Studies on low oxygen sensitivity mechanism of CAM photosynthesis

CAM光合作用低氧敏感性机制研究

• 批准号: 12460011
• 负责人: NOSE Akihiko
• 金额: $ 7.94万
• 依托单位: Saga University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2000
• 资助国家: 日本
• 起止时间: 2000 至 2003
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-12460011/
• 关键词: CAM photosynthesis; low oxygen; pineapple; mitochondria; malate; OAA shuttle; cyanide resistant respiration; PEP carboxykinase; decarboxylation; りんご酸オキザロ酢酸シャトル; 種間変異; リンゴ酸・アスパラギン酸シャトル; Rubisco; セイロンベンケイソウ; ^<18>Oディスクリミネイション; コダカラベンケイソウ

The phenomenon in which the depression of CO2 exchange in CAM photosynthesis (phase 3) disappeared under low oxygen conditions, could not be related to CAM subtype of CO2 decarboxylation, that is, PEP carboxykinase (PCK) type and malic enzyme (ME) type. For the oxygen concentration in which the phase 3 of CAM disappears, it has been indicated that cyanide resistant respiration of mitochondria is concerned in low oxygen sensitivity of CAM photosynthesis. However the low oxygen sensitivity of CAM photosynthesis could not be explained simply with cyanide resistant respiration. In the pineapple mitochondria purified with Percoll density method, malic acid was incorporated actively into, the mitochondria only under the condition in which malate/OAA shuttle of the inner membrane functioned. This result indicates that the of malate in the phase 3 dose not operate in the pineapple mitochondria. In addtion, it is suggested that the conversion of malate to OAA in the pineapple mitochondria matrix functions as a replenishment system to supply the OAA as the substrate to the decarboxylation using PCK in the pineapple CAM phase 3. In other words, it is suggestedd that the low oxygen sensitivity of CAM photosynthesis appear only under the condition where the malate in CAM phase 3 is decarboxylated actively by NAD-ME in mitochondria and the NADH produced by the decarboxylation is oxidized with the cyanide resistant respiration.

在低氧条件下，CAM光合作用（第3阶段）中CO2交换抑制消失的现象可能与CAM的CO2脱羧亚型，即PEP羧激酶（PCK）型和苹果酸酶（ME）型无关。对于CAM第3相消失时的氧浓度，表明线粒体的抗氰呼吸与CAM光合作用的低氧敏感性有关。然而，CAM光合作用的低氧敏感性不能简单地用抗氰呼吸来解释。在用Percoll密度法纯化的菠萝线粒体中，只有在内膜的苹果酸/OAA穿梭起作用的条件下，苹果酸才被积极地掺入线粒体中。这一结果表明，苹果酸在第3阶段不运作的菠萝线粒体。此外，有人建议，在菠萝线粒体基质中的苹果酸到OAA的转换作为补充系统的功能，以提供OAA作为底物的脱羧使用PCK在菠萝CAM阶段3。也就是说，只有在线粒体NAD-ME主动使CAM第3相的苹果酸脱羧，并使脱羧产生的NADH被抗氰呼吸氧化的条件下，CAM光合作用才出现低氧敏感性。