Ozone Alteration of Membrane Permeability in Chlorella

Abstract

(21,22), and ions (6, 10). Accordingly, the loss of K+ has been shown to be one of the first indications of membrane permeability changes under a variety of stresses (5,17,18,20).The net loss of K+ from ozone-treated Chlorella cells suspended in a Tris buffer has been measured using a cation-specific electrode (6). The electrode method measured only the net loss of K+ at a low external K+ concentration. Thus, the effect of ozone upon the K+ influx and efflux could not be studied separately under physiological conditions. The use of Tris as a buffer induces K+ loss itself, thus making the interpretation of K+ loss difficult (7). For influx measurements, I09 cells were added to a total volume of 5 ml of medium in a stirred and temperature-regulated cuvette (38 C). Label ("6RbCl, New England Nuclear) was added prior to cell addition and subsequent gassing. Either oxygen or ozone in oxygen, produced and measured as previously described (6, 11), was introduced into the agitated solution through a 50-,ul micropipette. At specific times, a 200-jul aliquot of the cell suspension was withdrawn, filtered on a Millipore filter (0.45 ,um), and washed with 5 ml of unlabeled medium. The cell sample on the filter was removed to a drying stand, bleached with I drop of Purex, and placed in a toluene-Triton cocktail for scintillation counting (14).Uptake rates were calculated from the amount of 8'Rb present in the cells at various time intervals, based upon the external specific radioactivity of Rb+ and K+.In experiments during which the initial uptake kinetics were examined, l-ml aliquots from a batch of cells (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)

Inhibition of the K+-Stimulated ATPase of the Plasmalemma of Pinto Bean Leaves by Ozone

“…Studies on ozone damage to plants have implicated the plasma membrane as the site of initial injury (2,3,8); subsequent ionic and pH imbalance within the protoplasts are likely to disrupt normal metabolic processes (6). The mechanisms of ozone damage to tissues at the molecular level have been studied extensively and are well reviewed (1,11).…”

Ozone Inhibition of Photosynthesis in Chlorella sorokiniana

“…There is variability among cell cultures, but the average depression is similar to that observed for respiration (11). To inhibit the photosynthetic rate by half, a delivered ozone dose of about 2.9 ,umol in 8 min was required.…”

“…It was shown previously that K+ is lost from cells exposed to ozone (2,11). In addition, it has been postulated that the loss of water potentiaL due to loss ofthis cation in ozone-fumigated green plants, causes the decline in photosynthesis (10,14).…”

“…Either 02 or ozone was bubbled into 10 ml of a stirred buffered phosphate solution containing 2 x 108 cells/ml for varying times (11). A 1.0-ml cell sample was removed and, after addition of 20 mm NaHCO3, assayed for 02 evolution.…”

“…Chlorella has been used previously to study ozone effects on ion transport pathways (1,11). In the present study, we describe ozone alterations of photosynthetic competence in Chlorella as they are measured by 02 evolution and fluorescence yield kinetics.…”