Growth and photosynthesis of Lemna minor L. exposed to different light conditions and sucrose supplies

Duckweed (Lemna minor L.) is a model plant suitable for investigation into plant physiology, biochemistry and ecotoxicology. Depending on the type of the experiment, duckweed is cultivated on different nutrient media under various chamber conditions. In our work, duckweed was cultivated on Pirson-Seidel’s nutrient solution supplemented with 5, 7.5 or 10 g L–1 sucrose under cool white (CW) or Gro-Lux (GL) light sources. When different light sources and sucrose supplies are compared, a significant stimulative effect of GL light on duckweed grown on 7.5 and 10 g L–1 sucrose was seen to start on day 9. Considering photosynthetic performance the results showed that there were no significant differences in maximum quantum yield of PSII (Fv/Fm) after 7 and 16 days of exposure, regardless of light source and sucrose supply. Effective quantum yield of PSII (FPSII) decreased only after 16 days of exposure to 5 g L–1 sucrose under CW light. The higher growth rate and photosynthetic performance in plants exposed to GL light is a consequence of its spectral distribution resembling the action spectrum of photosynthesis. Furthermore, enhanced growth noticed in plants cultivated on higher sucrose contents (7.5 and 10 g L–1) indicated the promotive effect of sucrose in plants grown under low light conditions

Transgenerational stress memory in Arabidopsis thaliana (L.) Heynh.: antioxidative enzymes and HSP70

Transgenerational transmission of information about stress exposure is manifested as an increase in the somatic homologous recombination frequency in plants. Our aim was to investigate whether information about changes of antioxidative enzyme activities and protein HSP70 induction are also transmitted in response to stress caused by UV-C irradiation. These stress indicators were investigated in Arabidopsis thaliana plants exposed to UV-C irradiation (6 and 600 J m-2) and its non-irradiated progeny. The activity of catalase was significantly decreased in the irradiated plants in comparison to the non-irradiated control plants, while the activity of guaiacol peroxidase was increased. The ascorbate peroxidase activity was not significantly changed. In irradiated plants there was an induction of a new HSP70 protein isoform. In the non- irradiated progeny of irradiated plants, a significant decrease in catalase and ascorbate peroxidase activity was noticed in comparison to plants whose parents were not irradiated. There was no significant change in guaiacol peroxidase activity or induction of HSP70 isoforms in the progeny. The obtained results indicate that, besides the already known increase in frequency of somatic homologous recombination, transmission of information about stress exposure can also include changes in activities of antioxidative enzymes catalase and ascorbate peroxidase. The explanations for the observed changes and the mechanism by which they occur have to be established in further research

The effect of salinity and osmotic stress on duckweed Lemna minor L.

The response of duckweed (Lemna minor L.) to salinity and osmotic stress was evaluated by monitoring growth and peroxidase activity every second day, for a period of 17 days. The nutrient medium was supplemented with isoosmolar concentrations of NaCl and mannitol (50 mM and 100 mM NaCl, 100 mM and 200 mM mannitol). Growth decreased markedly with increasing concentrations of NaCl and mannitol. The lower concentrations of NaCl (50 mM) and mannitol (100 mM) started to reduce growth significantly in the second week of the experiment, while the higher concentrations (100 and 200 mM) reduced growth from the beginning. Protein concentrations and peroxidase activity fluctuated during the growth period but, most of the time, they were increased in plants treated with NaCl and mannitol. These results suggest that Lemna minor is sensitive to both salinity and osmotic stress. However, the continued growth, and also the increase in peroxidase activity and protein concentration, during the NaCl and mannitol treatments, demonstrate its potential for adaptation to long-term stress. Although salinity and osmotic stress have similar overall effects on Lemna minor, consistent minor differences in growth, protein concentration and peroxidase activity between plants grown on NaCl and those grown on mannitol suggest overlapping, rather than identical, mechanisms of adaptation to salinity and osmotic stress

Response of dihaploid tobacco roots to salt stress

Salinity is a common abiotic factor that affects plant growth and development. Seedlings of tobacco (Nicotiana tabacum L.) F1 hybrid DH10 and three dihaploid lines (207B, 238C and 239K) obtained by diploidization of anther-derived haploids of hybrid DH10 were subjected to 0, 100 and 200 mM NaCl in in vitro conditions for 33 days and the effect on roots was evaluated. In all lines and in the hybrid DH10 exposed to 200 mM NaCl evident root growth inhibition and increased proline content were noticed. However, in some cases lines differed in the activity of antioxidative enzymes, which could account for differences in their salinity tolerance. Increased activity of catalase and peroxidase in roots of line 239K could contribute to the more pronounced salinity tolerance previously reported for shoots of this line

Effect of calcium chloride and calcium bromide on chloroplasts of Lemna minor L.

Saturated water solutions of CaCl2, CaBr, and a 1:1 mixture of them are commonly used as »high density brines« for pressure control in oil wells. To investigate the effect of these chemicals on chloroplast morphology and their sedimentation profile in a sucrose gradient, duckweed, Lemna minor L., was chosen as a test organism. By light microscopy, round to oval chloroplasts in control plants and in plants grown on media supplemented with 0.025 and 0.050 mol dm-3 of tested salts were observed. However, in plants grown on media containing higher concentrations of the salts ested (0.075 and 0.1 mol dm-3) most of the chloroplasts were of irregular shape, and bigger. The sedimentation profile of the control and the treated chloroplasts (based on chlorophyll determination in 200-pi fractions) also differed. Control samples showed three peaks, while treated samples showed an additional peak (fractions 5-8). One of the peaks obtained in the treated samples was sharper and more intensive than the peak present at the same position in the control extracts. The results obtained showed changes in chloroplast morphology and sedimentation profile after treatment with the higher concentrations (0.075 and 0.1 mol dm-3) of the salts tested that could be the consequence of starch accumulation in chloroplasts

Response of Kalanchoe daigremontiana to wounding and infection with Agrobacterium tumefaciens

Background and Purpose: Transformation of plant tissue with Agrobacterium tumefaciens includes wounding of plant and subsequent infection by bacteria. Polyphenol oxidase activity and oxidative stress parameters – the content of H2O2, as well as activity and isoenzymes of antioxidative enzymes catalase, pyrogallol and guaiacol peroxidase were investigated as markers of plant response to wounding and infection. Materials and Methods: Five tissue types – healthy tissue, wounded tissue, tissue in immediate proximity of the wound, tumour tissue and tissue next to the tumourwere collected on 7th, 14th and 21st day afterwounding or infection. Activities of antioxidative enzymes were evaluated spectrophotometrically. Isoenzymes were separated electrophoretically in native conditions. H2O2 content was estimated by measuring the titanium hydro--peroxide complex. Results and Conclusion: All measured parameters were remarkably different in tumour in comparison to healthy tissue. Activities of peroxidases were significantly increased, accompanied with induction of new isoenzymes. After two weeks of the experiment catalase activity was also significantly increased in tumour tissue as well as in tissue next to the wound. H2O2 content was lower in tumour after three weeks. Aside from tumour tissue, polyphenol oxidase activity was significantly increased in tissue next to the tumour. Remarkably increased peroxidase and polyphenol oxidase activity in tumour tissue, additional isoenzymes of peroxidases as well as decreased H2O2 content, indicated changes in tissue organisation and induction of defence mechanisms against pathogen, in which these two groups of enzymes are involved.Wounded tissue, as well as tissue next to the wound or infection, did not show significant variation from healthy tissue

Effect of calcium chloride and calcium bromide on chloroplasts of Lemna minor L.

Saturated water solutions of CaCl2, CaBr, and a 1:1 mixture of them are commonly used as »high density brines« for pressure control in oil wells. To investigate the effect of these chemicals on chloroplast morphology and their sedimentation profile in a sucrose gradient, duckweed, Lemna minor L., was chosen as a test organism. By light microscopy, round to oval chloroplasts in control plants and in plants grown on media supplemented with 0.025 and 0.050 mol dm-3 of tested salts were observed. However, in plants grown on media containing higher concentrations of the salts ested (0.075 and 0.1 mol dm-3) most of the chloroplasts were of irregular shape, and bigger. The sedimentation profile of the control and the treated chloroplasts (based on chlorophyll determination in 200-pi fractions) also differed. Control samples showed three peaks, while treated samples showed an additional peak (fractions 5-8). One of the peaks obtained in the treated samples was sharper and more intensive than the peak present at the same position in the control extracts. The results obtained showed changes in chloroplast morphology and sedimentation profile after treatment with the higher concentrations (0.075 and 0.1 mol dm-3) of the salts tested that could be the consequence of starch accumulation in chloroplasts

Rast i fotosinteza u vodene leće (Lemna minor L.) izložene kadmiju u kombinaciji s cinkom ili bakrom

Metals have a variety of negative outcomes on plants, essential components of any ecosystem. The effects of CdCl2 (5 μmol L-1), ZnCl2 (25 or 50 μmol L-1), and CuCl2 (2.5 or 5 μmol L-1) and combinations of CdCl2 with either ZnCl2 or CuCl2 on the growth, photosynthetic pigments, and photosystem II (PSII) efficiency of duckweed (Lemna minor L.) were investigated. All of the treatments caused growth inhibition and remarkable metal accumulation in plant tissue after 4 and 7 days. In the combined treatments, the accumulation of each metal applied was lesser in comparison to treatments with single metals. After 4 days, all of the treatments generally diminished chlorophyll a content and decreased the maximum quantum yield (Fv/Fm) and effective quantum yield (ΔF/F’m) of PSII. However, after 7 days of exposure to a combination of Cd and Zn, pigment content and PSII activity recovered to control levels. A higher concentration of Cu (5 μmol L-1) as well as Cd in combination with Cu had a prolonged inhibitory effect on photosynthetic features. Our results suggest that growth inhibition was due to the toxic effect of absolute metal quantity in plant tissue. Zn counteracted Cd uptake, as seen from the recovery of pigment content and PSII efficiency in plants exposed for 7 days to the Cd and Zn combination. Cu-induced oxidative stress led to a prolonged inhibitory effect in plants treated both with a higher concentration of Cu (5 μmol L-1) and simultaneously with Cd and Cu. Our findings could contribute to general knowledge on anthropogenic and environmental contaminants that endanger plant communities and significantly disrupt the sensitive balance of an ecosystem by influencing photosynthetic mechanisms.Izloženost metalima može izazvati različite štetne učinke u biljaka. Vodene leće izložili smo solima teških metala CdCl2 (5 μmol L 1), ZnCl2 (25 μmol L 1 ili 50 μmol L 1) i CuCl2 (2,5 μmol L 1 ili 5 μmol L 1) te kombinaciji CdCl2 sa svakom od navedenih koncentracija ZnCl2 i CuCl2. Rast biljaka, količina fotosintetskih pigmenata i učinkovitost fotosistema II (PSII) mjereni su nakon četiri i sedam dana tretmana. Utvrđeno je da su svi tretmani uzrokovali značajnu inhibiciju rasta te akumulaciju metala u biljci. U biljaka koje su bile izložene kombinacijama teških metala količina pojedinog metala u tkivu bila je niža u odnosu na količinu istog metala u biljaka izloženih samo tom metalu. Nakon četiri dana tretmana sva su tri metala, neovisno o tome jesu li bila primijenjena zasebno ili u kombinacijama, uzrokovala smanjenje količine klorofila a i pad vrijednosti maksimalnog (Fv/Fm) i efektivnog (ΔF/F’m) prinosa PSII. Međutim, u biljaka koje su bile istovremeno izlagane kadmiju i cinku, vrijednosti količine pigmenata i učinkovitost PSII vratile su se nakon sedam dana na kontrolnu razinu, a bakar u koncentraciji 5 μmol L 1 te kombinacija kadmija i bakra i dalje su imali inhibitorni učinak. Budući da smanjeno primanje pojedinog metala uočeno u biljaka izloženih kombiniranim tretmanima nije ublažilo inhibitorni učinak na rast, možemo zaključiti da je inhibicija rasta uzrokovana apsolutnom količinom metala primljenog u tkivo. Povećanje količine fotosintetskih pigmenata i učinkovitosti PSII nakon sedam dana tretmana kadmijem i cinkom upućuje na oporavak biljaka, što se može objasniti ublažavajućim djelovanjem cinka na učinak kadmija uslijed smanjenog primanja kadmija u biljku. Suprotno tome, dugotrajni inhibitorni učinak istovremenog tretmana biljaka kadmijem i bakrom te samim bakrom u koncentraciji 5 μmol L 1 može se objasniti oksidacijskim stresom uzrokovanim bakrom. Rezultati ovoga istraživanja pridonose saznanjima o štetnim učincima antropogenih i okolišnih onečišćivača, koji narušavanjem mehanizama fotosinteze ugrožavaju ne samo biljke i njihove zajednice nego i osjetljivu ravnotežu ekosustava

Procjena toksičnosti akrilamida pomoću standardiziranih biotestova

Acrylamide is a monomer widely used as an intermediate in the production of organic chemicals, e.g. polyacrylamides (PAMs). Since PAMs are low cost chemicals with applications in various industries and waste- and drinking water treatment, a certain amount of non-polymerised acrylamide is expected to end up in waterways. PAMs are non-toxic but acrylamide induces neurotoxic effects in humans and genotoxic, reproductive, and carcinogenic effects in laboratory animals. In order to evaluate the effect of acrylamide on freshwater organisms, bioassays were conducted on four species: algae Desmodesmus subspicatus and Pseudokirchneriella subcapitata, duckweed Lemna minor and water flea Daphnia magna according to ISO (International Organization for Standardisation) standardised methods. This approach ensures the evaluation of acrylamide toxicity on organisms with different levels of organisation and the comparability of results, and it examines the value of using a battery of low-cost standardised bioassays in the monitoring of pollution and contamination of aquatic ecosystems. These results showed that EC50 values were lower for Desmodesmus subspicatus and Pseudokirchneriella subcapitata than for Daphnia magna and Lemna minor, which suggests an increased sensitivity of algae to acrylamide. According to the toxic unit approach, the values estimated by the Lemna minor and Daphnia magna bioassays, classify acrylamide as slightly toxic (TU=0-1; Class 1). The results obtained from algal bioassays (Desmodesmus subspicatus and Pseudokirchneriella subcapitata) revealed the toxic effect of acrylamide (TU=1-10; Class 2) on these organisms.Akrilamid je monomer koji se koristi kao intermedijer u proizvodnji organskih kemikalija, npr. poliakrilamida (PAM-a). PAM se primjenjuje u različitim industrijama te u obradi otpadnih voda i tretmanu vode za piće, a prihvatljiv je i zbog niske cijene. Široka upotreba PAM-a u spomenute svrhe predstavlja rizik od toga da određena količina nepolimeriziranog akrilamida dospije u vodene ekosustave. PAM je netoksičan, ali akrilamid ima neurotoksične učinke u ljudi te je također dokazana njegova genotoksičnost, kancerogenost i štetan utjecaj na reprodukcijski sustav u laboratorijskih životinja. U cilju procjene toksičnosti akrilamida provedeni su biotestovi na četirima vrstama slatkovodnih organizama: na zelenim algama Desmodesmus subspicatus i Pseudokirchneriella subcapitata, vodenoj leći Lemna minor i vodenbuhi Daphnia magna. Biotestovi su provedeni prema standardiziranim ISO metodama, što osigurava procjenu toksičnosti akrilamida na organizme različitog stupnja organizacije, usporedivost rezultata i procjenu pogodnosti korištenja niza standardiziranih biotestova prihvatljive cijene za praćenje zagađenja i onečišćenja vodnih ekosustava. Rezultati su pokazali da su EC50 vrijednosti niže nakon izlaganja zelenih algi Desmodesmus subspicatus i Pseudokirchneriella subcapitata akrilamidu u odnosu na vrijednosti dobivene za vodenu leću Lemna minor i vodenbuhu Daphnia magna, što pokazuje veću osjetljivost algi. S obzirom na klasifikacijski sustav za izražavanje stupnja toksičnosti, a na temelju vrijednosti utvrđenih za vodenu leću Lemna minor i vodenbuhu Daphnia magna, akrilamid se može klasificirati kao slabo toksičan (TU=0-1; razred 1). Rezultati dobiveni testovima na algama (Desmodesmus subspicatus i Pseudokirchneriella subspicata) dokazuju toksičan učinak akrilamida na tim organizmima (TU=1-10; razred 2)