Phloroglucinol Mediated Plant Regeneration of Ornithogalum dubium as the Sole "Hormone-Like Supplement" in Plant Tissue Culture Long-Term Experiments

Low Caffeine Concentrations Induce Callus and Direct Organogenesis in Tissue Cultures of Ornithogalum dubium

Caffeine is a nitrogenous base that naturally occurs in coffee (Cafea arabica), tea (Thea sinensis), and cocoa (Theobroma cacao). Chemically, caffeine is 1,3,5-trimethylxanthine, a purine analogue. Due to significant human consumption, caffeine effects have been widely studied. Being a natural xanthine derivative, the key degradative enzyme is xanthine oxidase, converting caffeine into 1-methyluric acid. Ecologically, caffeine is believed to act as a repellent molecule against insect feeding behavior. Caffeine's chemical similarity to purines and plant hormones motivated this study, establishing the potential for cellular de-differentiation and re-differentiation. For this, a highly hormone-responsive plant species, Ornithogalum dubium, was used. As caffeine has been shown to induce endoreplication, the potential for new germlines in O. dubium is attractive. Using tissue culture, a range of caffeine concentrations were used (0.0125 mg/L to 2.0 mg/L) without additional hormones. A significant difference (p > 0.05) was observed for intermediate concentrations of 0.0125, 0.025, and 0.05 mg/L when compared to the control (no hormones). The highest rates of callus induction were obtained at a concentration of 0.025 mg/mL. Higher concentrations were phytotoxic (1.0 mg/L or greater). To conclude, caffeine-regenerated plants were not dissimilar to those obtained from canonical hormones.

An Efficient In Vitro Regeneration Protocol and the Feature of Root Induction with Phloroglucinol in Paeonia ostii

Paeonia ostii, a plant of substantial economic significance, continues to face constraints in achieving large-scale propagation. In vitro propagation offers a promising avenue for the production of disease-free plants and the genetic transformation of peonies to instill novel traits. However, significant challenges persist in tissue culture, particularly with regards to the reproduction coefficient of shoots and the rooting process. This study reports an efficacious protocol for P. ostii micropropagation, focusing on in vitro root development facilitated through the application of phloroglucinol (PG). Furthermore, the study unveils the molecular signature of P. ostii during in vitro root development. The results indicate that the modified Y3 medium (Y3M), supplemented with 1 mg/L 6-benzyladenine (BA) and 0.1 mg/L α-naphthaleneacetic acid (NAA), is optimal for adventitious bud induction, achieving a 96.67% induction rate and an average of 16.03 adventitious shoots per sample. The highest elongation percentage (92.15%) and the longest average shoot length (3.87 cm) were obtained with Y3M containing 0.3 mg/L BA and 0.03 mg/L NAA. Additionally, the optimal medium for inducing root formation in P. ostii was identified as WPM supplemented with 3 mg/L indole-3-butyric acid (IBA) and 100 mg/L phloroglucinol (PG). Lignin content detection, microscope inspection, and molecular signature results demonstrated that PG enhanced lignin biosynthesis, thereby promoting in vitro rooting of P. ostii.

Humic Substances as Microalgal Biostimulants—Implications for Microalgal Biotechnology

Humic substances (HS) act as biostimulants for terrestrial photosynthetic organisms. Their effects on plants are related to specific HS features: pH and redox buffering activities, (pseudo)emulsifying and surfactant characteristics, capacity to bind metallic ions and to encapsulate labile hydrophobic molecules, ability to adsorb to the wall structures of cells. The specific properties of HS result from the complexity of their supramolecular structure. This structure is more dynamic in aqueous solutions/suspensions than in soil, which enhances the specific characteristics of HS. Therefore, HS effects on microalgae are more pronounced than on terrestrial plants. The reported HS effects on microalgae include increased ionic nutrient availability, improved protection against abiotic stress, including against various chemical pollutants and ionic species of potentially toxic elements, higher accumulation of value-added ingredients, and enhanced bio-flocculation. These HS effects are similar to those on terrestrial plants and could be considered microalgal biostimulant effects. Such biostimulant effects are underutilized in current microalgal biotechnology. This review presents knowledge related to interactions between microalgae and humic substances and analyzes the potential of HS to enhance the productivity and profitability of microalgal biotechnology.