Hanson K R, Peterson R B
Arch Biochem Biophys. 1985 Mar;237(2):300-13. doi: 10.1016/0003-9861(85)90281-4.
The stoichiometry of photorespiration, S, is defined as the fraction of glycolate carbon photorespired. It is postulated that under steady-state conditions there are two determinants of the ratio of photorespiration to net photosynthesis: the partitioning of ribulose bisphosphate between oxidation and carboxylation, and the partitioning of glycolate between reactions leading to complete oxidation to CO2 (S = 100%) and those yielding CO2 plus serine (S = 25%). S may be calculated using two independent probes of the system. The physical probe, using an infrared gas analyzer, measured photorespiration and net photosynthesis, and hence their ratio PR/NPS = pn(phys). The metabolic probe employed tracer (3R)-D-[3-3H1,3-14C]glyceric acid to determine r, the fraction of 3H retained in the triose phosphates leaving the chloroplasts. It is deduced from the postulated model that S = pn(phys) . r/(1 - r). Experiments have been performed with illuminated tobacco leaf discs (inverted) under varying concentrations of O2 and CO2. Increasing O2 at constant CO2 increased pn(phys) and decreased r, whereas increasing CO2 at constant O2 had the opposite effect. S more than doubled at 32 degrees C on going from 16 to 40% O2 (340 microliters CO2/liter) and decreased 40% on going from 200 to 700 microliters CO2/liter (21% O2). For discs in normal air S was somewhat greater than 27%. It is suggested that net photosynthesis, and therefore crop yields, could be increased by selecting for crop plants with reduced photorespiration stoichiometry.
光呼吸的化学计量比S定义为光呼吸的乙醇酸碳的比例。据推测，在稳态条件下，光呼吸与净光合作用的比例有两个决定因素：二磷酸核酮糖在氧化和羧化之间的分配，以及乙醇酸在导致完全氧化为CO₂（S = 100%）和产生CO₂加丝氨酸（S = 25%）的反应之间的分配。S可以使用该系统的两个独立探针来计算。物理探针使用红外气体分析仪测量光呼吸和净光合作用，因此它们的比例PR/NPS = pn(phys)。代谢探针使用示踪剂(3R)-D-[3-³H,¹⁴C]甘油酸来确定r，即保留在离开叶绿体的磷酸丙糖中的³H的比例。从假设模型推导得出S = pn(phys)·r/(1 - r)。已经在不同O₂和CO₂浓度下对光照的烟草叶盘（倒置）进行了实验。在恒定CO₂下增加O₂会增加pn(phys)并降低r，而在恒定O₂下增加CO₂则有相反的效果。在32℃时，从16% O₂（340微升CO₂/升）增加到40% O₂时，S增加了一倍多，从200微升CO₂/升（21% O₂）增加到700微升CO₂/升时，S降低了40%。对于正常空气中的叶盘，S略大于27%。有人提出，通过选择光呼吸化学计量比降低的作物植物可以提高净光合作用，从而提高作物产量。
