Differentiated response of Hypericum perforatum to foliar application of selected metabolic modulators: Elicitation potential of chitosan, selenium, and salicylic acid mediated by redox imbalance.

Plants plastically alter their metabolism in response to environmental stimuli, which induces changes in the accumulation of specialized metabolites. This ability can be utilized to manipulate plant phytochemistry in a desired direction. However, the abundance of secondary metabolites in the different plant species, especially medicinal, is enormous; therefore, it is difficult to establish a clear direction for the effects of metabolic modulators on phytochemical composition, especially given the possibility of using different types thereof. In order to gain insight into these changes, we investigated the effects of foliar-applied chitosan (ChL, 100 mg/L), selenium (Se, 10 mg/L), salicylic acid (SA, 150 mg/L), or an equal volume mixture thereof on Hypericum perforatum L. metabolism. Selenium and SA proved to be the more effective than ChL in enhancing the accumulation of phenolic compounds. The greatest increase was found in the concentration of neochlorogenic acid after Se-spraying. The treatment with the elicitors generally increased the concentration of identified flavonoids, but not the level of naphthodianthrone or phloroglucinol metabolites. The most pronounced response was observed on day 10 following the application of the compounds, and is likely the consequence of elevated levels of O2-˙, free proline, and modulated activity of enzymatic antioxidants.

Comparative Effects of Two Forms of Chitosan on Selected Phytochemical Properties of Plectranthus amboinicus (Lour.).

In response to stress factors, plants produce a wide range of biologically active substances, from a group of secondary metabolites, which are applied in medicine and health prophylaxis. Chitosan is a well-known elicitor affecting secondary metabolism in plants, but its effect on the phytochemical profile of Plectranthus amboinicus has not been assessed yet. In the present experiment, the effectiveness of the foliar application of two forms of chitosan (chitosan suspension or chitosan lactate) was compared in order to evaluate their potential to induce the accumulation of selected polyphenolic compounds in the aboveground parts of P. amboinicus. It was shown that chitosan lactate had substantially higher elicitation efficiency, as the use of this form exerted a beneficial effect on the analysed quality parameters of the raw material, especially the content of selected polyphenolic compounds (total content of polyphenols, flavonols, anthocyanins, and caffeic acid derivatives) and the free radical-scavenging activity of extracts from elicited plants. Concurrently, it had no phytotoxic effects. Hence, chitosan lactate-based elicitation can be an effective method for optimisation of the production of high-quality P. amboinicus raw material characterised by an increased concentration of health-promoting and antioxidant compounds.

Protective, Biostimulating, and Eliciting Effects of Chitosan and Its Derivatives on Crop Plants.

Chitosan is a biodegradable and biocompatible polysaccharide obtained by partial deacetylation of chitin. This polymer has been gaining increasing popularity due to its natural origin, favorable physicochemical properties, and multidirectional bioactivity. In agriculture, the greatest hopes are raised by the possibility of using chitosan as a biostimulant, a plant protection product, an elicitor, or an agent to increase the storage stability of plant raw materials. The most important properties of chitosan include induction of plant defense mechanisms and regulation of metabolic processes. Additionally, it has antifungal, antibacterial, antiviral, and antioxidant activity. The effectiveness of chitosan interactions is determined by its origin, deacetylation degree and acetylation pattern, molecular weight, type of chemical modifications, pH, concentration, and solubility. There is a need to conduct research on alternative sources of chitosan, extraction methods, optimization of physicochemical properties, and commercial implementation of scientific progress outcomes in this field. Moreover, studies are necessary to assess the bioactivity and toxicity of chitosan nanoparticles and chitosan conjugates with other substances and to evaluate the consequences of the large-scale use thereof. This review presents the unique properties of chitosan and its derivatives that have the greatest importance for plant production and yield quality as well as the benefits and limitations of their application.

NaCl-Induced Elicitation Alters Physiology and Increases Accumulation of Phenolic Compounds in Melissa officinalis L.

In nature, plants usually produce secondary metabolites as a defense mechanism against environmental stresses. Different stresses determine the chemical diversity of plant-specialized metabolism products. In this study, we applied an abiotic elicitor, i.e., NaCl, to enhance the biosynthesis and accumulation of phenolic secondary metabolites in Melissa officinalis L. Plants were subjected to salt stress treatment by application of NaCl solutions (0, 50, or 100 mM) to the pots. Generally, the NaCl treatments were found to inhibit the growth of plants, simultaneously enhancing the accumulation of phenolic compounds (total phenolics, soluble flavonols, anthocyanins, phenolic acids), especially at 100 mM NaCl. However, the salt stress did not disturb the accumulation of photosynthetic pigments and proper functioning of the PS II photosystem. Therefore, the proposed method of elicitation represents a convenient alternative to cell suspension or hydroponic techniques as it is easier and cheaper with simple application in lemon balm pot cultivation. The improvement of lemon balm quality by NaCl elicitation can potentially increase the level of health-promoting phytochemicals and the bioactivity of low-processed herbal products.