Book of Abstracts

A widespread occurrence of melatonin (MEL) in plant kingdom has been reported. MEL is a highly conserved molecule occurring in evolutionary distant organisms. Its role in plants seems to be similar to that in animals. Although MEL function in plants is not well known, yet a hypothesis can be put forward that it probably functions as a night signal, coordinating responses to diurnal and photoperiodic environmental cues. It has also been suggested that MEL is an independent plant growth regulator, probably its action is analogous to IAA and it may mediate the actions of other plant growth regulators. Due to its antioxidant properties MEL may also stabilize cell red-ox status and protect them against reactive oxygen species (ROS) and other harmful environmental influence.     

Moringa oleifera Extract as a Natural Plant Biostimulant

Moringa, belonging to Moringaceae, is known as the “Miracle Tree” that has versatile uses in both animals and plants. The extract from Moringa oliefera serves as a cheap, eco-friendly, novel biostimulator, and bioenhancer that increases sustainable agriculture practices and crop production. Moringa contains several essential components like mineral nutrients, phytohormones (e.g., auxins, gibberellins, and cytokinins), vitamins, flavonols, phenols, sterols, and tannins, as well as several phytochemicals that make it highly beneficial for plants. It induces seed germination, plant growth, photosynthesis, and yields traits at a low cost. It also increases flowering, improves floral traits, fruiting, post-harvesting, and product quality of the fruit, and decreases senescence. Abiotic stresses have a detrimental effect on plant growth and development. The application of Moringa extracts on plants mitigates abiotic stress like salinity, drought, heavy metal, and heat by promoting the activity of antioxidant enzymes and increasing the content of phenols, flavonols, sugars, and osmolyte, which reduces the level of reactive oxygen species, lipid peroxidation, and electrolyte leakage. In particular, Moringa accelerates plant growth, relative water content, water use efficiency, mineral content, gas exchange traits, and yield attributes under stressful environmental conditions. Moringa serves as an essential biopesticide against plant pathogens, and is used in disease management and plant sustenance.

     

Dualities in plant tolerance to pollutants and their uptake and translocation to the upper plant parts

There is a duality in plant tolerance to pollutants and its response to the pollutants’ stress.On the one hand some plants, (hyper)tolerant to heavy metals, are able to hyperaccumulate these metals in shoots, which could be beneficial for phytoremediation purposes to clean-up soil and water. On the other hand tolerant food crops, exposed to heavy metals in their growth medium, may be dangerous as carriers of toxic metals in the food chain leading to food toxicity. There is an additional duality in plant tolerance to heavy metals and that is in food crops that are tolerant and/or hyperaccumulators, which could be used on one hand for phytoremediation, under controlled conditions and on the other hand for food fortification with essential metals.Similarly, plants are also exposed to a large number of xenobiotic organic pollutants. Because they generally cannot avoid these compounds, plants take up, translocate, metabolize and detoxify many of them. There is a large variability in tolerance (defence) mechanisms against organic pollutants among plant species. This includes production of reductants but also scavenger molecules like ascorbate and glutathione and expression of the P-450 defence system, and superfamilies of the enzymes glutathione- and glucosyl-transferases. Again, with view to organic pollutants, plant detoxification mechanisms might well protect the plant itself, but produce compounds with some deleterious potential for other organisms.In this review we discuss these dualities on the basis of examples of agricultural and ‘wild’ species exposed to metal contaminants (mainly Cd) and organic pollutants. Differences in uptake and translocation of various pollutants and their consequences will be considered. We will separately outline the effects of the organic and non-organic pollutants on the internal metabolism and the detoxification mechanisms and try to indicate the differences between both types of pollutants. Finally the consequences and solutions of these dualities in plant tolerance to pollutants will be discussed.     

Antioxidant and anti-inflammatory properties of tomato fruits synthesizing different amounts of stilbenes

Resveratrol, a plant phenolic compound, is found in grapes and red wine, but is not widely distributed in other common food sources. The pathway for resveratrol biosynthesis is well characterized. Metabolic engineering of this compound has been achieved in tomato plants ( Lycopersicon esculentum Mill.) in order to improve their nutritional value. Tomato plants synthesizing resveratrol were obtained via the heterologous expression of a grape ( Vitis vinifera L.) cDNA encoding for the enzyme stilbene synthase (StSy), under the control of the fruit-specific promoter TomLoxB. The resulting LoxS transgenic plants accumulated trans -resveratrol and trans -piceid, in particular in the skin of the mature fruits. Quantitative analyses carried out on LoxS fruits were compared with those of a tomato line constitutively expressing the stsy gene (35SS). The LoxS fruits contained levels of trans -resveratrol that were 20-fold lower than those previously reported for the 35SS line. The total antioxidant capability and ascorbate content in transformed fruits were also evaluated, and a significant increase in both was found in the LoxS and 35SS lines. These results could explain the higher capability of transgenic fruits to counteract the pro-inflammatory effects of phorbol ester in monocyte–macrophages via the inhibition of induced cyclo-oxygenase-2 enzyme.     

Bioregulators: unlocking their potential role in regulation of the plant oxidative defense system

Key message

Plant bioregulators play an important role in managing oxidative stress tolerance in plants. Utilizing their ability in stress sensitive crops through genetic engineering will be a meaningful approach to manage food production under the threat of climate change.

Abstract

Exploitation of the plant defense system against oxidative stress to engineer tolerant plants in the climate change scenario is a sustainable and meaningful strategy. Plant bioregulators (PBRs), which are important biotic factors, are known to play a vital role not only in the development of plants, but also in inducing tolerance in plants against various environmental extremes. These bioregulators include auxins, gibberellins, cytokinins, abscisic acid, brassinosteroids, polyamines, strigolactones, and ascorbic acid and provide protection against the oxidative stress-associated reactive oxygen species through modulation or activation of a plant’s antioxidant system. Therefore, exploitation of their functioning and accumulation is of considerable significance for the development of plants more tolerant of harsh environmental conditions in order to tackle the issue of food security under the threat of climate change. Therefore, this review summarizes a new line of evidence that how PBRs act as inducers of oxidative stress resistance in plants and how they could be modulated in transgenic crops via introgression of genes. Reactive oxygen species production during oxidative stress events and their neutralization through an efficient antioxidants system is comprehensively detailed. Further, the use of exogenously applied PBRs in the induction of oxidative stress resistance is discussed. Recent advances in engineering transgenic plants with modified PBR gene expression to exploit the plant defense system against oxidative stress are discussed from an agricultural perspective.

     

Tubular stress proteins and nitric oxide synthase expression in rat kidney exposed to mercuric chloride and melatonin.

Stress proteins such as HSP70 members (HSP72 and GRP75) and metallothionein (MT) protect the kidney against oxidative damage and harmful metals, whereas inducible nitric oxide synthase (iNOS) regulates tubular functions. A single dose of mercuric chloride (HgCl(2)) can cause acute renal failure in rats, its main target being the proximal tubule. Oxidative damage has been proposed as one of its pathogenic mechanisms. In this study we tested whether melatonin (MEL), a powerful antioxidant compound, is effective against HgCl(2) nephrotoxicity. Rats were treated with saline, HgCl(2) (3.5 mg/kg), MEL (5 mg/kg), and MEL + HgCl(2) and examined after 24 hr for HSP72, GRP75, MT, and iNOS by immunohistochemistry and immunoblotting. Tubular effects of the treatment were then characterized by ultrastructure. In the HgCl(2) group, all markers were overexpressed in convoluted proximal tubules and sometimes in distal tubules. In the MEL + HgCl(2) group, GRP75 and iNOS decreased in convoluted and straight proximal tubules, whereas HSP72 and MT persisted more than the saline and MEL-only groups. Tubular damage and mitochondrial morphometry were improved by MEL pretreatment. In conclusion, the beneficial effect of MEL against HgCl(2) nephrotoxicity was outlined morphologically and by the reduction of the tubular expression of stress proteins and iNOS. These markers could represent sensitive recovery index against mercury damage.     

Photosynthetic bacterium Rhodopseudomonas palustris GJ‐22 induces systemic resistance against viruses

Photosynthetic bacteria (PSB) have been extensively used in agriculture to promote plant growth and to improve crop quality. Their potential application in plant disease management, however, is largely overlooked. In this study, the PSB strain Rhodopseudomonas palustris GJ‐22 was investigated for its ability to induce resistance against a plant virus while promoting plant growth. In the field, a foliar spray of GJ‐22 suspension protected tobacco plants against tobacco mosaic virus (TMV). Under axenic conditions, GJ‐22 colonized the plant phyllosphere and induced resistance against TMV. Additionally, GJ‐22 produced two phytohormones, indole‐3‐acetic acid and 5‐aminolevulinic acid, which promote growth and germination in tobacco. Furthermore, GJ‐22‐inoculated plants elevated their immune response under subsequent TMV infection. This research may give rise to a novel biological agent with a dual function in disease management while promoting plant growth.     

Regulation in Plant Stress Tolerance by a Potential Plant Growth Regulator, 5-Aminolevulinic Acid

Exogenous application of different plant growth regulators is a well-recognized strategy to alleviate stress-induced adverse effects on different crop plants by regulating a variety of physiobiochemical processes such as photosynthesis, chlorophyll biosynthesis, nutrient uptake, antioxidant metabolism, and protein synthesis, which are directly or indirectly involved in the mechanism of stress tolerance. Of various environmental factors, salinity, drought, and extreme temperature (low or high) considerably diminish plant growth and yield by modulating endogenous levels as well as signaling pathways of plant hormones. Of various plant hormones/regulators, a potential plant growth regulator, 5-aminolevulinic acid (ALA), is known to be effective in counteracting the injurious effects of various abiotic stresses in plants. Until now the mechanisms behind ALA regulation of growth under stress have not been fully elucidated. It is also not yet clear how far growth and yield in different crops can be promoted by exogenous application of ALA and whether this ALA-induced growth and yield promotion is cost-effective. Thus, in this review we discuss at length the effects of ALA in regulating growth and development in plants under a variety of abiotic stress conditions, including salinity, drought, and temperature stress. Furthermore, advances in the functional and regulatory interactions of this plant growth regulator with plant stress tolerance, as well as the effective mode of exogenous application of ALA in inducing stress tolerance in plants are also comprehensively discussed in this review. In the future, overaccumulation of ALA in plants through manipulation of gene(s) could enhance plant stress tolerance. Thus, genetic manipulation of plants with the goal of attaining increased synthesis/accumulation of ALA and hence improved stress tolerance under stress conditions is an important area for research.     

Isoprene synthesis protects transgenic tobacco plants from oxidative stress

Isoprene emission represents a significant loss of carbon to those plant species that synthesize this highly volatile and reactive compound. As a tool for studying the role of isoprene in plant physiology and biochemistry, we developed transgenic tobacco plants capable of emitting isoprene in a similar manner to and at rates comparable to a naturally emitting species. Thermotolerance of photosynthesis against transient high-temperature episodes could only be observed in lines emitting high levels of isoprene; the effect was very mild and could only be identified over repetitive stress events. However, isoprene-emitting plants were highly resistant to ozone-induced oxidative damage compared with their non-emitting azygous controls. In ozone-treated plants, accumulation of toxic reactive oxygen species (ROS) was inhibited, and antioxidant levels were higher. Isoprene-emitting plants showed remarkably decreased foliar damage and higher rates of photosynthesis compared to non-emitting plants immediately following oxidative stress events. An inhibition of hydrogen peroxide accumulation in isoprene-emitting plants may stall the programmed cell death response which would otherwise lead to foliar necrosis. These results demonstrate that endogenously produced isoprene provides protection from oxidative damage.     

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.     

Antimicrobial activity and effects of resveratrol on human pathogenic bacteria

Resveratrol (3,4′,5-trihydroxistilbene) is a phytoalexin commonly found in food and drinks, which is thought to possess antimicrobial activity. These effects together with its well known antioxidant properties are beneficial for the prevention of some diseases, e.g. cancer. In this study we have verified that resveratrol has antibacterial activity against all tested Gram-positive bacteria using both the disk diffusion and broth microdilution methods. Time kill assays of this compound against Gram-positive bacteria showed that its effects on the growth of bacterial cells were due to bacteriostatic action. The addition of resveratrol has allowed the identification of changes in cell morphology and DNA contents, which have been assessed through microscopic analysis and flow cytometry; this suggests that the cell cycle is affected by resveratrol. This study indicates that this compound may have potential as a natural antibacterial agent for both food preservation and medicinal use.     

Phenolic production and antioxidant properties of some Macedonian medicinal plants

Investigations have been made to study the production of phenolic compounds (total phenolics, flavonoids and phenylpropanoids) and total antioxidant capacity in 27 Macedonian traditional medicinal plants to improve its potential as a source of natural antioxidants. Antioxidant potential of plant extracts was analyzed by five different assays: cupric reducing antioxidant capacity (CUPRAC), phosphomolybdenum method (PM), reducing power (RP), 2,2-diphenyl-1-picrylhydrazyl (DPPH^·) and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS^·+) radical scavenging activity. Origanum vulgare extract consistently exhibited the highest content of phenolic compounds and the strongest antioxidant capacity based on the tests performed, and can be proposed as a promising source of natural antioxidants. Melissa officinalis and Salvia ringens were also identified as valuable sources of antioxidant compounds. A positive linear correlation between antioxidant activity and total phenolics, flavonoids and phenylpropanoids indicates that these compounds are likely to be the main antioxidants contributing to the observed activities of evaluated plants. These findings suggest that the medicinal plants studied in this paper are good sources of bioactive compounds for the food and pharmaceutical industries.     

反式-2-己烯醛在植物防御反应中的作用

反式-2-己烯醛是绿色植物释放的一种小分子挥发性物质,在调节植物生长发育和抵抗各种环境胁迫中发挥重要作用。已有研究表明,反式-2-己烯醛可抑制植物根系生长,具有较高的抑菌和抗虫活性,也可以作为植物间的“信使”来传递防御信号。该文系统综述了反式-2-己烯醛的生物合成、代谢途径及其在生物胁迫防御反应中的重要作用,提出了研究...     

Effect of triadimefon: a triazole fungicide on oxidative stress defense system and eugenol content in <Emphasis Type="Italic">Ocimum tenuiflorum</Emphasis> L.

The effect of triadimefon (TDM) a triazole compound on antioxidant potential and eugenol content was studied in Ocimum tenuiflorum L. The plant was subjected to 15 mg/l TDM by soil-drenching on 50th, 70th and 90th days after planting (DAP). Analyses were carried out on 60th, 80th and 100th DAP. Both enzymatic and non-enzymatic antioxidant potential estimation was carried out. The non-enzymatic antioxidant viz ascorbic acid, α-tocopherol and reduced glutathione were found to increase under triadimefon treatment. The antioxidant enzyme like superoxide dismutase, ascorbate peroxidase and catalase activities showed significant increase in TDM treatment. Triazole-treated plants yielded more eugenol (a major component of Ocimum-essential oil) in comparison to control. The study evidenced that TDM residues could be detected in the upper soil layer only and does not accumulate in the soil. These preliminary results suggest that TDM may be useful to increase the antioxidant content in medicinal plants and also to act as an elicitor to enhance the production of secondary metabolites of medicinal plants.     

Impact of soil salinity on the plant-growth – promoting and biological control abilities of root associated bacteria

The effectiveness of plant growth – promoting bacteria is variable under different biotic and abiotic conditions. Abiotic factors may negatively affect the beneficial properties and efficiency of the introduced PGPR inoculants. The aim of this study was to evaluate the effect of plant growth – promoting rhizobacteria on plant growth and on the control of foot and root rot of tomatoes caused by Fusarium solani under different soil salinity conditions. Among the five tested strains, only Pseudomonas chlororaphis TSAU13, and Pseudomonas extremorientalis TSAU20 were able to stimulate plant growth and act as biological controls of foot and root rot disease of tomato. The soil salinity did not negatively affect the beneficial impacts of these strains, as they were able to colonize and survive on the roots of tomato plants under both saline and non-saline soil conditions. The improved plant height and fruit yield of tomato was also observed for plants inoculated with P. extremorientalis TSAU20. Our results indicated that, saline condition is not crucial factor in obtaining good performance with respect to the plant growth stimulating and biocontrol abilities of PGPR strains. The bacterial inoculant also enhanced antioxidant enzymes activities thereby preventing ROS induced oxidative damage in plants, and the proline concentrations in plant tissue that play an important role in plant stress tolerance.     

3,4,4'-Trihydroxy-trans-stilbene, an analogue of resveratrol, is a potent antioxidant and cytotoxic agent

Resveratrol (3,5,4'-trihydroxy-trans-stilbene) is a naturally occurring polyphenol widely distributed in food and dietary plants. This phytochemical has been intensively studied as an efficient antioxidant and anticancer agent, and a variety of substituted stilbenes have been developed in order to improve the potency of resveratrol. In this work, we described the synthesis of 3,4,4 -trihydroxy-trans-stilbene (3,4,4'-THS), an analogue of resveratrol, and studied its antioxidant and cytotoxic activity in vitro. 3,4,4 -THS was much more efficient than resveratrol in protecting against free radical-induced lipid peroxidation, photo-sensitized DNA oxidative damage, and free radical-induced hemolysis of human red blood cells. More potent growth inhibition in cultured human leukemia cells (HL-60) was also observed for 3,4,4 -THS. The relationship between the antioxidant efficiency and cytotoxic activity was discussed, with the emphasis on inhibition of the free radical enzyme ribonucleotide reductase by antioxidants. The result that this subtle structure modification of resveratrol drastically improves its bioactivity provides important strategy to develop novel resveratrol-based molecules.     

Metal/metalloid stress tolerance in plants: role of ascorbate,its redox couple,and associated enzymes

The enhanced generation of reactive oxygen species (ROS) under metal/metalloid stress is most common in plants, and the elevated ROS must be successfully metabolized in order to maintain plant growth, development, and productivity. Ascorbate (AsA) is a highly abundant metabolite and a water-soluble antioxidant, which besides positively influencing various aspects in plants acts also as an enigmatic component of plant defense armory. As a significant component of the ascorbate-glutathione (AsA-GSH) pathway, it performs multiple vital functions in plants including growth and development by either directly or indirectly metabolizing ROS and its products. Enzymes such as monodehydroascorbate reductase (MDHAR, EC 1.6.5.4) and dehydroascorbate reductase (DHAR, EC 1.8.5.1) maintain the reduced form of AsA pool besides metabolically controlling the ratio of AsA with its oxidized form (dehydroascorbate, DHA). Ascorbate peroxidase (APX, EC 1.11.1.11) utilizes the reduced AsA pool as the specific electron donor during ROS metabolism. Thus, AsA, its redox couple (AsA/DHA), and related enzymes (MDHAR, DHAR, and APX) cumulatively form an AsA redox system to efficiently protect plants particularly against potential anomalies caused by ROS and its products. Here we present a critical assessment of the recent research reports available on metal/metalloid-accrued modulation of reduced AsA pool, AsA/DHA redox couple and AsA-related major enzymes, and the cumulative significance of these antioxidant system components in plant metal/metalloid stress tolerance.     

The direct and ecological costs of an ant-plant symbiosis

How strong is selection for cheating in mutualisms? The answer depends on the type and magnitude of the costs of the mutualism. Here we investigated the direct and ecological costs of plant defense by ants in the association between Cordia nodosa, a myrmecophytic plant, and Allomerus octoarticulatus, a phytoecious ant. Cordia nodosa trees produce food and housing to reward ants that protect them against herbivores. For nearly 1 year, we manipulated the presence of A. octoarticulatus ants and most insect herbivores on C. nodosa in a full-factorial experiment. Ants increased plant growth when herbivores were present but decreased plant growth when herbivores were absent, indicating that hosting ants can be costly to plants. However, we did not detect a cost to ant colonies of defending host plants against herbivores. Although this asymmetry in costs suggests that the plants may be under stronger selection than the ants to cheat by withholding investment in their partner, the costs to C. nodosa are probably at least partly ecological, arising because ants tend scale insects on their host plants. We argue that ecological costs should favor resistance or traits other than cheating and thus that neither partner may face much temptation to cheat.