Dark respiration in the marine macroalga Chondrus crispus (Rhodophyceae)

Dark respiration in the red macroalga Chondrus crispus was studied under a variety of conditions. The components of respiration were examined using selective inhibitors in order to characterise pathways of respiration and examine regulation of respiration in marine macroalgae.In comparison to respiration rates generally reported for higher-plant leaves and roots, the steady-state rate of O2 consumption by this alga, after 30 min dark pretreatment, was found to be quite low (three- to sixfold lower than in higher plants). The addition of uncoupler had only a slight effect on the basal respiration rate, indicating that in these conditions, substrate supply could be limiting respiration. The addition of KCN inhibited respiration by approx. 60%, indicating the presence of alternative oxidase activity. The coefficient of engagement of the alternative pathway (calculated from the data herein) showed that under normal conditions there was little participation of the alternative pathway in O2 consumption. The response of respiration to O2 tension was examined with and without inhibitors and the apparent K m was 17 to 21 μM. The addition of KCN plus salicylhydroxamic acid almost completely blocked respiration in C. crispus. The hypothesis that respiratory substrate limits respiration in this alga was investigated by measuring respiration rates immediately after periods of photosynthetic activity. It was found that the respiration rate was dependent on the duration of the light period and could increase up to twofold. This stimulated rate of respiration declined in a first-order fashion during the next 20 to 30 min, finally reaching the basal, zero-order rate measured before illumination. These results strongly indicate a change in the nature of the respiratory substrates during this period. No change in the contribution of the alternative pathway of respiration could be detected following light pretreatment.