Aglika Edreva

Oxidative stress and some antioxidant systems in acid rain-treated bean plants Protective role of exogenous polyamines

The effect of simulated acid rain (AR) (pH 1.8) on H2O2 and malonyldialdehyde (MDA) levels and activities of peroxidase and catalase in bean plants were investigated. The influence of exogenous polyamines spermidine and spermine on these parameters was also studied. AR treatment induced lipid peroxidation and increased level of H2O2 in leaves. Pretreatment with spermidine and spermine prevented these changes. The protective effect of spermine was higher than that of spermidine. The impact of polyamines could be attributed to their acid neutralizing and antioxidant effects, as well as to their ability to stabilize membranes by associating with negatively charged phospholipids. It was also found that AR significantly increased peroxidase and decreased catalase activities at the first hours after treatment. Later, both enzyme activities were enhanced that could contribute to the scavenging and detoxification of active oxygen species.

Phenylamides in plants

Phenylamides, secondary metabolites, conjugates of aliphatic polyamines or arylmonoamines and hydroxycinnamic acids, combining the properties of both parent compounds, are a subject of increasing interest, as follows from their ubiquitous distribution and multiplicity of functions. In this paper the occurrence, distribution, localization, metabolism, as well as chemical structure and properties of phenylamides underlying their physiological functions are briefly reviewed, with an emphasis on their involvement in the developmental and stress-defense phenomena of plants. Basic knowledge on phenylamides is supplemented with recent data pointing to the structural similarity of plant phenylamides with those found in insect toxins. This finding challenges the view of phenylamides as plant-specific molecules and suggests their role as a common defense tool in various organisms.

Isoprene prevents the negative consequences of high temperature stress in Platanus orientalis leaves

The phenomenon of enhanced plant thermotolerance by isoprene was studied in leaves of the same age of 1- or 2-year-old Platanus orientalis plants. Our goals were to determine whether the isoprene emission depends on the age of the plant, and whether different emission rates can influence heat resistance in plants of different age. Two-year-old plants emit greater amounts of isoprene and possess better capacity to cope with heat stress than 1-year-old plants. After a high temperature treatment (38°C for 4 h), photosynthetic activity, hydrogen peroxide content, lipid peroxidation and antiradical activity were preserved in isoprene emitting leaves of 1- and 2-year-old plants. However, heat inhibited photosynthesis and PSII efficiency, caused accumulation of H2O2, and increased all indices of membrane damage and antioxidant capacity in leaves of plants of both ages in which isoprene was inhibited by fosmidomycin. In isoprene-inhibited leaves fumigated with exogenous isoprene during the heat treatment, the negative effects on photosynthetic capacity were reduced. These results further support the notion that isoprene plays an important role in protecting photosynthesis against damage at high temperature. It is suggested that isoprene is an important compound of the non-enzymatic defence of plants against thermal stress, possibly contributing to scavenging of reactive oxygen species (ROS) and membrane stabilising capacity, especially in developed plants.

Effect of water deficit and potassium fertilization on photosynthetic activity in cotton plants

Abstract Physiological mechanisms that can contribute to drought tolerance and the role of potassium fertilization in cotton were studied by evaluation of parameters describing photosynthetic performance. Gas-exchange and chlorophyll fluorescence characteristics were measured on leaves of two cotton genotypes, one drought sensitive (Nazilli 84-S) and the other drought tolerant (Sahin 2000), grown in field conditions in the Aegean region of Turkey under different regimes of water and potassium supply. It was shown that under drought conditions without potassium fertilization Sahin 2000 had a higher photosynthetic rate and stomatal conductance than Nazilli 84-S. Potassium fertilization to a great extent compensated for the inhibitory effect of drought on photosynthesis. Application of the JIP test by using chlorophyll fluorescence data revealed that the drought sensitive Nazilli 84-S was more responsive to potassium fertilization than Sahin 2000, as judged by a number of parameters representing quantum efficiency of the processes and energy fluxes in photosystem (PS) II. The observed decrease in photosynthetic CO2 assimilation in both cotton cultivars under drought conditions was not accompanied by any significant decrease in the electron transport flux in PSII and maximum quantum yield of primary photochemistry.

Tobacco polyamines as affected by stresses induced by different pathogens

A decrease of the polyamine content of tobacco leaves inoculated with fungal, bacterial and viral pathogens differing in symptom severity (mosaic, chlorosis, necrosis) was observed. The extent of the decrease was not related to the type of pathogens but to the severity of damage symptoms; hence, the polyamine decline may be regarded as a common response of tobacco to damage produced by pathogens.

Heat shock responses of bean plants: involvement of free radicals, antioxidants and free radical/active oxygen scavenging systems

In non-acclimated bean plants heat shock induced oxidative damage (increase of free radical concentration and drop of bound thiols, indicating aggregation of proteins) which was regulated by the enhanced activities of peroxidase and superoxide dismutase, as well as by the accumulation of polyphenols and especially of polyamines. In the plants acclimated to high temperature no oxidative damage occurred following heat shock.

Pathogenic and non-pathogenic stress effects on peroxidases in leaves of tobacco

Abstract The effects of stress stimuli of different sources, including pathogenic (fungi, bacteria, viruses), non-pathogenic (excess of water and manganese, γ-irradiation), as well as senescence, were examined in tobacco leaves. Some of these stimuli produced damage symptoms that differed in severity, whereas others did not produce visible damage symptoms. The activity, molecular heterogeneity, and localization of peroxidases (PO; E.C.1.11.1.7) in tobacco leaf tissues as influenced by stress stimuli were studied, using both biochemical and cytochemical approaches. Chlorophyll and lipid peroxide contents were also determined as related to tissue and cell membrane damage. All stress stimuli and senescene triggered an increase in PO activity. In tobacco-fungi interactions, this increase was a plant response to infection and not a contribution of the hyphal PO per se . The PO increases under stress conditions that caused visible tissue damage symptoms were concomitant with chlorophyll loss. The severity of damage corresponded to the rate of PO increase and chlorophyll loss. Under all stress conditions, increases in PO were accompanied by increased lipid peroxidation, resulting in damage to cell membranes. Thus, the responses of PO in tobacco leaves to various stress situations were shown not to depend on the origin of stress stimuli, but on the presence and degree of damage, suggesting a possible involvement of endogenous cell wall elicitors.

Reddening of Cotton (Gossypium Hirsutum L.) Leaves

Reddening of leaves is a physiological disorder in cotton induced by different abiotic stresses. Dramatic biochemical changes occurred in reddening leaves: strong accumulation of anthocyanins and drop of chlorophyll content, important increase of proline content and peroxidase activity. The lipid peroxide content indicative of membrane fragmentation was decreased. In this way a multicomponent system encompassing anthocyanins, proline, and peroxidase may act coordinately to overcome abiotic stress in cotton.

Singlet Oxygen Quenching by Phenylamides and their Parent Compounds

This paper demonstrates for the first time that plant metabolites of the phenylamide type, conjugates of putrescine with hydroxycinnamic acids (p-coumaric, caffeic and ferulic), possess 1O2 quenching properties. Data were obtained confirming that their acidic parent compounds were also able to quench 1O2, as did polyamines (putrescine, spermidine and spermine), and that this ability depends on the number of amino groups. Potentiation of the 1O2 quenching ability of the conjugates relative to both parent components was established. The importance of polyamines and phenylamides in the plant non-enzymatic antioxidant defence at sites of intensive 1O2 generation, such as the photosynthetic centers, was suggested.

Metabolic changes in tomato fruits and seeds after viral, bacterial and fungal infections

The metabolic changes in tomato fruits and seeds separately infected with cucumber mosaic virus, Pseudomonas syringae pv. tomato or Botrytis cinerea were investigated cytochemically. The changes of peroxidase (E.C. 1.11.1.7) and β-glucosidase (E.C. 3.2.1.21) were investigated biochemically as well. Tomato fruits were involved in the study because of their high economic value. Tomato seeds were investigated since they have been used most extensively as a model system for studying the physiology and biochemistry of seed development. The diseases caused by the pathogens under study are of special importance for yield reduction in tomato. The three pathogens provoked local changes in the activities of enzymes under study that affect the infected pericarp tissues and neighboring seeds. It was established non-specific and specific responses. The non-specific responses of invaded tissues were expressed as a local enhancement of peroxidase activity in both pericarp tissues and seeds as well as a decrease in activities of: i. enzymes taking part in aerobic and anaerobic respiration, ii. hydrolases esterase and acid phosphatase involved in the basic metabolism as well as an enhancement of their activities in neighboring tissues. Furthermore, it was observed an enhancement of α-galactosidase activity in infected area was observed. The specific responses depending on the type of the pathogen consisted in an enhancement of glucose-6-phosphate dehydrogenase activity by virus infection and an increase of β-glucosidase activity by fungal invasion.