PSI becomes more tolerant to fluoranthene through the initiation of cyclic electron flow

Mycorrhizal fungi reduce the photosystem damage caused by drought stress on Paris polyphylla var. yunnanensis

Drought stress (DS) is one of the important abiotic stresses facing cash crops today. Drought can reduce plant growth and development, inhibit photosynthesis, and thus reduce plant yield. In this experiment, we investigated the protective mechanism of AMF on plant photosynthetic system by inoculating Paris polyphylla var. yunnanensis(P.py) with a clumping mycorrhizal fungus (AMF) under drought conditions. The drought environment was maintained by weighing AMF plants and non-AMF plants. The relative water content (RWC) of plant leaves was measured to determine its drought effect. DS decreased the RWC of plants, but AMF was able to increase the RWC of plants. chlorophyll a fluorescence curve measurements revealed that DS increased the OKJIP curve of plants, but AMF was able to reduce this trend, indicating that AMF increased the light absorption capacity of plants. DS also caused a decrease in plant Y(I) and Y(II). ETRI and ETRII, and increased Y(NO) and Y(NA) in plants, indicating that DS caused photosystem damage in plants. For the same host, different AMFs did not help to the same extent, but all AMFs were able to help plants reduce this damage and contribute to the increase of plant photosynthesis under normal water conditions.

Potential ability of tobacco (Nicotiana tabacum L.) to phytomanage an urban brownfield soil

The ability of tobacco (Nicotiana tabacum L. cv. Badischer Geudertheimer) for phytomanaging and remediating soil ecological functions at a contaminated site was assessed with a potted soil series made by fading an uncontaminated sandy soil with a contaminated sandy soil from the Borifer brownfield site, Bordeaux, SW France, at the 0%, 25%, 50%, 75%, and 100% addition rates. Activities of sandblasting and painting with metal-based paints occurred for decades at this urban brownfield, polluting the soil with metal(loid)s and organic contaminants, e.g., polycyclic aromatic hydrocarbons, in addition to past backfilling. Total topsoil metal(loid)s (e.g., 54,700 mg Zn and 5060 mg Cu kg-1) exceeded by seven- to tenfold the background values for French sandy soils, but the soil pH was 7.9, and overall, the 1M NH4NO3 extractable soil fractions of metals were relatively low. Leaf area, water content of shoots, and total chlorophyll (Chl) progressively decreased with the soil contamination, but the Chl fluorescence remained constant near its optimum value. Foliar Cu and Zn concentrations varied from 17.8 ± 4.2 (0%) to 27 ± 5 mg Cu kg-1 (100%) and from 60 ± 15 (0%) to 454 ± 53 mg Zn kg-1 (100%), respectively. Foliar Cd concentration peaked up to 1.74 ± 0.09 mg Cd kg-1, and its bioconcentration factor had the highest value (0.2) among those of the metal(loid)s. Few nutrient concentrations in the aboveground plant parts decreased with the soil contamination, e.g., foliar P concentration from 5972 ± 1026 (0%) to 2861 ± 334 mg kg-1 (100%). Vulnerability to drought-induced embolism (P50) did not differ for the tobacco stems across the soil series, whereas their hydraulic efficiency (Ks) declined significantly with increasing soil contamination. Overall, this tobacco cultivar grew relatively well even in the Borifer soil (100%), keeping its photosynthetic system healthy under stress, and contaminant exposure did not increase the vulnerability of the vascular system to drought. This tobacco had a relevant potential to annually phytoextract a part of the bioavailable soil Zn and Cd, i.e., shoot removals representing here 8.8% for Zn and 43.3% for Cd of their 1M NH4NO3 extractable amount in the potted Borifer soil.

Effect of High-Temperature Stress on Plant Physiological Traits and Mycorrhizal Symbiosis in Maize Plants

Increasing high temperature (HT) has a deleterious effect on plant growth. Earlier works reported the protective role of arbuscular mycorrhizal fungi (AMF) under stress conditions, particularly influencing the physiological parameters. However, the protective role of AMF under high-temperature stress examining physiological parameters with characteristic phospholipid fatty acids (PLFA) of soil microbial communities including AMF has not been studied. This work aims to study how high-temperature stress affects photosynthetic and below-ground traits in maize plants with and without AMF. Photosynthetic parameters like quantum yield of photosystem (PS) II, PSI, electron transport, and fractions of open reaction centers decreased in HT exposed plants, but recovered in AMF + HT plants. AMF + HT plants had significantly higher AM-signature 16:1ω5cis neutral lipid fatty acid (NLFA), spore density in soil, and root colonization with lower lipid peroxidation than non-mycorrhizal HT plants. As a result, enriched plants had more active living biomass, which improved photosynthetic efficiency when exposed to heat. This study provides an understanding of how AM-mediated plants can tolerate high temperatures while maintaining the stability of their photosynthetic apparatus. This is the first study to combine above- and below-ground traits, which could lead to a new understanding of plant and rhizosphere stress.

Protection of PSI and PSII complexes of wheat from toxic effect of anthracene by Bacillus subtilis (NCIM 5594)

Contamination of polycyclic aromatic hydrocarbons (PAHs) in environment indicates a serious problem to the present era. These are carcinogenic and mutagenic compounds and pose a potential risk to photosynthetic organisms. The present study illustrates the protection of Photosystem I and Photosystem II complexes of wheat plant by Bacillus subtilis (NCIM 5594) from toxic effects of anthracene (ANT). Initially, Chl a fluorescence induction curve measurement revealed declined J-I and I-P phase in ANT-treated plants. Efficiency of light absorption, trapping, and electron transport was reduced in ANT-treated plants, while in ANT + Bacillus subtilis (NCIM 5594)-treated plants value of these parameters was restored. Effect of ANT and ANT + Bacillus subtilis (NCIM 5594) on energy conversion of Photosystem I and Photosystem II was measured. Quantum yield of Photosystem I (YI) and Photosystem II (YII) was decreased in the presence of ANT, while these values were recovered in ANT + Bacillus subtilis (NCIM 5594)-treated plants. Reduction in Y(II) was associated with an increase in non-regulated energy dissipation NO. Likewise the reduction of Y(I) was induced due to donor-side and acceptor-side limitation of Photosystem I caused by toxic effect of ANT. Toxic effects of ANT on electron transport rate (ETR_I and ETR_II) were found to be reduced in ANT + Bacillus subtilis (NCIM 5594)-treated plants. Activation of Cyclic electron flow around Photosystem I in ANT-treated plants was recovered by bacteria. It was concluded that toxic effect of ANT on Photosystem I and Photosystem II complexes was recovered by Bacillus subtilis (NCIM 5594) strain, and thus it is useful strain for crop improvement in ANT-polluted soil.

Photosynthetic response in wheat plants caused by the phototoxicity of fluoranthene

Environmental organic pollutants such as polycyclic aromatic hydrocarbons (PAHs) affect photosynthetic performance in plants. The photooxidation of PAHs in natural sunlight, especially UV radiation, enhances the toxicity of PAHs. However, it is unclear as how these compounds and their photoproducts affect the photosynthetic apparatus. In this study, measurements of PSI and PSII were simultaneously performed in wheat (Triticum aestivum L.) plants treated with fluoranthene (FLT) and photomodified fluoranthene (PFLT). The study aimed to investigate whether the phototoxicity of FLT has a different mechanism of toxicity on the two photosystems. With regard to PSII, FLT and PFLT produced a significant decrease in the quantum yield of PSII and a pronounced increase in the yield of nonregulated energy dissipation. A significant reduction was observed in the yield of nonphotochemical quenching. The toxic effects of the PFLT treatment on PSII's performance were more pronounced. Likewise, we noted severe disruption in the electron transport rate in PSII and a decline in Fm caused by FLT phototoxicity. A decline in the quantum yield of PSI and an increase in donor and acceptor side limitation were observed concomitantly. The impact of PFLT was more evident than that of FLT. The data demonstrated that PSI is more tolerant of FLT but for PFLT, particularly at higher concentrations, a pronounced inhibition was observed in the oxidation-reduction kinetics of P700. All these data suggest that increased cyclic electron flow can confer greater protection from FLT toxicity but not from toxicity induced by higher concentrations of PFLT.

Arbuscular Mycorrhizal fungi (AMF) protects photosynthetic apparatus of wheat under drought stress

Drought stress (DS) is amongst one of the abiotic factors affecting plant growth by limiting productivity of crops by inhibiting photosynthesis. Damage due to DS and its protection by Arbuscular Mycorrhizal fungi (AMF) was studied on photosynthetic apparatus of wheat (Triticum aestivum) plants in pot experiments. DS was maintained by limiting irrigation to the drought stressed (DS) and AMF + DS plants. Relative Water content (RWC) was measured for leaf as well as soil to ensure drought conditions. DS plants had minimum RWC for both leaf and soil. AMF plants showed increased RWC both for leaf and soil indicating that AMF hyphae penetrated deep into the soil and provided moisture to the plants. In Chl a fluorescence induction curve (OJIP), a declined J-I and I-P phase was observed in DS plants. Efficacy of primary photochemistry declined in DS plants as result of DS, while AMF plants showed maximum photochemistry. DS leads to declined quantum efficiency of PSI and PSII in DS plants while it was restored in AMF + DS plants. Electron transport (ETRI and ETRII) decreased while quantum yield of non-photochemical quenching Y(NPQ) increased as a result of drought stress. CEF around PSI increased in DS-stressed plants. Efficient PSI complexes decreased in DS plants while in case of AMF plants PSI complexes were able to perform PSI photochemistry significantly. Thus, it is concluded that drought stress-induced damage to the structure and function of PSII and PSI was alleviated by AMF colonization.