Ivanka Fedina

ABA as a Modulator of the Response of Pisum sativum to Salt Stress

Summary Ten-day-old pea plants ( Pisum sativum L., cultivar Ran 1) were treated for 24h with 10 -5 M or 10 -6 M ABA before a salinity treatment with 50 mM NaCl lasting 48 h. The sodium chloride treatment alone resulted in an increase of endogenous proline content, CO 2 compensation point, photorespiration and glycolate oxidase activity. Photosynthesis was significantly inhibited. ABA eliminated the inhibitory effect of NaCl and the values of the observed parameters were similar to those of the control. 14 CO 2 fixation of protoplasts isolated from salt stressed plants was inhibited about 60 %; 14 CO 2 fixation by protoplasts isolated from plants treated with ABA before salinization was almost equal to that of the control. 10 -5 M or 10 -6 M ABA added exogenously to the protoplast reaction medium did not affect 14 CO 2 fixation. The reduced CO 2 fixation of protoplasts isolated from NaCl stressed plants indicated a direct effect of NaCl on the photosynthetic process, which was not dependent upon stomatal closure.

Response of barley seedlings to UV-B radiation as affected by NaCl

The response of barley seedlings, subjected to 150 mmol/L NaCl for 4 days at different light regimes (4 d in the light, 4 d in darkness and a 12 h light/dark cycle) before UV-B radiation was investigated. NaCl treatment resulted in a decrease of total chlorophyll content and an increase in H2O2, free proline and lipid peroxidation, as quantified by measurement of malondialdehyde. Significantly more proline was accumulated in the light than in darkness. The combination of UV-B and NaCl treatment produced an additive effect on most of the parameters studied. UV-B radiation reduced the chlorophyll/carotenoids ratio and photochemical efficiency of PSII as estimated by chlorophyll fluorescence. NaCl pre-exposure decreased H2O2 generation and lipid peroxidation and alleviated the inhibitory effect of UV-B on PSII activity. Proline accumulated under salt stress conditions might be one of the reasons for the observed tolerance of barley seedlings to UV-B radiation.

Light-Dark Changes in Proline Content of Barley Leaves under Salt Stress

Proline accumulation in leaves of barley (Hordeum vulgare L. cv. Alfa) seedlings treated with 150 mM NaCl was promoted in the light and suppressed in the dark. The light/dark changes of proline content was enhanced with each 12 h light/12 h dark cycle and the proline content increased steadily. Root and shoot concentrations of Na+ and Cl− in salt treated plants increased about 10 to 25 times as compared to the control. The content of these ions and the content of malondialdehyde were higher in the shoot of seedlings exposed to salt stress for 4 d in the light in comparison with the seedlings exposed to NaCl for 4 d in darkness. Light stimulated both ions and proline accumulation in the leaves and has no effect in the roots. Oxygen uptake was higher in the seedlings kept 4 d in the light which have higher endogenous free proline content. Chlorophyll fluorescence measurements showed that the photochemical activity of PS 2 slightly decreased as a result of salt stress and was not influenced by light regimes during plant growth.

UV-B induced stress responses in three rice cultivars

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 H2O2 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.

Pre-treatment with H2O2 induces salt tolerance in Barley seedlings

Barley seedlings were pre-treated with 1 and 5 µM H2O2 for 2 d and then supplied with water or 150 mM NaCl for 4 and 7 d. Exogenous H2O2 alone had no effect on the proline, malondialdehyde (MDA) and H2O2 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 H2O2 treatment. NaCl enhanced CAT and POX activity. SOD activity and isoenzyme patterns were changed due to H2O2 pre-treatment, NaCl stress and leaf ageing. In pre-treated seedlings the rate of 14CO2 fixation was higher and MDA, H2O2 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 H2O2 metabolism is involved as a signal in the processes of barley salt tolerance.

Response of Scenedesmus Incrassatulus to Salt Stress as Affected by Methyl Jasmonate

Exposure of the freshwater green alga Scenedesmus incrassatulus Bohl, strain R-83 to salt stress (175 mM NaCl) resulted in a reduction of its growth and 14CO2 fixation and in an increase of accumulation of free proline and malondialdehyde (MDA). The accumulation of proline in the light was higher than in dark. NaCl significantly inhibited the Fe-induced release of organic chelators from the cells. Exogenously supplied 10−4M methyl jasmonate (JA-Me) did not considerably change the 14CO2 fixation, but increased proline and MDA accumulation in the cells and moderately inhibited the release of chelators from cells. JA-Me supplied simultaneously with NaCl helps the algae to counteract the salt stress.

Effect of pretreatment with methyl jasmonate on the response of Pisum sativum to salt stress

Summary 10-day-old pea seedlings ( Pisum sativum L. cv. Ran 1) were supplied with 10 −5 M methyl jasmonate for 3 days before salinization with 30 mmol/L NaCl for 3 and 6 days. Salt stress resulted in an increase of free proline content, CO 2 compensation concentration (Γ), photorespiration (R P ), stomatal resistance (r S ), and activity of glycolate oxidase (GO) and phosphoglycolate phosphatase (PGP). Net photosynthetic rate (P N ), transpiration (E), protein content and relative water content (RWC) were decreased. Pretreatment with methyl jasmonate helps the plants to counteract the salt stress or for adaptation to it. P N , RWC and protein content of these seedlings were higher in comparison to NaCl-treated seedlings. Exogenously supplied jasmonate itself plays the role of a stressor that causes typical stress responses — accumulation of free proline, high R P and Γ. Pretreatment with methyl jasmonate leads to a decrease of Na + and Cl − accumulation in the shoot. This protection is discussed with respect to involvement of methyl jasmonate in osmoregulation or osmoprotection based on increased proline accumulation and decreased ion accumulation.

Response of chlorina barley mutants to heat stress under low and high light

Barley plants (Hordeum vulgare L.) of wild type and two chlorina mutants, chlorina 126 and chlorina f2, were subjected to 42°C for 5 h at light intensities of 100 and 1000 μmol photons m-2 s-1. The exposure of plants to heat stress at a light intensity of 100 μmol m-2 s-1 induced enormous proline accumulation, indicating that the effect of heat stress was stronger when it was combined with low light intensity. The functional activity of PSII, O2evolution and flash-induced thermoluminescence B-band amplitude were strongly reduced when plants were exposed to heat at low light intensity. The results clearly showed that high light intensity had a protective effect on photosynthetic activity when barley plants were treated with high temperature. Comparison of the thermosensitivity of wild type plants and chlorina mutants revealed that O2 evolution in chlorina 126 and, especially, in chlorina f2 was more sensitive to heat than in wild type.

Response of Barley Seedlings to UV-B Radiation as Affected by Proline and NaCl

Barley (Hordeum vulgare L. cv. Alfa) seedlings were treated for 4 d before UV-B irradiation with 0.05 mM proline or 150 mM NaCl. UV-B exposure induced synthesis of yellow coloured compounds with maximum absorbance at 438 nm. The content of these compounds was increased in proline-treated and decreased in NaCl-treated plants. UV-B radiation reduced chlorophyll/carotenoids ratio, oxygen evolution rate and photochemical efficiency of PS 2 as estimated by chlorophyll fluorescence and increased proline accumulation, H2O2 generation and lipid peroxidation. Exogenous proline had no effect on the parameters studied and did not change the response of plants to UV-B radiation. NaCl inhibited photochemical efficiency of PS 2, reduced oxygen evolution and increased H2O2 concentration and lipid peroxidation. The combination of NaCl and proline treatment led to lowering the inhibitory effect of NaCl in non UV-B irradiated seedlings. There was not relationship between the level of UV-B-induced compounds and UV-B tolerance of barley seedlings.

UV-B response of green and etiolated barley seedlings

Abstract7-d-old etiolated and green barley seedlings (Hordeum vulgare L. cv. Alfa) were irradiated with UV-B for 30 min and then kept for 24 h in light or darkness. Chlorophyll (Chl) synthesis was inhibited by about 30 % as a result of UV-B irradiation, but there were no significant changes in photochemical activity measured by variable to maximum fluorescence ratio (Fv/Fm), quantum yield (ΦPS2) and oxygen evolution rate. Electron transport of etiolated seedlings was similar to that of green ones, nevertheless, the Chl content was more then 2-fold lower. Ribulose-1,5-bisphosphate carboxylase/oxygenase large and small subunits were diminished as a result of UV-B irradiation in etiolated and green plants, especially in those kept in the darkness. Catalase activity decreased and total superoxide dismutase activity increased in green and etiolated plants following UV-B treatment. When benzidine was used as a substrate, an isoform located between guaiacol peroxidases 2 and 3 (guaiacol peroxidase X) appeared, which was specific for UV-B treatment. As a result of irradiation, the contents of UV-B absorbing and UV-B induced compounds increased in green seedlings but not in etiolated seedlings.