A relationship between carbonic anhydrase and rubisco in response to moderate cadmium stress during light activation of photosynthesis

In our previous research, we showed that low Cd concentration increases the effectiveness of the process es leading to activation of ribulose-1,5-bisp hosphate carboxylase/oxygen ase (Rubisco). This stimulation was dependent o n carbonic anhydrase (CA) activity and resulted in protecting Rubisco activ ity against Cd toxicity. The aim of the present paper was to test whether t his mechanism has any influence on light activation of photosynthesis durin g the first 2 h of illumination. Both the "activation mechanism" of plant r esponse to Cd-stress conditions and its full efficiency at low Cd concentra tion were confirmed. The CA-dependent light activation of Rubisco at low Cd level was correlated with accelerated attaining of the maximum Rubisco act ivity by these plants. The amount of Rubisco was also Cd- and time-dependen t and varied from continuous accumulation in control plants till reaching t he maximum level within 30 minutes for the high Cd concentration. An increa se in CA activity that was found to be parallel to the decrease of the amou nt of CA suggested activation of the enzyme by low Cd concentration.