Nishio J N, Ting I P
Department of Botany and Plant Sciences, University of California, Riverside, California 92521.
Plant Physiol. 1987 Jul;84(3):600-4. doi: 10.1104/pp.84.3.600.
Leaves of Peperomia camptotricha contain three distinct upper tissue layers and a one-cell thick lower epidermis. Light and dark CO(2) fixation rates and the activity of ribulose bisphosphate carboxylase/oxygenase and several C(4) enzymes were determined in the three distinct tissue layers. The majority of the C(4) enzyme activity and dark CO(2) fixation was associated with the spongy mesophyll, including the lower epidermis; and the least activity was found in the median palisade mesophyll. In contrast, the majority of the C(3) activity, that is ribulose bisphosphate carboxylase/oxygenase and light CO(2) fixation, was located in the palisade mesophyll. In addition, the diurnal flux in titratable acidity was greatest in the spongy mesophyll and lowest in the palisade mesophyll. The spatial separation of the C(3) and C(4) phases of carbon fixation in P. camptotricha suggests that this Crassulacean acid metabolism plant may have low photorespiratory rates when it exhibits daytime gas exchange (that is, when it is well watered). The results also indicate that this plant may be on an evolutionary path between a true Crassulacean acid metabolism plant and a true C(4) plant.
毛果豆瓣绿的叶子包含三个不同的上层组织层和一层单细胞厚的下表皮。在这三个不同的组织层中测定了光下和暗中二氧化碳固定速率以及核酮糖二磷酸羧化酶/加氧酶和几种C4酶的活性。大部分C4酶活性和暗中二氧化碳固定与海绵叶肉有关，包括下表皮；而在中位栅栏叶肉中活性最低。相反，大部分C3活性，即核酮糖二磷酸羧化酶/加氧酶和光下二氧化碳固定，位于栅栏叶肉中。此外，可滴定酸度的日通量在海绵叶肉中最大，在栅栏叶肉中最低。毛果豆瓣绿碳固定的C3和C4阶段的空间分离表明，这种景天酸代谢植物在进行白天气体交换时（即浇水良好时）可能具有低光呼吸速率。结果还表明，这种植物可能正处于真正的景天酸代谢植物和真正的C4植物之间的进化路径上。
