Along with cyclic electron flow and non-photochemical quenching, water-to-water cycle is involved uniquely in alleviating Zn stress-caused photodamage in Melia azedarach.

Zinc (Zn) is a widespread industrial pollutant that has detrimental effects on plant growth and development. Photoprotective properties ensure plant survival during stress by protecting the photosynthetic apparatus. This occurs via numerous mechanisms, including non-photochemical quenching (NPQ), cyclic electron flow (CEF) and the water-to-water cycle (WWC). However, whether and how Zn stress affects the photoprotective properties of plants to enhance the tolerance of Zn toxicity remains unknown. In this study, we treated Melia azedarach plants with different Zn concentrations ranging from 200 to 1000 mg kg-1. We then analyzed the activities of two leaf photosynthetic pigment components-photosystems I and II (PSI and PSII)-and the relative expression levels of their subunit genes. As expected, we found that Zn treatment decreases photosynthesis and increases photodamage in M. azedarach leaves. The Zn treatments exacerbated a variety of photodamage phenotypes in photosystem activities and altered the expression levels of key photosystem complex genes and proteins. Furthermore, our results demonstrated that PSI was more seriously damaged than PSII under Zn stress. Subsequently, we compared differences in photodamage in the NPQ, CEF and WWC photoprotection pathways under Zn stress and found that each exerted a protective function again photodamage under 200 mg kg-1 Zn stress. The NPQ and CEF may also play major protective roles in the avoidance of irreversible photodamage and helping to ensure survival under higher (i.e., 500 and 1000 mg kg-1) levels of Zn stress. Thus, our study revealed that NPQ- and CEF-based photoprotection mechanisms are more effective than WWC in M. azedarach upon Zn stress.

In silico identification of natural fungicide from Melia azedarach against isocitrate lyase of Fusarium graminearum.

Isocitrate Lyase (ICL) is a crucial enzyme involved in the Glyoxylate pathway, essential for the virulence of several fungal pathogens including Fusarium graminearum. ICL is a novel target for the discovery of antifungal compounds and F. graminearum ICL inhibitors can be used to control the growth of this fungus. Although, several inhibitors of ICL have been identified, however, most of these inhibitors are not environment-friendly. Hence there is still a need to discover natural inhibitors of ICL that can be more effective. To identify a potential antifungal compound, we performed a structure-based screening of phytochemicals of Melia azedarach against the FgICL structure by molecular docking and 104 ligands were found to have a better docking score as compared to the reference molecule. These compounds were assessed for drug-likeness and ADMET prediction. After molecular docking, drug-likeness and toxicity analysis, six potential compounds (Melianoninol (-6.6 kcal/mol), Nimbinene (-7.7 kcal/mol), Vilasinin (-8.1 kcal/mol), Fraxinellone (-6.7 kcal/mol), Gedunin (-7.8 kcal/mol), and Meldenin (-7.8 kcal/mol)) were subjected for rescoring by X-Score. The structural stability and dynamics of screened compounds at the active site of FgICL were examined using MD simulation and MM-PBSA analysis. The result of MM-PBSA revealed that four phytochemicals viz. Melianoninol, Nimbinene, Vilasinin, and Fraxinellone had binding free energy of -17.25 kcal/mol, -59.35 kcal/mol, -64.79 kcal/mol, and -29.86 kcal/mol, respectively. Molecular dynamics simulation and MM-PBSA demonstrated that these four phytochemicals displayed considerable significant structural and pharmacological properties and could be probable antifungal drug candidates against F. graminearum. These phyotchemicals of M. azedarach may be suitable candidates for further experimental analysis. [Formula: see text]Communicated by Ramaswamy H. Sarma.

Difference in the rhizosphere microbiome of Melia azedarach during removal of benzo(a)pyrene from cadmium co-contaminated soil.

Benzo(a)pyrene (BaP) is a highly persistent biohazard polyaromatic hydrocarbon and often reported to be present in soils co-contaminated with heavy metals. The present study explains the rhizodegradation of BaP using bacterial consortium in the rhizosphere of Melia azedarach, along with a change in taxonomical and functional properties of the rhizosphere microbiome. The relative abundance of most dominant phylum Proteobacteria was 2% higher with BaP, while in the presence of both BaP and Cd, its abundance was 2.2% lower. Functional metagenome analysis also revealed the shifting of microbial community and functional gene abundance in the favor of xenobiotic compound degradation upon augmentation of bacterial consortium. Interestingly, upon the addition of BaP the range of functional abundance for genes of PAH degradation (0.165-0.19%), was found to be decreasing. However, augmentation of a bacterial consortium led to an increase in its abundance including genes for degradation of benzoate (0.55-0.64%), toluene (0.2-0.22%), naphthalene (0.25-0.295%) irrespective of the addition of BaP and Cd. Moreover, under greenhouse condition, the application of M. azedarach-bacterial consortium enhanced the degradation of BaP in the rhizosphere (88%) after 60 days, significantly higher than degradation in bulk soil (68.22%). The analysis also showed an increase in degradation of BaP by 15% with plant-native microbe association than in bulk soil. Therefore, the association of M. azedarach-bacterial consortium enhanced the degradation of BaP in soil along with the taxonomical and functional attributes of the rhizosphere microbiome.

Conjugation of antifungal benzoic acid derivatives as a path for detoxification in Penicillium brasilianum, an endophyte from Melia azedarach.

In this study, the consumption of 4-bromobenzoic acid and 4-chlorobenzoic acid by the fungus Penicillium brasilianum, an endophyte from Melia azedarach is evaluated. This fungus metabolizes these halobenzoic acids to produce three new brominated compounds, which have been isolated and characterized, and three new chlorinated derivatives identified by HRMS. Among these products, (4-bromobenzoyl)proline has been also chemically synthesized and employed in biological assays, thus providing insights for the elucidation of the defense mechanism of P. brasilianum towards these halobenzoic acids.

Characterization of photosynthetic gas exchange in leaves under simulated adaxial and abaxial surfaces alternant irradiation.

Previous investigations on photosynthesis have been performed on leaves irradiated from the adaxial surface. However, leaves usually sway because of wind. This action results in the alternating exposure of both the adaxial and abaxial surfaces to bright sunlight. To simulate adaxial and abaxial surfaces alternant irradiation (ad-ab-alt irradiation), the adaxial or abaxial surface of leaves were exposed to light regimes that fluctuated between 100 and 1,000 µmol m(-2) s(-1). Compared with constant adaxial irradiation, simulated ad-ab-alt irradiation suppressed net photosynthetic rate (Pn) and transpiration (E) but not water use efficiency. These suppressions were aggravated by an increase in alternant frequency of the light intensity. When leaves were transferred from constant light to simulated ad-ab-alt irradiation, the maximum Pn and E during the high light period decreased, but the rate of photosynthetic induction during this period remained constant. The sensitivity of photosynthetic gas exchange to simulated ad-ab-alt irradiation was lower on abaxial surface than adaxial surface. Under simulated ad-ab-alt irradiation, higher Pn and E were measured on abaxial surface compared with adaxial surface. Therefore, bifacial leaves can fix more carbon than leaves with two "sun-leaf-like" surfaces under ad-ab-alt irradiation. Photosynthetic research should be conducted under dynamic conditions that better mimic nature.

Melia azedarach plants show tolerance properties to water shortage treatment: an ecophysiological study.

Candidate species for reforestation of areas prone to drought must combine water stress (WS) tolerance and economic or medicinal interest. Melia azedarach produces high quality timber and has insecticidal and medicinal properties. However, the impact of WS on M. azedarach has not yet been studied. Two-month old M. azedarach plants were exposed to WS during 20 days. After this period, plant's growth, water potential, photosynthetic performance and antioxidant capacity were evaluated. WS did not affect plants' growth, but induced stomatal closure, reduced net CO2 assimilation rate (A) and the intercellular CO2 availability in mesophyll (C(i)). WS also reduced the photosynthetic efficiency of PSII but not the pigment levels. WS up-regulated the antioxidant enzymes and stimulated the production of antioxidant metabolites, preventing lipid peroxidation. Therefore, despite some repression of photosynthetic parameters by WS, they did not compromise plant growth, and plants increased their antioxidant capacity. Our data demonstrate that M. azedarach juvenile plants have the potential to acclimate to water shortage conditions, opening new perspectives to the use of this species in reforestation/afforestation programs of drought prone areas.