Metabolic, physiological and anatomical responses of soybean plants under water deficit and high temperature condition.

Water deficit (WD) combined with high temperature (HT) is the major factor limiting agriculture worldwide, and it is predicted to become worse according to the current climate change scenario. It is thus important to understand how current cultivated crops respond to these stress conditions. Here we investigated how four soybean cultivars respond to WD and HT isolated or in combination at metabolic, physiological, and anatomical levels. The WD + HT increased the level of stress in soybean plants when compared to plants under well-watered (WW), WD, or HT conditions. WD + HT exacerbates the increases in ascorbate peroxidase activity, which was associated with the greater photosynthetic rate in two cultivars under WD + HT. The metabolic responses to WD + HT diverge substantially from plants under WW, WD, or HT conditions. Myo-inositol and maltose were identified as WD + HT biomarkers and were connected to subnetworks composed of catalase, amino acids, and both root and leaf osmotic potentials. Correlation-based network analyses highlight that the network heterogeneity increased and a higher integration among metabolic, physiological, and morphological nodes is observed under stress conditions. Beyond unveiling biochemical and metabolic WD + HT biomarkers, our results collectively highlight that the mechanisms behind the acclimation to WD + HT cannot be understood by investigating WD or HT stress separately.

Can light intensity modulate the physiological, anatomical, and reproductive responses of soybean plants to water deficit?

Little is known about the role of light intensity in modulating plant responses to stress due to water deficit (WD). Thus, the objective of this study was to determine the WD and contrasting irradiance effects on the physiology, anatomy, and grain yield of soybean plants. The experimental design was a randomized block in a growth chamber and a 2 × 2 factorial treatment arrangement: 90% (well-watered, WW) and 40% (WD) of soil field capacities (FC); and 750 (medium irradiance, MI) and 1500 (higher irradiance, HI) µmol (photons) m-2  s-1 irradiance. The WD caused a lower photosynthetic rate - as well as observed in the light curve and in the relative parameters, such as apparent quantum efficiency -, less investment in shoot biomass and pollen grain germination, resulting in lower grain yield. However, there was an increase in non-photochemical energy dissipation, a higher concentration of total soluble sugars, proline, and malondialdehyde. The WD + MI-soybean plants developed thicker spongy parenchyma (related to higher mesophilic conductance of CO2 ). In the WW + HI condition the palisade parenchyma was thicker, conferring maintenance of photosynthetic efficiency. In addition, there was an increase in the activity of superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase antioxidant enzymes in leaves due to HI, regardless of FC. This induced higher energy expenditure, reflected in the reduction of the number of leaf and branches, leaf area, dry mass of leaves and stem in the WW + HI. Interestingly, these strategies of osmotic adjustment, photoprotection, and antioxidant defenses act together in the WD + HI.

Do fungicides affect the physiology, reproductive development and productivity of healthy soybean plants?

Fungicides are widely used to control diseases in soybean crops. We hypothesized that fungicides applied to healthy soybean plants compromise the plant's physiology, affect the reproductive process and reduce crop productivity. We aimed to evaluate the photosynthetic process, pollen grain viability and yield components of soybean plants exposed to three commercial fungicides. The experiment was performed twice using soybean cultivar SYN 1378C, disease-free plants, with four treatments: i) control treatment (without any fungicide application); ii) cyproconazole 150 g L-1 + difenoconazole 250 g L-1 (CPZ + DFZ; 250 mL ha-1; without adjuvant); iii) azoxystrobin 300 g Kg-1 + benzovindiflupyr 150 g Kg-1 (AZB + BZP; 200 g ha-1; Nimbus® adjuvant (Syngenta)); and iv) propiconazole 250 g L-1 + difenoconazole 250 g L-1 (PPZ + DFZ; 150 mL ha-1; without adjuvant) in both soybean pre-bloom (V8) and bloom (R1) developmental stages. The experimental design was randomized blocks with four replicates. Phytotoxicity, gas exchange and chlorophyll a fluorescence traits, pollen grain viability, pollen grain germination, flower abortion and soybean production components were evaluated. The fungicides did not affect the physiological traits, pollen grain germination and crop yield.

Potential of calcium nitrate to mitigate the aluminum toxicity in Phaseolus vulgaris: effects on morphoanatomical traits, mineral nutrition and photosynthesis.

Common bean (Phaseolus vulgaris) cultivation occurs mainly in regions with acidic soils, where high aluminum (Al) concentration is a major constraint to crop production. In this study, we evaluated tolerance and sensitivity traits to Al exposure and calcium (Ca) deficiency in bean plants, and determined the efficiency of Ca to mitigate the toxic Al effects. Two bean cultivars (BRS Estilo and Campos Gerais) were grown in three soil conditions: (I) soil liming with calcium hydroxide Ca(OH)2 and Al unavailable (-Al+Ca); (II) fertilized soil with calcium nitrate [Ca(NO3)2·4H2O] and Al available (+Al+Ca); and (III) soil without Ca addition and Al available (+Al-Ca). At the beginning of the reproductive stage, we evaluated the photosynthetic processes, mineral nutrition, and leaf anatomy and morphological traits of plants. The photosynthetic parameters were good tools for monitor Al sensitivity in bean. +Al+Ca soil treatment mitigated the deleterious effects of Al on growth and mineral nutrition of both bean cultivars. However, Ca did not prevent the toxic effects of Al on leaf anatomy. Al stress and Ca deficiency caused negative effects on nutrient content, photosynthetic activity and leaf anatomy of bean plants. Calcium mitigated Al toxicity, primarily in the Campos Gerais cultivar, showing the potential to improve bean crop productivity in acid soils.

Involvement of glutathione and glutathione metabolizing enzymes in Pistia stratiotes tolerance to arsenite.

Glutathione is essential for plant tolerance to arsenic but few studies have focused on the coordination between the enzymes involved in its metabolism. We exposed Pistia stratiotes to four treatments (control, 5, 10 and 20 µM AsIII) for 24 h to evaluate the role of glutathione metabolism in arsenic response and determined the arsenic uptake, growth, membrane integrity, glutathione concentration and enzyme activities (γ-glutamyl-cysteine synthetase, glutathione reductase, glutathione peroxidase, and glutathione-S-transferase). Despite absorbing high concentrations of AsIII, plants maintained growth and cell membrane integrity when exposed to concentrations of up to 10 µM AsIII. The maintenance of these parameters involved glutathione concentration increase due to an increase in its biosynthetic pathway (higher γ-glutamyl-cysteine synthetase). In addition, an increase in the activity of glutathione reductase, glutathione peroxidase and glutathione-S-transferase also contributed to the conserve the cellular homeostasis. However, at the concentration of 20 µM AsIII, the high toxicity of AsIII affected glutathione concentration and glutathione metabolizing enzymes activities, which resulted in drastic decrease in growth and damage to cell membranes. These results showed that not only the glutathione concentration but also the coordination of the enzymes involved in the synthesis, oxidation and reduction pathways of glutathione is essential for AsIII tolerance.