Parys Eugeniusz, Jastrzebski Hubert
Department of Plant Physiology, Faculty of Biology, University of Warsaw, ul. Miecznikowa 1, 02096 Warszawa, Poland.
J Plant Physiol. 2006 Apr;163(6):638-47. doi: 10.1016/j.jplph.2005.05.009. Epub 2005 Aug 30.
The rate of respiratory CO2 evolution from the leaves of Zea mays, Panicum miliaceum, and Panicum maximum, representing NADP-ME, NAD-ME, and PEP-CK types of C4 plants, respectively, was increased by approximately two to four times after a period of photosynthesis. This light-enhanced dark respiration (LEDR) was a function of net photosynthetic rate specific to plant species, and was depressed by 1% O2. When malate, aspartate, oxaloacetate or glycine solution at 50 mM concentration was introduced into the leaves instead of water, the rate of LEDR was enhanced, far less in Z. mays (by 10-25%) than in P. miliaceum (by 25-35%) or P. maximum (by 40-75%). The enhancement of LEDR under glycine was relatively stable over a period of 1 h, whereas the remaining metabolites caused its decrease following a transient increase. The metabolites reduced the net photosynthesis rate in the two Panicum species, but not in Z. mays, where this process was stimulated by glycine. The bundle sheath cells from P. miliaceum exhibited a higher rate of LEDR than those of Z. mays and P. maximum. Glycine had no effect on the respiration rate of the cells, but malate increased in cells of Z. mays and P. miliaceum by about 50% and 30%, respectively. With the exception of aspartate, which stimulated both the O2 evolution and O2 uptake in P. maximum, the remaining metabolites reduced photosynthetic O2 evolution from bundle sheath cells in Panicun species. The net O2 exchange in illuminated cells of Z. mays did not respond to CO2 or metabolites. Leaf mesophyll protoplasts of Z. mays and P. miliaceum, and bundle sheath protoplasts of Z. mays, which are unable to fix CO2 photosynthetically, also produced LEDR, but the mesophyll protoplasts, compared with bundle sheath protoplasts, required twice the time of illumination to obtain the maximal rate. The results suggest that the substrates for LEDR in C4 plants are generated during a period of illumination not only via the Calvin cycle reactions, but also by the conversion of endogenous compounds present in leaf cells. The stimulation of LEDR under glycine is discussed in relation to its direct or indirect effect on mitochondrial respiration.
分别代表NADP - 苹果酸酶、NAD - 苹果酸酶和磷酸烯醇式丙酮酸羧激酶型C4植物的玉米、黍稷和大黍叶片的呼吸性二氧化碳释放速率，在一段光合作用后增加了约两到四倍。这种光增强暗呼吸（LEDR）是特定于植物物种的净光合速率的函数，并受到1%氧气的抑制。当将50 mM浓度的苹果酸、天冬氨酸、草酰乙酸或甘氨酸溶液引入叶片而非水时，LEDR速率增强，在玉米中增强程度远低于黍稷（增强10 - 25%）或大黍（增强40 - 75%）。甘氨酸处理下LEDR的增强在1小时内相对稳定，而其余代谢物导致其在短暂增加后下降。这些代谢物降低了两种黍属植物的净光合速率，但对玉米没有影响，在玉米中甘氨酸刺激了这一过程。黍稷的维管束鞘细胞表现出比玉米和大黍更高的LEDR速率。甘氨酸对细胞呼吸速率没有影响，但苹果酸使玉米和黍稷细胞中的含量分别增加了约50%和30%。除了天冬氨酸刺激大黍的氧气释放和氧气吸收外，其余代谢物降低了黍属植物维管束鞘细胞的光合氧气释放。玉米光照细胞中的净氧气交换对二氧化碳或代谢物没有反应。玉米和黍稷的叶肉原生质体以及不能进行光合固定二氧化碳的玉米维管束鞘原生质体也产生LEDR，但与维管束鞘原生质体相比，叶肉原生质体需要两倍的光照时间才能达到最大速率。结果表明，C4植物中LEDR的底物不仅在光照期间通过卡尔文循环反应产生，还通过叶细胞中内源性化合物的转化产生。讨论了甘氨酸对LEDR的刺激与其对线粒体呼吸的直接或间接影响。
