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Nitric oxide (NO) is an important molecule in regulating plant growth, development and photosynthetic performance. This study investigates the impact of varying concentrations (0–300 µM) of sodium nitroprusside (SNP, a donor of NO) on the functions of the photosynthetic apparatus in sorghum (Sorghum bicolor L. Albanus) and maize (Zea mays L. Kerala) under physiological conditions. Analysis of the chlorophyll fluorescence signals (using PAM and the JIP-test) revealed an increased amount of open PSII reaction centers (qP increased), but it did not affect the number of active reaction centers per PSII antenna chlorophyll (RC/ABS). In addition, the smaller SNP concentrations (up to 150 μM) alleviated the interaction of QA with plastoquine in maize, while at 300 μM it predominates the electron recombination on QAQB−, with the oxidized S2 (or S3) states of oxygen evolving in complex ways in both studied plant species. At the same time, SNP application stimulated the electron flux-reducing end electron acceptors at the PSI acceptor side per reaction center (REo/RC increased up to 26%) and the probability of their reduction (φRo increased up to 20%). An increase in MDA (by about 30%) and H2O2 contents was registered only at the highest SNP concentration (300 µM). At this concentration, SNP differentially affected the amount of P700+ in studied plant species, i.e., it increased (by 10%) in maize but decreased (by 16%) in sorghum. The effects of SNP on the functions of the photosynthetic apparatus were accompanied by an increase in carotenoid content in both studied plants. Additionally, data revealed that SNP-induced changes in the photosynthetic apparatus differed between maize and sorghum, suggesting species specificity for SNP's impact on plants. [ABSTRACT FROM AUTHOR]

Sideritis scardica (S. scardica) is a mountain plant, endemic to the central part of the Balkan Peninsula, including the southern regions of Bulgaria. It is widely used in traditional medicine to treat some respiratory, gastrointestinal tract, or neurodegenerative diseases, but research data for its cytotoxic and anticancer properties are limited. In the present study, a hydroethanolic extract of S. scardica from region Trigrad, Bulgaria was prepared and its total polyphenolic and flavonoid content was determined. Further, its antioxidant, cytotoxic, and anticancer activities toward a mouse adenocarcinoma cell line, Colon 26 was evaluated in vitro. Higher antioxidant activity and higher total phenolic and flavonoid content were detected in the S. scardica hydroethanolic extract from region Trigrad as compared to the publish data for other ecotypes of this species. Also, the extract of S. scardica with a concentration higher than 200 µg mL-1 was found to inhibit the viability and growth of colon cancer cells but not those of the normal kidney MDCK cells pointing to a cell-specific and concentration-dependent cytotoxic effect. Thus, the current study demonstrates a high oxidation potential of S. scardica hydroethanolic extract from the region Trigrad and its cytotoxic effects on colon cancer cells when the extract was applied with concentrations of 200 µg mL-1 and higher. [ABSTRACT FROM AUTHOR]

The ability of eight Bulgarian common winter wheat varieties (Sadovska belya, Lusil, Diamant, Bononia, Tsarevets, Niky, Guinness and Petya) to tolerate drought stress as well as to recover after re-watering were evaluated by following the alterations in the leave pigment content, generation of hydrogen peroxide, lipid peroxidation, and levels of synthesized protective substances (anthocyanins). These parameters were used as fast and sensitive stress markers to assess varieties' susceptibility to drought. Results presented indicated that on the 7th day of dehydration alteration in the photosynthetic pigment content occurred as indicated by the decreased chlorophyll to carotenoid ratio showing that the amount of total chlorophylls was changed to a higher extent than that of carotenoids. Data demonstrated that the amount of stress-generated hydrogen peroxide (H2O2) was highest in Guinness, followed by Petya, Lusil and Tsarevets. The extend of membrane damage evidenced by the degree of dehydration-induced lipid peroxidation was highest in varieties Sadovska belya, Petya and Tsarevets. Furthermore, all investigated varieties responded to drought stress by increased synthesis of anthocyanins. Our results also suggested that varieties Guinness and Diamant were suitable for growing in areas with limited water availability as they have a good drought stress resistance and recovery capacity. [ABSTRACT FROM AUTHOR]

In this study, the effects of salt stress on the photosynthetic processes in sorghum (Sorghum bicolor L. Albanus concep) and maize (Zea mays L. Mayflower) were compared. The plants were grown in half-strength Hoagland solutions containing different NaCl concentrations (0, 50, 150 and 250 mM NaCl) for 6 days. Pulse Amplitude Modulated chlorophyll fluorescence, photooxidation of P700 and pigment analysis were used for characterization of the salinity effects on the studied plants. The treatment of plants with the high concentrations of NaCl led to an inhibition of the chlorophyll fluorescence parameters like the photochemical quenching, the rate of photosynthesis and the linear electron transport in sorghum and maize. All these changes corresponded to decrease in the pigment content and changes in chlorophyll a/b ratio. The analysis of the P700 photooxidation revealed that the photosystem I photochemistry was inhibited at the highest NaCl concentration in both studied plants. Data also revealed that sorghum is more sensitive to salt stress than maize. The reasons for different effects of salt stress on the maize and sorghum are described. [ABSTRACT FROM AUTHOR]

Results indicate that the calorimetric events correspond to the structural transitions of the pigment-protein complexes in the chloroplast thylakoid membranes. Data suggest that the chiral macrodomain structural changes are of thermooptic origin. Furthermore, a thermal transient band around 60 C is involved in the trimer-tomonomer transition of the chlorophyll a/b light-harvesting pigment-protein complex of photosystem II.

Salinity increases in the world’s land area and significantly affects the rate of photosynthesis and corresponding plant growth. In this study, the impact of salt stress (200 mM NaCl equivalent to an electrical conductivity of 18.6 mS cm−1) on the photosynthetic apparatus and some growth parameters were investigated in wheat DELLA mutant (Rht-B1c) and wild-type (Rht-B1a) seedlings grown on a half-strength Hoagland solution. Results revealed that salt toxicity was alleviated in the Rht-B1c mutant compared to the Rht-B1a wild type, as manifested by less-reduced leaf pigment content, relative water content, and photochemical activity of photosystem II (PSII) and photosystem I (PSI) after a 9-day salt exposure of plants. Compared to the wild-type wheat, a higher capacity for PSI-dependent cyclic electron flow, preventing the photosynthetic apparatus from oxidative damage, was observed in the mutant plants before and after salt treatment. In addition, an increase of PsaB proteins was detected in the mutant plants after long-term salt stress unlike the wild type. The observed higher oxidation level of P700 (P700+) in the mutant was consistent with higher abundance of PSI-related protein complexes. The data demonstrated that alterations in thylakoid membrane proteins and/or their structural reorganization in wheat DELLA mutant (Rht-B1c) significantly contribute to the alleviation of salt-induced damage of the photosynthetic apparatus. Molecular mechanisms involved in the photosynthetic responses of wheat DELLA mutants to salt stress are discussed. [ABSTRACT FROM AUTHOR]