Tenhunen J D, Weber J A, Yocum C S, Gates D M
The Biological Station and Matthaei Botanical Gardens, Division of Biological Sciences, The University of Michigan, Ann Arbor, Michigan 48109.
Plant Physiol. 1979 May;63(5):916-23. doi: 10.1104/pp.63.5.916.
An analysis of the kinetics of simultaneous photosynthesis and photorespiration at the end of a diffusion path is applied to observed net photosynthetic rate as a function of O(2) and CO(2) concentrations. The data of Ku and Edwards (Plant Physiol. 59: 991-999, 1977) from wheat (Triticum aestivum L.) are analyzed in detail. Ku and Edwards, using an analysis that ignored diffusion resistance between the intercellular air space and fixation site, the competitive effect of CO(2) on photorespiration, and the actual concentrations of gases at the fixation site, concluded that: (a) the affinity coefficient of the leaf for CO(2) was approximately 3.5 to 5 micromolar; (b) this affinity coefficient is independent of temperature between 25 and 35 C; (c) the effect of O(2) was independent of temperature over this range; and (d) competition between CO(2) and O(2) is responsible for the major share of CO(2) loss from photosynthesis due to photorespiration. They suggest that using gas concentrations calculated as equilibium values in the liquid phase is very important in reaching these conclusions. By applying a more complete analysis to their data which includes diffusion in the cell, it is concluded that: (a) the affinity coefficient of the leaf for CO(2) is 0.1 to 1.1 micromolar; (b) the temperature dependence of this affinity coefficient cannot be determined from existing data, but there is no evidence to refute independent temperature effect on the two functions of ribulose-1,5-bisphosphate carboxylase-oxygenase being important in the regulation of whole leaf net photosynthesis; and (c) the competitive interplay of CO(2) and O(2) at ribulose-1,5-bisphosphate carboxylase may under certain conditions lead to a stimulation of fixation by the Calvin cycle because of photorespiration. These conclusions are reached whether CO(2) and O(2) are expressed as dissolved concentrations or as gas concentrations in the intercellular air space. The relative merits of these two expressions of concentration are discussed.
在扩散路径末端对光合作用和光呼吸同时进行的动力学分析被应用于观察到的净光合速率，该净光合速率是氧气和二氧化碳浓度的函数。对Ku和Edwards（《植物生理学》59: 991 - 999, 1977）从小麦（普通小麦）获得的数据进行了详细分析。Ku和Edwards的分析忽略了细胞间隙与固定位点之间的扩散阻力、二氧化碳对光呼吸的竞争效应以及固定位点处气体的实际浓度，他们得出以下结论：(a) 叶片对二氧化碳的亲和系数约为3.5至5微摩尔；(b) 该亲和系数在25至35摄氏度之间与温度无关；(c) 在此温度范围内氧气的效应与温度无关；以及(d) 二氧化碳和氧气之间的竞争是光合作用中因光呼吸导致二氧化碳损失的主要原因。他们认为在得出这些结论时，使用液相平衡值计算的气体浓度非常重要。通过对他们的数据应用更完整的分析，该分析包括细胞内的扩散，得出以下结论：(a) 叶片对二氧化碳的亲和系数为0.1至1.1微摩尔；(b) 无法从现有数据确定该亲和系数的温度依赖性，但没有证据反驳对1,5 - 二磷酸核酮糖羧化酶 - 加氧酶的两个功能存在独立温度效应，这两个功能在调节全叶净光合作用中很重要；以及(c) 在1,5 - 二磷酸核酮糖羧化酶处二氧化碳和氧气的竞争性相互作用在某些条件下可能由于光呼吸而导致卡尔文循环对固定的刺激。无论二氧化碳和氧气是以溶解浓度还是以细胞间隙中的气体浓度表示，都能得出这些结论。讨论了这两种浓度表示方式的相对优点。
