Zornitsa Katerova

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.

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.

Glutathione and Herbicide Resistance in Plants

Pesticide use is inseparable part of food production. The efficacy of modern agriculture is quite dependent on the chemicals used to fight with pests, including weeds, fungi and insects. Herbicides are chemicals which destroy weeds. According to their mode of action herbicides are divided on 24 groups (Herbicide Resistance Action Committee). The balance between toxicity on weeds and resistance of crops defines herbicide selectivity. Herbicide tolerance depends on the plants variety, development phase, climate, mode of action, dose and the way plants were treated with herbicides. Glutathione is one of the major defense substances of plants. It takes part in many detoxifying mechanisms, like active oxygen species reducing, and also regulates cell defense systems. Glutathione has key role in detoxifying of toxic xenobiotics, including herbicides. In some crops the resistance against herbicides is due to its direct detoxification by forming conjugates with glutathione. The process can be catalyzed by the enzyme glutathione S-transferase. After their forming, conjugates can be metabolized and excreted or can be stored in vacuoles and dead tissues. Many herbicides, such as atrazine, paraquat, etc., induce oxidative events in plant cell. Glutathione takes part in detoxifying active oxygen species and this is a way for indirect enhancement of plant resistance against herbicides. In the current review the mode of action of herbicides inducing oxidative stress will be discussed. Examples of plant antioxidant system response against herbicide action will be presented. The role of glutathione in direct and indirect detoxification of herbicides and increase of plants sustainability will be deeply reviewed.

Auxin-like compounds act as protectors against UV-B irradiation in garden pea plants

Abstract Pretreatment with the original auxin physiological analogues 1-[2-chloroethoxycarbonylmethyl]-4-naphthalenesulfonic acid calcium salt (TA-12) and 1-[2-dimethylaminoethoxicarbonylmethyl]naphthalene chlormethylate (TA-14) and subsequent UV-B irradiation (180 min at λmax 312 nm for 6.6 kJ·m−2) of pea plants (Pisum sativum L.) was investigated to assess if foliar application of these compounds has ability to attenuate the negative effects caused by UV-B stress. UV-B treatment increased malondialdehyde (MDA) and proline levels as well as superoxide dismutase, catalase and guaiacol peroxidase activities, but decreased hydrogen peroxide, low-molecular thiols, total phenolics and total soluble protein contents. The pre-treatment with TA compounds decreased the oxidative stress provoked by UV-B radiation detected by lower level of MDA, increased the content of thiols and UV-absorbing compounds and had favourable effect on H2O2 content and enzymatic activities. Exogenous application of auxin-like compounds on pea plantlets successfully counteracted UV-B induced oxidative stress via activation of ROS detoxifying enzymes and non-enzymatic antioxidants.

Plant Secondary Metabolites and Some Plant Growth Regulators Elicited by UV Irradiation, Light And/Or Shade

Classification of plant secondary metabolites and characterization of major plant growth regulators are shortly described. A short account is also given to light, shade and ultraviolet radiation and their impact on plants. Recent investigations regarding secondary metabolite production and alterations in endogenous level of plant growth regulators in medicinal plants grown under light, shade or UV radiation are reviewed and discussed. Some conclusions and future perspectives to enlarge the investigations in this direction are also given.