Dessislava Todorova

Effect of cadmium and copper on the production of citric acid byAspergillus niger

Copper and cadmium inhibited the growth as well as citric acid production (depending on the heavy metal concentrations) by citric-acid-producingAspergillus niger. Activity of citrate synthase was connected with citrate synthesis in the absence as well as in the presence of heavy metals. The activity of aconitase, and both NAD- and NADP-isocitrate dehydrogenases was strongly inhibited by copper. The contents of DNA and proteins in the cells decreased but the contents of lipids and polysaccharides increased considerably in the presence of both heavy metals.

Mass transfer from solid particles to power law non-Newtonian fluid in granular bed at low Reynolds numbers

Abstract Dissolution rate of gypsum irregular particles in four non-Newtonian liquids at low Reynolds numbers (creeping flow regime) has been compared with the predictions of the available correlations based on the power law model for mass transfer in fixed bed. The flow behaviour index has been varied from 0.976 to 0.271. The shape coefficient and the coefficient of surface availability experimentally determined have been used as an attempt to reduce the problem to mass transfer from spheres. A new method for evaluation of the diffusivity of gypsum in the liquids have been applied. It has been shown that the empirical correlations based on the capillary model need to be complemented by the Pigford’s δ factor as to describe the mass transfer at very different flow behaviour index by a single equation.

PROTECTIVE EFFECT OF HUMIC ACIDS AGAINST HEAVY METAL STRESS IN TRITICALE

The effects of copper and cadmium and the preparation Biomin (natural substance extracted from coal with a.i. humic acids) on the biometric parameters, some stress markers and enzymatic activities in leaves and roots of triticale plants were investigated. The functional carbon distribution in Biomin was analyzed by 13 C NMR. It was found that all treatments retarded the growth and fresh weight of the plants. Heavy metals enhanced the content of stress markers proline and malondialdehyde and the activities of guaiacol peroxidase, superoxide dismutase and glutathione-S-transferase. The opposite trend was observed after Biomin application. Catalase activity was not affected considerably by the treatments. The free thiol-containing compounds were increased only in the roots of cadmium-treated plants. Comparative analysis of the measured parameters suggested that Biomin possessed protective effect against heavy metal toxicity.

Role of Polyamines in Alleviating Salt Stress

Salinity is one of the major abiotic stresses that reduce plant growth and productivity of many crops worldwide. Similarly to other stresses, salinity may cause oxidative stress via production of reactive oxygen species (ROS) which in high concentrations provoke oxidative damages to proteins, DNA, and lipids; disturb plant physiological processes and even lead to plant death. In low concentrations, ROS could activate defense mechanisms or repair programs that help plant cell to overcome the negative stress consequences. The diamine putrescine, triamine spermidine and tetraamine spermine are the major polyamines which are constitutive for all plant species. They are organic low-weight molecules with aliphatic amine structure possessing phytohormone-like features and are involved in various important processes of plant growth and development. Under physiological pH conditions they bear positive charge and may conjugate with other negatively charged molecules like phenolic acids, proteins, phospholipids or DNA. The participation of polyamines in the scavenging of free radicals, antioxidant activity and modulation of plant stress tolerance to various abiotic stresses has been extensively studied. The current review will focus on the recent investigations regarding the involvement of polyamines in plant tolerance to salinity stress. The alterations of the endogenous polyamine levels, the changes in their biosynthetic and catabolic enzymes in salt stressed plants, and the role of polyamine metabolism in alleviation of salinity stress is discussed. Possibilities for application of exogenous polyamines to overcome saline stress injuries and to induce plant salt tolerance are also summarized.

Effect of Ethylene and its Antagonist 1-MCP on the Senescence of Detached Leaves of Arabidopsis thaliana

Abstract1-Methylcyclopropene (1-MCP) applied alone did not influence significantly the chlorophyll and carotenoid content of the older leaves of Arabidopsis thaliana (L.) Heynh., but retarded the senescence of the younger ones (6th and 7th leaf nodes). However, 1-MCP effectively blocks the ethylene induced senescence of excised rosette leaves. The preliminary application of 1-MCP (3 h in advance to the treatment by Ethrel) almost totally eliminated the ethylene action. Similar trend was also observed after simultaneous application of Ethrel and 1-MCP, and the effects of both treatments on the chlorophyll and carotenoid destruction are comparable.

Polyamine Spermine Protects Young Pea Plants Against Ultraviolet-C Radiation

ABSTRACT The effects of ultraviolet-C (UV-C) irradiation and polyamine spermine on the content of some stress marker and non-enzymatic antioxidants in leaves of young pea plants were investigated. UV-C irradiation led to a decrease in pea fresh weight, the content of leaf pigments and free proline, accompanied with an increase in malondialdehyde. The initial augmentation in the free thiol levels was transient in UV-C treated plants and finally a substantial decrease was found. Spermine led to a significant augmentation of free thiols and proline content along with a decline in total phenols, but these alterations diminished during the experimental period. Based on comparative analyses of the results obtained for plants treated with UV-C and polyamine, it could be concluded that preliminary application of spermine protects pea plants against irradiation, by maintaining normal plant growth, stabilizing cell membranes and activating non-enzymatic antioxidants.

Influence of cytokinins and novel cytokinin antagonists on the senescence of detached leaves of Arabidopsis thaliana

Cytokinins N6-benzyladenine (BA) and 1-(2-chloropyridin-4-yl)-3-phenylurea (4PU-30) delayed the senescence of detached leaves (3rd to 7th leaf node) of wild and ethylene insensitive eti5 mutant of Arabidopsis thaliana. The novel anticytokinins, structural analogues of purine and phenylurea cytokinins also affected the senescence of detached rosette leaves of A. thaliana. They diminished to a significant extent the cytokinin-induced delay of chlorophyll destruction, but without a considerable difference in their action against both types of cytokinins. These results correlated with changes observed in ribonuclease (RNase) activity.

\Cytokinin oxidase/dehydrogenase (CKX) activity in wild and ethylene-insensitive mutant eti5 type of Arabidopsis thaliana (L.) Heynh plants and the effect of cytokinin N1-(2-chloro-4-pyridyl)-N2-phenylurea on enzymatic activity and leaf morphology

The specific activity of cytokinin oxidase/dehydrogenase (EC 1.5.99.12) (CKX) was determined in leaves of wild type (wt) and ethylene-insensitive mutant (eti5) of Arabidopsis thaliana (L.) Heynh plants. Comparative studies showed that this mutation has lower basal CKX activity than wt. Application of 4PU-30 (N1-(2-chloro-4-pyridyl)-N2-phenylurea) resulted in decreased CKX activity in both wt and mutant plants. The treatment increased leaf blade thickness and the volume of chlorophyll-containing cells per unit leaf area in wt but these changes were not observed in the eti5 mutant. The reduction in chlorophyll “a” and “b”, as well as in carotenoids content in the treated wt tissues resulting from altered leaf morphology was not detected in eti5 plants.

Effect of temperature stress on the endogenous cytokinin content in Arabidopsis thaliana (L.) Heynh plants

The levels of three endogenous cytokinin equivalents: zeatin (Z), iso-pentenyladenine (iP) and dihydrozeatin (dZ) in two Arabidopsis thaliana (L.) Heynh genotypes — wild type (wt) and ethylene-insensitive mutant (eti5), were compared using enzyme immunoassay (ELISA). Cytokinin content was measured after exposure to low (4 °C for 24 h in darkness) or high temperature (38 °C for 24 h in darkness). Measurements were performed immediately and 24, 48 and 120 h after treatments. It was found that at normal growth conditions eti5 plants contained more endogenous cytokinins compared to the wild type. At both temperature treatments mutant plants had decreased total cytokinin levels. Wild-type plants treated with high temperature (HT) exhibited reduced total cytokinins (with the exception of rates at 48 h), while low temperature (LT) treatment resulted in elevated total amount of the studied equivalents (except at 24 h). The obtained results suggested that HT had greater effect on cytokinin levels than LT since it caused more profound changes in the total content. We assume that this was due to the natural chilling tolerance of Arabidopsis plants.

Rosette Leaf Senescence in Wild Type and an Ethylene-Insensitive Mutant of Arabidopsis thaliana during Inflorescence and Fruit Development

Senescence is an important developmental process in plants, which eventually leads to whole plant, organ, tissue and cell death through highly regulated, endogenously controlled degenerative processes (Chandlee, 2001). Leaf senescence is a key developmental step in the life of an annual plant, as it is the time during which material built up by the plant during its growth phase is mobilized into the developing seed to prepare for the next generation (Smart, 1994; Smart et al., 1995). Obvious visual symptoms for leaf senescence are the loss of chlorophyll pigments, desiccation and eventual abscission. Cellular and molecular events contributing to these visual symptoms include chloroplast disintegration, a decline in photosynthesis and damages of proteins and nucleic acids. Other internal symptoms of senescence are loss in the ability to accumulate protein and nucleic acids because of enhanced degradation and/or diminution of synthesis, and loss of plasma membrane and endomembrane structure with associated increases in permeability to inorganic and organic solutes, as well as an increase in the levels of active oxygen species, the later forming organic free radicals (Smart, 1994; Buchanan-Wollaston, 1997). The free radicals impose a significant impact for the deterioration of cell constituents during plant senescence. They are highly reactive, self-propagating, potentially damaging, and are also formed during the normal metabolic processes. Their effective removal is of importance for the well-being of the plant organisms (Fridovich, 1976). One of the mechanisms by which plants defend against free radical mediated damage is the induction of the superoxide dismutase (SOD). Peroxidase and catalase then breakdown the formed hydrogen peroxide, and thus prevent the further formation of potent free radicals (Dhindsa et al., 1981).