Pratibha Misra

In the present scenario, remediation of heavy metals (HMs) contaminated soil has become an important work to be done for the well-being of human and their environment. Phytoremediation can be regarded as an excellent method in environmental technologies. The present contemporary research explores the Solanum viarum Dunal function as a potential accumulator of hazardous HMs viz. lead (Pb), cadmium (Cd), zinc (Zn), and their combination (CHM). On toxic concentrations of Pb, Cd, Zn, and their synergistic exposure, seeds had better germination percentage and their 90d old aerial tissues accumulated Pb, Cd, and Zn concentrations ranging from 44.53, 84.06, and 147.29 mg kg⁻¹ DW, respectively. Pattern of accumulation in roots was as Zn 70.08 > Pb 48.55 > Cd 42.21 mg kg⁻¹DW. Under HMs treatment, positive modulation in physiological performances, antioxidant activities suggested an enhanced tolerance along with higher membrane stability due to increased levels of lignin, proline, and sugar. Phenotypic variations were recorded in prickles and roots of 120 d old HM stressed plants, which are directly correlated with better acclimation. Interestingly, trichomes of the plant also showed HM accumulation. Later, SEM–EDX microanalysis suggested involvement of S. viarum capitate glandular trichomes as excretory organs for Cd and Zn. Thus, the present study provides an understanding of the mechanism that makes S. viarum to function as potent accumulator and provides information to generate plants to be used for phytoremediation.

Growth and production kinetics of three important glycoalkaloids viz. α-solanine, solanidine, and solasodine in two contrasting prickly and prickleless plants of Solanum viarum Dunal were evaluated under in vitro conditions. The prickleless plants showed improved accumulation of total glycoalkaloid content [7.11 and 6.85 mg g⁻¹ dry weight (DW)] and growth (GI = 11.08 and 19.26) after 45 and 50 days of culture cycle, respectively. For higher biomass (91.18 g l⁻¹) as well as glycoalkaloid (52.56 mg l⁻¹) recovery, the prickleless plants served as highly profitable platform. All the three studied glycoalkaloids were identified and quantified by mass spectrometry and HPLC. All the three studied glycoalkaloids accumulated in age-dependent manner. The presence of two constituents, i.e., solasodine and solanidine mainly contributed for higher accumulation of total glycoalkaloid content in the prickleless plants. However, the synthesis of α-solanine was highly age specific and could be detected after 4 to 5 weeks of culture cycle in both prickle containing as well as prickleless plants of S. viarum. The higher accumulation of glycoalkaloids in prickleless plants was also supported with the expression analysis of six key pathway enzymes viz. mevalonate kinase (MVK), 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (HMGR), farnesyl diphosphate synthase (FPS), UDP-galactose/solanidine galactosyltransferase (SGT1), UDP-glucose/solanidine glucosyltransferase (SGT2), and cytochrome P450 monooxygenase (CYP). The results indicated that the plants harvested after 45 and 50 days of culture cycle accumulated maximum bioactive in-demand glycoalkaloids in the prickly and prickleless plants of S. viarum Dunal, respectively.

Canna (Canna indica L.) is an ornamental landscape plant used specially for the garden borders and beds. It grows in tropical and subtropical countries including India. Canna is a less explored crop, mainly because it is a slow growing monocot with extremely hard seed coat and difficult to establish in vitro, as bacterial contamination is carried through the soil-grown rhizome. Many cultivars (ca. 150) of canna are being maintained in the garden germplasm of National Botanical Research Institute. To obtain 100% in vitro seed germination, chipping off of seeds with a sterilized nail clipper and soaking for 24–48 h or until radical emergence was a prerequisite. To obtain a foolproof tissue culture protocol of canna, in the present study, shoot multiplication was obtained through rhizome axillary buds. Among semisolid, liquid submerged and liquid media with glass beads, the highest multiplication of shoots (10) was obtained in liquid media with glass beads in ‘Canna Flaccida’ cv. within 6 weeks of culture incubation. During a comparative analysis of shoot regeneration among ten most attractive selected cultivars of canna, two did not respond, whereas a significant difference was obtained among eight cultivars. The regenerated shoots were rooted, acclimatized, and transferred to the pots, where they grew normally.

Prickles are epidermal outgrowth found on the aerial surface of several terrestrial plants. Microscopic studies on prickles ofS.viarumDunal indicated a crucial role of glandular trichomes (GTs) in their development. A spontaneously obtained prickleless mutant showed normal epidermal GTs, but its downstream developmental process to prickle was perturbed. Thus, prickleless mutant offers an ideal opportunity to unveil molecular regulators working downstream to GTs in the prickle formation. Differential transcriptome analysis of epidermis of prickly and prickleless mutant revealed that expression of several defense regulators like ethylene, salicylic acid, PR-proteins, etc. were significantly down-regulated in prickleless mutant, provide an important link between defense and prickle development. It was also noteworthy that the expression of few essential development related TFs like MADS-box, R2R3-MYB, REM, DRL1, were also down-regulated in the stem, petioles, and leaves of prickleless mutant indicating their potential role in prickle development. Interestingly, the gene expression of terpenoid, steroid, flavonoid, glucosinolate, and lignin biosynthesis pathways were up-regulated in prickleless mutant. The biochemical and qRT-PCR analysis also confirmed metabolite elevation. These results indicated that the loss of prickle was compensated by elevated secondary metabolism in the prickleless mutant which played important role in the biotic and abiotic stress management.

Glycyrrhiza glabra L. has become an endangered medicinal plant due to the unabated extraction of glycyrrhizin. Glycyrrhizin is a triterpenoid saponin that is a root centric secondary metabolite having numerous pharmacological properties, such as anti-inflammatory, immunomodulatory, antiallergic, antiulcer, and is found to be effective even against HIV. Harvesting of the roots for high value glycyrrhizin destroys the whole plant causing existential threat to the plant itself and consequent damage to biodiversity. The present study establishes that hairy root cultures of G. glabra, using an optimized elicitor, can dramatically enhance focused production of glycyrrhizin at a much faster pace year-round without causing destruction of the plant. Hairy root cultures of G. glabra were developed using the Agrobacterium rhizogenes A4 strain. The glycyrrhizin content was enhanced using different biotic and abiotic elicitors, for example, PEG (polyethylene glycol), CdCl₂, cellulase, and mannan at different concentrations and durations. PEG at 1% concentration enhanced the yield of glycyrrhizin up to 5.4-fold after 24 h of exposure, whereas 200 µg mL⁻¹ cellulase enhanced glycyrrhizin yield to 8.6-fold after 7 days of treatment. Mannan at 10 mg L⁻¹ concentration enhanced the production of glycyrrhizin up to 7.8-fold after 10 days of stress. Among different antioxidant enzymes, SOD activity was significantly enhanced under drought, cellulase and mannan stress. This identification of elicitors can result in abundant supply of valuable glycyrrhizin to meet broad spectrum demand through commercial production without endangering G. glabra L.

Solanum khasianum is a rich source of steroidal alkaloids that are important secondary metabolites with enormous pharmaceutical uses. Development of plantlets from somatic tissues, under in vitro conditions, takes place both through adventitious shoot bud differentiation or somatic embryogenesis (SE) pathway. We observed that the physical state of medium, solid or liquid, determined the regenerant differentiation patterns from root segment explants in S. khasianum. In the solidified medium, the root segments developed adventitious shoot buds whereas somatic embryos were regenerated in the liquid medium. Varying gradients from liquid to solid medium were further used to confirm the effect of solidified condition on regeneration pathway. Histological analysis of developing shoot buds and somatic embryos was also performed to confirm their development and differentiation patterns. In order to further confirm the developmental pathways, qRT-PCR analysis of the marker genes of SE and shoot regeneration was also performed. While SOMATIC EMBRYOGENESIS RECEPTOR KINASE1 (SkSERK1) expression was significantly up-regulated during the early embryogenic stage, the LATE EMBRYOGENESIS ABUNDANT (SkLEA) protein was found to be highly expressed in the mature embryos. Expression of the HISTONE DEACETYLASE (HDA6), a repressor of SE related genes, was highly decreased during embryogenesis in the liquid culture. Furthermore, expression of the ENHANCER OF SHOOT REGENERATION  (ESR) gene was comparatively increased during shoot regeneration in the culture using solid medium. Our results point out that the physical state of the medium in S. khasianum plays a decisive role in differentiation pattern which was independent of hormonal supplements.