NMR determination of photorespiration in intact leaves using in vivo 13CO2 labeling
NMR determination of photorespiration in intact leaves using in vivo 13CO2 labeling
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DOI：
10.1016/j.jmr.2005.10.010
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发表时间：
2006-01-01
影响因子：
2.2
通讯作者：
Schaefer, J
中科院分区：
文献类型：
--
作者：
Cegelski, L;Schaefer, J
对用 (CO2)-C-13 标记的完整大豆叶片进行固态 C-13 NMR 测量得出的结论是，对于浇水和受精良好的植物来说，光呼吸占光合作用的 17%。这是对功能植物的光呼吸水平的首次直接评估。 C-13{P-31} 旋转回波双共振 (REDOR) 测量跟踪 13C 标记与卡尔文循环中间体的结合随时间的变化。对于 5 分钟或更短的标记时间，卡尔文循环的同位素富集取决于来自 (CO2)-C-13 的标记碳通量，相对于来自光呼吸循环返回的甘油酸的未标记碳通量。对于(CO2)-C-13浓度固定值的这两个速率的比较表明，大豆叶片中核酮糖-1,5-二磷酸羧化酶/加氧酶(Rubisco)的光合作用速率与光呼吸速率的比率为5.7。这转化为光呼吸 CO2 损失，占 CO2 净同化量的 21%，约为 Rubisco 动力学参数估计值的 80%。根据净碳同化率测量，外部二氧化碳浓度较低时，速率比率会降低。碳同化是通过卡尔文循环的 REDOR 确定的同位素富集转化为总碳的 13 C 标记自旋计数来确定的。净碳同化速率表明甘氨酸脱羧速率并不像通常假设的那样与 Rubisco 加氧酶活性成正比。 (c) 2005 Elsevier Inc. 保留所有权利。
Solid-state C-13 NMR measurements of intact soybean leaves labeled by (CO2)-C-13 lead to the conclusion that photorespiration is 17% of photosynthesis for a well-watered and fertilized plant. This is the first direct assessment of the level of photorespiration in a functioning plant. A C-13{P-31} rotational-echo double-resonance (REDOR) measurement tracked the incorporation of 13C label into intermediates in the Calvin cycle as a function of time. For labeling times of 5 min or less, the isotopic enrichment of the Calvin cycle depends on the flux of labeled carbon from (CO2)-C-13, relative to the flux of unlabeled carbon from glycerate returned from the photorespiratory cycle. Comparisons of these two rates for a fixed value of the (CO2)-C-13 concentration indicate that the ratio of the rate of photosynthesis to the rate of photorespiration of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in soybean leaves is 5.7. This translates into a photorespiratory CO2 loss that is 21% of net CO2 assimilation, about 80% of the value estimated from Rubisco kinetics parameters. The ratio of rates is reduced at low external CO2 concentrations, as measured by net carbon assimilation rates. The carbon assimilation was determined from 13 C-label spin counts converted into total carbon by the REDOR-determined isotopic enrichments of the Calvin cycle. The net carbon assimilation rates indicate that the rate of decarboxylation of glycine is not directly proportional to the oxygenase activity of Rubisco as is commonly assumed. (c) 2005 Elsevier Inc. All rights reserved.