RATE-LIMITING FACTORS IN LEAF PHOTOSYNTHESIS .1. CARBON FLUXES IN THE CALVIN CYCLE
RATE-LIMITING FACTORS IN LEAF PHOTOSYNTHESIS .1. CARBON FLUXES IN THE CALVIN CYCLE
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DOI：
10.1016/0005-2728(84)90041-0
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发表时间：
1984-01-01
期刊：
影响因子：
--
通讯作者：
HEBER, U
中科院分区：
文献类型：
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作者：
DIETZ, KJ;HEBER, U
菠菜叶片的光合速率随光照强度和CO2浓度的变化而变化。然后通过在液氮中冷冻来阻止叶子的代谢。叶绿体分离的非水程序。在叶绿体组分中，碳还原循环的中间产物的水平被确定并被认为与冷冻前的时间叶片的光合通量情况有关。在诱导光合作用，核酮糖1，5-二磷酸水平增加与CO2固定平行。在稳定状态下，在0和50 W之间的光强度下观察到1，5-二磷酸核酮糖水平和CO2吸收之间的类似关系。m-2进一步增加光照强度增加CO2固定率，但不增加核酮糖1，5-二磷酸水平。增加CO2浓度导致CO2吸收增加，而1，5-二磷酸核酮糖水平下降。即使在CO2饱和下，1，5-二磷酸核酮糖水平也为约100 nmol/mg叶绿素，对应于叶绿体基质中约3.5 mM 1，5-二磷酸核酮糖。即使在CO2饱和下，核酮糖-1，5-二磷酸羧化酶也明显限制光合CO2吸收。从测定的代谢物水平计算的质量作用比表明，核酮糖1，5-二磷酸从磷酸己糖和磷酸丙糖的再生所需的热力学梯度增加相当大的光合通量增加。类似的计算表明，酶的装置负责减少3-磷酸甘油二羟丙酮磷酸是没有位移太多的平衡，即使在最大速率的光合作用在饱和CO2。醛缩酶也是如此。果糖-1，6-二磷酸酶也不限制卡尔文循环周转。只有在非常低的光强度和在诱导期的第一分钟是果糖1，6-二磷酸果糖6-磷酸的比例高。这一观察结果更容易解释的果糖1，6-二磷酸结合核酮糖-1，5-二磷酸羧化酶，而不是由果糖-1，6-二磷酸酶的活化不足所施加的速率限制。
Rates of photosynthesis of spinach leaves were varied by varying light intensity and CO2 concentration. Metabolism of the leaves was then arrested by freezing them in liquid nitrogen. Chloroplasts were isolated by a nonaqueous procedure. In the chloroplast fractions, levels of intermediates of the carbon reduction cycle were determined and considered in relation to the photosynthetic flux situation of the leaves at the time before freezing. During induction of photosynthesis, ribulose 1,5-bisphosphate levels increased in parallel with CO2 fixation. In the steady state, a similar relation between ribulose 1,5-bisphosphate levels and CO2 uptake was observed at light intensities between 0 and 50 W .cntdot. m-2. A further increase in light intensity increased CO2 fixation rates but not ribulose 1,5-bisphosphate levels. Increasing the CO2 concentration resulted in increased CO2 uptake, whereas ribulose 1,5-bisphosphate levels decreased. Even under CO2 saturation, ribulose 1,5-bisphosphate levels were about 100 nmol/mg chlorophyll corresponding to about 3.5 mM ribulose 1,5-bisphosphate in the chloroplast stroma. Even under CO2 saturation, ribulose-1,5-bisphosphate carboxylase apparently limits photosynthetic CO2 uptake. Mass action ratios calculated from measured metabolite levels demonstrated that the thermodynamic gradient required for the regeneration of ribulose 1,5-bisphosphate from hexosephosphate and triosephosphate increased considerably as photosynthetic flux increased. Similar calculations revealed that the enzymatic apparatus responsible for the reduction of 3-phosphoglycerate to dihydroxyacetone phosphate is not displaced much from equilibrium even under maximum rates of photosynthesis at saturating CO2. The same is true for aldolase. Fructose-1,6-bisphosphatase also did not limit Calvin cycle turnover. Only at very low light intensities and during the first minutes of the induction period was the ratio of fructose 1,6-bisphosphate to fructose 6-phosphate high. This observation was more readily explained in terms of fructose 1,6-bisphosphate binding to ribulose-1,5-bisphosphate carboxylase than by a rate limitation imposed by insufficient activation of fructose-1,6-bisphosphatase.