Sueltemeyer D F, Klug K, Fock H P
Fachbereich Biologie, Universitaet Kaiserslautern, Postfach 3049, D-6750 Kaiserslautern, Federal Republic of Germany.
Plant Physiol. 1986 Jun;81(2):372-5. doi: 10.1104/pp.81.2.372.
A closed system consisting of an assimilation chamber furnished with a membrane inlet from the liquid phase connected to a mass spectrometer was used to measure O(2) evolution and uptake by Chlamydomonas reinhardtii cells grown in ambient (0.034% CO(2)) or CO(2)-enriched (5% CO(2)) air. At pH = 6.9, 28 degrees C and concentrations of dissolved inorganic carbon (DIC) saturating for photosynthesis, O(2) uptake in the light (U(o)) equaled O(2) production (E(o)) at the light compensation point (15 micromoles photons per square meter per second). E(o) and U(o) increased with increasing photon fluence rate (PFR) but were not rate saturated at 600 micromoles photons per square meter per second, while net O(2) exchange reached a saturation level near 500 micromoles photons per square meter per second which was nearly the same for both, CO(2)-grown and air-grown cells. Comparison of the U(o)/E(o) ratios between air-grown and CO(2)-grown C. reinhardtii showed higher values for air-grown cells at light intensities higher than light compensation. For both, air-grown and CO(2)-grown algae the rates of mitochondrial O(2) uptake in the dark measured immediately before and 5 minutes after illumination were much lower than U(o) at PFR saturating for net photosynthesis. We conclude that noncyclic electron flow from water to NADP(+) and pseudocyclic electron flow via photosystem I to O(2) both significantly contribute to O(2) exchange in the light. In contrast, mitochondrial respiration and photosynthetic carbon oxidation cycle are regarded as minor O(2) consuming reactions in the light in both, air-grown and CO(2)-grown cells. It is suggested that the "extra" O(2) uptake by air-grown algae provides ATP required for the energy dependent CO(2)/HCO(3) (-) concentrating mechanism known to be present in these cells.
使用一个封闭系统来测量莱茵衣藻细胞的氧气释放和摄取，该系统由一个装有与质谱仪相连的来自液相的膜入口的同化室组成，这些细胞生长在环境空气（0.034% CO₂）或富含CO₂的空气（5% CO₂）中。在pH = 6.9、28℃以及光合作用溶解无机碳（DIC）浓度饱和的条件下，在光补偿点（每秒每平方米15微摩尔光子）时，光下氧气摄取量（Uₒ）等于氧气产生量（Eₒ）。Eₒ和Uₒ随着光子通量率（PFR）的增加而增加，但在每秒每平方米600微摩尔光子时未达到速率饱和，而净氧气交换在每秒每平方米近500微摩尔光子时达到饱和水平，这对于在CO₂中生长和在空气中生长的细胞几乎相同。比较在空气中生长和在CO₂中生长的莱茵衣藻的Uₒ/Eₒ比值，发现在高于光补偿的光强下，空气中生长的细胞该比值更高。对于在空气中生长和在CO₂中生长的藻类，在光照前和光照后5分钟立即测量的黑暗中线粒体氧气摄取速率远低于净光合作用饱和PFR时的Uₒ。我们得出结论，从水到NADP⁺的非循环电子流以及通过光系统I到O₂的伪循环电子流在光下对氧气交换都有显著贡献。相比之下，线粒体呼吸和光合碳氧化循环在光下被认为是在空气中生长和在CO₂中生长的细胞中消耗氧气的次要反应。有人认为，在空气中生长的藻类“额外”摄取的O₂为这些细胞中已知存在的能量依赖性CO₂/HCO₃⁻浓缩机制提供所需的ATP。
