Physiological and Antioxidant Response to Different Water Deficit Regimes of Flag Leaves and Ears of Wheat Grown under Combined Elevated CO2 and High Temperature.

Triticum aestivum L. cv. Gazul is a spring wheat widely cultivated in Castilla y León (Spain). Potted plants were grown in a scenario emulating the climate change environmental conditions expected by the end of this century, i.e., with elevated CO2 and high temperature under two water deficit regimes: long (LWD) and terminal (TWD). Changes in biomass and morphology, the content of proline (Pro), ascorbate (AsA) and glutathione (GSH), and enzymatic antioxidant activities were analyzed in flag leaves and ears. Additionally, leaf gas exchange was measured. LWD caused a decrease in biomass and AsA content but an increase in Pro content and catalase and GSH reductase activities in flag leaves, whereas TWD produced no significant changes. Photosynthesis was enhanced under both water deficit regimes. Increase in superoxide dismutase activity and Pro content was only observed in ears under TWD. The lack of a more acute effect of LWD and TWD on both organs was attributed to the ROS relieving effect of elevated CO2. Gazul acted as a drought tolerant variety with anisohydric behavior. A multifactorial analysis showed better adaptation of ears to water deficit than flag leaves, underlining the importance of this finding for breeding programs to improve grain yield under future climate change.

Theoretical and Experimental Considerations for a Rapid and High Throughput Measurement of Catalase In Vitro.

A rapid and high throughput protocol to measure the catalase activity in vitro has been designed. Catalase is an enzyme with unusual kinetic properties because it does not follow the standard Michaelis-Menten model and is inactivated by H2O2. This makes the analysis of the two rate equations of the second-ordered reactions of the kinetic model rather complex. A two-degree polynomial fitting of the experimental data is proposed after transforming the exponential form of the integrated rate equation of the [H2O2] into a polynomial using the Taylor series. The fitting is validated by establishing an experimental linear relationship between the initial rate of the H2O2 decomposition and the protein concentration, regardless of the suicide inactivation that catalase might undergo beyond t > 0. In addition, experimental considerations are taken into account to avoid statistical bias in the analysis of the catalase activity. ANOVA analyses show that the proposed protocol can be utilized to measure the initial rate of the H2O2 decomposition by catalase in 32 samples in triplicates if kept below 8 mM min-1 in the microplate wells. These kinetic and statistical analyses can pave the way for other antioxidant enzyme activity assays in microplate readers at small scale and low cost.

1-Methyltryptophan Treatment Increases Defense-Related Proteins in the Apoplast of Tomato Plants.

The activation of induced resistance in plants may enhance the production of defensive proteins to avoid the invasion of pathogens. In this way, the composition of the apoplastic fluid could represent an important layer of defense that plants can modify to avoid the attack. In this study, we performed a proteomic study of the apoplastic fluid from plants treated with the resistance inducer 1-methyltryptophan (1-MT) as well as infected with Pseudomonas syringae pv. tomato (Pst). Our results showed that both the inoculation with Pst and the application of the inducer provoke changes in the proteomic composition in the apoplast enhancing the accumulation of proteins involved in plant defense. Finally, one of the identified proteins that are overaccumulated upon the treatment have been expressed in Escherichia coli and purified in order to test their antimicrobial effect. The result showed that the tested protein is able to reduce the growth of Pst in vitro. Taken together, in this work, we described the proteomic changes in the apoplast induced by the treatment and by the inoculation, as well as demonstrated that the proteins identified have a role in the plant protection.

Expression of miR159 Is Altered in Tomato Plants Undergoing Drought Stress.

In a scenario of global climate change, water scarcity is a major threat for agriculture, severely limiting crop yields. Therefore, alternatives are urgently needed for improving plant adaptation to drought stress. Among them, gene expression reprogramming by microRNAs (miRNAs) might offer a biotechnologically sound strategy. Drought-responsive miRNAs have been reported in many plant species, and some of them are known to participate in complex regulatory networks via their regulation of transcription factors involved in water stress signaling. We explored the role of miR159 in the response of Solanum lycopersicum Mill. plants to drought stress by analyzing the expression of sly-miR159 and its target SlMYB transcription factor genes in tomato plants of cv. Ailsa Craig grown in deprived water conditions or in response to mechanical damage caused by the Colorado potato beetle, a devastating insect pest of Solanaceae plants. Results showed that sly-miR159 regulatory function in the tomato plants response to distinct stresses might be mediated by differential stress-specific MYB transcription factor targeting. sly-miR159 targeting of SlMYB33 transcription factor transcript correlated with accumulation of the osmoprotective compounds proline and putrescine, which promote drought tolerance. This highlights the potential role of sly-miR159 in tomato plants' adaptation to water deficit conditions.

1-Methyltryptophan Modifies Apoplast Content in Tomato Plants Improving Resistance Against Pseudomonas syringae.

Plants can produce numerous natural products, many of which have been shown to confer protection against microbial attack. In this way, we identified 1-methyltryptophan (1-MT), a natural compound produced by tomato plants in response to Pseudomonas syringae attack, whose application by soil drench provided protection against this pathogen. In the present work, we have studied the mechanisms underlying this protection. The results demonstrated that 1-MT can be considered a new activator of plant defense responses that acts by inhibiting the stomatal opening produced by coronatine (COR) and could thereby, prevent bacteria entering the mesophyll. Besides, 1-MT acts by blocking the jasmonic acid (JA) pathway that, could avoid manipulation of the salicylic acid (SA) pathway by the bacterium, and thus hinder its growth. Although the concentration of 1-MT reached in the plant did not show antimicrobial effects, we cannot rule out a role for 1-MT acting alone because it affects the expression of the fliC gene that is involved in synthesis of the flagellum. These changes would result in reduced bacterium motility and, therefore, infective capacity. The results highlight the effect of a tryptophan derivative on induced resistance in plants.

Elucidating the mechanism of action of copper heptagluconate on the plant immune system against Pseudomonas syringae in tomato (Solanum lycopersicum L).

BACKGROUND: Phytopathogenic problems caused by the bacterial pathogen Pseudomonas syringae in tomato are becoming more serious due to the emergence of strains resistant to classical pesticides. This has led to research into new formulations with lower environmental problems. One of the most promising alternatives to the use of classical pesticides is the induction of natural plant defences. New formulations based on Cu complexed with heptagluconic acid induce plant innate defences and could be an alternative to classical treatments based on inorganic Cu against bacterial speck. To study the efficacy of this compound in tomato against P. syringae, we tested its systemic effect Applying the treatments via radicular. RESULTS: Treated plants showed less infection development and lower number of viable bacteria in leaves. We also observed better performance of parameters involved in plant resistance such as the antioxidant response and the accumulation of phenolic compounds. CONCLUSION: Results showed that soil drench applications can be highly effective for the prevention and control of bacterial speck in tomato plants, showing a reduction in symptoms of ∼ 50%. Moreover, application of Cu heptagluconate induced accumulation of the plant polyphenols caffeic and chlorogenic acids, and reduced the amount of reactive oxygen species in infected plants. © 2018 Society of Chemical Industry.

Epigenetic regulation of the expression of WRKY75 transcription factor in response to biotic and abiotic stresses in Solanaceae plants.

KEY MESSAGE: SlyWRKY75: gene expression was induced in response to biotic stresses, especially in Botrytis cinerea-infected tomato plants, in which Sly-miR1127-3p is a putative SlyWRKY75 regulator and epigenetic marks were detected. WRKY75 transcription factor involved in Pi homeostasis was recently found also induced in defense against necrotrophic pathogens. In this study, we analyzed by RT-qPCR the expression of SlyWRKY75 gene in tomato plants in response to abiotic stresses (drought or heat) and biotic stresses (Colorado potato beetle larvae infestation, Pseudomonas syringae or Botrytis cinerea infection) being only differentially expressed following biotic stresses, especially upon B. cinerea infection (55-fold induction). JA and JA-Ile levels were significantly increased in tomato plants under biotic stresses compared with control plants, indicating that SlyWRKY75 might be a transcriptional regulator of the JA pathway. The contribution of miRNAs and epigenetic molecular mechanisms to the regulation of this gene in B. cinerea-infected tomato plants was explored. We identified a putative Sly-miR1127-3p miRNA predicted to bind the intronic region of the SlyWRKY75 genomic sequence. Sly-miR1127-3p miRNA was repressed in infected plants (0.4-fold) supporting that it might act as an epigenetic regulation factor of SlyWRKY75 gene expression rather than via the post-transcriptional mechanisms of canonical miRNAs. It has been proposed that certain miRNAs can mediate DNA methylation in the plant nucleus broadening miRNA functions with transcriptional gene silencing by targeting intron-containing pre-mRNAs. Histone modifications analysis by chromatin immunoprecipitation (ChIP) demonstrated the presence of the activator histone modification H3K4me3 on SlyWRKY75 transcription start site and gene body. The induction of this gene in response to B. cinerea correlates with the presence of an activator mark. Thus, miRNAs and chromatin modifications might cooperate as epigenetic factors to modulate SlyWRKY75 gene expression.

Bioassimilable sulphur provides effective control of Oidium neolycopersici in tomato, enhancing the plant immune system.

BACKGROUND: Developments of alternatives to the use of chemical pesticides to control pests are focused on the induction of natural plant defences. The study of new compounds based on liquid bioassimilable sulphur and its effect as an inductor of the immune system of plants would provide an alternative option to farmers to enhance plant resistance against pathogen attacks such as powdery mildew. In order to elucidate the efficacy of this compound in tomato against powdery mildew, we tested several treatments: curative foliar, preventive foliar, preventive in soil drench and combining preventive in soil drench and curative foliar. RESULTS: In all cases, treated plants showed lower infection development, better physiological parameters and a higher level of chlorophyll. We also observed better performance in parameters involved in plant resistance such as antioxidant response, callose deposition and hormonal levels. CONCLUSION: The results indicate that preventive and curative treatments can be highly effective for the prevention and control of powdery mildew in tomato plants. Foliar treatments are able to stop the pathogen development when they are applied as curative. Soil drench treatments induce immune response mechanisms of plants, increasing significantly callose deposition and promoting plant development. © 2016 Society of Chemical Industry.