Changes in oxidative properties of Kalanchoe blossfeldiana leaf mitochondria during development of Crassulacean acid metabolism
Changes in oxidative properties of Kalanchoe blossfeldiana leaf mitochondria during development of Crassulacean acid metabolism
复制标题
景天酸代谢发育过程中长寿花叶线粒体氧化特性的变化
作者：
P. Rustin;C. Queiroz
在长日照（16 小时光照）下生长的长寿花植物表现出 C3 型光合代谢。切换到短日照（9 小时光照）会导致景天酸代谢 (CAM) 的逐渐发展。在后一种条件下，暗二氧化碳固定产生大量苹果酸。在一天的最初几个小时，苹果酸通过胞质 NADP+ 或线粒体 NAD+ 依赖性苹果酸酶的作用迅速脱羧为丙酮酸。从长日照下或经过越来越多的短日照处理后生长的植物的叶子中分离出线粒体。三羧酸循环中间体以及外源 NADH 和 NADPH 很容易被从两种植物中分离的线粒体氧化。已知被 C3 植物线粒体氧化的甘氨酸在 CAM 建立后仍然被氧化。实验表明，CAM 水平的增加和分离线粒体的底物氧化能力的增加，特别是在氰化物存在下氧化苹果酸的能力的增加具有明显的平行性。 CAM 水平和线粒体特性的这些同时变化表明线粒体 NAD+-苹果酸酶至少可以解释苹果酸氧化的一部分。全叶呼吸的研究证实线粒体与体内苹果酸降解有关。此外，在白天的最初几个小时内，当苹果酸被胞质和线粒体苹果酸酶氧化为丙酮酸时，观察到叶子呼吸的氰化物抗性增加。
Kalanchoe blossfeldianaplants grown under long days (16 h light) exhibit a C3-type photosynthetic metabolism. Switching to short days (9 h light) leads to a gradual development of Crassulacean acid metabolism (CAM). Under the latter conditions, dark CO2fixation produces large amounts of malate. During the first hours of the day, malate is rapidly decarboxylated into pyruvate through the action of a cytosolic NADP+-or a mitochondrial NAD+-dependent malic enzyme. Mitochondria were isolated from leaves of plants grown under long days or after treatment by an increasing number of short days. Tricarboxylic acid cycle intermediates as well as exogenous NADH and NADPH were readily oxidized by mitochondria isolated from the two types of plants. Glycine, known to be oxidized by C3-plant mitochondria, was still oxidized after CAM establishment. The experiments showed a marked parallelism in the increase of CAM level and the increase in substrate-oxidation capacity of the isolated mitochondria, particularly the capacity to oxidize malate in the presence of cyanide. These simultaneous variations in CAM level and in mitochondrial properties indicate that the mitochondrial NAD+-malic enzyme could account at least for a part of the oxidation of malate. The studies of whole-leaf respiration establish that mitochondria are implicated in malate degradation in vivo. Moreover, an increase in cyanide resistance of the leaf respiration has been observed during the first daylight hours, when malate was oxidized to pyruvate by cytosolic and mitochondrial malic enzymes.