Role of Biogenic Silver Nanoparticles on Hyperhydricity Reversion in Dianthus chinensis L. an In Vitro Model Culture

Hyperhydricity (HH) is one of the major problems in plant tissue culture. Increased frequency (75%) of HH in the cultures of. Dianthus chinensis L. cultivar telstar scarlet raised from nodal segments on agar (0.85%) gelled, benzyladenine (2.5 µM) supplemented Murashige and Skoog (MS) medium was noticed in the third subculture onwards. To reduce HH and to resume normal growth, the addition of silver nitrate is routinely recommended in the culture medium. However, the impact of biogenic silver nanoparticles (AgNPs) on HH reversion has not been well investigated. In this study, biogenic AgNPs prepared from leaf extract of D. chinensis were used to control HH in D. chinensis cultures. The characterization of bioynthesized AgNPs has been done by UV–Vis spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction analysis, energy-dispersive X-ray spectrum, transmission electron microscopy, and atomic force microscopy. Higher water content or addition of ethylene precursor, ethephon, in culture medium induced plantlet with unhealthy, pale green, glassy shoots (HH). Due to the biological activity of Ag⁺ ions and water regulating mechanism, AgNPs treatment on hyperhydric explant (4 weeks) resulted in high retroversion coupled with reduced relative water content. Supplementation of 100 µg L⁻¹ AgNPs in MS medium significantly reduced the percentage of HH to 13.3%, in contrast to control (100%). Addition of AgNPs effectively reduced hydrogen peroxide (H₂O₂) content (50%) characterized by green, healthy shoots with proper stomata in contrast to hyperhydric shoots. The gene expression pattern of 1-aminocyclopropane-1-carboxylase synthase (ACS1) and 1-aminocyclopropane-1-carboxylic acid oxidase (ACO1) showed reduced expression after the retroversion of microshoots in 100 µg L⁻¹ AgNPs medium compared to hyperhydric shoot. The relative gene expression profile of ACS1 and ACO1 at 100 µg L⁻¹ AgNPs treatment was 9.8 and 1.8-fold over normal shoots (1), respectively. Inter simple sequence repeat (ISSR) analysis on AgNPs directed HH reverted shoots showed genetic stability thus proved safe to adopt this technique to produce true to type plants. Combined manipulation, coordination of water permeability, and anti-ethylene activity of AgNPs were responsible for effective HH reversion. These finding will put forward the future utilization of bioencapsulated AgNPs in plant tissue culture and agriculture practices.