Distribution, Chemical Constituents and Biological Properties of Genus Malaxis.

The genus Malaxis (family Orchidaceae), comprises nearly 183 species available across the globe. The plants of this genus have long been employed in traditional medical practices because of their numerous biological properties, like the treatment of infertility, hemostasis, burning sensation, bleeding diathesis, fever, diarrhea, dysentery, febrifuge, tuberculosis, etc. Various reports highlight their phytochemical composition and biological activities. However, there is a lack of systematic review on the distribution, phytochemistry, and biological properties of this genus. Hence, this study aims to conduct a thorough and critical review of Malaxis species, covering data published from 1965 to 2022 with nearly 90 articles. Also, it examines different bioactive compounds, their chemistry, and pharmacotherapeutics as well as their traditional uses. A total of 189 unique compounds, including the oil constituents were recorded from Malaxis species. The highest active ingredients were obtained from Malaxis acuminata (103) followed by Malaxis muscifera (49) and Malaxis rheedei (33). In conclusion, this review offers an overview of the current state of knowledge on Malaxis species and highlights prospects for future research projects on them. Additionally, it recommends the promotion of domestication studies for rare medicinal orchids like Malaxis and the prompt implementation of conservation measures.

Insights into nuclear DNA content, hydrogen peroxide and antioxidative enzyme activities during transverse thin cell layer organogenesis and ex vitro acclimatization of Malaxis wallichii, a threatened medicinal orchid.

Malaxis wallichii (Lindl.) Deb, a small, perennial, monopodial, terrestrial orchid, is endemic to tropical Himalayas at an altitude of 1200-2000 m asl. The pseudobulbs are important ingredients of century old drug 'Ashtavarga' and a polyherbal energetic tonic 'Chyavanprash'. An efficient genetically stable in vitro propagation protocol using transverse thin cell layer culture system was established for M. wallichii. In the present report, meta-topolin alone proved to be three times more beneficial compared to other routinely used cytokinins in inducing highest number of shoot buds, plant height and growth of regenerated shoots. The highest regeneration frequency (89%) along with maximum number of adventitious shoots per explant (22.5 ± 0.6) was observed in MS medium supplemented with 1.0 mg/l meta-topolin and 0.5 mg/l α-naphthalene acetic acid. Highest rooting frequency with highest number of roots (8.66 ± 0.3) was achieved in half-strength MS medium fortified with 1.0 mg/l indole acetic acid. Clonal stability of in vitro-derived plantlets was evaluated and compared to donor plant using intron splice junction (ISJ) markers and flow cytometry. ISJ markers revealed 4.76% clonal variability indicating high degree of genetic stability amongst the in vitro-derived regenerants. The nuclear DNA content of M. wallichii (2n) was found to be 2C = 2.760 ± 0.02 pg and therefore, 1349.64 Mbp (1C). Flow cytometry analysis of actively growing young and mature leaves from donor as well as in vitro-derived plantlets revealed presence of three peaks corresponding to 2C, 4C and 8C, while 2C was the most abundant. In the present investigation, there was no significant difference in the 2C DNA content between the mother and in vitro-derived plants; however, the frequency of endopolyploid cells varied in young and adult plants. An increased H2O2 content as well as lipid peroxidation activities were observed during early stages of acclimatization which declined afterwards. The enhanced activities of antioxidant enzymes like superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase in acclimatized plantlets as compared to in vitro-grown ones revealed their active involvement in growth and development against oxidative stress under external adverse environment.

Studies on secondary metabolite profiling, anti-inflammatory potential, in vitro photoprotective and skin-aging related enzyme inhibitory activities of Malaxis acuminata, a threatened orchid of nutraceutical importance.

Malaxis acuminata D. Don., a small, terrestrial orchid, is endemic to tropical Himalayas at an altitude of 1200-2000m asl. The dried pseudobulbs are important ingredients of century old ayurvedic drug 'Ashtavarga' and a polyherbal immune-booster nutraceutical 'Chyavanprash', known to restore vigour, vitality and youthfulness. Considering tremendous medicinal importance of this threatened orchid species, a detailed study was undertaken for the first time to address its antioxidant potential, secondary metabolite contents and biological activities against skin-aging related enzymes (anti-collagenase, anti-elastase, anti-tyrosinase and xanthine oxidase) and anti-inflammatory activity (5-lipoxygenase and hyaluronidase) in different plant parts of wild and in vitro-derived plants of M. acuminata. Methanolic leaf and stem extracts were further evaluated for in vitro photoprotective activity against UV-B and UV-A radiations. Furthermore, secondary metabolite profiling of various plant parts was carried out by Gas Chromatography Mass Spectrometry (GC-MS). A significantly higher antioxidant potential (DPPH, metal chelating and ABTS•+) with a comparative higher yield of secondary metabolites was observed in in vitro-derived plantlets as compared to the wild plants. Among various solvent systems used, methanolic leaf and stem extracts showed promising inhibitory activity against major skin aging-related enzymes and anti-inflammatory potential. Methanolic leaf and stem extracts of both wild and in vitro-derived plants showed promising photoprotective activity against UV-B and UV-A radiations in vitro with comparatively higher sun protection factor (SPF). Furthermore, GC-MS analysis of methanolic extracts of leaves and stems of wild as well as in vitro-derived plantlets revealed presence of many bioactive metabolites such as, dietary fatty acids, α-hydroxy acids, phenolic acids, sterols, amino acids, sugars and glycosides which substantially explain the use of M. acuminata as one of the potential rejuvenator and anti-aging ingredient in many Ayurvedic formulations.

Direct somatic embryogenesis of Malaxis densiflora (A. Rich.) Kuntze.

A protocol for induction of direct somatic embryogenesis and subsequent plant regeneration for the medicinally important and endangered plant of Malaxis densiflora has been developed for the first time. In the present study, in vitro seed derived protocorm explants were cultured on half strength Murashige and Skoog (MS) medium supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D), Picloram and Dicamba individually and in combination with cytokinins BAP, TDZ and Kn for its effectiveness to induce the differentiation of somatic embryos. The best response was observed in protocorms cultured half strength MS medium supplemented with 2,4-D at 3.39 µM and TDZ at 6.80 µM. Both epidermal and sub epidermal cells were involved in the formation of embryos. The proembryos developed into globular stage and subsequently developed into protocoms. Complete plantlets were formed after 60 days of culture. The plantlets were acclimatized in plastic pots containing sterilized vermiculite. The survival rate was 76%.