Volk R J, Jackson W A
Department of Soil Science, North Carolina State University, Raleigh, North Carolina 27607.
Plant Physiol. 1972 Feb;49(2):218-23. doi: 10.1104/pp.49.2.218.
Concurrent O(2) evolution, O(2) uptake, and CO(2) uptake by illuminated maize (Zea mays) leaves were measured using (13)CO(2) and (18)O(2). Considerable O(2) uptake occurred during active photosynthesis. At CO(2) compensation, O(2) uptake increased. Associated with this increase was a decrease in O(2) release such that a stoichiometric exchange of O(2) occurred. The rate of O(2) exchange at CO(2) compensation was directly related to O(2) concentration in the atmosphere at least up to 8% (v/v).When illuminated maize leaves were exposed to saturating CO(2) concentrations containing approximately equal amounts of (12)CO(2) and (13)CO(2), the latter was taken up more rapidly, thus depressing the atom% (13)C in the atmosphere. Moreover, upon exposure to CO(2) containing 96 atom% (13)C, there occurred a directly measurable efflux of (12)CO(2) from the leaves for at least 15 minutes. During this period an equimolar evolution of (16)O(2) and uptake of (13)CO(2) was observed. Thereafter, although the rate of (16)O(2) evolution remained unchanged, the rate of (13)CO(2) uptake declined markedly, suggesting continual (13)C enrichment of the photorespiratory substrate.It is concluded that a finite photorespiratory process occurs in maize and that the CO(2) generated thereby is efficiently recycled. Recycling maintains the internal CO(2) concentration at a level difficult to detect by most photorespiratory assays.
利用¹³CO₂和¹⁸O₂测定了光照下玉米叶片同时进行的O₂释放、O₂吸收和CO₂吸收。在活跃光合作用期间发生了大量的O₂吸收。在CO₂补偿点时，O₂吸收增加。与此增加相关的是O₂释放减少，从而发生了O₂的化学计量交换。CO₂补偿点处的O₂交换速率与大气中的O₂浓度直接相关，至少在高达8%（v/v）时如此。当光照下的玉米叶片暴露于含有大致等量¹²CO₂和¹³CO₂的饱和CO₂浓度时，后者被吸收得更快，从而降低了大气中¹³C的原子百分比。此外，当暴露于含有96原子百分比¹³C的CO₂时，叶片中至少在15分钟内出现了可直接测量的¹²CO₂外流。在此期间，观察到了¹⁶O₂的等摩尔释放和¹³CO₂的吸收。此后，尽管¹⁶O₂释放速率保持不变，但¹³CO₂吸收速率显著下降，这表明光呼吸底物的¹³C持续富集。得出的结论是，玉米中发生了有限的光呼吸过程，并且由此产生的CO₂被有效地再循环。再循环将内部CO₂浓度维持在大多数光呼吸测定难以检测到的水平。
