The possibility of being able to “switch off” or down regulate the operation of the Anthoceroate CCM is not unrealistic in the light of recent work by Smith and Griffiths (2000) who established that CA plays a role in the operation of the CCM in Phaeoceros laevis , as in all microalage investigated. Smith and Griffiths (2000) conducted an investigation into the role of CA in photosynthesis and the activity of the CCM in Anthocerotae by using the membrane-permeable CA inhibitor ethoxzolamide (EZ), drawing a comparison to a range of liverworts and mosses.
The results showed that inhibition of assimilation occurred in all bryophyte treated with EZ, however the degree of inhibition was greatest in Phaeoceros laevis. Furthermore, there was a pronounced decline in Ci-uptake efficiency and a decrease in the initial slope of CO2-affinity curve at low external levels where Ci-uptake efficiency in other liverworts were unaffected. There were no significant differences between the convexities of the light response curves in Phaeoceros which would indicate a diversion of ATP to energise the CCM.
In studies on light dark transients on Phaeoceros treated with EZ a speculation made was that although active transport of CO2 was still occurring (due to the appearance of a CO2 release pool), the Ci transported to the stroma is not being utilized by Rubisco when CA is suppressed by EZ. This point may raise the question as what the exact mechanism of Ci transport is if EZ does not suppress the active uptake of CO2 in the Anthocerotae.
The major drawback with using EZ to manipulate the operation of the Anthocerotae CCM in future studies is that CA is involved in other non CCM photosynthetic processes, as shown by the depressions of gross assimilation rates in mosses of 65 % and 50% in other non CCM based liverworts treated with EZ.
The usefulness of being able to "switch of " or down regulate the Phaeoceros CCM with a high CO2 environment will be critical in elucidating the operation of the Anthocerotae CCM. However in terms of the ecology of Phaeoceros, a relatively rapid response (of approx. 14 days) to variations in external CO2 (initially 5% CO2) may not be seen, due to the fact that fluctuations in CO2 in the aerial environment is relatively minimal, or at least not as irritate as in a water column.