Spermine-Mediated Tolerance to Selenium Toxicity in Wheat (Triticum aestivum L.) Depends on Endogenous Nitric Oxide Synthesis

Excess selenium (Se) causes toxicity, and nitric oxide (NO)’s function in spermine (Spm)-induced tolerance to Se stress is unknown. Using wheat plants exposed to 1 mM sodium selenate—alone or in combination with either 1 mM Spm, 0.1 mM NO donor sodium nitroprusside (SNP) or 0.1 mM NO scavenger cPTIO—the potential beneficial effects of these compounds to palliate Se-induced stress were evaluated at physiological, biochemical and molecular levels. Se-treated plants accumulated Se in their roots (92%) and leaves (95%) more than control plants. Furthermore, Se diminished plant growth, photosynthetic traits and the relative water content and increased the levels of malondialdehyde, H2O2, osmolyte and endogenous NO. Exogenous Spm significantly decreased the levels of malondialdehyde by 28%, H2O2 by 37% and electrolyte leakage by 42%. Combined Spm/NO treatment reduced the Se content and triggered plant growth, photosynthetic traits, antioxidant enzymes and glyoxalase systems. Spm/NO also upregulated MTP1, MTPC3 and HSP70 and downregulated TaPCS1 and NRAMP1 (metal stress-related genes involved in selenium uptake, translocation and detoxification). However, the positive effects of Spm on Se-stressed plants were eliminated by the NO scavenger. Accordingly, data support the notion that Spm palliates selenium-induced oxidative stress since the induced NO elicits antioxidant defence upregulation but downregulates Se uptake and translocation. These findings pave the way for potential biotechnological approaches to supporting sustainable wheat crop production in selenium-contaminated areas.

Rapid estimation of photosynthetic leaf traits of tropical plants in diverse environmental conditions using reflectance spectroscopy

Tropical forests are one of the main carbon sinks on Earth, but the magnitude of CO2 absorbed by tropical vegetation remains uncertain. Terrestrial biosphere models (TBMs) are commonly used to estimate the CO2 absorbed by forests, but their performance is highly sensitive to the parameterization of processes that control leaf-level CO2 exchange. Direct measurements of leaf respiratory and photosynthetic traits that determine vegetation CO2 fluxes are critical, but traditional approaches are time-consuming. Reflectance spectroscopy can be a viable alternative for the estimation of these traits and, because data collection is markedly quicker than traditional gas exchange, the approach can enable the rapid assembly of large datasets. However, the application of spectroscopy to estimate photosynthetic traits across a wide range of tropical species, leaf ages and light environments has not been extensively studied. Here, we used leaf reflectance spectroscopy together with partial least-squares regression (PLSR) modeling to estimate leaf respiration (Rdark25), the maximum rate of carboxylation by the enzyme Rubisco (Vcmax25), the maximum rate of electron transport (Jmax25), and the triose phosphate utilization rate (Tp25), all normalized to 25°C. We collected data from three tropical forest sites and included leaves from fifty-three species sampled at different leaf phenological stages and different leaf light environments. Our resulting spectra-trait models validated on randomly sampled data showed good predictive performance for Vcmax25, Jmax25, Tp25 and Rdark25 (RMSE of 13, 20, 1.5 and 0.3 μmol m-2 s-1, and R2 of 0.74, 0.73, 0.64 and 0.58, respectively). The models showed similar performance when applied to leaves of species not included in the training dataset, illustrating that the approach is robust for capturing the main axes of trait variation in tropical species. We discuss the utility of the spectra-trait and traditional gas exchange approaches for enhancing tropical plant trait studies and improving the parameterization of TBMs.

On the hybrid origin of the C2Salsola divaricata agg. (Amaranthaceae) from C3 and C4 parental lineages

C2 photosynthesis is characterized by recapturing photorespiratory CO2 by RuBisCO in Kranz-like cells and is therefore physiologically intermediate between C3 and C4 photosynthesis. C2 is either interpreted as an evolutionary precursor of C4 or as the result of hybridization between a C3 and C4 lineage. We compared the expression of photosynthetic traits among populations of the Salsola divaricata agg. (C2) from humid subtropical to arid habitats on the coasts of the Canary Islands and Morocco, and subjected them to salt and drought treatments. We screened for enhanced C4-like expression of traits related to habitat or treatment. We estimated species trees with a transcriptome dataset of Salsoleae and explored patterns of gene tree discordance. With phylogenetic networks and hybridization analyses we tested for hybrid origin of the Salsola divaricata agg. We observed independent variation of photosynthetic traits within and among populations and no clear evidence for selection towards C4-like trait expression in more stressful habitats or treatments. We found reticulation and gene tree incongruencies in the Salsoleae supporting a putative hybrid origin of the Salsola divaricata agg. C2 photosynthesis in the Salsola divaricata agg. combines traits inherited from its C3 and C4 parental lineages and seems well adapted to a wide climatic amplitude.

Inoculation of ACC Deaminase-Producing Brevibacterium linens RS16 Enhances Tolerance against Combined UV-B Radiation and Heat Stresses in Rice (Oryza sativa L.)

UV-B radiation and high temperature have detrimental effects on plant physiological and biochemical processes. The use of bacterial inoculants for stress alleviation has been regarded as a sustainable and eco-friendly approach. Hence, this study was conducted to evaluate the ability of 1-aminocyclopropane-1-caboxylate (ACC) deaminase-producing Brevibacterium linens RS16 in enhancing stress tolerance in rice against combined UV-B radiation and heat stresses. A combination of 0.5 Wm−2 UV-B radiation and 40 °C of temperature were imposed on rice plants for 5 days. The plants imposed with combined stress had shown significantly higher ethylene emissions compared to the plants grown under normal conditions. In addition, the stress imposition had shown negative effects on the photosynthetic traits, biomass, and genetic material of rice plants. The inoculation of bacteria had shown a 26.5% and 31.8% decrease in ethylene emissions at 3 and 4 days of stress imposition compared to the non-inoculated plants. Additionally, bacterial inoculation had also enhanced plant biomass and photosynthetic traits, and had proved to be effective in restricting DNA damage under stress conditions. Taken together, the current study has shown the effective strategy of enhancing stress tolerance against the interactive effects of UV-B radiation and heat stresses by regulation of ethylene emissions through inoculating ACC deaminase-producing bacteria.