100 mg) were incubated in 10 ml of I mm KCI containing 8'Rb or 36C1 and different concentrations of alkylguanidines. The pH was adjusted with KOH or HCI. The experiments were conducte...
Effects of octylguanidine (OG) were studied on the permeability of cells of the adaxial epidermis of Allium cepa bulb scales to water and methyl urea and on the protoplast surface. Interference of OG with the Ca2+ and Al3 action on the ceUl surface was also investigated.Permeability of the ceil membrane for water and methyl urea increased nearly three times in presence of OG. The effect of OG on cel permeability depended on its direct contact with the protoplast surface.The effect of OG on the interaction between the protoplast surface and the cel wal (wall attachment) was marked and rapid; OG (225 micromolar During the early part of this investigation, OG was found to have a dramatic effect on the attachment between the protoplast surface and the cell wall. Cell wall attachment has been known to increase in presence of AlCl3 (1). The strength of this attachment has been related to the electrical potentials between plasmalemma and cell wall (15). Also, OG is known to inhibit K+ transport (6). Therefore, one of the objectives of this study was to investigate the effect of OG on the cell wall attachment in relation to various ions, e.g. Al3", Ca2+, K+. MATERIALS AND METHODSOnions (A Ilium cepa L., cv. Downing Yellow Globe) were grown at the University of Minnesota Sand Plain Experimental Field without the use of herbicides or growth inhibitors. The bulbs were harvested in September of 1977 and stored at 5 C. Onions used for the work were brought to room temperature 1 day before the experiments.Octylguanidine has been shown to inhibit K+ transport in excised roots of Hordeum vulgare (5) and Avena sativa seedlings (6) and it has been suggested that this inhibitor acts at the cell surface level by interfering with the plasma membrane ATPase complex. This conclusion was drawn from studies conducted on multicellular structures (excised roots; 5, 6) and on subcellular fractions (mitochondria; 11). Studies at the cellular level can provide information important for understanding the nature and mechanism of OG3 inhibition. So far no such studies have been undertaken. In the present investigation, we attempted to observe and study the effect of OG at the cellular level by using various 'This work was supported by the Minnesota Agricultural Experiment
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