Metabolic Regulation of Chloroplastic Respiration of Carbohydrates

本研究的主要焦点是在延长光合作用和黑暗间隔期间光合活性的保持。生物学试验材料为分离的菠菜和衣藻叶绿体及其亲本组织。分离的完整菠菜叶绿体的二氧化碳固定能力在光合作用大约2-40分钟后下降，即使电子传递链和卡尔文循环基质酶的活性保持正常。叶绿体在黑暗中保持10-20分钟也失去了随后的光合作用二氧化碳固定活性。在光合作用期间或在光合作用前的黑暗阶段，在外部培养基中添加镁离子与ATP或叶绿体可呼吸底物之间的复合物可以保持光合作用活性。其他核苷酸不能替代ATP，非呼吸性叶绿体底物也不能替代ATP。同样地，预处理暗端菠菜叶会导致二氧化碳固定能力失活。失活的程度似乎取决于叶片的营养状况（也许是碳水化合物含量）。与叶绿体衰老一样，失活也极度依赖于pH值。将阐明导致光合作用二氧化碳固定丧失的基本事件以及保护机制的基本原理。这项研究应该提供大量的信息来支持这一概念，即叶绿体二氧化碳固定活性的保留依赖于叶绿体外事件，如细胞呼吸，并在一定程度上依赖于叶绿体呼吸。叶绿体与这些事件的分离导致其迅速不可逆的破坏，除非细胞器受到线粒体产生的呼吸产物或细胞器内淀粉分解的保护。叶绿体能力与其他细胞事件的联系将为我们理解应激生理学（即水状态、温度、离子平衡和其他因素）增加一个基本组成部分。

The primary focus of this research is the retention of photosynthetic activity during extended photosynthesis and during dark intervals. The biological test materials are isolated spinach and Chlamydomonas chloroplasts and the parent tissues. The carbon dioxide fixing capability of the isolated intact spinach chloroplast falls off during photosynthesis after approximately 2-40 minutes, even though a functional electron transport chain and activity of stromal enzymes of the Calvin cycle are maintained. Chloroplasts kept in the dark for 10-20 minutes also lose their subsequent photosynthetic carbon dioxide fixing activity. Addition of a complex between magnesium ions and ATP or a chloroplastic respirable substrate to the external medium during photosynthesis or during the dark phase prior to photosynthesis allows retention of photosynthetic activity. Other nucleotides will not substitute for ATP nor do non-respirable chloroplastic substrates function in this capacity. Similarly, pre-treatment of the darkended spinach leaf results in an inactivation of the carbon dioxide fixing capacity. The level of inactivation seems to depend upon the nutritional status (perhaps carbohydrate content) of the leaf. Inactivation is extremely pH dependent as is senescence of the chloroplast. The basic events that result in the loss of photosynthetic carbon dioxide fixation will be elucidated as well as the underlying principles of the protective mechanisms. This research should provide substantial information supporting the concept that the retention of chloroplastic carbon dioxide fixing activity is dependent upon extrachloroplastic events such as cellular respiration and, to a limited extent, on chloroplastic respiration. Separation of the chloroplast from these events leads to its rapid irreversible destruction unless the organelle is protected by the products of respiration generated in the mitochondrion or within the organelle by starch break-down. The linkage of chloroplastic competency with other cellular events will add a basic component to our understanding of stress physiology, i.e. water status, temperature, ionic balance and other factors.