**About the Editors**

#### **Laura Pistelli**

Laura Pistelli is an assistant professor in plant biology at the University of PISA. Her research deals with the production of specific natural metabolites (antioxidants, nutraceuticals, pharmaceuticals) of aromatic and medicinal plants. The metabolites are isolated from various organs (leaves, roots, flowers, fruits, seeds) and quantified with modern technologies. The tolerance or susceptibility of plants to abiotic stress (e.g., temperature, water availability, pollutants) can promote the production of secondary metabolites. *In vitro* cultures (organ tissues, cell biomass, hairy roots) are also used, which offer a valuable source for optimizing plant proliferation and metabolite production under controlled conditions.

#### **Kalina Danova**

Kalina Danova graduated as a Master of Pharmacy from the Faculty of Pharmacy, Medical University, Sofia, Bulgaria. Her PhD on the topic of the in vitro cultivation, physiological behavior, and secondary metabolites production of *Pulsatilla and Hypericum* species and the cryopreservation of *Hypericum rumeliacum* Boiss. was obtained from the Faculty of Plant Physiology, Sofia University, Bulgaria. She is currently an associate professor at the Institute of Organic Chemistry with the Centre of Phytochemistry, Bulgarian Academy of Sciences, and is in charge of the topic of plant cell tissue and organ culture development in medicinal and aromatic plants, with a focus on secondary metabolites and physiological studies as well as germplasm conservation.

### *Editorial* **Plant Tissue Culture and Secondary Metabolites Production**

**Kalina Danova 1,\* and Laura Pistelli 2,\***


Plants have developed a complex biochemical system for interacting and coping with dynamic environmental challenges throughout their whole life. Plant secondary metabolites are specifically produced and accumulated in low quantities in response to numerous factors such as bacteria, viruses, fungi, nematodes, insects and herbivores, as well as to climatic factors and seasonal fluctuations, soil and water parameters, etc.

To optimize secondary metabolites production, plants have fine-tuned early signal systems for differentiating general mechanical damage from an attack by an insect/herbivore, for example. In addition, plants distinguish the degree of damage caused by herbivore feeding guilds, insect oral secretions, oviposition fluids, etc. The consecutive steps of the production of the respective defense secondary metabolites is mediated by cellular messengers and events such as metabolic changes, gene activation, jasmonic acid (JA) accumulation, kinase cascades, hydrogen peroxide production, cytosolic calcium ion fluxes, as well as membrane potential changes [1] and references cited therein.

The key role of secondary metabolites for plant survival also underline the pharmacological roles that these substances play in mammalian organisms and hence their applicability in veterinarian and humanitarian medicinal practices.

Plant cell tissue and organ cultures are based on the "totipotency" of the plant cell and its capability to regenerate up to a whole integral organism. The technique allows for the cultivation of separate cells, tissues, differentiated organs, or integral plants in a growth medium in sterile conditions and out of the indigenous natural environment of the plants. The contemporary development of the method has nowadays led to its routine use as a supplementary to conventional plant breeding for an array of applications such as the rapid and disease-free micropropagation of plantlets, independent of seasonal, climatic, and geographic factors; the rapid testing and practical introduction of new cultivars using conventional or genetic engineering selection approaches. An important and rapidly developing field of the application of plant biotechnology is its use for the yield of plant secondary metabolites, allowing for the standardization of the levels of the secondary metabolites produced due to the capability of tissue culture techniques to optimize culture conditions and obtain the desired environment for the production of the target compounds.

Considering the importance of plant secondary metabolites and the high relevance of the establishment of scientifically based approaches for their biotechnological production, we are pleased to present this Special Issue of *Plants* dedicated to "Plant Tissue Culture and Secondary Metabolites Production". The present collection aims to provide readers with up-to-date research dedicated to the scientific accomplishments in the production of plant secondary metabolites of different chemical types through the development of plant cells, tissues, and organs in diverse in vitro culture systems.

We have received seven scientific research papers on tissue culture development and secondary metabolite production of medicinal and aromatic plants of different regions of the world.

**Citation:** Danova, K.; Pistelli, L. Plant Tissue Culture and Secondary Metabolites Production. *Plants* **2022**, *11*, 3312. https://doi.org/10.3390/ plants11233312

Received: 2 November 2022 Accepted: 27 November 2022 Published: 30 November 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Ramabulana et al. [2] established that the exogenous application of auxin (2,4-dichlorop henoxyacetic acid—2,4-D) and cytokinin (benzylaminopurine, BAP) could induce the manipulation of the metabolome of the callus culture of *Bidens pilosa* L. (Asteraceae), dominated by chlorogenic acids consisting of caffeoyl and feruloyl derivatives of quinic acid. Xanthones production in differentiated shoot cultures of the endangered *Gentianella lutescens* (Gentianeceae) was evaluated for the first time by Krsti´c-Miloševi´c et al. [3] in an experiment focusing on the modification of the concentration of sucrose, sorbitol, and abiotic elicitors salicylic acid (SA), jasmonic acid (JA), and methyl jasmonate (MeJA). Wojtania and Mieszczakowska-Fr ˛ac [4] proposed an efficient biotechnological method to produce anthocyanins-rich planting material for selected genotypes of the Polish Culinary rhubarb 'Malinowy' cultivar. In a carrot (*Daucus carota*, Apiaceae) callus culture experimental design of a combination of the components of the Gamborg [5] and Murashige and Skoog [6] culture media, Oleszkiewicz et al. [7] established that the N concentration and the NO3:NH4 ratio affected carotenoid accumulation. In this work, changes to the medium other than N, such as microelements, vitamins, growth regulators, and sucrose, had no effect on callus growth and carotenoid accumulation. Mamdouh et al. [8] developed an in vitro protocol for micropropagation of *Lycium schweinfurthii* (Solanaceae). Investigations on genetic stability, phenolic, flavonoid, ferulic acid contents, and antioxidant activity were performed, leading to the selection of an effective protocol for the in vitro propagation of plant material with desired quality. Erst et al. [9] studied the combined effects of NO3, as well as NH4:K<sup>+</sup> ratio and the cytokinins BAP and naphthylacetic acid (NAA) on the growth and production of total phenolics callus culture of *Rhodiola rosea* (Crassulaceae). The study of Pieracci et al. [10] on shoot cultures of halophyte *Artemisia caerulescens* L. (Asteraceae) demonstrated the potential of the tissue culture technique for both the ex situ conservation and production of essential oils and phenolic compounds of this species.

**Author Contributions:** All authors contributed equally to this article. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Data Availability Statement:** Not appliable.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

