Moore B D, Edwards G E
Department of Botany, Washington State University, Pullman, Washington 99164-4230.
Plant Physiol. 1986 Jun;81(2):669-73. doi: 10.1104/pp.81.2.669.
The metabolism of fixed (14)CO(2) and the utilization of the C-4 carboxyl of malate and aspartate were examined during photosynthetic induction in Flaveria trinervia, a C(4) dicot of the NADP-malic enzyme subgroup. Pulse/chase experiments indicated that both malate and aspartate appeared to function directly in the C(4) cycle at all times during the induction period (examined after 30 seconds, 5 minutes and 20 minutes illumination). However, the rate of loss of (14)C-label from the C-4 position of malate plus aspartate was relatively slow after 30 seconds of illumination, compared to treatments after 5 or 20 minutes of illumination. Similarly, the appearance of label in other photosynthetic products (e.g. 3-phosphoglycerate, sugar phosphates, alanine) during the chase periods was generally slower after only 30 seconds of leaf illumination, compared to that after 5 of 20 minutes illumination. This may be due to the lower rate of photosynthesis after 30 seconds illumination. The appearance of label in carbons 1-->3 of each C(4) acid during the chase periods was relatively slow after either 30 seconds or 5 minutes illumination, while there was a relatively rapid accumulation of label in carbons 1-->3 of both C(4) acids after 20 minutes illumination. Thus, while the turnover rate of the (14)C-4 label in both C(4) acids increased only during the first 5 minutes of the induction period, only later during induction is there an increased rate of appearance of label in other carbon atoms of the C(4) acids. The implied source of (14)C for labeling of the 1-->3 positions of the C(4) acids is an apparent carbon flux from 3-phosphoglycerate of the reductive pentose phosphate pathway to phosphoenolpyruvate of the C(4) cycle.
在三脉黄菊（NADP - 苹果酸酶亚组的一种C4双子叶植物）的光合诱导过程中，研究了固定的（14）CO2的代谢以及苹果酸和天冬氨酸C - 4羧基的利用情况。脉冲/追踪实验表明，在诱导期的所有时间（光照30秒、5分钟和20分钟后检测），苹果酸和天冬氨酸似乎都直接在C4循环中起作用。然而，与光照5分钟或20分钟后的处理相比，光照30秒后苹果酸加天冬氨酸C - 4位上（14）C标记的损失速率相对较慢。同样，在追踪期，与光照5分钟或20分钟后相比，仅叶片光照30秒后，其他光合产物（如3 - 磷酸甘油酸、磷酸糖、丙氨酸）中标记的出现通常较慢。这可能是由于光照30秒后光合作用速率较低。在追踪期，光照30秒或5分钟后，每种C4酸的碳1→3位上标记的出现相对较慢，而光照20分钟后，两种C4酸的碳1→3位上标记积累相对较快。因此，虽然两种C4酸中（14）C - 4标记的周转率仅在诱导期的前5分钟增加，但仅在诱导后期，C4酸其他碳原子上标记的出现速率才增加。C4酸碳1→3位标记的（14）C的明显来源是从还原戊糖磷酸途径的3 - 磷酸甘油酸到C4循环的磷酸烯醇式丙酮酸的明显碳通量。
