The effect of external pH on two laboratory-cultured acid-intolerant species (Chlorella pyrenoidosa Chick and Scenedesmus qudaa Turp.Breb.) and one acid-tolerant species from a natural population (Euglena mutabilis Schmitz) was examined by measuring internal pH. These measurements were made with the weak acid 'C-dimethyloxazolidine-2,4-dione after cels had been incubated for 2 and 6 hours at external pH levels from 3.0 to 8.0. Photosynthetic and respiration rates of the three species were also measured over the range of external pH levels.AU three species regulated their internal pH levels over the 6-hour incubation time. C. pyrenoidosa and S. qa had internal pH levels around 7.0, regardless of external pH. E. mutabilis had a wider internal pH range, from 5.0 at low external pH to 8.0 at high external pH. External pH had no effect on either photosynthetic or respiration rates. Statistical comparisons showed that there was a significant difference between the acid-intolerant and acid-tolerant species with regard to the level of internal pH maintained and the response of internal pH to external pH.Many streams in Pennsylvania and other parts of Appalachia have become polluted with H2SO4 from coal mines in the region. As a consequence, the pH levels in these streams are very low, in the range of 1.4 to 4.5 (6). The low environmental pH, along with other factors such as high acidity and high iron concentrations, strongly affects the biota of these streams (3). Algal species diversity is quite low (3, 24) and decreases as the pH level decreases. Nevertheless, certain species of algae flourish in these streams (3,10,24).Studies, such as those cited, have characterized a number of aspects ofnatural populations of these algae. However, little about the physiology at low external pH of acid-tolerant species is known.The measurement of internal (cytoplasmic) pH with ['4CJDMO2 provides one method by which the effect of external pH on a cell can be investigated (see Ref. 15 for a review of internal pH and methods of its measurement). None of the algae that have been studied with this method have been acid-tolerant species. Furthermore, internal pH levels have not been measured when external pH levels are as low as those encountered by acid-tolerant species.In this study, [(4CIDMO was 3.0 to 8.0. For comparative purposes, the internal pH levels of two laboratory-cultured acid-intolerant species were also measured over the same external pH range. The objective of the study was to determine whether or not the three species maintained constant internal pH levels regardless of external pH and whether there were differences between the internal pH levels ofthe acid-tolerant species and the acid-intolerant species.Results of the internal pH measurements indicate that differences do exist in both the actual values of internal pH that the acid-tolerant and acid-intolerant species have and in the way in which the internal pH of each species responds as external pH changes. MATERIALS AND METHODSOrganisms. The two acid-in...
A method was devised to quantify short-term photorespiratory rates in terrestrial plants using 180-intermediates of the glycolate pathway, specifically glycolate, glycine, and serine. The pathway intermediates were isolated and analyzed on a GC/MS to determine molecular percent 180-enrichment. Rates of glycolate synthesis were determined from '10-labeling kinetics of the intermediates, derived rate equations, and nonlinear regression techniques. Glycolate synthesis in wheat (Triticum aestivum L.), a C3 plant, and maize (Zea mays L.), a C4 plant, was stimulated by high 02 concentrations and inhibited by high CO2 concentrations. The synthesis rates were 7.3, 2.1, and 0.7 micromoles per square decimeter per minute under a 21% 02 and 0.035% Co2 atmosphere for leaf tissue of wheat, maize seedlings, and 3-month-old maize, respectively. Photorespiratory CO2 evolution rates were estimated to be 27, 6, and 2%, respectively, of net photosynthesis for the three groups of plants under the above atmosphere. The results from maize tissue support the hypothesis that C4 plants photorespire, albeit at a reduced rate in comparison to C3 plants, and that the C02/02 ratio in the bundle sheath of maize is higher in mature tissue than in seedling tissue. The pool size of the three photorespiratory intermediates remained constant and were unaffected by changes in either CO2 or 02 concentrations throughout the 10-minute labeling period. This suggests that photorespiratory metabolism is regulated by other mechanism besides phosphoglycolate synthesis by ribulose-1,5-bisphosphate carboxylase/oxygenase, at least under short-term conditions. Other mechanisms could be altemate modes of synthesis of the intermediates, regulation of some of the enzymes of the photorespiratory pathway, or regulation of carbon flow between organelles involved in photorespiration. The glycolate pool became nearly 100% 10-labeled under an atmosphere of 40% 02. This pool failed to become 100% 180-enriched under lower 02 concentrations.
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