Effect of salicylic acid during heavy metal stress

The effect of salicylic acid (SA) on Cd-induced stress was investigated in young maize (hybrid Norma) plants. When SA and Cd were applied simultaneously, the damage was less pronounced than without SA. However, SA treatment itself also caused oxidative stress and damage to the root system, and inhibited the phytochelatin synthase enzyme, so when the SA treatment was used before the Cd stress, it accelerated the damaging effect

Changes in salicylic acid and polyamine contents following powdery mildew infection of near-isogenic Thatcher-based wheat lines carrying different Lr genes

Changes in endogenous salicylic acid and polyamine contents were investigated following infection with powdery mildew in four near-isogenic Thatcher-based wheat lines. Although the infection could not affect the quantum efficiency of photosystem 2 after 7 days in the investigated genotypes, significant changes were observed in the levels of salicylic acid and polyamines of inoculated plants. Powdery mildew infection caused decrease in salicylic acid content after 3 days, but on the 7th day of infection increased it significantly in line carrying Lr33 gene. Infection also increased the salicylic acid content after 7 days in line carrying Lr19 gene, while the other genotypes were hardly affected. Infection increased the levels of cadaverine, spermidine and spermine in the free form, as well as the levels of spermidine and spermine in the conjugated form. Infection could not affect either of the polyamines associated with various macromolecules (bound form). It was concluded that although salicylic acid and polyamines have important role in plant responses and defence mechanisms during biotic stress, there is no correlation between pathogen induced changes in the levels of them and the level of tolerance to powdery mildew of the investigated four wheat lines

Drought stress and polyamines in maize

Drought is one of the most common environmental stresses that affect growth, development and in turn yield of crop plants. Thus, understanding of plant responses to drought and investigations on compounds capable of reducing the stress sensitivity of plants are of great importance and crucial to progress in genetic engineering and/or conventional breeding. Polyamines (PAs), which are small, positively charged, aliphatic amines found in all plant cells, are able to bind to negatively charged molecules, e.g. nucleic acids, acidic phospholipids and various types of proteins, thus having a protective role under stress conditions. Results of several studies suggested that PAs can be promising compounds for the reduction of abiotic stress sensitivity in plants, since both seed priming and adding PAs to the hydroponic solution have been shown to protect various plant species against abiotic stress factors. Many reports have indicated that the stress tolerance of plants is correlated with their capacity to enhance the synthesis of PAs upon exposure to stress. In addition, mutant and transgenic Arabidopsis plants with altered PAs synthesis pointed to involvement of PAs in different abiotic and biotic stresses responses and have elucidated their key functions in stress signaling networks in plants; however the exact mechanism remains enigmatic. The main questions of the present study are: 1. how influence PA treatment PEG-induced drought stress in maize? 2. is the statement: “the more PAs, the better” true in this case? 3. if not, what are the reasons

Speculation: Polyamines are important in abiotic stress signaling

The main role of polyamines was originally assumed to be as direct protective compounds important under stress conditions. Although in some cases a correlation was found between the endogenous polyamine content and stress tolerance, this relationship cannot be generalized. Polyamines should no longer be considered simply as protective molecules, but rather as compounds that are involved in a complex signaling system and have a key role in the regulation of stress tolerance. The major links in polyamine signaling may be H2O2 and NO, which are not only produced in the course of the polyamine metabolism, but also transmit signals that influence gene expression via an increase in the cytoplasmic Ca2+ level. Polyamines can also influence Ca2+ influx independently of the H2O2- and/or NOmediated pathways. Furthermore, these pathways may converge. In addition, several protein kinases have been shown to be influenced at the transcriptional or post-translational level by polyamines. Individual polyamines can be converted into each other in the polyamine cycle. In addition, their metabolism is linked with other hormones or signaling molecules. However, as individual polyamines trigger different transcriptional responses, other mechanisms and the existence of polyamine-responsive elements and the corresponding transacting protein factors are also involved in polyamine-related signaling pathways

Abscisic acid may alter the salicylic acid-related abiotic stress response in maize

The effect of abscisic acid (ABA) treatment on chilling tolerance and salicylic acid (SA)-related responseswas investigated in young maize seedlings. Although the pre-treatment of plants with ABA slightly decreased the chlorophyll content, it also reduced the level of chilling injury caused by 6 days of cold treatment at 5 ̊C. Under normal growth conditions increased levels of bound SA and of bound ortho-hydroxycinnamic acid (oHCA) were observed in the leaves during ABA treatment. In the roots ABA did not affect the free and bound SA levels, but increased the amount of free and bound oHCA. The activity of glutathione-S-transferase (GST) increased on the 3rd day of ABA treatment, while it did not change when followed by cold stress, compared to the control leaves. In the roots the activities of glutathione reductase, GST and ascorbate peroxidase (APX) increased during the ABA treatment, and those of GST and APX were also stimulated when ABA pre-treatment was followed by cold stress, compared to the control roots. Our results suggest that an overlap may exist between the ABA-induced cold acclimation and the SA-related stress response

Alacsony hőmérsékleti stressztolerancia és antioxidáns aktivitás közti kapcsolat vizsgálata gabonaféléknél = Investigation of the connection between tolerance to low temperature stress and antioxidant activity in cereals

A kutatási munka célja a gabonafélék stressztűrő képességének kialakításában szerepet játszó szabályozási folyamatok jobb megismerése volt, különös tekintettel a reaktív oxigénformák mennyiségének szabályozását végző antioxidáns rendszerekre. Több gazdasági növény, elsősorban kukorica és búza esetében jellemeztük az antioxidáns enzimrendszerek hozzájárulását abiotikus stresszfaktorok elleni védelemben. Kimutattuk, hogy a különböző gabonafajok eltérő stratégiákat dolgoztak ki a reaktív oxigénformák mennyiségének szabályozásához. Igazoltuk a fény szerepét a búza maximális fagyállóságának kialakulásában. Ehhez kapcsolódóan bemutattuk a ciklikus elektrontranszportlánc, egyes antioxidánsok, a szalicilsav-metabolizmus, valamint a membránlipidek alakulását eltérő fényviszonyok melletti alacsony hőmérsékleti edzés során. Eredményeink azt mutatják, hogy a szalicilsavfüggő jelátviteli utak szerepének tanulmányozásakor nemcsak magára a szalicilsavra, hanem egyes prekurzorainak a változásaira is figyelemmel kell lenni. Mindemellett bizonyítottuk, hogy intakt levelekben az egy elektronátmenetet megengedő fényfelvillanás általi gerjesztés egy összetett termolumineszcencia sávot eredményez, melynek magasabb hőmérsékleti (40 °C körüli) komponense egy AG-sáv. Jellemeztük az AG termolumineszcencia sávot, és bemutattuk alkalmazását gazdasági növények stressztűrő képességének vizsgálatában. | The research aimed to obtain a better insight into the regulatory processes involved in the development of stress tolerance in cereals, with special regard to antioxidant systems that regulate the quantity of reactive oxygen species (ROS). The contribution of antioxidant enzyme systems to defence against abiotic stress factors was investigated in several crops, particularly maize and wheat. Different cereal species were found to have elaborated diverse strategies for the regulation of ROS quantities. Light was proved to play a role in the achievement of maximum frost resistance in wheat. In this connection, changes occurring in the cyclic electron transport chain, in various antioxidants, in the salicylic acid metabolism and in membrane lipids during low temperature hardening were investigated under varying light conditions. It was found that when studying the role of salicylic acid-dependent signal transduction pathways it is important to consider not only salicylic acid itself, but also changes in its precursors. In addition it was demonstrated that in intact leaves a single turnover flash resulted in a complex thermoluminescence band, the high temperature (~ 40°C) component of which is an AG band. The latter was analysed, and its application in determining the stress tolerance of crops was discussed

Impact of UV-B on drought- or cadmium-induced changes in the fatty acid composition of membrane lipid fractions in wheat

UV-B radiation may have either a positive or negative impact under the same conditions in wheat, depending on the type of secondary abiotic stressor: Cd or drought. Supplemental UV-B prevented the wilting and leaf rolling induced by PEG treatment. In contrast, combined UV-B and Cd treatment resulted in pronounced oxidative stress. The opposite effect of UV-B radiation in the case of drought or cadmium stress may be related to the alteration induced in the fatty acid composition. UV-B caused changes in the unsaturation of leaf phosphatidylglycerol fractions, and the accumulation of flavonoid in the leaves may prevent the stress induced by subsequent drought treatment. However it resulted in pronounced injury despite the increased flavonoid content in roots exposed to Cd. This was manifested in a drastic decrease in the unsaturation of the leaf monogalactosyldiacylglycerol and the root phosphatidylglycerol and digalactosyldiacylglycerol fractions. Data on the flavonoid content and fatty acid composition showed that oxidative stress was induced by drought in the leaves, by Cd in the roots, and interestingly, by UV-B radiation in both the leaves and roots. The additive effect of the combined stresses was also detected in the roots. The results presented here suggest a relationship between the capacity of the plant to remodel the fatty acid composition and its resistance to various stress factors

Salicylic acid and photosynthesis : signalling and effects

Salicylic acid (SA) is a well-known signalling molecule playing a role in local and systemic acquired resistance against pathogens as well as in acclimation to certain abiotic stressors. As a stress-related signalling compound, it may directly or indirectly affect various physiological processes, including photosynthesis. The effects of exogenously applied SA on plant physiological processes under optimal environmental conditions are controversial. Several studies suggest that SA may have a positive effect on germination or plant growth in various plant species. However, SA may also act as a stress factor, having a negative influence on various physiological processes. Its mode of action depends greatly on several factors, such as the plant species, the environmental conditions (light, temperature, etc.) and the concentration. Exogenous SA may also alleviate the damaging effects of various stress factors, and this protection may also be manifested as higher photosynthetic capacity. Unfavourable environmental conditions have also been shown to increase the endogenous SA level in plants. Recent results strongly suggest that controlled SA levels are important in plants for optimal photosynthetic performance and for acclimation to changing environmental stimuli. The present review discusses the effects of exogenous and endogenous SA on the photosynthetic processes under optimal and stress conditions

Interactions between plant hormones and thiol-related heavy metal chelators

Upon toxic metal stress numerous defence mechanisms have been induced, including the synthesis of metal-binding ligands and plant hormones or plant growth regulators in plants. As several elements in the promoter region of the heavy metal-responsive genes can be activated by plant hormones and growth regulators, understanding and revealing possible and special relationships between these regulator compounds and the metal chelator phytochelatins, which are in the first line of heavy metal defence mechanism is of great important. Phytochelatins are synthetized from glutathione and have a structure of [(-Glu-Cys)n]-Gly, where n is the number of repetition of the (-Glu-Cys) units. Evidences for the role of PCs in heavy metal tolerance are very strong; however, little information is available on how plant growth regulators influence the phytochelatin synthesis at molecular or even gene expression level. In the present review we provide an overview of the role and synthesis of phytochelatins in metal-tolerance mechanism from a new point of view, i.e. their relation to the plant growth regulator molecules, with special regard also on those cases, when close direct relationship exists because of the partly overlapped synthesis pathways of plant growth regulators and glutathione/phytochelatins