Transient Changes in Cellular Gas Exchange and the Problem of Maximum Efficiency of Photosynthesis

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Abstract
The two-vessel manometric method has sometimes been applied to measurement of photosynthesis during periods of transient rates without proper regard for its limitations. Tests show that diffusion lag is an important factor, and that vessel pairs equal in diffusion lag with respect to oxygen can be selected. Theoretical considerations show, however, that equality with respect to two gases of different solubility is not possible. When the method is applied with vessels matched for oxygen, the results indicate transient maxima in both oxygen and carbon dioxide exchange. If the evidence for oxygen maxima is accepted, then values of [image]-1 (the number of quanta required per molecule of oxygen produced) as low as 3 can be calculated, and actual metabolic rates must represent still lower values. However, evidence is presented which suggests that the transient gas exchanges are not representative of respiration and photosynthesis. Steady-rate measurements, which may be regarded as representative of respiration and photosynthesis, lead to values of [image]-1 from about 8 to 12.