Omitting the far‐red in LED lighting for bioreactors is inexplicable because it affects photosynthetic efficiency and photomorphogenetic activity. Therefore, this work compares three light sources (fluorescent—white light (WL), and LED: blue + red—BRL and blue + red + far‐red—BRFRL) for cultures of Chlorella vulgaris. Metabolic activity was determined by isothermal calorimetry. Changes in the chemical composition of biomass were examined by spectrofluorimetry and Raman spectroscopy. Maximum quantum yield of photosystem II was determined on the basis of chlorophyll a fluorescence parameters. The algae grown under BRL produced significantly more thermal energy than those cultured under BRFRL and WL. The Raman spectra of cultures showed characteristic bands for carotenoids, chlorophyll, phenolics, lipids, aliphatic carbohydrates, pectins, and disaccharides. According to the cluster analysis, the chemical composition of cultures grown under BRL and BRFRL was very similar, whereas the WL represented a distinct group. BRL and BRFRL stimulated the biosynthesis of an unidentified compound(s) with fluorescence maximum at 614 nm. At the beginning of the cultivation, photosystem II had very weak photochemical activity. Under BRFRL, ratios of Fv/Fm reached the maximum after 4 days, whereas under BRL and WL, after 6 days of cultivation. The results point to the favorable influence of the far‐red on the metabolism of microalgae.

In this study we tested the possibility that foliar-applied caraway or peppermint essential oils (EOs) can selectively inhibit the growth of Echinochloa crus-galli (a typical maize weed) but not that of maize plants, attempting to develop an eco-friendly botanical herbicide.We tested the phytotoxic potential of oil-in-water emulsions of each EO with addition of commercial adjuvant mainly composed of fatty acids methyl esters, studying their effect on 2 visible plants injuries, biomass accumulation, chlorophyll a fluorescence and changes to biochemical patterns of both the main crop (maize) and the weed (E. crus-galli) via an untargeted metabolomic approach. We found that oil-in-water emulsion containing 2.5% of adjuvant and of caraway EO did not affect significantly the growth of maize plants, did not induce foliar symptoms and did not alter the status of the photosynthetic apparatus, as revealed by chlorophyll a fluorescence. On the contrary, this emulsion exerted significantly negative effects against E. crus-galli growth, inducing foliar injuries and reducing the photosynthetic efficiency of photosystem II. We also found that the studied emulsions caused a series of biochemical changes in the plant tissues, with caraway emulsion being more phytotoxic, as compared to the peppermint EO-emulsion. We conclude that oil-in-water emulsion containing 2.5% of caraway EO could be used in future as a foliar-applied botanical herbicide against E. crus-galli in maize cultivation.

In plants cultivation, some species influencing each other in a favorable manner, and others adversely affect the result of the release of physiologically active substances. These substances, called allelopathic compounds are excreted primarily by underground and aboveground plants’ organs or formed during the decomposition of their remains. Allelopathins show the inhibitory or stimulating effects on the processes of seed germination, growth and physiological activity of plants. The aim of the study was to determine the allelopathic effects of aqueous extracts from the peppermint (Mentha × piperita L.) leaves at various concentrations (1, 3, 5, 10, 15%) on seeds germination and the selected physiological processes of common sunflower (Helianthus  annuus L.) seedlings. Seeds were germinated and plants were grown under greenhouse conditions for 30 days. Germination of sunflower seeds was reduced and electrolyte leakage from seedlings increased with increasing concentrations of aqueous extracts of the peppermint leaves. Increasing concentrations of aqueous extracts of peppermint also caused decrease of chlorophyll a and an increase of chlorophyll b content. The highest increase of the maximum photochemical efficiency of photosystem II was observed in H. annuus L. treated with 15% peppermint extract in comparison to the lower concentration of extracts  and to the control. Non-photochemical and photochemical quenching and vitality index of hotosystem II decreased with increasing concentrations of allelopathic substances in peppermint extracts.

This article is devoted to some aspects of the fragrant substances of plant origin applied in the food industry and perfumery as well. Since antiquity many extractive techniques have been developed to obtain essential oils. Some of them are still applied, but new ones, like microwave or ultrasound-assisted extractions, are more and more popular and they save time and cost. Independently of the procedure, the resulting essential oils are the source of many so-called isolates. These can be applied as food additives, medicines, or can be used as starting materials for organic synthesis. Some substances exist in very small amounts in plant material so the extraction is not economically profitable but, after their chemical structures were established and synthetic procedures were developed, in some cases they are prepared on an industrial scale. The substances described below are only a small fraction of the 2000–3000 fragrant molecules used to make our life more enjoyable, either in food or perfumes. Additionally, a few examples of allelopathic fragrant compounds, present in their natural state, will be denoted and some of their biocidal features will be mentioned as an arising “green” knowledge in agriculture.

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