Espie G S, Colman B
Department of Biology, York University, Downsview, Ontario, Canada.
Plant Physiol. 1987 Jan;83(1):113-7. doi: 10.1104/pp.83.1.113.
The effect of pH, O(2) concentration, and temperature on the CO(2) compensation point (capital GHE, Cyrillic[CO(2)]) of isolated Asparagus sprengeri Regel mesophyll cells has been determined in a closed, aqueous environment by a sensitive gas-chromatographic technique. Measured values range between 10 and 100 microliters per liter CO(2) depending upon experimental conditions. The capital GHE, Cyrillic(CO(2)) increases with increasing temperature. The rate of increase is dependent upon the O(2) concentration and is more rapid at high (250-300 micromolar), than at low (30-60 micromolar), O(2) concentrations. The differential effect of temperature on capital GHE, Cyrillic(CO(2)) is more pronounced at pH 6.2 than at pH 8.0, but this pH-dependence is not attributable to a direct, differential effect of pH on the relative rates of photosynthesis and photorespiration, as the O(2)-sensitive component of capital GHE, Cyrillic(CO(2)) remains constant over this range. The capital GHE, Cyrillic(CO(2)) of Asparagus cells at 25 degrees C decreases by 50 microliters per liter when the pH is raised from 6.2 to 8.0, regardless of the prevailing O(2) concentration. It is suggested that the pH-dependence of capital GHE, Cyrillic(CO(2)) is related to the ability of the cell to take up CO(2) from the aqueous environment. The correlation between high HCO(3) (-) concentrations and low capital GHE, Cyrillic(CO(2)) at alkaline pH indicates that extracellular HCO(3) (-) facilitates the uptake of CO(2), possibly by increasing the flux of inorganic carbon from the bulk medium to the cell surface. The strong O(2)- and temperature-dependence of capital GHE, Cyrillic(CO(2)) indicates that isolated Asparagus mesophyll cells lack an efficient means for concentrating intracellular CO(2) to a level sufficient to reduce or suppress photorespiration.
通过灵敏的气相色谱技术，在封闭的水环境中测定了pH值、氧气浓度和温度对离体石刁柏叶肉细胞二氧化碳补偿点（大写GHE，西里尔文[CO₂]）的影响。根据实验条件，测量值在每升10至100微升二氧化碳之间。大写GHE，西里尔文（CO₂）随温度升高而增加。增加速率取决于氧气浓度，在高（250 - 300微摩尔）氧气浓度下比在低（30 - 60微摩尔）氧气浓度下更快。温度对大写GHE，西里尔文（CO₂）的差异效应在pH 6.2时比在pH 8.0时更明显，但这种pH依赖性并非归因于pH对光合作用和光呼吸相对速率的直接差异效应，因为大写GHE，西里尔文（CO₂）的氧气敏感成分在此范围内保持恒定。无论当时的氧气浓度如何，当pH从6.2升高到8.0时，25℃下石刁柏细胞的大写GHE，西里尔文（CO₂）每升降低50微升。有人认为，大写GHE，西里尔文（CO₂）的pH依赖性与细胞从水环境中吸收二氧化碳的能力有关。碱性pH下高碳酸氢根（HCO₃⁻）浓度与低大写GHE，西里尔文（CO₂）之间的相关性表明，细胞外HCO₃⁻可能通过增加无机碳从大量介质到细胞表面的通量来促进二氧化碳的吸收。大写GHE，西里尔文（CO₂）对氧气和温度的强烈依赖性表明，离体石刁柏叶肉细胞缺乏将细胞内二氧化碳浓缩到足以降低或抑制光呼吸水平的有效手段。
