High CO2 concentrations (HC) in air induce partial deactivation of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO, EC 4.1.1.39). Under saturating irradiance, increase in [CO2] to 1 200 cm3 m-3 reduces the concentration of operating carboxylation centres by 20–30 %. At a further increase in [CO2], the activity remained on the same level. Under limiting irradiance, the lowest activity was reached at 600 cm3 (CO2) m-3. The presence of oxygen diminished deactivation, but O2 failed to stimulate reactivation under high CO2. Conditions that favour oxygenation of ribulose-1,5- bisphosphate (RuBP) facilitated reactivation. Even HC did not act as an inhibitor. HC induces deactivation of RuBPCO by increasing the concentration of free reaction centres devoid of the substrate, which are more vulnerable to inhibition than the centres filled with substrates or products. and J. Viil ... [et al.].
Four-d-old seedlings were exposed to ultraviolet-B, UV-B (20 pinol ht^), and UV-B supplemented with red, R {X 612 nin, 5 pmol nr^) or far-red, FR (X 712 nin, 4.5 pmol nr^) radiation for 30 min during the middle of tlie light phase. Three d of UV-B treatment caused reduction in shoot elongation and expansion of cotyledonaiy leaves. The reduction was largely reversed by supplementary R and FR radiations. Supplementation of FR accelerated senescence process. Similar changes were also noted in the contents of photosynthetic piginents, while the level of anthocyanin was enhanced by all treatments. Flavonoid accumulation was enhanced by UV-B, whereas R and FR radiations suppressed its synthesis to various degrees. The chlorophyll (Chl) fluorescence ratio Fy/F,„ and half-rise time of maximum fluorescence were greatly reduced by UV-B and with FR supplementation. R reversed this UV-B inhibition to a great extent. Likewise, tlie P-S dechne was higher under control and +UV-B+R than under +UV-B and +UV-B+FR treatments, At the protein level both the subunits of ribulose 1,5-bisphosphate carboxylase alone were regulated by phytochrome. All these experiments indicated a possible role of phytochrome in regulating the UV-B induced changes in plant morphology and chloroplast proteins.
The article deals with two sermons by a Prague Dominican known as Iohannes Carmelita that were delivered at the Archdiocesan Synod in Prague in 1401 and 1404. Based on critical editions of both sermons, the article presents Carmelita’s preaching style and the authorities referred to by him and places them in the context of other extant Prague synodal sermons in the pre-Hussite period.