RNA gel hybridization showed that the expression of monodehydroascorbate reductase (MDHAR) in the wild type (WT) tomato was decreased firstly and then increased under salt- and polyethylene glycol (PEG)-induced osmotic stress, and the maximum level was observed after treatment for 12 h. WT, sense transgenic and antisense transgenic tomato plants were used to analyze the antioxidative ability to cope with osmotic stresses. After salt stress, the fresh mass (FM) and height of sense transgenic lines were greater than those of antisense lines and WT plants. Under salt and PEG treatments, sense transgenic plants showed a lower level of hydrogen peroxide (H2O2) and malondialdehyde (MDA), a higher net photosynthetic rate (PN), and the maximal photochemical efficiency of PSII (Fv/Fm) compared with WT and antisense transgenic plants. Moreover, sense lines maintained higher ascorbate peroxidase (APX) activity than WT and antisense plants under salt- and PEG-induced osmotic stress. These results indicate that chloroplastic MDHAR plays an important role in alleviating photoinhibition of PSII by elevating ascorbate (AsA) level under salt- and PEG-induced osmotic stress., F. Li ... [et al.]., and Obsahuje bibliografii
Chlorophyll (Chl) fluorescence temperature cinve (FTC) of primary leaves of spring barley (Hordeum vulgare L.), cultivated imder a low irradiance, was studied at low actinic radiation excitation (436 nm, 2 W m'^) under a heating regime consisting of a linear increase of temperature (0.083 °C s’*), followed by a period of constant temperature. After prompt cooling of the sample to 77 K, Chl fluorescence spectra at defined points of the temperature regime were measured. Two distinct temperature and kinetic regions expressed by two discemible temperature maxima were observed for ťhis type of the FTC. Two triggering temperatures of successive irreversible changes are postulated at 45-48 “C and 53-55 °C temperature intervals, respectively; they may correlate with the heat inactivation of photosystem 2 and with changes of the chloroplast and cytoplasmic membrane integrity.
At various intervals after inoculation of the roots of groundnut plants with the fungus Macrophomina phaseoli, 14CO2 was administered to branch 2 (from the base) of the plants in the light. The effects of the disease on the translocation of 14C-photosynthates out of the source branch to the rest of the plant were studied 24 h after labelling. As the plant aged and the disease symptom development became more evident, an increasing percentage of the fixed 14C-photosynthates was exported from branch 2 of the inoculated plants (IP) compared to the non-inoculated plants (NIP). The apex, main stem, and branch 1 of NIP imported more of the total fixed 14C throughout the developmental stages of the plant except for day 10 after inoculation when branch 1 of IP imported almost 76 % of the total fixed 14C. The roots of IP were the major sink and imported higher percent of the total fixed 14C than the roots of NIP.
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.