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A large number of reviews have discussed many aspects of oxidative burst due to plant exposure to biotic and abiotic stresses, including the dual role of reactive oxygen species (ROS) as both signaling and toxic compounds, and the strategies developed by plants to cope with this oxidative imbalance. In this review, we have concentrated on fresh new information and other promising and emerging topics of oxidative stress and antioxidant mechanisms in plants, giving particular attention to genotoxicity, transgenerational alterations and quantitative trait loci (QTL) associated with enhancements in the plant tolerance to stresses. Furthermore, besides the discussion of the “classical” enzymatic and non-enzymatic components of plant defense, novel aspects about the components of the antioxidant machinery, which now includes sugars, annexins and dehydrins, are also presented, along with a final section on future directions in this field.

Heat stress can impact crop development and yield and amino acids play diverse essential roles in plants. This work aimed to study the long-term effects of foliar spray with L-arginine in antioxidant machinery, physiology, nutrition, productivity and fruit quality of tomato plants subjected to transient heat stresses. Six concentrations of L-arginine were sprayed on the plants: 0 (control), 0.10, 0.25, 0.50, 1.0 and 2.0 g·L–1. The content of hydrogen peroxide (H2O2), a reactive oxygen species, decreased concurrently to the increasing arginine concentration. The ascorbate peroxide (APX) activity had an inverse behavior to that observed for H2O2 content (r = –0.79), not only indicating that arginine is able to modulate APX, but also suggesting that this enzyme plays an important role on the mitigation of H2O2 generation under heat stress. Ascorbate peroxide and catalase (CAT) activities had a positive correlation (r = 0.82), showing that these enzymes may work in tandem. The influence of arginine on photosynthesis activity and gas exchange was generally weak and depended mainly on the plant developmental stage. Yield was increased by 19.8 and 23.1% in plants that received 1.0 and 0.5 g·L–1 of arginine, respectively, when compared to control plants. In conclusion, the use of exogenous L-arginine can protect tomato plants against oxidative imbalance under transient heat within protected environments.

The present study aimed to investigate the Cd-induced transgenerational effects on plants. Grafted tomato plants, which exhibited the same cultivar as scion and distinct cultivars with contrasting Cd-tolerance as rootstocks, were grown in soil without and with artificial addition of Cd (less than 2.0, and 6.9 mg kg-1 of Cd, respectively) in a pot experiment carried out in a greenhouse. Their fruits were harvested to extract seeds (i.e., the progenies), which were sown over either Cd-free (control) or Cd-containing germitest paper (germination testing paper with 0 and 35 μM of CdCl2, respectively) and grown in a growth chamber. The immediate progeny of all grafting combinations from stressed plants presented an elevated germinability, despite high internal Cd concentration. When sown in Cd-containing germitest paper, the immediate progeny of plants grown in soil with no Cd addition was generally able to maintain or even increase the content of carotenoids and chlorophylls a and b (up to 93.3, 62.8 and 76.1%, respectively), indicating a Cd-induced hormetic effect on photosynthetic pigments. Two of the grafting combinations from stressed plants yielded seeds that generated seedlings with enhanced dry mass when they were sown in Cd-free media (~41%), suggesting a Cd-induced transgenerational enhancement of biomass production. Because only one tomato cultivar was used as scion, data indicated that type and degree of Cd-induced transgenerational effects depend strongly on signals generated and/or processed in roots of the parental plants. When sown in Cd-contaminated germitest paper, the immediate progeny of Cd-treated plants presented major reductions in the leaf area (35-69%) and content of photosynthetic pigments (57-93%) in comparison to the progeny from control plants. However, one of the grafting combinations exhibited satisfactory performance after "double" exposure to Cd, showing 91% of the biomass that was produced in the seedlings of control seeds from control plants. Further investigation indicated that adjustments in the chlorophyll fluorescence behavior might counterbalance losses in leaf pigments and area. Taken together, our data provide new insights on the origin, outcomes and mode of action of the Cd-induced transgenerational effects.

The objective of the present study was to assess the response of tomato cultivars with different fruit colors to exposure to increasing Cd levels in the substrate by measuring the impacts of Cd on the oxidative stress indicators and physicochemical features of fruits, as well as plant development and yield components. A completely randomized experiment in a 3 × 3 factorial design [tomato cultivar (which produces purple, red, or white fruits) vs Cd level in the substrate (0, 3.6, or 12 mg kg−1)] was performed. The cultivation of plants in substrate containing 3.6 mg kg−1 Cd did not affect yield, but fruits exhibited nonpermissive Cd concentrations in both peel and mesocarp across all cultivars. By contrast, yield was decreased in plants with red and white fruits after their cultivation in substrate containing 12 mg kg−1 Cd, while the productivity of plants with purple fruits was maintained under such conditions. The hydrogen peroxide content in the fruit mesocarp depended only on cultivar. However, an increased lipid peroxidation level was detected in the mesocarp of purple fruits at the highest Cd concentration. No parameters of fruit quality [i.e., diameter, length, °Brix, pH, titratable acidity, color (L*, a*, and b*), and concentrations of lycopene and β-carotene in mesocarp] were affected by long-term exposure to Cd at 12 mg kg−1. In conclusion, the results of this study suggested that the potential Cd side effects on diverse tomato quality features can be buffered at the fruit level because these features were maintained at the usual values despite high Cd concentrations in tomato peel and pulp. Moreover, these buffering mechanisms are independent of lycopene and β-carotene concentrations in fruit peel, since the three tomato cultivars that were evaluated in the present study (white fruits, possessing no or negligible concentrations of these carotenoids, and red and purple tomato, possessing high lycopene and β-carotene concentrations) were able to sustain several fruit quality parameters after long-term exposure to high Cd concentrations in the substrate.

This work aimed to develop a reliable and fast approach to estimate the plant tolerance degree to heavy metal (HM) phytotoxicity. Two independent experiments were carried out using tomato accessions, with contrasting morphological features, that were grown in a hydroponic solution containing different CdCl2 concentrations for 7 days. Plant dry weight and chlorophyll content (SPAD units) were evaluated, and tolerance degree to Cd toxicity was estimated according to the tolerance index (TI), which is a new mathematical formula based on plant biomass proposed in this study. Although with different magnitudes, tomato exhibited reductions in their dry weight concurrently with the increasing CdCl2 concentration. By contrast, chlorophyll content presented no standard response, decreasing and even increasing according to CdCl2 concentrations, indicating that only under certain conditions (particularly, at CdCl2 50 μM), this parameter can be used to estimate plant tolerance to Cd toxicity. TI was efficiently able to segregate tomato cultivars with similar performance (based on the total dry weight of plants), and such segregation was optimized when the hydroponic solution contained from 25 to 50 μM CdCl2. Within this range, data pointed at 35 μM CdCl2 as the best concentration to be employed in studies related to the tomato tolerance/sensitivity to Cd toxicity. In conclusion, TI proved to be a reliable estimator of tolerance degree to Cd exposure in genetically distinct tomato accessions. Moreover, TI can be used for this same purpose in plants under other HM-induced stresses.

In general, the effects of Cadmium (Cd) on crop quality are evaluated solely by Cd accumulation in the edible plant parts; thus, the potential effects on several nutritional features are not often taken into account. This study evaluated Cd effects on the enzymatic activities of lysine (Lys) metabolism, storage protein and amino acid profile in maize. Stress parameters were also assessed. In vegetative organs, Cd was accumulated in the following decreasing order: roots > stems > leaves. Cadmium accumulation in grains decreased at grain maturity (from 0.25 to 0.07 µg g−1 DW). In leaves, neither hydrogen peroxide content nor superoxide dismutase, catalase, ascorbate peroxide and guaiacol peroxidase activities did not change in Cd-treated plants compared to control plants. Lipid peroxidation was not detected in immature grains and leaves of plants under Cd exposure, indicating that Cd accumulation mainly in the roots is a mechanism to avoid oxidative stress in aboveground parts of the plant. However, Lys metabolism in immature grains was modified, showing increases in the specific activities of aspartate kinase (AK) and dihydrodipicolinate synthase (DHDPS) after Cd exposure. AK sensitivity to Lys feedback inhibition increased, but decreased in DHDPS in Cd-treated plants, suggesting differential regulation for these enzymes. In mature grains, the Lys content did not change, while the proline content increased by 54 % in Cd-treated plants. This is the first report on Cd effects on amino acid profile, storage protein contents and enzymes from Lys metabolism in grains of a cereal plant species.

This work aimed to quantify the concentration of soluble amino acids, nitrogen (N) and Cd in the developing seeds of maize plants that were grown in Cd-contaminated soil from seed sowing to the reproductive stages. The specific activities and feedback inhibition properties of lysine (Lys) metabolic enzymes were also determined in developing seeds. The potential maize yield was depressed by Cd exposure. Cadmium concentration in plant organs followed the decreasing order: roots > stems = leaves > developing seeds (37.04, 1.95, 1.46 and 0.22 mg kg−1 Cd, respectively). The relatively low Cd concentration in the remained developing seeds was a result from root- and ear-mediated reductions of the Cd translocation in plants. Plants under Cd exposure presented developing seeds with an increased N concentration (up to 7%) when compared to control plants. Furthermore, the level of soluble amino acids (particularly histidine, glycine, tyrosine, methionine, isoleucine and valine) was increased in the developing seeds of Cd-treated plants. In addition, changes in the feedback properties of dihydrodipicolinate synthase (DHDPS), an enzyme from lysine metabolism, were observed in developing seeds. In conclusion, the current study showed that maternal plant exposure to Cd can alter the concentration of soluble amino acids and the behavior of Lys metabolic enzymes in developing seeds. This study provided not only new information about the influence of the long-term Cd exposure on plants, but also data about protective plant strategies against Cd toxicity.

Tolerance level to cadmium (Cd) toxicity is generally associated with reductions of the internal Cd accumulation in living organisms. In plants, Cd exposure frequently triggers negative effects on their growth and productivity. However, an increased number of studies has reported the improved performance of some plant species (or their accessions/genotypes/varieties/cultivars/clones) to Cd exposure, despite Cd accumulation in their roots and shoots. These results indicate that plants have developed protective strategies to neutralize the side-effects from Cd toxicity or, more controversially, mechanisms that employ Cd as beneficial element. Here, we gathered information about Cd-induced hormetic effects on plants, and explored the potential mechanisms that allow them to have a better performance under Cd exposure. The promotion of plant development depends on both direct and indirect Cd-induced alterations in the metabolism of plants and their surround environment. In addition, the mechanisms behind the positive Cd-induced transgenerational effects were also discussed in the present paper.

O presente estudo tem como objetivo comparar a rentabilidade da produção de cana-de-açúcar através dos sistemas de arrendamento e fornecimento próprio, visando auxiliar na tomada de decisão do proprietário da terra quanto a alternativa mais viável diante da atual situação de mercado. O sistema de fornecimento foi divido em duas modalidades: "cana spot" e "cana esteira". Para a análise financeira, foram utilizados dados da safra de 2014/2015 de fornecedores filiados à uma associação, localizada em Chavantes, região centro-oeste de São Paulo. Em seguida foram projetados fluxos de caixa para cada sistema de produção; calculados o valor presente líquido (VPL), a taxa interna de retorno (TIR), o payback simples e realizada a análise de sensibilidade. Os cálculos indicaram a inviabilidade da produção de cana-de-açúcar em todos os casos, pois apresentaram VPL negativo e TIR inferior à taxa mínima de atratividade (TMA). No entanto, após a análise de sensibilidade com valores de remuneração mais altos ao produtor, as opções de fornecimento de "cana spot" e arrendamento exibiram resultados otimistas. Deste modo, conclui-se que a produção de cana-de-açúcar é uma atividade inviável para proprietários de terra com pequenas área em Chavantes/SP. Porém, considerando a análise de sensibilidade, a modalidade de fornecimento próprio de cana "spot" é a alternativa mais atrativa economicamente, pois o VPL e TIR apresentaram valores mais elevados do que aqueles encontrados no arrendamento. No entanto, aquela opção possui elevado risco para o produtor, que fica condicionado à demanda de mercado.

Cadmium (Cd) is an environmental pollutant that limits crop production. Among the deleterious effects by metal induced stress on plant development, cell leakage and nutrient losses have been observed, whereas root morphology is severely affected. However, the mechanisms by which genotypes contrasting in tolerance level to heavy metal excess maintain root cells integrity and nutrient absorption are still unclear. In this work, tomato (Solanum lycopersicum) genotypes with contrasting tolerance to Cd toxicity, Calabash Rouge (sensitive) and Pusa Ruby (tolerant), were used to shed some light on possible tolerance mechanisms against Cd toxicity. For this purpose, plants were grown in hydroponics containing 0 or 35 μM CdCl2 for 7 days. Temporal variations (on the 1st, 4th and 7th days of Cd exposure) in nutrient management (absorption and use efficiency), relative plant growth, biomass partitioning, root morphology and Cd accumulation were evaluated in control and Cd-treated plants. Furthermore, multivariate analyses, in which information about the antioxidant machinery was also included, were performed in order to identify the set of parameters related to plant tolerance. The results showed that Pusa Ruby was able to improve biomass allocation to roots, further increasing their capacity to accumulate this metal. The tolerant genotype was also more capable to modulate nutrient uptake by roots under Cd excess. In conclusion, the current study revealed that Pusa Ruby is more tolerant to Cd exposure than Calabash Rouge due to its ability in reducing Cd-induced damages on root morphology and on nutrient absorption and use efficiency.

Distinct tomato genotypes possess different tolerance degree to cadmium (Cd), but the mechanisms behind this phenomenon are scarcely understood. To this end, the physiological, biochemical, anatomical, nutritional and molecular mechanisms associated to the plant tolerance against Cd toxicity were investigated in five tomato accessions with contrasting sensitivity to Cd exposure. Firstly, the data revealed that larger biomass loss was not always coupled to higher Cd concentration, indicating that other events, in addition to the internal Cd accumulation, impact tomato performance at early stages of Cd exposure. Secondly, the results indicated that the fine regulation of nutrient status, particularly magnesium (Mg), boron (B) and manganese (Mn), is associated to the mitigation of Cd toxicity. Magnesium status was coupled to the modulation of root development, resulting in changes in root hair formation and biomass allocation. Boron accumulation in leaves was linked to Cd toxicity, suggesting that tolerance mechanisms involved strategies to decrease or even avoid B excess in photosynthetic tissues. Disturbances in Mn status, i.e. Mn excess in leaves and Mn deficiency in roots, were also related to tomato sensitivity to Cd exposure. Thirdly, plant capacity to maintain leaf blade expansion is a relevant strategy for a better tomato development after short-term Cd exposure. Fourthly, tomato tolerance to Cd-induced stress does not depend on CAT activity enhancements in such conditions. In conclusion, tomato ability to quickly manage its nutritional status is necessary for alleviation of the Cd effects at early stages of exposure to this metal. The better understanding about tolerance mechanisms and mode of action of Cd toxicity in plants can help in the establishment of strategies to mitigate its impacts on crops.

This study aimed to investigate the mode of action of cadmium (Cd) toxicity at cell level, especially at early stages of plant exposure. Tomato seedlings were cultivated in growth media containing from 0.1 to 70 µM CdCl2 for 24 h. Mitotic index, chromosome abnormality, DNA integrity and organization of tubulin-based structures were assessed in root cells. As higher the Cd concentration in the growth media, higher was the DNA damage intensity and the occurrence of chromosomal abnormalities that included chromosome lost, bridges, stickiness, C-metaphase and polyploidy. The profile of chromosomal aberrations also varied with elevated Cd concentration, being observed increases in the frequency of chromosome stickiness. The mitotic index was reduced at the lowest Cd concentration, but such reduction was statistically similar to that detected at the highest concentration, suggesting that mitotic depression is a rapid outcome and, at same time, a Cd-induced effect that is limited at the first 24 h of direct root exposure to this metal. Under exposure to 20 µM CdCl2, heterogenous distribution of the spindle fibers, formation of two spindle complexes in both of the cell poles, absence of centrosome center, polarization of the spindle fibers during cell division, and non-uniform tubulin deposition in microtubule and phragmoplast were noticed. The results indicate that the tubulin-dependent components of cytoskeleton are Cd targets, and the sensitivity of tubulin-based structures to Cd exposure depends on cell cycle phase. Moreover, DNA damage intensity and chromosomal abnormality profile can be employed as markers of Cd toxicity level.

Cadmium (Cd) toxicity is frequently coupled to its accumulation in plants, but not always the highest Cd concentration triggers the worst damages, indicating that additional events influence the magnitude of Cd side-effects. We investigated the early mechanisms behind the differential Cd-induced impacts on plant development of four tomato accessions with contrasting tolerance to Cd toxicity. At organ level, the highest Cd concentration was not associated with the largest biomass losses. In leaves, changes in superoxide dismutase and catalase activities were not related to differences in Cd concentration, which was unable to provoke H2O2 overproduction on the sixth day of plant exposure to this metal. Further investigation in the mineral profile revealed that magnitude of Cd toxicity depends probably on synergic effects from increased B status, in addition to the own Cd accumulation. Furthermore, disbalances in Mn status (i.e., excess in leaves and deficiency in roots) may enhance Cd toxicity degree. According to data, however, the low magnesium (Mg) status can be linked to tomato tolerance against Cd toxicity. In conclusion, the tomato tolerance degree under short-Cd exposure depends on actively, finely regulation of mineral homeostasis that results in different development of plant organs. The better understanding on the mode of action of Cd toxicity in plants can help in the establishment of strategies to mitigate its impacts on crop yield.

Although negative effects on the offspring fitness can be triggered by the mother-plant exposure to environmental stresses, some plants are able to “remember” past incidents and enhance the progeny tolerance. Here, the mineral profile, cytogenetic modifications, and physiological potential of seeds from two tomato cultivars, with contrasting tolerance degrees to cadmium (Cd) toxicity, were evaluated after plant exposure to this metal. Both cultivars exhibited high Cd translocation to the seeds; however, the tolerant tomato accumulated more Cd than did the sensitive one. As a consequence of the Cd accumulation, reductions in the Mn concentration in Cd-challenged plants were detected. Surprisingly, seed germination and vigor were increased in the tolerant tomato cultivar after Cd exposure, despite increases in the chromosomal abnormalities. By contrast, seeds from the sensitive cultivar exhibited no changes in their physiological potential after Cd exposure, despite Cd-induced reductions in the mitotic index. Moreover, bunch position exerted effects on the vigor and type of chromosomal abnormality. The results show that maternal plant exposure to Cd can affect tomato offspring by changing the seed physiological potential, and such effect can be partially explained by alterations in the seed-derived elements (essential and non-essential) and genotype-dependent tolerance mechanisms.

Tomato is an important crop worldwide. Cadmium (Cd) concentrations in fruits depend on tomato genotype. This work aimed to study the relation among Cd accumulation, tolerance mechanisms, and fruit features in two tomato cultivars with contrasting tolerance to Cd stress. Tolerant (Yoshimatsu) and sensitive (Tropic Two Orders) plants were grown in control and contaminated soils (0.04 and 3.77mg/kg Cd, respectively) from the seedling stage to fruit production. Both cultivars were able to acclimatize to Cd exposure, probably through mechanisms associated with reductions in the magnesium status. Cadmium concentrations varied according to the following descending order: roots=leaf blades > (peduncle+sepals) > stem=fruits. However, the tolerant cultivar accumulated more Cd than did the sensitive one. Although Cd reached the fruits from the first to the fourth bunches, peduncle and sepals may act as a barrier to Cd entrance in tomato pulp and peel. The Cd-induced changes in the fruit mineral profile varied according to plant cultivar, organ, tomato tissue, and bunch position. Moreover, plant yield was not affected by the Cd stress, which was able to improve fruit size and weight in the tolerant cultivar. In conclusion, new insights about the Cd-induced effects on tomato development and fruit attributes were provided by growing plants in soil, which is the media generally used to cultivate this crop, rather than hydroponics. It was shown that tomato cultivars with contrasting tolerance to Cd toxicity can reach sexual maturity and produce fruits with no yield losses, despite impacts on development from long-term Cd exposure. This study also revealed the role of floral receptacle and its related structures in limiting, even partially, Cd translocation to the fruits. Furthermore, Yoshimatsu's capacity to produce bigger and heavier fruits, in plants under Cd exposure, may probably be associated with enhanced Cd accumulation. Fundacao de Amparo a Pesquisa do Estado de Sao Paulo [2009/54676-0, 2013/15217-5]; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico [303749/2016-4, 476096/2013-8]