Oxygen Inhibition of Photosynthesis

Abstract

ABSTRACIThe response of whole leaf photosynthesis of wheat (Tridcum activum L.) in relation to soluble CO2 availble to the mesophyU celLs, under low (1.5%) 02 at 25, 30, and 35 C, followed Michaelis-Menten kinetics up to saturating CO2 but deviated at higb CO2 levels where the experimental Vmax is considerably less than the calculated V... The Although temperature is important in environmental regulation of photosynthesis, the degree of temperature-dependent variation in factors controlling photosynthesis in C3 plants at the cellular level such as affinity for C02, nature of 02 inhibition of photosynthesis, maximum velocity of photosynthesis based on enzyme potential, and solubility of 02 and CO2 is uncertain. In order to make a kinetic analysis of whole leaf photosynthesis in response to levels of CO2 and 02 at various leaf temperatures, it is necessary to consider the concentrations of the gases on a solubility basis in the leaf. From such an analysis, the Km(CO2), Ki(02), Vmax for photosynthesis, CO2 compensation point (IF), and effect of 02 on carboxylation efficiency were determined in the present study for wheat at three temperatures.In the previous study with various C3 species (16) MATERIALS AND METHODS Growth Conditions. Triticum aestivum L. was grown in a growth chamber at a day/night temperature of 30/25 C with other conditions as previously described (16). Newly expanded leaves of 2-to 3-week-old plants were used for all experiments.Gas Exchange Measurements. Measurements of CO2, 02 and water vapor, determination of intercellular CO2 concentration, and calculation of solubility ratio of 02/CO2 in the leaf were fully described in the preceding paper (16).Carboxylation Efficiency. Carboxylation efficiency (CE) as previously defined (10)

CO2assimilation in young Prosopis plants

“…Differences in the compensation point and C0 2 evolution in C0 2 -free air were also detected. The carboxylation efficiency (Ku and Edwards, 1977) was 5.6 x 10-2 mol ' ppm-1 C0 2 in plants with high growth, 22% higher than those with low growth which had 4.6 x 10-2 mol-ppm-1 C0 2.…”

Solubility of Gases and the Temperature Dependency of Whole Leaf Affinities for Carbon Dioxide and Oxygen

“…The relative merits of these two expressions of concentration are discussed. Ku and Edwards (12,13) the whole leaf affinity coefficients for CO2 and 02 regulating total photosynthesis and the photorespiratory process according to the Bowes-Ogren hypothesis (2)? The objective of this paper is to reevaluate the conclusions of Ku and Edwards (12, 13) using an alternative analysis.…”

“…It has likewise become apparent that suggested simplifications of these kinetic equations may heavily bias results. Although Ku and Edwards (12,13) …”

“…The objective of this paper is to reevaluate the conclusions of Ku and Edwards (12,13) using an alternative analysis. This second interpretation explains the original data but may lead to very different conclusions, which are fundamental to understanding the photosynthetic response of whole plant leaves to environmental factors.…”

“…It has likewise become apparent that suggested simplifications of these kinetic equations may heavily bias results. Although Ku and Edwards (12,13) To describe a particular set of data, it is necessary to determine the values of five parameters: RM, the diffusion resistance from the intercellular air space to the fixation site; Kc, the leaf affinity coefficient for CO2 in CO2 fixation; Ko2, the leaf affinity coefficient for 02 in oxygenation (photorespiration based on the rate of CO2 evolution); PM, the maximum rate of CO2 fixation at saturating C02; and WM, the maximum rate of oxygenation at saturating 02. It may be possible in the future to relate the leaf affinity coefficient for CO2 more closely to biochemical kinetics (cf.…”