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Hormesis or hormetic effect is characterized by a biphasic response caused by a stressor or stressor agent. The first phase of hormesis is stimulation at low or sublethal doses, whereas the second phase occurs through inhibition or death at high or lethal doses of the stressor. Both phases are represented using mathematical models in the form of dose-response curves. In plants, hormesis has morphological, physiological, biochemical and molecular effects. These effects act as response mechanisms of adjustment or coupling to the stressor. Adjustment or coupling mechanisms can be exploited in plant tissue culture (PTC) to increase or promote plant length, number of leaves, number of roots, biomass and secondary metabolites, or to induce or enhance morphogenesis in vitro. This review compiles recent findings on hormesis using PTC techniques and the mechanisms of response to different stressors. Stressor agents that present a hormetic dose response (stimulation, inhibition) include silver nanoparticles (50, 100 mg/L), arsenic (1.15, 50.15 mg/kg), multi-walled carbon nanotubes (50, 200 mg/L), 60Co gamma rays (20, 60 Gy), microplastics (0.01, 0.1 mg/L), and a magnetic field (65, 172 mT), among others. In addition, topics such as general plant hormetic response to abiotic stressors, physiological and biochemical aspects of hormesis, hormetic response to metals and nanomaterials, and other curious examples of hormesis are included. Hormesis could be considered as a novel strategy to improve growth and differentiation in different PTC areas and applications. It is suggested to document new cases of hormesis and carry out future studies to elucidate and understand the hormetic effect response mechanisms to different stressors through in vitro biological models. [ABSTRACT FROM AUTHOR]

The term in vitro photomixotrophism refers to the ability of explants to obtain metabolic energy from the culture medium and as a product of photosynthesis. The objective of this research was to study the physiological and biochemical mechanisms of V. planifolia during in vitro multiplication using a photomixotrophic system with different sucrose contents (0, 15 and 30 g L–1) and CO2 supply levels (500, 800 and 1200 ppm) using a Temporary Immersion Modular System (SMIT®). After 45 days of multiplication, response percentage, number of shoots per explant, shoot length, number of leaves per shoot, stomatal index (%), percentage of closed stomata, and chlorophyll, β-carotene, Phosphoenolpyruvate (PEP) and Rubisco contents were evaluated. In addition, the survival rate during acclimatization at 60 days was evaluated. For the multiplication stage, the highest response percentage was obtained in the treatments with 15 g L–1 sucrose with 500 and 800 ppm CO2, and 30 g L–1 sucrose with 500 ppm CO2. In the latter treatment, the best development parameters were obtained, with 14.75 shoots per explant, a shoot length of 2.38 cm and 2.5 leaves per shoot. In general, the highest chlorophyll, β-carotene, PEP and Rubisco contents were observed with 30 g L–1 sucrose + CO2. No effects of the treatments on stomatal index (%) were observed, while the percentage of closed stomata showed differences among treatments. At the acclimatization stage, the highest survival percentages were obtained from the treatments of 30 g L–1 sucrose with 500 and 800 ppm CO2. In conclusion, this study demonstrates physiological and biochemical mechanisms for a better understanding of photomixotrophism during in vitro multiplication in vanilla and may be applied to other species. Key message: In vitro photomixotrophism can be induced by injecting carbon dioxide to promote photosynthesis. [ABSTRACT FROM AUTHOR]

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Copyright of Agro Productividad is the property of Colegio de Postgraduados and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)