A momentary increase in cytoplasmic Ca²⁺ generates an oscillation responsible for the activation of proteins, such as calmodulin and kinases, which interact with reactive oxygen species (ROS) for the transmission of a stress signal. This study investigated the influence of variations in calcium concentrations on plant defense signaling and photosynthetic acclimatization after mechanical damage. Solanum lycopersicum Micro-Tom was grown with 0, 2 and 4 mM Ca²⁺, with and without mechanical damage. The expression of stress genes was evaluated, along with levels of antioxidant enzymes, hydrogen peroxide, lipid peroxidation, histochemistry, photosynthesis and dry mass of organs. The ROS production generated by mechanical damage was further enhanced by calcium-free conditions due to the inactivation of the oxygen evolution complex, contributing to an increase in reactive species. The results indicated that ROS affected mechanical damage signaling because calcium-free plants exhibited high levels of H₂O₂ and enhanced expression of kinase and RBOH1 genes, necessary conditions for an efficient response to stress. We conclude that the plants without calcium supply recognized mechanical damage but did not survive. The highest expression of the RBOH1 gene and the accumulation of H₂O₂ in these plants signaled cell death. Plants grown in the presence of calcium showed higher expression of SlCaM2 and control of H₂O₂ concentration, thus overcoming the stress caused by mechanical damage, with photosynthetic acclimatization and without damage to dry mass production.

The current climate change setting necessitates the development of methods to mitigate the effects of water scarcity to ensure the sustainability of agricultural activities.f Hydrogen peroxide (H₂O₂) is a plant signaling molecule that can trigger metabolic defense mechanisms in response to adverse environmental circumstances like as drought. The purpose of this study was to investigate if foliar application of H₂O₂ stimulates modifications in photosynthetic metabolism for adaptation of tomato plants to a period of water deficit and recovery. The study, which was carried out in a factorial scheme, tested plants subjected to two water conditions (well-watered plants and plants subjected to water deficit), as well as foliar application of 1 mM H₂O₂ (zero, one, or two applications, 24 h after the first), and was evaluated in two moments, during the deficit period and after recovery. Foliar application of 1 mM H₂O₂ resulted in a 69% increase in the maximum rate of RuBisCO carboxylation in well-watered plants, contributing to tomato photosynthetic adjustment. H₂O₂ treatment resulted in a 37% increase in dry mass in these plants. In plants subjected to water deficiency, 2× H₂O₂ increased stress tolerance by reducing the maximal rate of RuBisCO carboxylation by only 18%, but in plants that did not receive H₂O₂ treatment, the reduction was 86% in comparison to the wet plants. Plants exposed to a water shortage and given 2× H₂O₂ stored sucrose in the leaves and had a 17% higher relative water content than plants not given H₂O₂. Thus, H₂O₂ foliar treatment can be used in tomato management to induce drought tolerance or to boost photosynthetic activity and dry mass formation in well-watered plants.

This study investigated whether inoculation of Azospirillum brasilense in the seeds or sowing furrow could reduce the need for nitrogen fertilizer application in the corn grown in the first and second crop harvest. The experiments were conducted, in the municipality of Chapadão do Sul, MS, Brazil, in the first crop harvest (2014/2015) and in the second crop harvest (2016). The early maturity hybrids CD 384 HX and P3132H were used in the first and in the second harvest corn, respectively. In both experiments, the experimental design was the randomized blocks with eight treatments and three repetitions. At the silking (R1 stage), the leaf N concentration, relative chlorophyll index and nitrate reductase activity were measured, at the physiological maturity (R6 stage), the plant height, first ear insertion height, one hundred grain mass, grain yield and grain N concentration were measured. In the first crop harvest, the application of Azospirillum brasilense at the sowing furrow resulted in higher N concentration and relative chlorophyll index in corn leaves, while the inoculation of A. brasilense in the seeds provided higher N concentration in the grains. The nitrate reductase activity in corn leaves was lower when inoculation was performed. In the second crop harvest, the inoculation did not affected the N concentration in the leaves and in the grains, the relative chlorophyll index and the growth of corn plants. Inoculation in the sowing furrow associated with the application of 20 kg N ha^-1 at sowing and 120 kg N ha^-1 at topdressing resulted in lower nitrate reductase activity.

Water limits may have a disastrous impact on agricultural productivity, and the current climate change scenario presents additional problems for crops that rely on regular rainfall. Reactive oxygen species, such as hydrogen peroxide (H₂O₂), are a recognized stress-sensing mechanism in plants, and may be investigated as an approach for reducing stress impact via systemic acquired acclimation. Here, we looked at how H₂O₂ foliar application impacts tomato plants’ photosynthetic activity, antioxidant system, sugar chemical profile, and osmotic adjustment during drought and recovery. The experiment was in randomized blocks, 3 × 2 factorial design, with no, one, or two foliar application of 1 mM H₂O₂, on plants that were either continually watered or subjected to drought. The plants were tested both during the drought period and after they had resumed irrigation (recovered). Leaf water potential, chlorophyll a fluorescence, gas exchange, lipid peroxidation, H₂O₂ concentrations, phenols, proline, antioxidant enzyme activity, and sugar chemical profile were all measured. Our findings showed that H₂O₂ application generated metabolic alterations in tomato plants independent of water status, and that two applications in drought plants resulted in a 30% decrease in oxidative stress during drought and faster recovery following irrigation return, with greater production of defence-related molecules such as the APX enzyme, phenols, arabinose, and mannose. Continually watered plants also benefited from H₂O₂ application, which increased carbon assimilation by 35%.

Reactive oxygen species are generated during the processes of photosynthesis and nitrate reduction, which can compromise the integrity of biomolecules and membranes. During the vegetative phase of Fabaceae species, around half of translocated carbohydrate is used for nodule growth, while the other half returns to the aerial part with nitrogen incorporated. These sugars may be yet involved with membrane stabilization, signaling, and activation of important genetic pathways for plant development. Thus, the aim was to study the adjustments of the photosynthetic and antioxidant systems and the accumulation of carbohydrates and biomass in Glycine–Bradyrhizobium cultivated with nitrate (NO${}_3^{-}$). Four treatments were evaluated in completely randomized blocks. Glycine–Bradyrhizobium was grown with 1.7 mM of NO${}_3^{-}$ (GB: 1.7 mM NO${}_3^{-}$) and without NO${}_3^{-}$ (GB: 0 mM NO${}_3^{-}$), and Glycine was grown with 1.7 mM of NO${}_3^{-}$ (G: 1.7 mM NO${}_3^{-}$) and without NO${}_3^{-}$ (G: 0 mM NO${}_3^{-}$). Glycine–Bradyrhizobium symbiosis contributes to photosynthetic metabolism and total sugars, reduces the action of antioxidant enzymes, and minimizes the use of nitrate in soybean cultivation.; Glycine–Bradyrhizobium with nitrate provided greater plant dry mass in the vegetative phase, along with increased enzymatic activity and reduced nodule mass.

Atemoya (Annona × atemoya Mabb.), a climacteric fruit of the Annonaceae family, is becoming increasingly popular due to its organoleptic and nutritional properties. Anthracnose, a fungus of the Colletotrichum genus, is one of the most serious diseases in orchards, causing significant damage if not controlled, so producers use phytosanitary products. The current study sought to investigate the quality of atemoya fruits after harvest in an orchard with anthracnose controlled by Cu(OH)² application: T1—no Cu(OH)², T2—7.8 mL Cu(OH)² L1 divided into two applications, T3—15.6 mL Cu(OH)² L1 divided into four, T4—8.0 mL Cu(OH)² L1 divided into eight, and T5—13.0 mL Cu(OH)² L1 divided into thirteen applications. The sugar profile of fruits was examined, as well as MDA, H₂O₂, and quality parameters such as pH, mass, soluble solids, titratable acidity, and maturation index. MDA, such as H₂O₂, can function as a signal molecule. Eight applications of 1.0 mL L-1 Cu(OH)² resulted in increased concentrations of H₂O₂ and MDA, signal molecules involved in sugar modification profiles such as glucose, fructose, and trehalose. It also had a high titratable acidity, a lower maturation index, better fruit quality, and a longer shelf life.