This study aimed to highlight the positive effects of various recycled organic substrates on lettuce plants (Lactuca sativa L.) and to promote sustainable waste management practices, contributing to the concept of a circular economy. Over a two-month period, the growth potential and rhizosphere microflora of lettuce plants grown in soil amended with different recycled substrates were investigated. All data were compared, and the effects of the culture substrates were evaluated. All groups containing soil improvers offered a significant increase in the number of leaves per plant and, in two cases, an increase in dry biomass as well as an increase in the concentration of all leaf pigments. Both MDA and H₂O₂ concentrations were the lowest in two groups containing soil improvers (VG 5% and PLUS 10%). At the end of the culture period, isolation and culture of bacteria from the plant rhizosphere were performed. Different bacterial strains were isolated and tested for the production of antimicrobial agents against six microbial indicators (B. subtilis, E. coli, S. aureus, S. cerevisiae, C. albicans, and P. aeruginosa). The greater percentage of the isolated strains showed an ability to inhibit the growth of the B. subtilis index. Most of the strains with antimicrobial activity were isolated from the soil samples of the plain soil group and the soil amended with the commercial fertilizer. Three of the isolated strains originating from the Ginagro 5% group are multiproducers as they inhibit the growth of three microbial indicators or more.

Ceratonia siliqua L. (Fabaceae) is an evergreen sclerophyllous species that successfully overcomes the challenges of the Mediterranean climate. Commonly, biosynthesis of secondary metabolites is a major reaction of the plants thriving in the Mediterranean formations against temperature stress. Due to concerns about the climate crisis, we studied the impact of 6-day low (5 °C) and high (40 °C) temperature stress on young carob seedlings. In stressed plants, mainly the heat-treated, the leaves appear xeromorphic. Parameters of the physiology of the plants such as chlorophyll-a and -b, total phenolic content, and oxidative stress were measured and presented via Principal Component Analysis. Chlorophyll-a and -b contents are inferior in cold-stressed leaves while heat-stressed leaves accumulate more phenolics and experience higher oxidative stress as compared to their cold-stressed counterparts. The phytochemical profile of different extracts obtained from stressed carob leaves was identified so as to gain insight into metabolites produced under stress. Moreover, LC-HRMS/MS metabolomic workflow was utilized for the discovery of biomarkers, over- or under-regulated in stressed conditions. The antimicrobial activity of carob leaf extract fractions was assessed against six human pathogen strains and three phytopathogen bacterial strains. MeOH-H₂O and dichloromethane (DCM) extracts presented notable activity against Candida albicans and Saccharomyces cerevisiae, while DCM extracts inhibited the growth of Erwinia amylovora. We may conclude that carob tree exposure to temperature stress does not have a significant influence on secondary metabolic pathways.

Background: The germination and early development of Origanum vulgare L. subsp. hirtum (Link) Ietswaart (Greek oregano) were studied to assess the plant’s response to different temperatures. Methods: After germination, seedlings were cultivated in control (25 °C) and cold (15 °C) chambers with standard growth parameters. Comparative analyses of plant morphology and leaf anatomy were conducted to identify structural modifications induced by different temperatures. Physiological evaluations, including photosynthetic pigment measurements, phenolic content, and antioxidant activity, were performed to assess differences between the plants grown under the two temperature conditions. Methanolic extracts from the leaves were tested for cytotoxicity on MCF-7 breast adenocarcinoma cells and SH-SY5Y neuroblastoma cells, as well as on nine microbial strains. Additionally, biomarkers from the leaves affected by temperature changes were determined using LC-HRMS/MS analysis. Results: Comparative analyses revealed distinct structural and physiological modifications under cold conditions. The methanolic extracts from plants grown at 15 °C exhibited notably higher cytotoxic activity in both cell lines but demonstrated no activity against microbial strains. The results highlight the influence of low temperature on enhancing the bioactive properties of Greek oregano. Conclusions: The findings provide valuable insights into the environmental adaptability of oregano, demonstrating the impact of low temperature on its bioactive properties. The therapeutic potential of methanolic extracts cultured at 15 °C is imprinted in cytotoxicity in SH-SY5Y and MCF-7 cells and the absence of any activity against microbial strains.