Regulation mechanism of excitation energy transfer between phycobilisomes (PBS) and the photosynthetic reaction centres was studied by the state transition techniques in PBS-thylakoid membrane complexes. DCMU, betaine, and N-ethylmaleimide were applied to search for the details of energy transfer properties based on the steady fluorescence measurement and individual deconvolution spectra at state 2 or state 1. The closure of photosystem (PS) 2 did not influence on fluorescence yields of PS1, i.e., energy could not spill to PS1 from PS2. When the energy transfer pathway from PBS to PS1 was disturbed, the relative fluorescence yield of PS2 was almost the same as that of PS2 in complexes without treatment. If PBSs were fixed by betaine, the state transition process was restrained. Hence PBS may detach from PS2 and become associated to PS1 at state 2. Our results contradict the proposed "spill-over" or "PBS detachment" models and support the mobile "PBS model". and Ye Li ... [et al.].
In Evernia prunastri, photosynthetic gas exchange was saturated with yellow radiation (SOX) at 400 μmol m-2s-1, and then red (R), far-red (FR), or blue (B) radiations at irradiance of 15 μmol m-2s-1 were added. Because of photosynthesis saturation, any stimulation or decay in CO2 assimilation by any radiation quality could be attributed to the involvement of a non-photosynthetic photoreceptor. Thus CO2 assimilation, effective quantum yield, and photochemical quenching were enhanced when R was included, and decreased with FR. Blue radiation completely abolished CO2 fixation. Hence different spectral radiation qualities may activate non-photosynthetic photoreceptors such as phytochrome and blue photoreceptors, which are involved in regulating the photosynthetic activity in E. prunastri. and M. Segovia, F. L. Figueroa.
A low irradiance mediated regulation of C4 metabolism during acclimation is reported for first time in Amaranthus hypochondriacus L., a NAD-ME dicot, Eleusine coracana (L.) Gaertn., an NAD-ME monocot, and Gomphrena globosa, a NADP-ME dicot. Significant decline in activities of key C4 enzymes were observed under limited irradiances in each of the species studied. When the plants were transferred to full natural irradiance, the enzyme activities were restored to originál State in 3-5 d, a similar time frame needed for acclimation to limiting irradiance. This identifies the decarboxylation reaction involving NAD-ME in Amaranthus and Eleusine or NADP-ME in Gomphrena as crucial sites of regulation under limiting irradiance.
A surprísingly high level of the CPI membrane-bound apoprotein was found through ELISA test in barley coleoptiles, cotnpared with etiolated leaves. Non-synchronous changes of the chlorophyll (Chl) a and CPI apoprotein contents were found in greening etiolated seedlings after brief preinradiation, in green leaves after continuous darkness and the second weak irradiation, and in old leaves after a period of darkness. The complexity of these fmdings gives a possibility of the CPI apoprotein formation without direct cotmection to Chl a biosynthesis. The CPI apoprotein accumulation in young etiolated leaves was stimulated by S-aminolevulinic acid.
Effect of high temperature on the plastid gene expression during the light induced chloroplast development in etiolated seedlings was determined by Northern hybridisation using cloned DNA fragments of wheat chloroplast genome. Based on their response to high temperature, plastid genes were grouped into three categories: (1) plastid genes whose expression was not affected by high temperature (genes for rRNA, ribosomal proteins, tRNAs, and some genes coding for putative NADH dehydrogenase); (2) plastid genes whose expression increased at high temperature (genes coding for α-subunit of RNA polymerase and some unidentified transcripts, and (3) plastid genes whose expression decreased at high temperature (genes coding for proteins involved in photosynthetic process). Loss of a number of primary transcripts originating from operons consisting of genes that code for proteins involved in the photosynthetic process was observed. The expression of all the light inducible plastid genes was inhibited suggesting that the light inducibility property was lost at high temperature. and Abhay K. Singh, G. S. Singhal.
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.