Iskren Sergiev

Cytokinin and Anticytokinin Effects on Growth and Free Polyamine Content in Etiolated and Green Radish Cotyledons

Summary The effects of high active cytokinins (kinetin and 4-PU-30) and their structurally related antagonists, 4-cyclopentyl-amino-2-methylthiopyrrolo[2,3-d]pyrimidine (CPP) and N-(4-pyridyl)-0-(4-chlorophenyl)-carbamate (PC), on growth and free polyamine content of green and etiolated radish ( Raphanus sativa L.) cotyledons were studied. Both cytokinins expressed strong stimulating activity, but subsequent application of the anticytokinins partly removed kinetin and 4-PU-30 action. The effects observed were found to be stronger when structural analogy between cytokinin and antagonist existed.

Synthesis and Plant Growth Regulating Activity of New Triazolo- and Pyrazolopyrimidine Derivatives Of Aminomethyl, Aminoalkyloxymethyl Dimethylphosphine Oxides and (Aminomethane)Phosphonic Acid Esters

Abstract New triazolo[4,5-d]pyrimidine and pyrazolo[3,4-d]pyrimidine derivatives of aminomethyl-and aminomethyloxymethyl dimethylphosphine oxides 8–14 as well as of esters of (aminomethane) phosphonic acid 18–20 were synthesized. The structure of the compounds prepared was confirmed by means of elemend analysis, IR, 1H- and 31P(1H)-NMR spectroscopy. Tertiary phosphine oxides 8, 9 and 12 as well as phosphonate 20 showed herbicidal and plant growth regulating activity.

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.

Novel Physiological Properties of Two Cytokinin Antagonists

Summary The promotive effect of two cytokinin antagonists 2-chloro-4-cyclobutyl-amino-6-ethylamino-1,3,5-triazine and N-(4-pyridyl)-O-(4-chlorophenyl) carbamate on somatic embryos production directly or through callus in leaf explants of the grass Dactylis glomerata L. (orchardgrass) was established. The data for the endogenous contents of hydrogen peroxide and lipid peroxidation products during the earliest stages of somatic embryogenesis suggest that anticytokinins induce some alterations in the production of active oxygen species. Both compounds activated the defence enzymes 5 days after culture initiation. The triazine derivative enhanced catalase activity in more differentiated leaf segments while the phenyl ureatype anticytokinin had the same effect on peroxidase activity. Additional activation of catalase and slight reduction of peroxidase activity were determined in 10-day-old cultures. During induction of somatic embryogenesis in Dactylis leaf explants the main difference in the physiological action of the cytokinin antagonists tested was related to IAA-oxidase activity. A possible role of the anti cytokinin-induced changes in cell oxidative status on the explant embryogenic response is discussed.

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.

Antagonistic effects of triazolo[4,5-d]pyrimidine and pyridylurea derivatives on cytokinin-induced cytokinin oxidase/dehydrogenase activity in young pea plants

The effect of strong and weak cytokinin antagonists, belonging to the groups of triazolo[4,5-d]pyrimidines (TP), and pyridyl-phenylurea derivatives (PU), on cytokinin oxidase/dehydrogenase activity (CKX) in the tissues of young pea plants was studied. Tested anticytokinins, with the exception of the most efficient one – PU-1, were able to promote increased CKX activity in roots, when applied alone, but they had no significant influence on the enzymatic activity in leaves. N6-benzyladenine (BA) and 1-(2-chloropyridin-4-yl)-3-phenylurea (CPPU) provoked strong increase in CKX activity in roots, while in leaves considerable inhibition of enzymatic activity was observed. Different types of anticytokinins exhibited diverse preference towards taking off the action of purine and phenylurea cytokinins over CKX activity.

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).