Unplanned urbanization and heavy automobile use by the rapidly growing population contribute to a variety of environmental issues. Roadside plants can mitigate air pollution by modifying their enzymatic activity, physiological and anatomical traits. Plant enzymes, physiological and anatomical traits play an important role in adaptation and mitigation mechanisms against vehicular emissions. There is a significant gap in understanding of how plant enzymes and anatomical traits respond or how they participate in modulating the effect of vehicular emissions/air pollution. Modulation of leaf anatomical traits is also useful in regulating plant physiological behavior. Hence, the present study was conducted to evaluate the effects of vehicular pollution on the enzymatic activity, physiological, and anatomical traits of plant species that grow in forests (S1) and alongside roads (S2-1 km away from the S1 site) during different seasons. The present study examines four commonly found roadside tree species i.e. Grevillea robusta, Cassia fistula, Quercus leucotrichophora and Cornus oblonga. The study found that the activities of catalase and phenylalanine ammonium enzymes were higher in G. robusta species of roadside than control site (S1). Non-enzymatic antioxidants such as flavonoid and phenol were also found in higher concentrations in roadside tree species during the summer season. However, the measured values of physiological traits were higher in Q. leucotrichophora tree species of S1 during the summer season. When compared to the other species along the roadside, Q. leucotrichophora had the highest number of stomata and epidermal cells during the summer season. Hence, we found that tree species grown along the roadside adapted towards vehicular emissions by modulating their enzymatic, physiological, and anatomical traits to mitigate the effect of air pollution.

Trees have been recognized as air quality bioindicators, but they have still not been fully implemented in tropical areas. In this study, bark of Cassia fistula was used to inspect accumulation of air pollutants (metals) emitted from road traffic in the city of Chiang Mai, Thailand. The mean concentrations of metal accumulated on tree bark (ng/cm2) in descending order were Al (1,238) > Fe (707) > Zn (162) » Cu (21.1) » Pb (6.37) > Cr (2.14). Correlations of Enrichment Factors: EFTS (metal concentrations on bark compared to those in soil) among metals were relatively strong (r > 0.6) meaning that they were probably generated from the same sources. Moreover, principal component analysis and cluster analysis of EFTS values revealed that Al and Fe were generated from soil resuspension that were attached on vehicle wheels and on road surfaces, while Cr, Cu, Pb and Zn resulted directly from vehicle emissions. The results lead to the conclusion that tree bark is a good bioindicator for air pollutant accumulation in this area. In addition, pollution indices, including total geoaccumulation index (IGEO-tot) and pollution load index (PLI), were applied to generate air quality maps of the city. The maps illustrated that the most polluted areas in the city are the areas that have high traffic volume and building density, in which hospitals and schools are located. The degree of pollution presented in each area was influenced by both road traffic volume and density of buildings in relation to air ventilation capacity.

Air pollutant concentration of Trivandrum, the capital of Kerala, exceeded the limits of National Ambient Air Quality (NAAQ) standards, according to a study conducted in 2015 by NATPAC. These polluted corridors harbour vegetation on roadsides and traffic islands, planted solely for aesthetic appeal. Analysis of air pollution tolerance levels of existing plants can act as a scientific basis for efficient planning of the urban landscape. Sixty-seven species, including flowering, fruit-bearing, ornamental, shade-providing and timber-yielding species, were screened for their relative resistance to air pollution. Based on leaf pH, relative water content, chlorophyll and ascorbic acid levels, the Air Pollution Tolerance Indices (APTI) of each species were formulated and they were grouped into the following: tolerant, moderately tolerant, intermediate and sensitive groups. Agave americana (18.40), Cassia roxburghii (17.63), Anacardium occidentale (11.97), Cassia fistula (11.60), Mangifera indica (11.59) and Saraca asoca (10.88) may be considered for planting near green spaces like roundabouts and near pollution prone industrial areas, as they belong to tolerant category. Comparison of APTI during summer and monsoon also revealed the stability of Agave americana, Saraca asoca, Ficus benghalensis, Peltophorum pterocarpum, Ficus elastica, Ixora finlaysoniana, Mangifera indica, Canna indica and Delonix regia in maintaining pollution tolerance even during water disparity. Agave americana, Anacardium occidentale, Ficus elastica, Mangifera indica, Syzygium cumini, Ficus benghalensis, Nerium oleander and Ficus benjamina were found to be suited for mass planting, as was evident from their Anticipated Performance Indices (API).

The present study explained the effect of pretreatments on the biosorption of Cr (III) and Cr (VI) by Cassia fistula biomass from aqueous solutions. For this purpose Cassia fistula biomass was pretreated physically by heating, autoclaving, boiling and chemically with sodium hydroxide, formaldehyde, gluteraldehyde, acetic acid, hydrogen peroxide, commercial laundry detergent, orthophosphoric, sulphuric acid, nitric acid, and hydrochloric acid. The adsorption capacity of biomass for Cr (III) and Cr (VI) was found to be significantly improved by the treatments of gluteraldehyde (95.41 and 96.21 mg/g) and benzene (85.71 and 90.81 mg/g) respectively. The adsorption capacity was found to depend on pH, initial metal concentration, dose, size, kinetics, and temperature. Maximum adsorption of both the Cr (III) and Cr (VI) was observed at pH 5 and 2. When Freundlich and Langmuir isotherms were tested, the latter had a better fit with the experimental data. The kinetic studies showed that the sorption rates could be described better by a second order expression than by a more commonly applied Lagergren equation.

The present study investigated the antimutagenic, antioxidant, and antiproliferative properties of extracts of Cassia fistula prepared by sequentially fractionation of 80% methanolic (CaLM extract) extract of C. fistula leaves, namely CaLH (hexane), CaLC (chloroform), CaLE (ethyl acetate), CaLB (n-butanol), and CaLA (aqueous) fractions. The antimutagenicity of the fractions was tested against mutagens viz. S9-independent, namely 4-nitro-o-phenylenediamine (TA98) and sodium azide (TA100) and S9-dependent, 2-AF (2-aminofluorene). Among the tested fractions, CaLE fraction showed a potent efficacy with an inhibition percentage of 85.57% (TA98) and 89.93% (TA100) against the mutagenicity induced by 2-aminofluorene. The CaLE fraction could significantly scavenge free radicals in various assays, namely DPPH, lipid peroxidation inhibition, and superoxide anion radical scavenging assays with an IC₅₀ of 12.80, 144, and 257.3 μg/ml respectively. The antiproliferative potential of the effective CaLE fraction was assessed using MTT assay against HeLa and MCF-7 cancer cells with GI₅₀ value of 243.4 and 324.6 μg/ml respectively. The fraction exhibited remarkable apoptosis-inducing effects through the externalization of phosphatidylserine in HeLa cells as analyzed by annexin V-FITC/PI double staining assay. The HPLC analysis of CaLE revealed the presence of catechin, epiafzelechin, and chlorogenic acid which are responsible for its antimutagenic and antiproliferative efficacy. Graphical abstract

The current study was performed to evaluate the antiproliferative and apoptosis-inducing potential of n-hexane fraction from Cassia fistula L. (Caesalpinioideae) fruits. The antiproliferative property of the fraction was determined by MTT assay against cancer cell lines including HeLa, MG-63, IMR-32, and PC-3 with GI₅₀ value of 97.69, 155.2, 143, and 160.2 μg/ml respectively. The fraction was further explored for its apoptotic effect using confocal, SEM, and flow cytometry studies in HeLa cells. It was observed that the treatment of fraction revealed fragmentation of DNA, chromatin condensation, membrane blebbing, and formation of apoptotic bodies in a dose-dependent manner. The fraction also showed a remarkable increase in the level of ROS, mitochondrial depolarization and G₀/G₁ phase cell cycle arrest, and induction in the phosphatidylserine externalization analyzed using Annexin V-FITC/PI double staining assay in HeLa cells. Kaempferol, Ellagic acid, and Epicatechin are the major phytoconstituents present in the fraction as revealed by the HPLC. The treatment of n-hexane fraction showed downregulation in the gene expression of Bcl-2 and upregulation in the expression level of p53, Bad, and caspase-3 genes analyzed using semi-quantitative RT-PCR in HeLa cells. These results suggest that n-hexane fraction from C. fistula inhibited the proliferation of cervical cancer cells efficiently by the induction of apoptosis. Graphical abstract

Cassia fistula L. (Caesalpinioideae) is a highly admirable medicinal plant and is traditionally recommended for the treatment of rheumatism, liver disorders, jaundice, and other inflammatory diseases. This study was designed to investigate the hepatoprotective properties of ethyl acetate fraction from C. fistula leaves in an animal model. Treatment with thioacetamide significantly elevated the level of serum glutamic-oxaloacetic transaminase (1.75-fold), alkaline phosphatase (4.07-fold), and total bilirubin (2.29-fold) as compared to the control. It was found that pretreatment of fraction followed by consecutive 2 days thioacetamide reduced the conversion of thioacetamide carcinogen to its reactive metabolites by phase I enzymes and increased the level of detoxification phase II along with antioxidative enzymes. The histopathological studies revealed the hepatoprotective nature of the fraction in restoring the normal architecture of thioacetamide-intoxicated damaged liver. The fraction showed downregulation in the expression level of p-PI3K, p-Akt, and p-mTOR pointing towards its chemopreventive potential. The HPLC analysis of the fraction had shown the dominance of three phenolic compounds namely, catechin, epicatechin, and chlorogenic acid. The above studies comprising histopathological, immunohistochemical, and hepatic enzymes are strong indicative of the potential protective ability of ethyl acetate fraction phytoconstituents against thioacetamide-induced toxicity. Graphical abstract