Tolerance of Mentha crispa L. (garden mint) cultivated in cadmium-contaminated oxisol

Unveiling the Dual Nature of Heavy Metals: Stressors and Promoters of Phenolic Compound Biosynthesis in Basilicum polystachyon (L.) Moench In Vitro

The global industrial revolution has led to a substantial rise in heavy metal levels in the environment, posing a serious threat to nature. Plants synthesize phenolic compounds under stressful conditions, which serve as protective agents against oxidative stress. Basilicum polystachyon (L.) Moench is an herbaceous plant of the Lamiaceae family. Some species within this family are recognized for their capacity to remediate sites contaminated with heavy metals. In this study, the effects of mercury (II) chloride and lead (II) nitrate on the in vitro propagation of B. polystachyon were investigated. Shoot tips from in vitro plantlets were cultured in Murashige and Skoog's (MS) media with heavy metals ranging from 1 to 200 µM to induce abiotic stress and enhance the accumulation of phenolic compounds. After three weeks, MS medium with 1 µM of lead (II) supported the highest shoot multiplication, and the maximum number of roots per explant was found in 100 µM of lead (II), whereas a higher concentration of heavy metals inhibited shoot multiplication and root development. The plantlets were hardened in a greenhouse with a 96% field survival rate. Flame atomic absorption spectroscopy (FAAS) was used to detect heavy metal contents in plant biomass. At both 200 µM and 50 µM concentrations, the greatest accumulation of mercury (II) was observed in the roots (16.94 ± 0.44 µg/g) and shoots (17.71 ± 0.66 µg/g), respectively. Similarly, lead (II) showed the highest accumulation in roots (17.10 ± 0.54 µg/g) and shoots (7.78 ± 0.26 µg/g) at 200 µM and 50 µM exposures, respectively. Reverse-phase high-performance liquid chromatography (RP-HPLC) identified and quantified various phenolic compounds in B. polystachyon leaves, including gallic acid, caffeic acid, vanillic acid, p-coumaric acid, ellagic acid, rosmarinic acid, and trans-cinnamic acid. These compounds were found in different forms, such as free, esterified, and glycosylated. Mercury (II)-exposed plants exhibited elevated levels of vanillic acid (1959.1 ± 3.66 µg/g DW), ellagic acid (213.55 ± 2.11 µg/g DW), and rosmarinic acid (187.72 ± 1.22 µg/g DW). Conversely, lead (II)-exposed plants accumulated higher levels of caffeic acid (42.53±0.61 µg/g DW) and p-coumaric acid (8.04 ± 0.31 µg/g DW). Trans-cinnamic acid was the predominant phenolic compound in control plants, with a concentration of 207.74 ± 1.45 µg/g DW. These results suggest that sublethal doses of heavy metals can act as abiotic elicitors, enhancing the production of phenolic compounds in B. polystachyon. The present work has the potential to open up new commercial opportunities in the pharmaceutical industry.

Evaluating the ability of green roof plants in capturing air pollutants using biogas-digestate: Exploring physiological, biochemical, and anatomical characteristics

The undeniable impact of plants in reducing air pollution and the crucial role of nutrition in improving stress tolerance in plants has brought attention to the use of eco-friendly fertilizers. The objective of the study was to investigate how Biogas-digestate (BD) can enhance the tolerance of green roof plants in capturing air pollutants. Four plant species, namely reflexed stonecrop (Sedum reflexum), blue fescue (Festuca glauca), garden mum (Chrysanthemum morifolium), and Peppermint (Mentha piperita) were planted in three urban sites in Mashhad, Iran, with different levels of air pollution. The physiological, biochemical, and morphological characteristics of the treated plants were compared to assess their ability to trap air pollutants. The results showed that the treated M. piperita at Razavi with BD, exhibited the highest level of APTI. Although it was influenced by the site conditions, the determination of the optimum API yielded same results. The F. glauca treated in Khayyam had the highest proline content, while S. reflexum at the Honarestan site had the lowest H2O2 level, without significantly affecting BD. F. glauca, S. reflexum, and M. piperita exhibited the highest levels of SOD, PPO, and GPX activity, respectively, which were significantly increased by the BD treatment. Most of the heavy elements showed increased levels with BD treatment, and M. piperita had the highest concentrations of heavy elements. The leaf surfaces of S. reflexum and M. piperita, had the highest and lowest deposition of particulate matter (PMs), respectively. Carbon and oxygen constituted the majority of PMs on the surface of leaves at all three study locations. The following ranks included the elements Si, Ca, Mg, and Al. BD, particularly in the case of S. reflexum and M. piperita, enhanced the plants' tolerance to air pollution. It is recommended to cultivate S. reflexum using BD on the green roof in polluted areas due to its superior capacity to absorb PMs and the fact that it is not edible.