Biochemical Defense Research Articles

Burkholderia phytofirmans PsJN and tree twigs derived biochar together retrieved Pb-induced growth, physiological and biochemical disturbances by minimizing its uptake and translocation in mung bean (Vigna radiata L.)

Anthropogenic activities like industrial mining, refining and smelting release substantial amounts of lead (Pb) into the soil causing potential ecological menaces to environment, soil productivity and food security. Present pot scale study was undertaken to investigate the effects of tree twigs-derived biochar and a bacterium Burkholderia phytofirmans PsJN on Pb accumulation, growth, physiological, biochemical and antioxidative defense responses of mung bean grown in Pb spiked soil. The original soil was spiked with Pb (600 mg kg−1) and amended with biochar (1% w/w). Upon screening in laboratory, B. phytofirmans PsJN exhibited high Pb tolerance and was able to grow at high Pb concentrations. Surface-disinfected seeds of mung bean were inoculated with B. phytofirmans PsJN and sown in pots along with un-inoculated seeds. Data were collected for various growth, physiological and biochemical parameters from fully matured harvested plants. Application of biochar and B. phytofirmans PsJN ameliorated Pb induced negative impacts in mung bean both individually and in combination, but better growth, physiological and seed quality responses were observed with their combined use. Compared with respective controls, their combined use increased the following parameters in normal and Pb spiked soils, respectively: plant height (69% and 159%), root dry weight (97% and 130%), shoot dry weight (42% and 104%), number of pods (70% and 210%), grains weight (58% and 194%) and number of root nodules (71% and 255%). Moreover, combined use increased chlorophyll contents (27% and 37%), photosynthetic rate (93% and 204%), transpiration rate (42% and 132%), stomatal conductance (70% and 218%), sub-stomatal conductance (93% and 148%) and water use efficiency (35% and 43%). In addition, combined application of biochar and B. phytofirmans PsJN retarded Pb-induced oxidative stress by intensifying antioxidant enzyme activities and reducing activities of reactive oxygen species. Similarly, considerable reduction in Pb uptake, translocation and bioaccumulation in mung bean was noticed in Pb spiked soil due to applied amendments. Furthermore, their combined use resulted in considerable increase in grain quality parameters (protein, fat, ash) both in normal and Pb-spiked soils. Therefore, it can be inferred that interactive use of biochar and B. phytofirmans PsJN provides an efficient innovative strategy to repossess Pb induced growth, physiological, biochemical and oxidative disturbances in mung bean.

Silicon and Plant Natural Defenses against Insect Pests: Impact on Plant Volatile Organic Compounds and Cascade Effects on Multitrophic Interactions.

Environmental factors controlling silicon (Si) accumulation in terrestrial plant are key drivers to alleviate plant biotic stresses, including insect herbivory. While there is a general agreement on the ability of Si-enriched plant to better resist insect feeding, recent studies suggest that Si also primes biochemical defense pathways in various plant families. In this review, we first summarize how soil parameters and climate variables influence Si assimilation in plants. Then, we describe recent evidences on the ability of Si to modulate plant volatile emissions, with potential cascade effects on phytophagous insects and higher trophic levels. Even though the mechanisms still need to be elucidated, Si accumulation in plants leads to contrasting effects on the levels of the three major phytohormones, namely jasmonic acid, salicylic acid and ethylene, resulting in modified emissions of plant volatile organic compounds. Herbivore-induced plant volatiles would be particularly impacted by Si concentration in plant tissues, resulting in a cascade effect on the attraction of natural enemies of pests, known to locate their prey or hosts based on plant volatile cues. Since seven of the top 10 most important crops in the world are Si-accumulating Poaceae species, it is important to discuss the potential of Si mobility in soil-plant systems as a novel component of an integrated pest management.

Changes in grapes composition during ripening of five Vitis vinifera L varieties as related to Tephritidae and Drosophilidae infestations.

Vitis vinifera (L) isa great economically important crop. However, huge loss in fruits due to destructive pests hinders the improvement of its performance. The study of their biochemical profile, ripening dynamics, and defense mechanisms presents a great scientific interest. In this work, phenylalanine ammonia lyase (PAL), tyrosine ammonia lyase (TAL) activities, proteins, sugar and malondialdehyde (MAD) were investigated during ripening of five grape varieties in Loudaya region (Marrakech, Morocco), three of them are allochthonous while two are autochthonous. The Dipterans infestations by Drosophila suzukii and Ceratitis capitata have been highlighted as a factor that stimulates the defense mechanism in ripeness stage of grapes. Sugars, proteins and MDA have shown a gradual increase in grapes maturation in all varieties. TAL activity decrease in the course of the maturation in contrast to the PAL activity increasing in the ripe grapes. High content of PAL, TAL, and MDA compounds were noted in the ripe infested grapes as compared to the healthy ones. A significant difference (P < 0.05) for all biochemical assays according to varieties, maturity and the condition (damaged/undamaged) were found. A PCA analysis highlighted different biochemical behaviours from the grapes concerning the flies' infestations (79.64% of total variation). The variables that have contributed to the discrimination of the grapes according to their stage of maturities were sugar, proteins and TAL. The higher concentrations of PAL (6.64 ± 0.57 EU), TAL (0.93 ± 0.05 EU) and MDA (58.32 ± 2.55 EU) especially in the injured grapes prove that flies infestation triggered a priming defense mechanism, directly activating defense reactions. The results obtained could be crucial in establishing a database of the Moroccan grapes biochemical defense which provides a foundation for new methodologies in the plants behavior against fruit flies stress.

Plants responses and their physiological and biochemical defense mechanisms against salinity: A review

Plants responses and their physiological and biochemical defense mechanisms against salinity: A review

When resistance is futile, tolerate instead: silicon promotes plant compensatory growth when attacked by above- and belowground herbivores.

Plants have evolved numerous herbivore defences that are resistance- or tolerance-based. Resistance involves physical and chemical traits that deter and/or harm herbivores whereas tolerance minimizes fitness costs of herbivory, often via compensatory growth. The Poaceae frequently accumulate large amounts of silicon (Si), which can be used for herbivore resistance, including biomechanical and (indirectly) biochemical defences. To date, it is unclear whether Si improves tolerance of herbivory. Here we report how Si enabled a cereal (Triticum aestivum) to tolerate damage inflicted by above- and belowground herbivores. Leaf herbivory increased Si concentrations in the leaves by greater than 50% relative to herbivore-free plants, indicating it was an inducible defensive response. In plants without Si supplementation, leaf herbivory reduced shoot biomass by 52% and root herbivory reduced root biomass by 68%. Si supplementation, however, facilitated compensatory growth such that shoot losses were more than compensated for (+14% greater than herbivore-free plants) and root losses were minimized to -16%. Si supplementation did not improve plant resistance since Si did not enhance biomechanical resistance (i.e. force of fracture) or reduce leaf consumption and herbivore relative growth rates. We propose that Si-based defence operates in wheat via tolerance either in addition or as an alternative to resistance-based defence.

Evolution: An Early Role for Flavonoids in Defense against Oomycete Infection

Biochemical defenses against oomycete infection were already present in early diverging plant lineages, suggesting parallel selection for phenylpropanoid metabolites.

Oxidative stress resistance as a factor in aging: evidence from an extended longevity phenotype of Drosophila melanogaster.

Longevity of a species is a multifactorial quantitative trait influenced by genetic background, sex, age and environment of the organism. Extended longevity phenotypes (ELP) from experimental evolution in the laboratory can be used as model systems to investigate the mechanisms underlying aging and senescence. ELPs of Drosophila are correlated with various life history attributes such as resistance to environmental stressors (starvation, desiccation, cold and paraquat), developmental time, biochemical defenses, etc. The association between oxidative stress resistance and longevity is not clear and ELPs offer an opportunity to examine the role of oxidative stress resistance in longevity. Here, we have investigated the hypothesis that enhanced oxidative stress resistance and elevated antioxidant defense system play a positive role in longevity using an ELP of Drosophila melanogaster. An ELP of D. melanogaster isolated and characterized in our laboratory through artificial selection (inbred laboratory strain of Oregon K) is employed in this study. Our ELP, named as long lifespan (LLS) flies, shows marked extension in lifespan when compared to the progenitor population (normal lifespan, NLS) and makes a suitable model to study the role of mitochondrial genome in longevity because of its least heterogeneity. In this study, sensitivity to ethanol with age was employed as a measure of resistance to oxidative stress in NLS and LLS flies. Effect of age and oxidative stress on longevity was examined by employing NLS and LLS flies of different age groups against ethanol-induced oxidative stress. Results show that the lower mortality against ethanol was associated with enhanced oxidative stress resistance, higher antioxidant defenses, lower reactive oxygen species (ROS) levels, enhanced alcohol dehydrogenase activity and better locomotor ability attributes of LLS flies. In addition, age-related changes like locomotor impairments, decreased antioxidant defenses, higher ROS levels and sensitivity to oxidative stress were delayed in LLS flies when compared to NLS. Our study supports the hypothesis that higher oxidative stress resistance and enhanced antioxidant defenses are significant factors in extending longevity.

Molecular Interactions Between Plants and Insect Herbivores.

Diverse molecular processes regulate the interactions between plants and insect herbivores. Here, we review genes and proteins that are involved in plant-herbivore interactions and discuss how their discovery has structured the current standard model of plant-herbivore interactions. Plants perceive damage-associated and, possibly, herbivore-associated molecular patterns via receptors that activate early signaling components such as Ca2+, reactive oxygen species, and MAP kinases. Specific defense reprogramming proceeds via signaling networks that include phytohormones, secondary metabolites, and transcription factors. Local and systemic regulation of toxins, defense proteins, physical barriers, and tolerance traits protect plants against herbivores. Herbivores counteract plant defenses through biochemical defense deactivation, effector-mediated suppression of defense signaling, and chemically controlled behavioral changes. The molecular basis of plant-herbivore interactions is now well established for model systems. Expanding molecular approaches to unexplored dimensions of plant-insect interactions should be a future priority.

Physiological changes of sweet and hot peppers in vegetative and reproductive growth stages treated by Ca and H2O2 under unforeseen heat stresses

High ambient temperature has adverse effects on plant vegetative and reproductive development and reduces crop yield. This experiment was designed to better understand the effects of unforeseen heat stresses on reproductive and vegetative growth of two species of pepper, and to find out whether or not Ca and hydrogen peroxide (H2O2) have any significant effects on the levels of heat tolerance as well as on the reproductive and vegetative traits of the peppers. Two species of hot and sweet peppers, exposed to exogenous H2O2 and CaCl2, were subject to the high temperature (40° ±2C). Both species showed higher stress indices, including MDA, H2O2, electrolyte leakage, antioxidant capacity, phenol content, and chlorophyll fluorescence under heat stresses. Moreover, the given parameters were greater in the reproductive stage compared with the vegetative stage. Also, sweet peppers absorbed greater amounts of Ca in comparison with the hot peppers under stress conditions. The dominant fatty acid of the pepper leaves was found to be linolenic acid in all conditions. Under heat stresses, the saturate/unsaturated ratio of the fatty acid changed. This ratio increased in the hot pepper and conversely, decreased in the sweet pepper. On the other hand, a decrease in the levels of glucose and fructose was observed under heat stresses, while hydrogen peroxide significantly increased the two sugars. Nonetheless, the changes observed were greater in the sweet pepper in comparison with the hot pepper. All in all, it seems that, under the treatment, on the one hand, the fatty acids and existing sugars due to applying hydrogen peroxide, and on the other hand, the biochemical defense system of the peppers increased due to the presence of Ca, increasing its heat tolerance.

NO protect the wheat embryo from oxidative damage by triggering the biochemical defence network and amylolytic activity

Nitric oxide has been reported to enhance the tolerance of plants to biotic and abiotic stresses. Wheat is highly affected by heat stress at different stages of growth and development. Tolerance to heat stress (HS) at germination stage is important for wheat crop in Central and Peninsular India. Here, we studied the effect of pre-treatment of seeds with NO (150 µmol) on the activity of enzymes associated with germination and overall tolerance of seedlings of contrasting wheat cvs. Raj3765 and HD2932 under differential HS. NO was observed to self-regulate it’s biosynthesis through upregulation of NOS and NR in seedlings under NO and HS treatments. HSP90, HSP70, SOD and CAT showed very high expression in response to NO and HS, as compared to control. An increase in the activities of α/β-amylases were observed in response to NO and HS in seedlings. The NO effect was more pronounced in the seedlings of thermotolerance cv. Raj3765, as compared to thermosusceptible cv. HD2932. We observed an increase in the activities of antioxidant enzymes (SOD, CAT and POX) in response to NO. Enhancement of biochemical traits associated with thermotolerance were also observed in seedlings treated with NO under HS. NO mitigated the effect of HS by triggering the SAGs and antioxidant enzymes associated defence network and thus tolerance of wheat seedling to HS. This provides an easy and cheap method to mitigate the effect of HS on germination in wheat.

New traits to identify physiological responses induced by different rootstocks after root-knot nematode inoculation (Meloidogyne incognita) in sweet pepper

Root-knot nematodes (RKNs) are one of the major phytopathological problems that limit potential yields in intensive agriculture worldwide. Grafting with resistant rootstocks has been demonstrated to be a viable technique to manage Meloidogyne incognita in several crops (tomato, melon, watermelon, etc.). However, little research has been conducted on sweet pepper (Capsicum annuum L.) grown in greenhouses under Mediterranean-climate conditions. Therefore, we studied a susceptible scion variety (Gacela) grafted onto resistant rootstocks (C19, C25, and RT17), in comparison with ungrafted and self-grafted (GAL) plants. The RKN produced significant root galling in ungrafted and GAL plants; however, RT17 was unaffected. This differing response to infection is discussed from physiological and agronomic perspectives. Thus, following the inoculation of susceptible rootstocks, leaf photosynthesis was impaired by altered stomatal regulation and photochemical efficiency (chlorophyll a fluorescence), which led to unbalanced fruit nutrient concentrations (especially Ca) and to enhanced allocation of carbon from photosynthesis to the production of biochemical defense compounds. Consequently, total phenolics and carotenoids were significantly affected, as was the amino acid profile. These results provide new insights into the traits that can identify RKN-resistant rootstocks, and therefore new tools to induce resistance, while avoiding the use of disinfectants in the soil.

Silicon-enhanced resistance of plants to biotic stresses review article

The emerging role of silicon (Si) has attracted a great deal of interest from researchers because of the numerous agronomic benefits of this element to plants. Indeed, silicon improves plant resistance to a range of biotic and abiotic stresses, with consequent yield increases. Furthermore, it enhances resistance in several crops of great economic importance to diseases and insect pests. Until recently, the exact nature of protective effects of silicon in plants is uncertain. To date, two major defense mechanisms due to silicon application have been documented: physical defense and biochemical defense. In this review, the interaction between silicon-treated- plants and reduced biotic stresses (disease and insect pests) incidence was explored. The current research presents the agronomic importance of silicon in plants, the control of fungal and bacterial pathogens and insect pests according to their lifestyle, and viral agents, and different mechanisms of silicon-enhanced resistance. By regrouping the data presented in this paper, a good knowledge of the association between silicon treatment, increasing plant resistance, and decreasing biotic stresses occurrence could be achieved.

Research progress on the underlying mechanisms of plant defense enzymes in response to pest stress.

Plants respond to herbivory through a series of physiological and biochemical defense mechanisms to counter the stress of herbivorous pests, including the dramatic changes in activities of various defense enzymes. Here, we reviewed the recent research progress on the response mechanisms of six common plant defense enzymes, SOD, CAT, POD, PPO, LOX and PAL, to insect stress, and compared their similarities and disparities. We sorted out their interactive sequences in response to the insect stress and analyzed the changes of defense enzyme activities and their associations with defense enzyme genes after being attacked by pests. Finally, we discussed the key problems/challenges in this area and proposed the prospects for studying the mechanisms of plant defense enzymes.

Non-destructive and rapid interrogation of biochemical response of the leaves of wheat seedlings towards Al2O3 nanoparticles stress using attenuated total reflectance Fourier transform infrared spectroscopy

There has been tremendous development in the field of nanotechnology and consequently the release of nanoparticles in the environment and its interaction with the biotic components is inevitable. However, knowledge concerning nanomaterial biosafety, adverse effects, fate, and acquired biological reactivity is still at infancy and requires further scientific efforts to assess their possible nano-agricultural risks. Therefore, the present study aims to reveal the molecular alterations in the leaves of the wheat seedlings caused by direct exposure of Al2O3 NPs in non-destructive and rapid manner using attenuated total reflectance Fourier transform infrared spectroscopy. For this, the seedlings of wheat have been grown in sand matrix under controlled growth conditions and the toxicity of Al2O3 NPs has been introduced to the seedlings at different concentrations (0.2, 0.6, 1.0, 1.4, 1.8, 2.2, 2.6 and 3.0 mM). For determining the biochemical alterations, the infrared spectra of the leaves of control and Al2O3 NPs treated seedlings have been recorded in the wavenumber range 4000–400 cm−1. The principle component analyses of the preprocessed spectra indicate significant discrimination between the spectral signatures of control and Al2O3 NPs treated seedlings. The treatment of Al2O3 NPs enhances the spectral features of cellulose, hemicelluloses, lignin and pectin in the leaves of wheat seedlings. The treatment also increases the area of mehtylene bands of lipids, carboxyl and amine groups of amino acids and protein. Enhancement is also observed in carbonyl fingerprint region. The increase in the area of these molecules indicates the physiological significance of these molecules in the modulation of Al2O3 NPs stress in the wheat seedlings. The study adds substantive spectral data base to the existing elusive knowledge of nanotoxicity especially Al2O3 NPs to the plants and provides a molecular mechanism that defines the occurrence of biochemical changes and defense strategy of plants towards Al2O3 NPs toxicity.

Capsicum-Colletotrichum interaction: Identification of resistance sources and quantification of secondary metabolites in unripe and ripe fruits in response to anthracnose infection

Anthracnose, caused by Colletotrichum species complex, is one of the main fungal diseases in pepper (Capsicum spp.) crops, resulting in extensive fruit losses during pre- and post-harvesting. Plants have structural and biochemical defense mechanisms produced before and/or after the pathogen attack. Biochemical defense involve the production of compounds that accumulate at the site of infection and are toxic to the pathogen. However, the accumulation and biosynthesis of these compounds during Capsicum-Colletotrichum interaction, especially during fruit development stages remain poorly understood. In order to identify potential resistant genotypes and to improve our knowledge about the metabolites produced by pepper fruits against fungus infection, we inoculated unripe and ripe fruits of 59 accessions of Capsicum spp. with C. gloeosporioides and analyzed the disease severity during 8 days after inoculation. In this study, we observed a wide variability of fungus resistance response in unripe and ripe fruits of Capsicum spp. accessions, and ripe fruits presented greater resistance to anthracnose than unripe. Six accessions (GBUEL06, GBUEL28, GBUEL73, GBUEL87, GBUEL104 and GBUEL106) were considered as resistant for both fruits development stages and have potential to be used in future breeding programs. In addition, we selected two C. annuum accessions GBUEL103 (susceptible) and GBUEL104 (resistant), to describe the histological aspects of C. gloeosporioides infection in pepper fruits, followed by the quantification of secondary metabolites produced during this plant-pathogen interaction, using light microscopy and ultra-high performance liquid chromatography (UHPLC), respectively. The quantification of secondary metabolites produced in pepper fruits during fungus infection showed different values according genotype characteristic (susceptible or resistant), fruit development stages (unripe and ripe) and time (1st and 8th day post-inoculation). Interestingly, high concentrations of caffeic and chlorogenic acid were quantified in unripe and ripe fruits characterized as resistant genotype, showing that these biochemical compounds are putatively involved in fruit defense mechanism in response to anthracnose disease.

TaMIR1119, a miRNA family member of wheat (Triticum aestivum), is essential in the regulation of plant drought tolerance

Through regulating target genes via the mechanisms of posttranscriptional cleavage or translational repression, plant miRNAs involve diverse biological processes associating with plant growth, development, and abiotic stress responses. In this study, we functionally characterized TaMIR1119, a miRNA family member of wheat (Triticum aestivum), in regulating the drought adaptive response of plants. TaMIR1119 putatively targets six genes categorized into the functional classes of transcriptional regulation, RNA and biochemical metabolism, trafficking, and oxidative stress defense. Upon simulated drought stress, the TaMIR1119 transcripts abundance in roots was drastically altered, showing to be upregulated gradually within a 48-h drought regime and that the drought-induced transcripts were gradually restored along with a 48-h recovery treatment. In contrast, most miRNA target genes displayed reverse expression patterns to TaMIR1119, exhibiting a downregulated expression pattern upon drought and whose reduced transcripts were re-elevated along with a normal recovery treatment. These expression analysis results indicated that TaMIR1119 responds to drought and regulates the target genes mainly through a cleavage mechanism. Under drought stress, the tobacco lines with TaMIR1119 overexpression behaved improved phenotypes, showing increased plant biomass, photosynthetic parameters, osmolyte accumulation, and enhanced antioxidant enzyme (AE) activities relative to wild type. Three AE genes, NtFeSOD, NtCAT1;3, and NtSOD2;1, encoding superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) proteins, respectively, showed upregulated expression in TaMIR1119 overexpression lines, suggesting that they are involved in the regulation of AE activities and contribution to the improved cellular reactive oxygen species (ROS) homeostasis in drought-challenged transgenic lines. Our results indicate that TaMIR1119 plays critical roles in regulating plant drought tolerance through transcriptionally regulating the target genes that modulate osmolyte accumulation, photosynthetic function, and improve cellular ROS homeostasis of plants.

Tree host-pathogen interactions as influenced by drought timing: linking physiological performance, biochemical defence and disease severity.

There is increasing concern about tree mortality around the world due to climatic extremes and associated shifts in pest and pathogen dynamics. Yet, empirical studies addressing the interactive effect of biotic and abiotic stress on plants are very rare. Therefore, in this study, we examined the interaction between drought stress and a canker pathogen, Quambalaria coyrecup, on the eucalypt - Corymbia calophylla (marri), which is experiencing increasing drought stress. We hypothesized that drought stress would increase marri's susceptibility to canker disease, and cankers would have the largest negative effect on plants that are already drought stressed before pathogen inoculation. To test the hypotheses, in a glasshouse, marri saplings were exposed to drought either before or after pathogen inoculation, or were well-watered or droughted throughout the experiment either with or without inoculation. Canker development was greater in well-watered saplings than in droughted saplings, with the fastest development occurring in well-watered saplings that had experienced drought stress before inoculation. Irrespective of water treatments, marri saplings employed phenol-based localized biochemical defence against the pathogen. Drought reduced photosynthesis and growth, however, a negative effect of canker disease on saplings' physiological performance was only observed in well-watered saplings. In well-watered saplings, canker-induced loss of sapwood function contributed to reduced whole-plant hydraulic conductance, photosynthesis and growth. The results provide evidence that timing of drought stress influences host physiology, and host condition influences canker disease susceptibility through differences in induced biochemical defence mechanisms. The observations highlight the importance of explicitly incorporating abiotic and biotic stress, as well as their interactions, in future studies of tree mortality in drought-prone regions worldwide.

Biochemical defence responses of resistant and susceptible rice genotypes against blast pathogen Magnaporthe oryzae

Rice blast is the leading fungal disease which is caused by Magnaporthe oryzae that contributes for the significant decline in the rice yield throughout the globe. There is a need for the understanding of biochemical changes in rice plant during blast infection for the development of novel disease control strategies. In the present study, we isolated M. oryzae from the local paddy fields and the fungal isolates (VCF and PON) were identified by ITS-PCR using genomic DNA samples. Further, we inoculated resistant (BR2655 and TUNGA) and susceptible (INTAN and HR12) rice cultivars with PON and VCF isolates. PON isolate showed relatively high virulence compared to VCF and standard MTCC fungal strains. Therefore, we evaluated the effect of PON on the total protein content and plant defence-related key enzymes (peroxidase, polyphenol oxidase, phenylalanine ammonia lyase, β-glucosidase, chitinase and lipoxygenase) activities between 24- and 120-hour post-inoculation (hpi). The results demonstrated the decrease in total protein content in all the inoculated cultivars. In addition, we observed the variation in the activity of peroxidase, polyphenol oxidase, β-glucosidase, chitinase and lipoxygenase at different time points in all the tested rice plants compared to respective controls. However, no significant difference was observed in the phenylalanine ammonia lyase activity relative to its control. Taken together, this study emphasizes on the variation in the activities of plant defence enzymes in different plant cultivars against the tested fungal pathogen and also implementation of defence enzymes as biochemical markers for resistant breeding.

Silicon as a Beneficial Element and as an Essential Plant Nutrient: An Outlook (Review)

Silicon application has been known to enhance the plant tolerance against several biotic and abiotic stresses. The mechanisms of alleviation of UV-radiation, drought, salt, and heavy metal stresses have been investigated but still definitely unknown. As a consequence, the needs for understanding the role of Si in the physiological and biochemical processes in plants are of a major importance. In most cases, the published data supported the role of Si in regulation and alleviation the adverse effects of several environmental stresses under specific conditions and for specific plant species. The physiological functions of Si in plants have been studied and showed that Si influx and efflux is regulated by specific genes in plasma membrane of plant cells. The role of these genes in Si transport and alleviation several stress conditions is still poorly understood. The occurrence of high Si content in tissues of graminaceous plants (rice, barley and maize) has positively activated physiological, physical and biochemical defense mechanisms for increasing stress balance, such as decreased lipid peroxidation, reduced membrane permeability, and stimulation of defense enzymes activities. The activities of stress defense enzymes, also called antioxidative enzymes (ascorbate peroxidase, catalase, peroxidase, and superoxide dismutase), have been found to be linked to Si nutrition especially under abiotic stress conditions. There are genotypic differences controls the accumulation of Si within a specific plant species, such as rice. These differences are originated from variations in abundance of certain transporters of Si in roots or/and shoot of plant. These genotypic differences allow the plant to facilitate high growth under abiotic stress conditions. However, the responsible genes for Si accumulation in plant varieties have not yet been well characterized. Harvesting cultivated high Si – accumulator plant species results in removal of large quantity of available Si from soil. In order to replenish the needed amount of available Si from such soil, application of Si – fertilizer would improve its status in soil and maintain appreciable amount of available Si in this soil. Fertilization of soil by the required and safe rate of Si has been found to improve the chemical, physical and biological properties of plant and soil. Tests for available Si in soil and for Si content in specific plant tissue in combination with evaluation of the quantitative relationship between both would be reliable guides for Si–fertilization. In this concern, whether Si is known as a beneficial element or as an essential plant nutrient, the use of Si compounds as a fertilizer or as an amendment has been proved to be of a major importance in the present and near future.

Roles of the KEAP1-NRF2 system in mammalian skin exposed to UV radiation

The KEAP1 (Kelch-like ECH-associated protein 1)-NRF2 (NF-E2-related factor 2) system controls the biochemical defense activity against agents toxic to mammals and responds to exogenous and endogenous stressors such as electrophilic and oxidative substances, which can have destructive and genotoxic effects on affected mammalian tissues. Although this system can be activated by various environmental stressors, it remains unclear whether ultraviolet radiation (UVR), which is one of the major environmental agents that has inflammatory and carcinogenic impacts on human skin and eyes, induces NRF2-dependent defense activity. Here, we review the recent progress in the study of the contributions of NRF2 and related factors to protection against UVR. The KEAP1-NRF2 system is not always efficient in responding to UVR, especially to short wavelengths such as UVC/UVB, indicating that UVR is a poor activator of the KEAP1-NRF2 system. However, sustained activation of NRF2 appears to suppress the harmful effects of chronic UVR exposure, such as photoaging of and carcinogenesis in the skin, indicating that NRF2 activation is beneficial for the protection of the skin from the harmful effects of UVR. However, it should be noted that prolonged and strong activation of NRF2 may also have adverse effects on skin, especially in the case of UVR-induced carcinogenesis. We present working models describing mechanisms underlying the involvement of the KEAP1-NRF2 system in skin photoaging and carcinogenesis.