H2O2-Elicitation of Black Carrot Hairy Roots Induces a Controlled Oxidative Burst Leading to Increased Anthocyanin Production

Application of In Vitro Plant Tissue Culture Techniques to Halophyte Species: A Review

Halophytes are plants able to thrive in environments characterized by severe abiotic conditions, including high salinity and high light intensity, drought/flooding, and temperature fluctuations. Several species have ethnomedicinal uses, and some are currently explored as sources of food and cosmetic ingredients. Halophytes are considered important alternative cash crops to be used in sustainable saline production systems, due to their ability to grow in saline conditions where conventional glycophyte crops cannot, such as salt-affected soils and saline irrigation water. In vitro plant tissue culture (PTC) techniques have greatly contributed to industry and agriculture in the last century by exploiting the economic potential of several commercial crop plants. The application of PTC to selected halophyte species can thus contribute for developing innovative production systems and obtaining halophyte-based bioactive products. This work aimed to put together and review for the first time the most relevant information on the application of PTC to halophytes. Several protocols were established for the micropropagation of different species. Various explant types have been used as starting materials (e.g., basal shoots and nodes, cotyledons, epicotyls, inflorescence, internodal segments, leaves, roots, rhizomes, stems, shoot tips, or zygotic embryos), involving different micropropagation techniques (e.g., node culture, direct or indirect shoot neoformation, caulogenesis, somatic embryogenesis, rooting, acclimatization, germplasm conservation and cryopreservation, and callogenesis and cell suspension cultures). In vitro systems were also used to study physiological, biochemical, and molecular processes in halophytes, such as functional and salt-tolerance studies. Thus, the application of PTC to halophytes may be used to improve their controlled multiplication and the selection of desired traits for the in vitro production of plants enriched in nutritional and functional components, as well as for the study of their resistance to salt stress.

Hairy Root Cultures as a Source of Polyphenolic Antioxidants: Flavonoids, Stilbenoids and Hydrolyzable Tannins

Due to their chemical properties and biological activity, antioxidants of plant origin have gained interest as valuable components of the human diet, potential food preservatives and additives, ingredients of cosmetics and factors implicated in tolerance mechanisms against environmental stress. Plant polyphenols are the most prominent and extensively studied, albeit not only group of, secondary plant (specialized) metabolites manifesting antioxidative activity. Because of their potential economic importance, the productive and renewable sources of the compounds are desirable. Over thirty years of research on hairy root cultures, as both producers of secondary plant metabolites and experimental systems to investigate plant biosynthetic pathways, brought about several spectacular achievements. The present review focuses on the Rhizobium rhizogenes-transformed roots that either may be efficient sources of plant-derived antioxidants or were used to elucidate some regulatory mechanisms responsible for the enhanced accumulation of antioxidants in plant tissues.

Production and Secretion of Isowighteone in Hairy Root Cultures of Pigeon Pea (Cajanus cajan) Co-Treated with Multiple Elicitors

Isowighteone (3’-isoprenyl genistein) is a prenylated stilbenoid derivative that exhibits neuroprotective, antibacterial, and anti-inflammatory properties. To establish a bioproduction system for this bioactive compound, hairy root cultures of pigeon pea (Cajanus cajan (L.) Millsp.) were developed via Agrobacterium rhizogenes-mediated transformation. The cultures were co-treated with methyl jasmonate, cyclodextrin, hydrogen peroxide, and magnesium chloride to enhance the production of isowighteone. The amount of isowighteone that accumulated in the culture medium upon elicitation varied with the period of elicitation. Isowighteone was purified from extracts of the culture medium by semi-preparative HPLC, and its identity was confirmed by tandem mass spectrometry. After 144 h of elicitation in 12-day-old hairy root culture, the total yield of isowighteone was 8058.618 ± 445.78 μg/g DW, of which approximately 96% was found in the culture medium. The yield of isowighteone in the elicited hairy root culture was approximately 277-fold higher than in the non-elicited root culture. The difference between the phenotypes of the elicited and non-elicited pigeon pea hairy roots was studied using scanning electron microscopy. The non-elicited hairy roots had uniform surfaces whereas the elicited roots had non-uniform shapes. Pigeon pea hairy roots provide a sustainable platform for producing and studying the biosynthesis of isowighteone.