Morpho-histological characterization and direct shoot organogenesis in two types of explants from <Emphasis Type="Italic">Bacopa monnieri</Emphasis> on unsupplemented basal medium

In the present study, high frequency regeneration has been obtained via de novo direct shoot organogenesis from leaf and internode explants in Murashige and Skoog (MS) basal medium without any phytohormone supplementation in Bacopa monnieri, an indigenous traditionally used medicinal herb. Leaves and internodes from different positions were excised from 4-weeks-old in vitro propagated B. monnieri plants and cultured on MS basal medium supplemented with 3% (w/v) sucrose and 0.75% (w/v) agar for 4 weeks. The induction of de novo shoot buds was observed at petiolar cut edges of leaf and both proximal and distal cut ends of internode explants within 10–15 days of culture. The first histological changes could be observed after 4–5 days, with meristematic activity of vascular bundles. Proliferation of epidermal cells gave rise to dome-shaped protuberances followed by shoot apical meristems formation and their vascular connections with explant tissues within 2 weeks of culture. However, a basipetal gradient of shoot regeneration from both types of explants collected along the branch axis was noticed after 4 weeks of culture. Leaf and internode explants near the basal region exhibited significantly higher number of shoot buds and micro shoots (8.8/leaf explant and 15/internode explant). Microshoots (7–12 micro shoots/leaf or internode explants) elongated (shoot length 8–9 cm) within 8 weeks on phytohormone free MS medium. Excised micro shoots rooted (100%) in hormone free MS medium within two weeks of culture. Rooted plants were then acclimatized and transferred to field with 95% survival. This protocol may be used for micropropagation, genetic transformation as well as a model system for evaluation of changes associated with acquisition of competence of differentiated cells in phytohormone free medium.     

Effects associated with insertion of rol genes on morphogenic potential in explants derived from transgenic Bacopa monnieri (L.) Wettst

Plant Cell, Tissue and Organ Culture (PCTOC) - The present study deals with the establishment of rolA-transgenic and rolB-transgenic plants for the first time through Agrobacterium tumefaciens...     

Elicitation: A biotechnological tool for enhanced production of secondary metabolites in hairy root cultures

Elicitation is a possible aid to overcome various difficulties associated with the large‐scale production of most commercially important bioactive secondary metabolites from wild and cultivated plants, undifferentiated or differentiated cultures. Secondary metabolite accumulation in vitro or their efflux in culture medium has been elicited in the undifferentiated or differentiated tissue cultures of several plant species by the application of a low concentration of biotic and abiotic elicitors in the last three decades. Hairy root cultures are preferred for the application of elicitation due to their genetic and biosynthetic stability, high growth rate in growth regulator‐free media, and production consistence in response to elicitor treatment. Elicitors act as signal, recognized by elicitor‐specific receptors on the plant cell membrane and stimulate defense responses during elicitation resulting in increased synthesis and accumulation of secondary metabolites. Optimization of various parameters, such as elicitor type, concentration, duration of exposure, and treatment schedule is essential for the effectiveness of the elicitation strategies. Combined application of different elicitors, integration of precursor feeding, or replenishment of medium or in situ product recovery from the roots/liquid medium with the elicitor treatment have showed improved accumulation of secondary metabolites due to their synergistic effect. This is a comprehensive review about the progress in the elicitation approach to hairy root cultures from 2010 to 2019 and the information provided is valuable and will be of interest for scientists working in this area of plant biotechnology.     

A Combined Spectroscopic and Theoretical Analysis of Plasmonic Silver Nanoparticle Sensor Towards Detailed Microscopic Understanding of Heavy Metal Detection

Plasmonic nanoparticles are of great importance owing to their highly responsive ‘localized surface plasmon resonance’ (LSPR) behaviour to self-agglomeration/aggregation leading to the development of various nanosensors. Herein, we demonstrated the definite self-assembly of citrate functionalized silver nanoparticles (AgNPs) into a one-dimensional linear chain in presence of charged lead ions (Pb²⁺), one of the most toxic heavy metal pollutants. We have explored detail mechanism using a variety of spectroscopic tools and electron microscopy. The self-aggregation of AgNPs leads to the generation of new LSPR modes due to coupling of nearby existing modes. The conclusion of our experimental findings is duly supported by our developed numerical modelling based on the quasi-static approximation that the generated new LSPR modes are solely due to formation of chain-like aggregation of AgNPs. We have also monitored the LSPR spectra in the presence of other metal ions; however, only Pb²⁺ found to give such unique self-assembled geometry may due to its high interaction affinity with citrate. These findings play a key role for citrate functionalised AgNPs to be used as a low cost highly selective and sensitive lead ion sensor for potential application in industrial lead pollution monitoring. We have further varied several sensor parameters such as AgNPs size, concentration, and the allowed reaction time for it to be practically implemented as an efficient lead sensor meeting the Environmental Protection Agency recommendations.

Graphical abstract

The possible sensing mechanism of citrate-functionalized silver nanoparticles towards Pb2?+?followed by unique chain-like aggregation for potential atmospheric and industrial lead pollution monitoring.