Twelve-day-old barley seedlings were supplied with 23 μM methyl jasmonate (MeJA) or 10 μM paraquat (Pq) via the transpiration stream and kept in the dark for 24 h. Then they were exposed to 100 μmol m-2 s-1 PAR and samples were taken 1, 2, 3, and 6 h after irradiation. Treatment of seedlings with MeJA alone resulted in decreased content of chlorophyll (Chl), and net photosynthetic (PN) and transpiration rates. Pq treatment led to a decrease in Chl content and to a very strong inhibition of PN, the effects were manifested by 1 h of irradiation. Pq treatment did not affect the activity of ribulose-1,5 bisphosphate carboxylase (RuBPC, EC 4.1.1.39) but increased the activity of the photorespiratory enzymes phosphoglycolate phosphatase (PGP, EC 3.1.3.18), glycolate oxidase (GO, EC 1.1.3.1), and catalase (EC 1.11.1.6). Pre-treatment of seedlings with MeJA before exposure to Pq fully blocked the inhibitory effect of Pq on photosynthesis and protected against subsequent Pq-induced oxidative damage. and V. A. Hristova, L. P. Popova.
Tribute to Jean Lavorel (16 March 1928–12 January 2021), a pioneer of the ‘Light Reactions of Photosynthesis’. He was known not only for his ingenuity in devising new instruments but in thoroughly analyzing all the available data theoretically and mathematically – mostly all by himself. He measured, elegantly, oxygen evolution and light given off by photosynthetic organisms, both prompt and delayed chlorophyll fluorescence. He ingeniously used these data to understand how light energy is converted to chemical energy in natural systems. We present below a summary of his life and research.
The photosynthesis and related plant productivity aspects of plants and cyanobacteria depend upon the functioning of photosystem 2 (PS2), associated with D1 and D2 heterodimer reaction centre core proteins. The D1 protein is encoded by psbA gene, genetically localized on the plastid genome (cpDNA), contains functional cofactors of PS2 in association with D2 protein, and also functions for radiant energy transformation through oxidation of water and reduction of plastoquinone. Surprisingly, D1 protein accounts for even less than 1% of the total thylakoid membrane protein content. In spite of that, its rate of turnover is very much comparable to ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) large subunit, most abundantly present in green tissue. The normal functioning of PS2 possesses damage-repair cycles of D1 protein. Generally, rate of photodamage does not exceed the rate of repair under optimal growth conditions, therefore, no adverse effect on photosynthetic efficiency is manifest. However, under strong irradiance coupled with elevated temperature, level of photodamage exceeds the rate of repair, resulting in photoinhibition, photodegradation of D1 protein, and lowering photosynthetic efficiency linked with plant productivity eventually. The features of D1 turnover process are reviewed, particularly with respect to molecular mechanisms.
A double ínductíon mechanism of Dl protein degradatíon in isolated photosystem 2 (PS2) core complexes and reaction centres is described, showing the existence of two potentíal sites for primáty cleavage. Donor side inhibition conditi- o n s (presence of electron acceptors but no electron donors and pH 8.0) trigger the hydrolysis of the Dl protein between the putatíve helices 1 and II on the lumenal side of the thylakoid membrane. This results in the generation of a C-terminal 24 kDa fragment. However, when the donor-side is actíve (presence of electron donors but no electron acceptors and pH 6.0, acceptor side inhibition conditions) both preparations are able to produce a N-terminal 23 kDa fragment, indicating cleavage between helices IV and V, on the stromal side of the membrane.
This paper analyses two lists of errors in the Waldesian cult, as contained in manuscripts I F 230 (from 1399, and its twin manuscript Mil II 58), as well as I F 707 (from the early 15th century). The list in manuscript I F 230 was compiled earlier, whereas the one from manuscript I F 707 is identical with the list included in manuscript No. 229 from the library in Pelplin. The comparison of the anti-heretic lists of errors from manuscripts I F 230 and I F 707, as well as the analysis of their contents, reveals similarities and leads to a conclusion that they both refer to writings by inquisitor Petrus Zwicker, while the list in I F 230 could have been even authored by him.
High (HI, 200 W m'^) and low (LI, 30 W m"^) irradiance treatments on the cells of cyanobactenum Synechococcus elongatus Nfig., var. thermalis Geitl. strain KOVROV 1972/8 were perfonned in the presence of chloramphenicol (CAP), and with addition of DCMU and hydroxylamine (HA), respectively, at growth (56 °C) and low (20 °C) temperatures, to distínguish allegedly different mechanisms of PS 2 photoinactivation (PS 2 PI). At both temperatures HI caused a decline of Fy and Hill reaction activity (HRA) followed by degradation of Dl and to a lesser extent also D2 protein. Fq increased slowly during irradiance at 56 while at 20 ®C it quickly rose to constant level. Degradation of proteins was slowed at a lower temperature. The presence of DCMU during photoinhibition significantly blocked the Fq rise and also prevented PS 2 protein degradation at both temperatures. The course of PS 2 PI under LI resembled tlmt, observed at HI, but changes were much slower. During irradiation of the cells, in which oxygen evolving complex (OEC) was impaired by HA, we observed: (/) at least a ten-fold faster decline of PS 2 electron transport activity than in the cells vňth fimctional OEC under the same conditions; (2) an extensive degradation not only of Dl and D2, but also of the apoprotein of chlorophyll-protein CP43 {ACP43y, (3) almost complete inhibition of PS 2 protein degradation in the presence of DCMU. Thus under all conditions tested in vivo which do not affect the fimction of OEC, the fimction of OEC, PS 2 PI proceeds via the acceptor side and a fimctional impairment of OEC is necessary for induction of the donor side mechanism. When OEC is impaired (e.g. by HA) this mechanism can come in action.
The paper studies the typology of the initials following the way of construction of their corpus in the mutual ties in the development – departing from the late antique, considering the Byzantine and Pre-Romanesque and Romanesque types. The modifications of the initials are studied together with the changes of their function in the decoration system and in the cultural-historical context. The contribution also studies the changes of the terminology connected with the typology of the initials.
The paper studies the typology of the initials following the way of construction of their corpus in the mutual ties in the development – departing from the late antique, considering the Byzantine and Pre-Romanesque and Romanesque types. The modifications of the initials are studied together with the changes of their function in the decoration system and in the cultural-historical context. The contribution also studies the changes of the terminology connected with the typology of the initials.