Brassinosteroids, as unique plant steroid hormones that bear structural similarity to animal steroids, play a crucial role in modulating plant growth and development. These hormones have a positive impact on plant resistance and, under stressful conditions, stimulate photosynthesis and antioxidative systems (enzymatic and non-enzymatic), leading to a reduced impact of environmental cues on plant metabolism and growth. Although these plant hormones have been studied for several decades, most studies analyze the primary site of action of the brassinosteroid phytohormone, with a special emphasis on the activation of various genes (mainly nuclear) through different signaling processes that influence plant metabolism, growth, and development. This review explores another issue, the secondary influence (the so-called mode of action) of brassinosteroids on changes in growth, development, and chemical composition, as well as thermodynamic and energetic changes, mainly during the early growth of corn seedlings. The interactions of brassinosteroids with other phytohormones and physiologically active substances and the influence of these interactions on the mode of action of brassinosteroid phytohormones were also discussed. Seen from a cybernetic point of view, the approach can be labeled as “black box” or “gray box”. “Black box” and “gray box” are terms for cybernetic systems, for which we know the inputs and outputs (in an energetic, biochemical, kinetic, informational, or some other sense), but whose internal structure and/or organization are completely or partially unknown to us. The findings of many researchers have indicated an important role of reactive species, such as oxygen and nitrogen reactive species, in these processes. This ultimately results in the redistribution of matter and energy from source organs to sink organs, with a decrease in Gibbs free energy from the source to sink organs. This quantitative evidence speaks of the exothermic nature and spontaneity of early (corn) seedling development and growth under the influence of 24-epibrassinolide. Based on these findings and a review of the literature on the mode of action of brassinosteroids, a hypothesis was put forward about the secondary effects of BRs on germination and the early growth of plant seedlings.

Plant protection with natural products is a new trend in environmentally friendly agriculture. Nepeta rtanjensis Diklic et Milojevic is an endemic and critically endangered plant species in Serbia. We explored the phytotoxic potential of a water emulsion of Nepeta rtanjensis essential oil (NrEO) with high amounts of trans,cis-nepetalactone on five weeds. The most sensitive was Stellaria media (L.) Vill., as NrEO (from 0.013% to 0.1%) completely inhibited germination. Germination of Amaranthus retroflexus L. and Artemisia vulgaris L. was completely inhibited at the highest applied concentrations of NrEO (0.1%), while Ambrosia artemisiifolia L. germination was reduced to 48% at the same concentration of NrEO. The most tolerant species was Cephalaria transsylvanica (L.) Schrad. ex Roem. & Schult. as the final germination rate at the highest applied concentration of NrEO (0.1%) was 81%, like the control (82%). To our knowledge, this is the first time the interaction of essential oils on the germination and growth of A. vulgaris and C. transsylvanica is reported. The germination dynamics of S. media in pots with soil were significantly inhibited when the soil was initially treated with the highest applied concentration of the NrEO water emulsion (1%). Spraying S. media seedlings with NrEO significantly inhibited growth parameters (shoot height, shoot fresh weight, and the number of nodes) at the higher applied concentrations of NrEO (0.5% and 1%). Therefore, the water emulsion of the essential oil of N. rtanjensis could be potentially developed for use in the control of invasive and allergenic weeds.

The paper provides an overview of various aspects of desiccants and bleaching herbicides, from different chemical groups, which have in common the drying and bleaching of leaf mass. In weed plants, they can act as total or selective herbicides, and be applied in the mature stages of the crop, where by drying the leaf mass they promote the maturation of some important crops such as sunflower, soybeans, and potatoes. More or less, all these various herbicides are highly or significantly toxic, which greatly complicates their application. In the EU, there was an initiative to ban some of them (e.g. paraquat). However, despite their significant toxicity, we believe they should be considered as an alternative to some other herbicides.

Chlorophylls, which are associated with carotenoids and photosynthetic protein complexes, acquire optical properties that enable the absorption of sunlight, necessary for the synthesis of energy and redox equivalents, necessary for photosynthetic absorption of CO₂ and the production of oxygen as an intermediate product. These processes are important for plants, but also for the biosphere. In stressful situations, when photosynthesis is limited, the production of reactive oxygen and other species increases, and the activation of various protective systems is necessary to remove the aforementioned reactive species or reduce the excessive reduction in photosynthetic electron transport, as the cause of the production of the reactive species. A review of studies where the content and physiological state of chlorophyll are monitored, using destructive and non-destructive methods, such as various optical methods for monitoring its content and physiological activity, is given. Polyphenolic compounds belong to non-enzymatic systems for quenching the reactive species. In addition to their presence in monomeric and oligomeric forms of polyphenols, polymerization of this type of compound can occur. In addition to having a protective effect on the plants that synthesize them, polyphenolic compounds also have a beneficial effect on the health of animals and humans who consume them from plants.

Studying plant species rich in bioactive compounds, including allelochemicals, could lead to the development of biodegradable and environmentally safe herbicides. In this study, a water extract of hemlock (Conium maculatum L.), known to be rich in alkaloids, was used to investigate its effects on the germination of Amaranthus retroflexus L., Ambrosia artemisiifolia L., Stellaria media (L.) Vill., and Lactuca sativa L., providing valuable insights into its phytotoxic properties. Among the C. maculatum water extracts (CmWEs) tested, that of dry leaves showed the strongest inhibitory effect on the germination of all species analyzed. The CmWE of dry leaves (50%) completely inhibited seed germination of all species tested. The CmWE of dry stems (50%) reduced seed germination in S. media, A. retroflexus, and A. artemisiifolia by 20% to 89%, whereas the germination of L. sativa was less affected (9%). In addition, a CmWE of dry stems (5%) selectively inhibited ragweed germination (45%), while the germination of Lactuca sativa was not significantly affected. The CmWE of dry leaves (20%) inhibited early root and shoot growth of S. media more effectively than suppressing seed germination. Moreover, the dry leaves and inflorescences of C. maculatum demonstrate strong allelopathic properties even after two years of storage, highlighting the long-term potential of C. maculatum as a source of natural herbicides.