Pereira Paula Natália, Smith James Andrew Charles, Purgatto Eduardo, Mercier Helenice
Department of Botany, Institute of Biosciences, Universidade de São Paulo, CEP 05508-090, São Paulo, SP, Brazil.
Department of Plant Sciences, University of Oxford, Oxford, OX1 3RB, UK.
Funct Plant Biol. 2017 Jun;44(6):646-653. doi: 10.1071/FP16293.
Crassulacean acid metabolism (CAM) is one of the key innovations in the Neotropical family Bromeliaceae that has enabled many of its species to occupy seasonally water-limited terrestrial environments or microclimatically arid epiphytic niches. However, the relationship between CAM activity and the transport processes responsible for vacuolar organic-acid accumulation at night has not been systematically explored in this family. In the present investigation, ATP- and PPi-dependent proton transport rates were studied in tonoplast membrane vesicles isolated from leaves of six CAM and one C3 species of bromeliads. A consistent feature of these species was the high activity of the tonoplast ATP-driven H+ pump, which, when averaged across the seven species tested, showed a higher specific activity than the tonoplast PPi-driven H+ pump. For all CAM species, the rate of ATP-dependent proton transport into the tonoplast vesicles was strongly influenced by the nature of the balancing organic-acid anion, which displayed the following order of effectiveness: fumarate>malate>citrate. Measurements of leaf organic-acid content in six CAM bromeliads at dusk and dawn showed that nocturnal accumulation of malate exceeded citrate by a factor of ~2.4-20.0-fold in five of six bromeliad species used in this study, demonstrating a close correlation between the CAM rhythm and the intrinsic properties of the vacuolar membrane across which these organic acids are transported.
景天酸代谢（CAM）是新热带凤梨科植物的关键创新之一，这使得该科许多物种能够占据季节性水分受限的陆地环境或微气候干旱的附生生态位。然而，在这个科中，CAM活性与夜间负责液泡有机酸积累的转运过程之间的关系尚未得到系统研究。在本研究中，对从六种CAM凤梨科植物和一种C3凤梨科植物叶片中分离得到的液泡膜囊泡中的ATP和PPi依赖性质子转运速率进行了研究。这些物种的一个一致特征是液泡膜ATP驱动的H+泵活性很高，在测试的七个物种中，其平均比活性高于液泡膜PPi驱动的H+泵。对于所有CAM物种，依赖ATP的质子转运到液泡膜囊泡中的速率受到平衡有机酸阴离子性质的强烈影响，其有效性顺序如下：富马酸>苹果酸>柠檬酸。对六种CAM凤梨科植物在黄昏和黎明时叶片有机酸含量的测量表明，在本研究使用的六种凤梨科植物中的五种中，夜间苹果酸的积累量比柠檬酸高出约2.4 - 20.0倍，这表明CAM节律与这些有机酸运输所跨越的液泡膜的内在特性之间存在密切相关性。
