Libor Babák

Diurnal regulation of ribulose -1,5 -bisphosphate carboxylase/oxygenase activity and its content in Norway spruce needles

Diurnal changes of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity and its content were measured to find the mechanism of RuBPCO activity regulation in Norway spruce needles. Both initial and total RuBPCO activities as well as the activation state had a typical pattern with two peaks in the morning and afternoon, respectively, and a midday depression. On the 19 October, RuBPCO content decreased during the day from 3.1 to 1.4 g m−2, while on the 20 October it was approximately constant both in the morning and in the afternoon (2.7 g m−2). Neither initial nor total activity of RuBPCO copied irradiances. Relatively low morning and evening values of total activities indicate that nocturnal inhibitor CA1P is important in Norway spruce. However, the midday depression of total activity indicates that besides CA1P there function some other inhibitors of RuBPCO. In addition, the diminution of RuBPCO content during the day may indicate repression of its gene expression.

Seasonal changes of Rubisco content and activity in Fagus sylvatica and Picea abies affected by elevated CO2 concentration

We studied Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) content and activity in juvenile tree species — broadleaved Fagus sylvatica L. and coniferous Picea abies (L.) Karsten exposed for three growing seasons to ambient (A = 385 μmol mol−1) and elevated (E = 700 μmol mol−1) CO2 concentrations. Rubisco content was determined by the SDS-PAGE method, Rubisco activity was assayed spectrophotometrically. The highest content of Rubisco enzyme in F. sylvatica was measured immediately after full leaf development followed by a gradual decrease throughout the growing season. By contrast, Rubisco content in P. abies increased markedly during the growing season. In both tree species, down-regulation of Rubisco content in trees cultivated under elevated CO2 concentration was observed. Rubisco activity was stimulated in F. sylvatica by E treatment but not in P. abies. Because no significant differences were found in Rubisco activation state between A and E, we assume that stimulation of Rubisco activity in E is not a consequence of higher carbamylation but could be caused by the release of inhibitors from active sites of Rubisco under elevated CO2.