Rafael de Souza Miranda

Enhanced salt tolerance in maize plants induced by H2O2 leaf spraying is associated with improved gas exchange rather than with non-enzymatic antioxidant system

Hydrogen peroxide (H2O2) is an essential signaling molecule that mediates plant responses against several biotic and abiotic stresses. H2O2 pretreatment has emerged as a signaling way, inducing salt stress acclimation in plants. Here, we analyzed the effects of H2O2 leaf pretreatment on the non-enzymatic defense system (ascorbate and glutathione), plant growth, relative water content (RWC), relative chlorophyll content, H2O2 content, and gas exchange in maize plants under NaCl stress. The results showed that salinity reduced the leaf area and shoot and root dry mass as compared to control, and the leaf spraying with H2O2 significantly improved the growth of salt stressed plants. Photosynthesis and transpiration, stomatal conductance and intercellular CO2 concentration were strongly decreased by salinity after 7 and 14 days of salt exposure; however, the decrease was lower in plants sprayed with H2O2. The improved gas exchange in H2O2-sprayed stressed plants correlated positively with higher RWC and relative chlorophyll content and lower leaf H2O2 accumulation under NaCl stress conditions. Ascorbate and glutathione did not play any obvious effects as non-enzymatic antioxidants in the ROS scavenging. In conclusion, the salt tolerance induced by H2O2 leaf pretreatment is attributed to a reduction in the H2O2 content and maintenance of RWC and chlorophyll in maize leaves. These characteristics allow maize plants to maintain high rates of photosynthesis under salt stress and improve the growth.

Exogenous nitric oxide improves salt tolerance during establishment of Jatropha curcas seedlings by ameliorating oxidative damage and toxic ion accumulation

Jatropha curcas is an oilseed species that is considered an excellent alternative energy source for fossil-based fuels for growing in arid and semiarid regions, where salinity is becoming a stringent problem to crop production. Our working hypothesis was that nitric oxide (NO) priming enhances salt tolerance of J. curcas during early seedling development. Under NaCl stress, seedlings arising from NO-treated seeds showed lower accumulation of Na+ and Cl- than those salinized seedlings only, which was consistent with a better growth for all analyzed time points. Also, although salinity promoted a significant increase in hydrogen peroxide (H2O2) content and membrane damage, the harmful effects were less aggressive in NO-primed seedlings. The lower oxidative damage in NO-primed stressed seedlings was attributed to operation of a powerful antioxidant system, including greater glutathione (GSH) and ascorbate (AsA) contents as well as catalase (CAT) and glutathione reductase (GR) enzyme activities in both endosperm and embryo axis. Priming with NO also was found to rapidly up-regulate the JcCAT1, JcCAT2, JcGR1 and JcGR2 gene expression in embryo axis, suggesting that NO-induced salt responses include functional and transcriptional regulations. Thus, NO almost completely abolished the deleterious salinity effects on reserve mobilization and seedling growth. In conclusion, NO priming improves salt tolerance of J. curcas during seedling establishment by inducing an effective antioxidant system and limiting toxic ion and reactive oxygen species (ROS) accumulation.

Deficiência nutricional em plântulas de feijão-de-corda decorrente da omissão de macro e micronutrientes

Resumo - O feijao-de-corda [ Vigna unguiculata (L.) Walp] cv. Pitiuba e uma importante cultura nos âmbitos economico e social do Nordeste do Brasil, especialmente no Estado do Ceara, que e considerado o maior produtor desta regiao. Com a finalidade de caracterizar os sintomas de deficiencias nutricionais em plântulas de feijao-de-cor da, as sementes for am semeadas em areia exaustivamente lavada e, apos um periodo de cinco dias, as plântulas foram transferidas para uma solucao nutritiva completa para o periodo de aclimatacao. Apos tres dias, as plântulas foram submetidas aos diferentes tratamentos. O experimento teve os seguintes tratamentos: solucao nutritiva completa (N; P; K; Ca; Mg; S e micronutrientes) e omissao individual de cada elemento -N; -P; -K; -Ca; -Mg; -S; -B; -Fe, bem como ausencia de aeracao. Os sintom as das deficiencias foram observados, caracterizados e registrados por fotografias. No final do experimento, as medidas de comprimento e os teores de materias fresca e seca das raizes e parte aerea das plântulas foram analisados. Todos os macros e micronutrientes causaram sintomas de deficiencia e afetaram o desenvolvimento das plântulas. Os sintomas foram desenvolvidos primeiramente em plântulas com carencia em Fe, Ca e N. A materia seca total foi reduzida em todo s os tratamentos com ausencia de nutrientes. A ausencia de Ca, N e Fe foi responsavel por uma maior reducao da biomassa. A ordem decrescente de reducao foi a seguinte: Ca > N > Fe > P > K > Mg > S > Aeracao > B > Completo. Palavras-chave - Hidroponia. Nutricao mineral. Plantas-efeito dos minerais. Sintomas. Vigna unguiculata.

Integrative Control Between Proton Pumps and SOS1 Antiporters in Roots is Crucial for Maintaining Low Na+ Accumulation and Salt Tolerance in Ammonium-Supplied Sorghum bicolor

An effective strategy for re-establishing K+ and Na+ homeostasis is a challenge for the improvement of plant performance in saline soil. Specifically, attempts to understand the mechanisms of Na+ extrusion from plant cells, the control of Na+ loading in the xylem and the partitioning of the accumulated Na+ between different plant organs are ongoing. Our goal was to provide insight into how an external nitrogen source affects Na+ accumulation in Sorghum bicolor under saline conditions. The NH4+ supply improved the salt tolerance of the plant by restricting Na+ accumulation and improving the K+/Na+ homeostasis in shoots, which was consistent with the high activity and expression of Na+/H+ antiporters and proton pumps in the plasma membrane and vacuoles in the roots, resulting in low Na+ loading in the xylem. Conversely, although NO3--grown plants had exclusion and sequestration mechanisms for Na+, these responses were not sufficient to reduce Na+ accumulation. In conclusion, NH4+ acts as an efficient signal to activate co-ordinately responses involved in the regulation of Na+ homeostasis in sorghum plants under salt stress, which leads to salt tolerance.

Putative role of glutamine in the activation of CBL/CIPK signalling pathways during salt stress in sorghum

ABSTRACT The salt overly sensitive (SOS) pathway is the only mechanism known for Na+ extrusion in plant cells. SOS pathway activation involves Ca2+-sensing proteins, such as calcineurin B-like (CBL) proteins, and CBL-interacting protein kinases (CIPKs). In this signalling mechanism, a transit increase in cytosolic Ca2+ concentration triggered by Na+ accumulation is perceived by CBL (also known as SOS3). Afterward, SOS3 physically interacts with a CIPK (also known as SOS2), forming the SOS2/SOS3 complex, which can regulate the number downstream targets, controlling ionic homeostasis. For instance, the SOS2/SOS3 complex phosphorylates and activates the SOS1 plasmalemma protein, which is a Na+/H+ antiporter that extrudes Na+ out of the cell. The CBL-CIPK networking system displays specificity, complexity and diversity, constituting a critical response against salt stress and other abiotic stresses. In a study reported in the journal Plant and Cell Physiology, we showed that NH4+ induces the robust activation of transporters for Na+ homeostasis in root cells, especially the SOS1 antiporter and plasma membrane H+-ATPase, differently than does NO3−. Despite some studies having shown that external NH4+ ameliorates salt-induced effects on ionic homeostasis, there is no evidence that NH4+ per se or some product of its assimilation is responsible for these responses. Here, we speculate about the signalling role behind glutamine in CBL-CIPK modulation, which could effectively activate the SOS pathway in NH4+-fed stressed plants.

Ion accumulation in young plants of the ‘green dwarf’ coconut under water and salt stress

Water scarcity and salinity are two major limitations on agricultural production. The aim of this study was to investigate the biochemical mechanisms associated with the separate and/or concurrent effects of water deficit and soil salinity on young plants of the ‘green dwarf’ coconut from the responses of ion accumulation (potassium, sodium and chloride) in the leaves and roots. The experiment was carried out in a screened greenhouse in Fortaleza, in the State of Ceara, Brazil. A randomised complete block statistical design was used in a scheme of treatments in subdivided plots, to evaluate the effects of different levels of water deficiency (plots) using different percentages for the replacement of water lost through potential crop evapotranspiration (20, 40, 60, 80 and 100%), associated with sub-plots comprising increasing levels of soil salinity (1.72, 6.25 , 25.80 and 40.70 dS m-1) found in soils collected in the Morada Nova Irrigated Perimeter (Morada Nova/Limoeiro do Norte, Ceara). Under conditions of water scarcity, K+ is maintained and/or accumulated in the leaves; while in the roots, levels are jointly affected by water deficiency and soil salinity, where these stress agents act in an antagonistic way on the K+ content. Conditions of salt stress lead to increases in the levels of Na+ both in the leaves and especially in the roots. The Cl- ion content of the leaves and roots responds to the interaction between water deficiency and salinity, demonstrating synergy in the relationship between stress agents. The accumulation of inorganic solutes in the leaves and roots of the coconut follows the order: Cl- > K+ > Na+.

Guidelines for Successful Quantitative Gene Expression in Real- Time qPCR Assays

This chapter was developed to provide some important guidelines for studies with quantitative PCR (qPCR) using either dyes or probes, citing several essential compo‐ nents necessary for a good PCR assay. The efficiency and specificity of quantitative PCR (qPCR) depend on several parameters related to mRNA quantification that must be controlled to avoid mistakes in data interpretation. Avoiding contamination with proteins, carbohydrate and phenolic compounds during RNA extraction and purifica‐ tion processes will improve RNA quality and provide reliable results. Specific primers and sensible probes are also crucial to intensify efficiency, specificity and fluorescence. Other parameters such as the optimization of primer concentrations and efficiency primer curves must be done. During gene‐expression profile quantification, qPCR assays using reference genes are required to normalize the target gene expression data. These reference genes are checked for stability to identify the most stable genes among a group of candidate genes that will be used to normalize the qPCR data, using programs such as geNorm, BestKeeper and NormFinder. Additionally, the choice of appropriate reference genes for a specific experimental condition is fundamental. The main aim of this chapter is to provide guidelines and highlight precautions to obtain a successful qPCR assays.