Walker David
Robert Hill Institute, Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK.
New Phytol. 1992 Jul;121(3):325-345. doi: 10.1111/j.1469-8137.1992.tb02935.x.
Photosynthesis is largely to do with energy transduction; the conversion of light energy into electrical energy into chemical energy. Precisely how much light energy is needed to bring about the reduction of one molecule of carbon dioxide and the release of one molecule of oxygen (the quantum requirement) is a matter of fundamental importance and one which has attracted much past controversy. This article concludes that a minimum quantum requirement of eight, as demanded by the Z-scheme, is obviously consistent with much contemporary work which puts the measured value for C leaves close to nine. Moreover, while values of less than eight (obtained in some circumstances with micro-organisms), are a reminder that nothing is beyond challenge they are not, in the absence of confirmation and extension, sufficiently compelling to demand rejection of either the Z-scheme or current measuring procedures. This article also shows why, even if the underlying minimum requirement was now accepted beyond all reasonable doubt, there would still be very good reasons for continuing, indefinitely, to measure actual photosynthetic efficiency in the natural environment. It discusses some of the implications of the fact that all plants, if not stressed, appear to photosynthesize at the same rate in low light. It explains the role of fluorescence in its relation to quantum yield, the possibility that the rate of photosynthesis might be determined from fluorescence measurements alone, and that a combination of fluorescence and gas exchange measurements could provide new information about the manner in which 'dark respiration' is affected by light. It indicates how contemporary interest in all of these matters has focused attention on the necessity for safe dissipation of excitation energy by leaves and on the manner by which this might be achieved. CONTENTS Summary 325 I. Excitation 325 II. Quantum requirement 326 III. Learning from fluorescence 335 IV. Safely dissipated 340 Acknowledgements 342 References 342.
光合作用在很大程度上与能量转换有关；即将光能转换为电能再转换为化学能。精确计算还原一分子二氧化碳并释放一分子氧气所需的光能（量子需求）是一个至关重要的问题，过去也曾引发诸多争议。本文得出结论，Z 方案所要求的最低量子需求为 8，这显然与许多当代研究结果相符，这些研究测得 C 叶的量子需求值接近 9。此外，虽然在某些情况下微生物的量子需求值小于 8，但这提醒我们没有什么是不可挑战的，但在缺乏进一步证实和拓展的情况下，这些值并不足以令人信服地要求摒弃 Z 方案或当前的测量程序。本文还表明，即使现在已经毫无疑问地接受了潜在的最低需求，仍有充分理由无限期地继续测量自然环境中的实际光合效率。文中讨论了所有植物在低光照下（若未受胁迫）似乎以相同速率进行光合作用这一事实的一些影响。解释了荧光在与量子产率关系中的作用，仅通过荧光测量确定光合作用速率的可能性，以及荧光和气体交换测量相结合如何能提供有关“暗呼吸”受光影响方式的新信息。指出了当代对所有这些问题的关注如何聚焦于叶片安全耗散激发能的必要性以及实现这一目标的方式。目录 摘要 325 一、激发 325 二、量子需求 326 三、从荧光中学习 335 四、安全耗散 340 致谢 342 参考文献 342 。
