The Effect of Ultraviolet Light on the Sodium and Potassium Composition of Resting Yeast Cells

Abstract

The Na + and K + content of non-metabolizing yeast cells was determined before and after monochromatic ultraviolet (UV) irradiation. UV facilitated the uptake of Na + into and the loss of K + from the cells (net ion flux); the effect is greatest for the shortest wavelength employed (239 m#) and is partly dependent upon the presence of oxygen. The UV effect on net ion flux persists for at least 90 minutes during which tests were made and it occurs following dosages which are without measurable effect on colony formation. The UV effect on net ion flux is decreased by acidity and prorooted by alkalinity. Addition of calcium ions in sufficient amount prevents the usual net ion flux changes observed in irradiated yeast. Increase in concentration gradient between the inside and the outside of the cell increases the net ion flux of irradiated yeast, Na + uptake leading K + loss in all cases. UV appears to act by disorganizing the constituents of the cell surface, permitting K + to leave the cell in exchange for Na +. At low intensities of UV this ionic exchange approaches equivalence, but at higher intensities more lqa + is taken up than K + is lost. Some evidence suggests that the Na + in excess over that exchanged for K + is adsorbed to charged groups produced by the photochemical effect of UV on the cell surface.

Effects of Calcium Ion and the Protective Action on Survival and Growth Inhihition of Pollen

“…Possibly at some point in the irradiation treatment an eqnilibrium was reached whereby the amount of Ca being removed from the cell wall, was being replaced by the supplemented Ca. Sanders and Giese (1959) have shown that Ca can rednce nltraviolet damage to the osmoregulatory system of the yeast cell. Weijer (1963) has recently shown that Ca ions cause an increased proportion of conidium germination of Neiirospora crassa and protect against the consequences of X-irradiation injury.…”