Neelu Joshi

Salinity stress is a major environmental constraint that limits plant growth and productivity by disrupting ionic balance, inducing osmotic stress, and promoting oxidative damage. Chitosan (Ch), a naturally derived biopolymer, enhances plant tolerance to abiotic stresses, but its effectiveness may be limited by poor solubility and reduced interaction with plant tissues. Chitosan nanoparticles (ChNP) may overcome these limitations through improved bioavailability and cellular interaction. This study evaluated the effectiveness of Ch and ChNP in alleviating salinity stress in in vitro shoot cultures of tobacco ( Nicotiana tabacum L.), a valuable model system. Shoot cultures maintained on shoot multiplication medium (Murashige and Skoog (MS) medium, 0.2 mg L ⁻¹ NAA (1‐Naphthaleneacetic acid) and 2.0 mg L ⁻¹ BAP (6‐Benzylaminopurine)) were cultured on medium containing 150 mM NaCl with or without 20 ppm Ch or ChNP for 30 days. Salinity stress significantly reduced shoot length, shoot number, and shoot fresh weight by 33.3%, 39.7%, and 40%, respectively, compared with non‐stressed shoots. Both Ch and ChNP alleviated these effects, with ChNP showing greater efficacy by increasing shoot length, shoot number, and shoot fresh weight by 3.6‐, 2.0‐, and 3.2‐fold, respectively, relative to untreated stressed shoots. ChNP also reduced hydrogen peroxide, superoxide radical, and malondialdehyde levels while enhancing catalase, superoxide dismutase, and peroxidase activities. Furthermore, ChNP increased chlorophyll a, chlorophyll b, total chlorophyll, and proline contents by 77.9%, 167.5%, 86.8% and 27%, respectively. These findings demonstrate that ChNP effectively enhanced salinity tolerance by strengthening physiological and biochemical stress‐response mechanisms in tobacco under in vitro conditions.

Antibacterial drug resistance is a global issue that arises as bacteria adapt over time to certain medications, making illnesses more difficult to cure and raising the possibility of contracting a disease, getting sick, or possibly dying. Quorum-sensing communication routes are used by bacteria to control a variety of physiological processes and it relies on bacterial receptors, which are manufactured by bacteria, to recognize small signaling molecules called autoinducers. The activation of the genes necessary for biofilm formation occurs when autoinducers bind to receptors. The purpose and concentration of the chapter is to comprehend the process underlying the development of biofilms brought on by the quorum sensing system, which gives both gram-positive and negative microorganisms resistance to antibacterial medications. It also examines recent developments and strategies for bacterial biofilm breakdown with an emphasis on quorum-sensing inhibitors.

The present study is the first report on the quantitative determination of secondary metabolites in callus cultures of B. prionitis L, an important medicinal plant. We examined the stem-derived and leaf-derived callus for their antioxidant potential and accumulation of phenolics, flavonoids, and active principles viz. shanzhiside methyl ester (SME) and squalene and compared these parameters vis a vis mother plant counterpart. Four solvents viz. methanol, ethanol, acetone, and distilled water (aqueous) extracts were prepared for analysis. Callus cultures not only preserved the metabolite profile of the mother plant but also displayed their elevated levels. Leaf-derived callus surpassed stem-derived callus in most of the parameters studied. The highest phenolic content (21.46 mg GAE g^− 1 FW) and flavonoid content (24.58 mg of RE g^− 1 FW) was observed in methanol extract of leaf-derived callus, representing a 3-fold and 2-fold increase over mother plant leaf, respectively. Antioxidant capacity based on FRAP and DPPH assay was highest in methanol extract of leaf-derived callus (7-fold and 3-fold increase over mother plant, respectively) while ABTS assay showed the highest activity (122-fold increase) in acetone extract of leaf-derived callus. HPTLC analysis revealed an enhanced concentration of squalene (10-fold) and SME (2.3-fold) in acetone and methanol extract of leaf-derived callus, respectively, compared to mother explants. Results of RP-HPLC for phenolics showed the highest gallic acid content (99-fold increase) in ethanol extract of stem-derived callus whereas catechol was maximum (37- fold increase) in aqueous extract of leaf-derived callus. These findings suggest that callus cultures of B. prionitis can be a potential source of active metabolites. Further, cell suspension cultures can be established from the callus which could be an avenue for the large-scale production of bioactive compounds.

The present investigation reports the growth kinetics and diosgenin accumulation in callus cultures of Costus speciosus. Effect of explants, media and plant growth regulators was evaluated with respect to callus induction and growth. Out of the two explants viz pseudostem and seed, pseudostem showed maximum callus induction frequency of 90% on MS medium. The fresh weight of callus was maximum (9-folds) on 28th day on 1.0 mg/L picloram containing medium. The callus obtained was white compact hard (WCH). For growth kinetics study pseudostem derived callus was transferred on different media supplemented with 1.0 mg/L picloram. All phases of growth were seen in callus inoculated on all the three media except the absence of stationary phase on MS and SH media. MS medium proved to be the best for maximum biomass accumulation (9-fold) on 28th day of culture and callus in post-exponential phase showed maximum diosgenin accumulation (33 ppm).

In vitro adventitious shoot bud regeneration systems are considered most suitable for Agrobacterium-and biolisticsmediated genetic transformation to obtain transgenic plants. In the present investigation, multiple adventitious shoot buds could be induced directly from Feronia limonia hypocotyl explants inoculated on Murashige and Skoog (MS) medium containing different growth regulators. During the initial phase, the hypocotyl segments nearer to the cotyledons responded quickly compared to those closer to the root. The response, however, was comparable in both the segments in subsequent subculture. Of the various cytokinins, 2.22 μM 6-benzylaminopurine (BA) proved to be more effective compared to kinetin (Kn). The two-way interaction of BA and Kn significantly influenced shoot regeneration and contributed the most among the interactions studied. The best response, however, was obtained when 2.22 μM BA and 2.32 μM Kn were combined. Although the effect of auxins like α-naphthaleneactic acid (NAA) combined with cytokinins evoked a significant responsein terns of number of shoot buds, this response did not supersede the effect of combined cytokinins. Vone of the polyamines tested induced shoot buds on hypocotyl segments. Adventitious shoots were multiplied on MS medium containing 2.22 μM BA, 6.96 μM Kn, and 0.05 μM NAA. More than 60% of the shoots produced roots when cultured on medium containing one-quarter strength MS salts, 10% suerose, 0.6% agar, and 7.36μM indole-3-butyric acid. The adventious origin of shoot buds showing continuous vascular connections was confirmed through histological investigations.