Isolation and Characterization of Mutants of Common Ice Plant Deficient in Crassulacean Acid Metabolism1[W][OA]
Isolation and Characterization of Mutants of Common Ice Plant Deficient in Crassulacean Acid Metabolism1[W][OA]
复制标题
景天酸代谢缺陷的常见冰植物突变体的分离和鉴定1[W][OA]
作者：
J. Cushman;S. Agarie;Rebecca L. Albion;S. Elliot;Tahar Taybi;A. Borland
景天科酸代谢（CAM）是一种特殊的光合作用模式，通过将部分或全部大气CO2净吸收转移到夜间来提高水分利用效率。CAM的调节和代谢属性的遗传解剖受到鉴定突变体筛选的可靠表型的困难的限制。我们开发了一种新的和简单的比色法来测量叶片pH值筛选快速中子诱变群体的常见冰植物（Mesembryocyanum stac um），兼性CAM物种，检测CAM缺陷突变体有限的夜间酸化。孤立的CAM缺陷突变体表现出可忽略不计的净黑暗CO2吸收与野生型植物相比，在施加盐胁迫。突变体和野生型植物在叶片中积累的钠水平几乎相当，但突变体比野生型植物生长得更慢。在盐胁迫下，突变体相对于野生型也具有显著降低的结实率和种子重量。从4个月大的植物收集的种子的碳同位素比值表明，C3光合作用作出了更大的贡献，种子生产的突变体相比，野生型。CAM缺陷型突变体缺乏叶淀粉，缺乏质体磷酸葡萄糖变位酶，一种对植物异生和淀粉形成至关重要的酶，导致夜间C4酸形成的底物限制。恢复夜间酸化的盐胁迫突变体与葡萄糖或蔗糖喂养离体叶片支持这一缺陷，并有助于说明CAM的灵活性。这里描述的CAM缺陷突变体构成了探索CAM的调节功能和代谢后果的重要模型。
Crassulacean acid metabolism (CAM) is a specialized mode of photosynthesis that improves water use efficiency by shifting part or all of net atmospheric CO2 uptake to the night. Genetic dissection of regulatory and metabolic attributes of CAM has been limited by the difficulty of identifying a reliable phenotype for mutant screening. We developed a novel and simple colorimetric assay to measure leaf pH to screen fast neutron-mutagenized populations of common ice plant (Mesembryanthemum crystallinum), a facultative CAM species, to detect CAM-deficient mutants with limited nocturnal acidification. The isolated CAM-deficient mutants showed negligible net dark CO2 uptake compared with wild-type plants following the imposition of salinity stress. The mutants and wild-type plants accumulated nearly comparable levels of sodium in leaves, but the mutants grew more slowly than the wild-type plants. The mutants also had substantially reduced seed set and seed weight relative to wild type under salinity stress. Carbon-isotope ratios of seed collected from 4-month-old plants indicated that C3 photosynthesis made a greater contribution to seed production in mutants compared to wild type. The CAM-deficient mutants were deficient in leaf starch and lacked plastidic phosphoglucomutase, an enzyme critical for gluconeogenesis and starch formation, resulting in substrate limitation of nocturnal C4 acid formation. The restoration of nocturnal acidification by feeding detached leaves of salt-stressed mutants with glucose or sucrose supported this defect and served to illustrate the flexibility of CAM. The CAM-deficient mutants described here constitute important models for exploring regulatory features and metabolic consequences of CAM.