Effects of photoacclimation on plasma membrane ferricyanide reductase from the rhodophyta Gracilaria tenuistipitata

Abstract

The red macroalga Gracilaria tenuistipitata has a plasma membrane redox system easily assayed as a ferricyanide reductase (EC 1.6.99.13) activity. This activity is associated with acidification of the medium and is modulated by light conditions. G. tenuistipitata thalli adapt to light conditions by changes affecting their morphology, physiology and biochemistry. Thalli adapted to high photon fluence rates exhibited lower ferricyanide reductase activity than those adapted to darkness or low irradiance (40 μmol photon m −2 s −1). When thalli were changed from low to high irradiance (500 μmol photons m −2 s −1), there was a continuous decrease in ferricyanide reductase activity with time. When these thalli were changed to darkness, they recovered to control values of ferricyanide reductase activity after a 24 h additional incubation. Adaption of thalli to different qualities of light also produced significant changes in their ferricyanide reductase activity: under the same low irradiance (40 μmol photons m −2 s −1), thalli exposed for two or more weeks to blue or red light exhibited higher ferricyanide reductase activity levels than those exposed to white light; after four weeks of culture, thalli under blue light had higher ferricyanide reductase activity levels than those under red light. It is concluded that the differences in ferricyanide reductase activity observed under different light conditions are the result of acclimation and that this activity could play a relevant role in G. tenuistipitata bioenergetics.