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Changes in phenolics (PhC) measured as UV-absorbing compounds (UVAC) and their localization as well as growth, lipid peroxidation (TBARS level), H(2)O(2) and Cu accumulation and other ions content in roots of two lentil cultivars (cv. Krak and cv. Tina) contrasting in Cu sensitivity were examined. The aim of this study was to reveal the importance of PhC in Cu tolerance. During Cu treatment, inhibition of growth and increases in lipid peroxidation in roots of both cultivars were observed, but the effects were more pronounced in cv. Tina (more sensitive) than in cv. Krak (less sensitive). Cu at 0.5 mM caused higher Cu and H(2)O(2) accumulation, but lower K(+) content and UVAC levels in the root tips of cv. Tina. Opposite changes were recorded in cv. Krak. Fluorescence microscopic analyses confirmed greater PhC accumulation in cv. Krak (less sensitive) than in cv. Tina (more sensitive) after Cu treatment and showed that these compounds accumulated particularly in vacuoles and the cell wall. Taken together, these results show that, in spite of the high concentration of Cu-stimulated PhC accumulation in cv. Krak, it was not sufficient to counteract the amount of ROS generated by the metal. The role of PhC in different reactions to Cu stress in lentil roots is discussed.

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The relationship between germination and melatonin applied during osmo- and hydropriming was studied in cucumber seeds. The proportion of nuclei with different DNA contents, the mean ploidy and the (2C + 4C = 8C)/2C ratio in unprimed and primed, dry and imbibed at 10 degrees C seeds were established by flow cytometry. Thiobarbituric acid reactive substances and protein oxidation were also estimated. Melatonin and indole-3-acetic acid (IAA) concentrations in the seeds were determined using high-performance liquid chromatography with electrochemical detection. Being sensitive to chilling stress, seeds that germinated well (99%) at 25 degrees C showed only 30% germination at 15 degrees C, and almost no germination (4%) at 10 degrees C. Hydropriming in water improved seed germination to 50-60% at 15 degrees C and the addition of melatonin (25-100 M) also increased the rate of germination. Osmopriming in polyethylene glycol increased germination at 15 degrees C to 78%, and 98% when combined with 50 M melatonin. Osmoprimed seeds germinated even at 10 degrees C and reached 43%, and 83% when 50 M melatonin was applied. None of the treatments induced DNA synthesis, although during the first 24 hr of imbibition at 10 degrees C the mean ploidy and the (2C + 4C = 8C)/2C ratio increased, which is indicative of the advanced Phase II of germination. Hydro- and osmopriming slightly decreased IAA content in the seeds in most of the cases; only hydropriming with 100 and 500 M melatonin increased it. Melatonin protected membrane structure against peroxidation during chilling, but excessive melatonin levels in cucumber seeds (approximately 4 microg/g fresh weight) provoked oxidative changes in proteins. There is still lack of information explained clearly the role of melatonin in plant physiology. This molecule acts multidirectionally and usually is alliged to other compounds.

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The phenolics: anthocyanin (ATH), sinapoyl esters and activity of antioxidant enzymes: superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POX), ascorbate peroxidase (APX), glutathione peroxidase (GPX) and glutathione reductase (GR), in red cabbage seedlings subjected to Cu2+ stress were investigated. Cu2+ at low doses (0.5 mM), increased the levels of ATH and sinapoyl derivatives in red cabbage. High Cu2+ concentration (2.5 mM) provoked oxidative stress and enhanced thiobarbituric acid reactive substances (TBARS) content in tissues. A lower level of TBARS was correlated with high ATH content. It seems that synthesis of these isoflavonoids is an effective strategy against reactive oxygen species (ROS). The analysis of the antioxidant enzymes activity suggested that peroxidases were the most active enzymes in red cabbage seedlings exposed to Cu2+ stress. It could results from the fact that phenolic compounds (PhC), which could be also substrates for different peroxidases, were the first line of defence against metal stress.

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L(-)-, and D(+)-enantiomers of 1-amino-2-phenylethylphosphonic acid (PheP), a phosphonic analogue of phenylalanine, inhibit the activity of L-phenylalanine ammonia-lyase (EC 4.3.1.5) of potato tuber tissue in vitro. The apparent type of inhibition depends on concentration of PheP; as the concentration of D-PheP is raised from 10(-5) M to 2.5 X 10(-3) M, the type of inhibition shifts from competitive through mixed and non-competitive to uncompetitive. L-PheP exerts either a competitive or mixed-type inhibition at low (10(-6)-10(-5) M) or moderate (5 X 10(-5)-2 X 10(-4) M) concentration. Ki for the concentration range of competitive inhibition were 6.5 X 10(-6) M, 5.3 X 10(-5)M and 1.6 X 10(-5) M for L-, D-, and D,L-PheP, respectively. These Ki values are valid for a relatively narrow range of L-Phe concentration (0.2-4 mM) as L-phenylalanine ammonia-lyase does not follow the Michaelis-Menten kinetics of the reaction.

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