UV-B responses of three rice (Oryza sativa L.) cultivars (Sasanishiki, Norin 1 and Surjamkhi) with different photolyase activity were investigated. Carbon dioxide assimilation data support that Sasanishiki was less sensitive to UV-B than Norin 1 and Surjamkhi. UV-B radiation sharply decreased the content of Rubisco protein in Surjamkhi and has no effect in Sasanishiki. The photochemical activities of photosystem (PS) 1 and PS 2 was slightly affected by UV-B treatment. The content of H 2 O 2 and the activities of antioxidant enzymes, catalase (CAT), peroxides (POX) and superoxide dismutase (SOD) were enhanced after UV-B treatment. The activities of CAT and POX isoenzymes in Sasanishiki were more enhanced by UV-B radiation than those in Norin 1 and Surjamkhi.Additional key words: catalase, 14 CO 2 fixation, hydrogen peroxide, peroxidase, Rubisco, superoxide dismutase. ⎯⎯⎯⎯UV-B sensitivity of plants is determined by the balance of damage incurred and by the efficiency of repair processes that can restore the impaired functions. This balance is influenced by several factors, including the genetic background of the species, growth conditions of the studied plants, as well as the simultaneous occurrence of other stresses. UV-B sensitivity in rice cultivars is controlled by at least three recessive genes (Sato et al. 2003). DNA is one of the targets of UV-B radiation, which induces photodamage in DNA resulting in the production of cyclobutane pyrimidine dimers (CPDs) and pyrimidinepyrimidone photoproducts (Britt 1996). Photoreactivation involving enzyme photolyase, is the main pathway in plants for repairing UV-B induced DNA damage. Examinations of 17 rice cultivars (Teranishi et al. 2004) and several wild rice species (Iwamatsu et al. 2008) show that the UV-B resistant cultivars had higher photolyase activities in comparison to less resistant ones. Hidema et al. (2005) demonstrated that CPD photorepair ability is one of the crucial factors determining UV-B sensitivity in rice.Furthermore, transgenic rice plants in which the CPD photolyase was overexpressed had higher CPD photolyase activity and showed significantly greater resistance to UV-B than wild plants (Hidema et al. 2007). Therefore, the CPD photolyase activity is an excellent indicator for UV-B sensitivity of rice plant but it is important to examine other factors that would promote UV-B tolerance in order to develop plants with greater UV-B resistance.Under UV-B radiation plant cells produce reactive oxygen species (ROS) that induces oxidative damage to DNA, proteins and other cell components (Caldwell 1993, Foyer et al. 1994, Mahdavian 2008. To cope with oxidative stress, various ROS-scavenging systems in plants are involved. They include superoxide dismutase, catalase, ascorbate peroxidase, glutathione S-transferase, and low molecular mass antioxidants such as ascorbate, glutathione, and carotenoids (Asada 1999).In this study UV-B response of three rice cultivars (Oryza sativa L. cvs. Norin 1, Sasanishiki and Surjamkhi), with different photolyase activity ...

Barley seedlings were pre-treated with 1 and 5 µM H 2 O 2 for 2 d and then supplied with water or 150 mM NaCl for 4 and 7 d. Exogenous H 2 O 2 alone had no effect on the proline, malondialdehyde (MDA) and H 2 O 2 contents, decreased catalase (CAT) activity and had no effect on peroxidase (POX) activity. Three new superoxide dismutase (SOD) isoenzymes appeared in the leaves as a result of 1 µM H 2 O 2 treatment. NaCl enhanced CAT and POX activity. SOD activity and isoenzyme patterns were changed due to H 2 O 2 pre-treatment, NaCl stress and leaf ageing. In pre-treated seedlings the rate of 14 CO 2 fixation was higher and MDA, H 2 O 2 and proline contents were lower in comparison to the seedlings subjected directly to NaCl stress. Cl -content in the leaves 4 and 7 d after NaCl supply increased considerably, but less in pre-treated plants. It was suggested that H 2 O 2 metabolism is involved as a signal in the processes of barley salt tolerance.

The role of exogenously applied phytohormone methyl jasmonate (MeJA) in counteracting the ultraviolet B (UV‐B) stress in barley seedlings was investigated. Barley seedlings (Hordeum vulgare L., cv. Alfa) 4 days old were supplied with 5 × 10−5 m MeJA through the roots for 3 days and then exposed for 2 days for 5 h per day to UV‐B (312 nm, biological effectiveness of UV‐B radiation 28.8 kJ m−2day−1). The rate of 14CO2 fixation, PSI and PSII activities and chlorophyll content decreased, but flavonoids, H2O2, malondialdehyde, proline and UV‐B induced compounds increased after UV‐B treatment. The rate of photosynthetic oxygen evolution was more strongly inhibited by UV‐B‐irradiation than PSI and PSII efficiency. MeJA itself increased the content of free proline, which acts as a stress protector due to its radical scavenging ability. Increased superoxide dismutase, catalase and peroxidase (POX) activities in the leaves and in the roots and the POX isoforms induction revealed the MeJA involvement in plant tolerance to oxidative stress caused by UV‐B irradiation. It was shown that pre‐treatment with MeJA counteracted UV‐B stress. Therefore, it was suggested that MeJA could acts as a mediator in plant defense responses to UV‐B irradiation by enhancing the activity of antioxidant system and free radical scavenging capability of plant cells.

Bulgaria is famous for its oil-bearing rose. R. damascena Mill. and R. alba L. are mainly cultivated in the country, but a recent survey of industrial plantations in 2020 revealed that R. centifolia L. and hybrids of R. damascena Mill. X R. gallica L. are also common in the rose valley. Although their essential oil cannot be compared in quality with the classic, these species are preferred by farmers with high yields of flowers and resistance to diseases and pests. All these roses are also used to produce rose water and extracts. The aim of this investigation was to compare the yield and chromatographic fingerprints of seven rose oils and hydrosols produced in Bulgaria. The quantitative composition of the main components of the oils was compared with the norms of the world standards. Our study showed that the yield of essential oil from these roses was in the range of 0.015–0.048%. The main group in the chemical composition is terpene alcohols, which vary in range: geraniol (15.85–34.02%), citronellol (6.70–28.72%), and nerol (5.80–11.90%) but with a different ratio. Hydrocarbons are represented by saturated aliphatic homologs with an odd number of carbon atoms, the main ones being nonadecane (8.10–22.67%), heneicosane (4.37–10.21%), heptadecane (1.07–2.98%), and triclosan (0.81–5.90%). In contrast, the chemical profile of the hydrosols was performed using phenylethyl alcohol (27.45–69.88%), geraniol (13.72–28.67%), and citronelol+nerol (4.56–17.37%). The results show that the presence of plantations with a genotype different from that of R. damascena implies differences in the quality of rose oils and hydrosols. This determines their properties of use.

Aims:  To investigate the relationship between growth, heavy metal ions uptake and participation of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) in the protection of Apergillus niger B 77 against cadmium stress. Methods and Results:  The stress response of the model fungal strain, under conditions of a wide range of Cd (II) ion concentrations, was investigated by determining the biomass formation, protein biosynthesis, SOD and CAT activities and heavy metal uptake in growing cells. Exposure to heavy metal ions induced an increase in protein content, heavy metal uptake and SOD activity, and a heavy decrease in CAT activity. Conclusion:  The results obtained indicated that the tolerance of A. niger to Cd (II) was correlated with the heavy metal uptake, reactive oxygen species generation in the cells and the efficiency of antioxidative defence system. Significance and Impact of the Study:  Evidence is provided for the possibility that oxidative stress plays a major role in the effect of Cd (II) ions on A. niger. These data could offer useful information when creating new strategies and methodological improvements for bioremediation with the participation of fungi.

The effect of copper (Cu) excess (1.5, 4.7, 31, 78, 156 µM) and exogenously supplied succinate on plant growth, chlorophyll content, chlorophyll fluorescence, and isoenzym profiles of some antioxidant enzymes in maize plants was studied. Excessive Cu supply led to a reduction in the relative growth rate (RGR), tolerance index (TI), chlorophyll a and chlorophyll b contents, and the quantum yield of PSII electron transport in the light-adapted state (UPSII). Copper treatment induced several changes in the anionic and cationic peroxidases (PODs), as well as superoxide dismutase (SOD) isoenzyme profiles. After 8 d of 78 µM-Cu treatment, two new anionic and two new cationic peroxidase isoenzymes in the roots were registered. Copper applied at concentrations above 31 µM resulted in higher levels of manganese superoxide dismutase (Mn-SOD) in the roots and Cu,Zn-superoxide dismutase (Cu,Zn-SOD) in the leaves. However, the addition of Nasuccinate (200 µM) to the root medium prior to Cu treatment increased the capacity of the plants to partially overcome Cu toxicity. AbbreviationsChl-chlorophyll; FW-fresh weight; TI-tolerance index; RGR-relative growth rate; F o -the initial fluorescence yield; F m -maximum total fluorescence; F v : F m -measure of PSII effectiveness in the primary photochemical reactions; PS IIphotosystem II; UPSII-quantum yield of PSII photochemistry; SOD-superoxide dismutase; POD-peroxidase, Rmrelative mobility.

The effect of the sources of nitrogen nutrition (nitrogen fixation or nitrate assimilation) and a gradual water stress on the relative water content, total fresh and dry biomass production, leaf growth, and changes in the total soluble protein spectra were studied. The plants were cultivated as soil cultures in a naturally illuminated greenhouse. Comparative studies were carried out with respect to well-watered, control plants. Nitrogen-fixing control and drought plants had relatively smaller root development but be�er relative water content and large leaf area on the last sampling day than nitrate-fed soybean plants. Water deficit effects on plant biomass at the end of the period studied (21 days) were independent on the nitrogen source. There was no qualitative difference in the total soluble protein spectra of nitratefed and nitrogen-fixing soybean leaves neither with the progress of development nor under drought conditions. But there was a difference in response to drought in termostable proteins of nitrate-fed and nitrogen-fixing plants. The quantity of termostable proteins in inoculated control plants was lower in some degree compared to uninoculated ones. In inoculated plants the water stress caused an increase in the amount of soluble termostable proteins.

The response of the antioxidant enzymes peroxidase [EC 1.11.1.11], superoxide dismutase (SOD) [EC 1.15.1.1] and catalase [EC 1.11.1.6] to dehydration stress caused by low and high temperature, salinity (0.2 M NaCl) and hyperosmoticum (0.5 M sucrose), as well as to exogenous ABA and H 2 O 2 , was examined in germinating wheat seeds. The data presented here confirm and complete previous results for other stages of wheat seedling development (Bakalova et al., 2004; 2007). Catalase was the most susceptible antioxidant enzyme under the chronic stress conditions applied. Its activity correlated closely to the decrease in the growth rate of wheat seedlings. Low temperature had the strongest effect of all the stress factors applied. There was a significant decrease in anionic peroxidase activity, accompanied by catalase inhibition, after low temperature treatment. An analysis of all the data obtained revealed that the treatments had mostly non-specific effects on gene expression, protein and enzyme profiles. Catalase and peroxidase activity were suppressed not only by low temperature, but by hyperosmoticum (0.5 M sucrose) as well. This result confirmed findings that a significant number of genes induced by one particular stress are also upregulated by other stresses (Kreps et al., 2002; Munns, 2002; Rabbani et al., 2003).