On the nature of the oxygen uptake in the light by Chondrus crispus. Effects of inhibitors, temperature and light intensity

Abstract

The nature of the different processes of O₂ uptake involved in the light in the red macroalga Chondrus crispus Stackhouse (Rhodophyta, Gigartinales) was investigated. At limiting CO₂, INH (2.5 mM) did not alter the O₂ uptake rate. Glycolate was not excreted and did not accumulate within the cells. KCN reduced the rate of O₂ uptake in the light by 76% at limiting CO₂ and by 43% at saturating CO₂, but caused > 95% inhibition of O₂ evolution. DCMU (5 μM) totally blocked the photosynthetic electron transport chain, but allowed a residual O₂ uptake of 3.0±0.6 μmol O₂ .h⁻¹.g⁻¹ FW, irrespective of the CO₂ concentration. In saturating CO₂, a high light intensity pretreatment significantly stimulated the rate of O₂ uptake compared to net O₂ evolution, suggesting the persistence, in the light, of mitochondrial respiration. Irrespective of the CO₂ concentration, the optimum temperature for O₂ evolution was 17°C whereas dark O₂ uptake increased linearly with temperature. In contrast, O₂ uptake in the light showed an optimum at 17°C in limiting CO₂, and 21–25° C in saturating CO₂; its Q₁₀ was 2.4 at limiting CO₂, a value close to that of RuBP oxygenase, and 3.1 at saturating CO₂, a value close to that of dark respiration. It is concluded that: 1) mitochondrial respiration and Mehler reaction are both involved at all CO₂ concentrations, 2) RuBP oxygenase activity cannot account for more than 45%, and Mehler reaction for less than 20%, of the total O₂ uptake observed in the light at limiting CO₂.