Bacopa monnieri Wettst., an extensively documented medicinal plant, for its nootropic properties had witnessed a burgeoned interest towards analyses of plant growth, role of culture conditions and elicitations on metabolites yield and their bio-activities.The growing disease burden of neurological disorders, especially in developing countries like India , further augment the need to explore the phyto-pharmacological importance of this plant. Last decade had witnessed extensive studies on the phyto-constituents in the extract of Bacopa monnieri, beyond saponin . Such studies are significant, owing to the vast therapeutic application, beyond nootropic ability, exhibited by the phytocompounds of Bacopa monnieri . However, some of the trivial bottlenecks, encountered while cultivation of Bacopa monnieri could be the variation in yield of phytocompounds. Such variation often evident in plant growth are primarily due to agro-climatic and genotypic variations along with seasonal variation in the yield of phytocompounds and the bio-activities of extract and herbal formulations.Tissue culture techniques have been optimized for the production of therapeutic phytocompounds rich biomass and studies are underway to explore a sustainable scalable solution to mass production of biomass rich in phytocompounds. These concerns obtrude exigencies for exploring alternative robust cultivation strategies. In order to circumvent the impact of cultivation conditions vis-a-vis improving the growth rate and yield of pytocompounds, there is a need to explore some innovative cultivation techniques.
Hydroponic culture, also called soil-less culture is obtruding as a well-accepted technique for improving growth and biomass yield in vegetables and herbs.Due to the slow, but steady integration and application of hydroponic technique for medicinal plants, scant information highlighting the role of hydroponic nft cultivation on growth and saponin yield is available. Maneeply et al. proposed the positive effect of NFT and DFT with higher growth and saponin accumulation than field cultivation, in hydroponic culture of Bacopa monnieri, in Hoagland’s solution. The need to explore alternative media composition and effect of abiotic factors that may synergistically affecting the growth of Bacopa monnieri have not been explored. In current study, the effect of Murashige and Skoog media, ‘Leafy 200’ hydroponic media and light intensity were explored, to design a robust bacosides production strategy using hydroponics.Bacopa monnieri was chosen among the available geographical variants, for the study, due to comparatively higher saponin yield, reported previously.These plants were maintained in a pot, for a year, within campus premises. The chemicals, growth hormone and basal media were purchased from HiMedia, and methanol for phytochemical extraction was purchased from Qualigens Fine Chemicals Pvt. Ltd, . The experiments were conducted in phytajars containing 20 mL of Murashige and Skoog media. Hydroponic media, used in the study with brand name ‘Leafy 200’, was purchased from GreenLoop .
The amount of powdered media used to constitute 1x media solutions, were as per manufacturer’s instruction. The saponin standard ‘Bacopaside I’ used in the study was purchased from Natural Remedies, Bangalore .The milliQ water, used in the study, had resistivity of 18.3 Mohms cm 1 medium with 0.8% agar. Surface sterilization involved the treatment of explant with 0.1 % mercuric chloride for 30 s, followed by washing in sterile distilled water. The plant material was further treated with 0.1 % sodium hypochlorite for 40 s and again washed in sterile distilled water. Finally, the explant was washed with 70% sterile ethanol followed by washing with water. The sterile plants were inoculated on MS Agar media. The media also contained antibiotics viz., ampicillin and amphotericin B ; and 1mg.L 1 phytohormone BAP , as reported previously . The phytajars with sterile plants were propagated in the growth chamber maintained at 25 2 C, illuminated with white light with photoperiod of 12 h.The statistical design of experiment with 4-run experiment was performed and the phytajars with explants were incubated under specified conditions. The harvested plants, after 9-day acclimatization and growth under four different experimental conditions showed significant variations in morphology of the plants . It was observed that propagation of plant in MS liquid media under white and blue/red light showed significant variations in morphology and. Previous studies have reported the photomorphogenesis, due to three main families of photoreceptors, viz. phytochromes, blue-light receptor and less explored UV-B photoreceptors . Studies by Najafabadi et al. , highlighted the significance of red light on the growth and hypericins from in vitro culture of Hypericum perforatum. In another study, Macedo et al. , reported the contrasting effect of red and blue light on the leaf mass density in the tissue culture of Alternanthera brasiliana. Studies by Chrysargyris et al. , indicated the effect of nitrogen supplementation during hydroponic culture on plant growth, chlorophyll content and yield of essential oil, highlighting the need of plant specific optimization of the media.
Ronga et al. , reported the benefits of digestate on dry matter, aromatic compound and sesquiterpenes. The result in our studies showed more number of leaves and adventitious shoots in hydroponic media illuminated with white light. The leaf area and thickness of the leaves of plant cultured in MS media with white light were more other culture conditions. The explant in MS media under blue/red light showed stunted growth with small leaves. The effect of ‘Leafy 200’ hydroponic media was also evident in the morphologies of the harvest and showed morphological alternation and. The plant propagated in ‘Leafy 200’ hydroponic media under white light showed adventitious rooting from the nodes. Also in comparison to plant propagated under white light in MS media, the number of nodes and leaves in plant in ‘Leafy 200’ and white light are more.The results for the first time highlight the effect of light intensity and commercial hydroponic media on the morphogenesis of Bacopa monnieri. Further the effect of culture conditions on total saponin yield as also compared .The result of ANOVA showed insignificant variation in the yield of saponin cultured in both, MS media and hydroponic media . The results suggest that the yield of saponin is not significantly affected on changing the light intensity with either media. The study is important as it suggest hydroponic media ‘Leafy 200’ to be a cost effect substitute of costly tissue culture technique. Moreover, previous studies have shown that hydroponics or soil-less cultivation have provided a robust solution to the growing concern of variable plant growth or yield of phytocompounds thereof. Recently, Maneeply et al reported the high yield of active compounds and higher production of Bacopa sp. through hydroponic technique.
The strategy may be extended to further optimize hydroponic cultivation condition of highly demanded nootropic plant Bacopa monnieri. Moreover, the study to explore the molecular regulation of media components and light intensity for this high value plant will assist cultivars and farmers to mass cultivate the plant under optimized conditions. The effect of different abiotic components on bacosides yield was observed .Wastewater hydroponic system is the integration of wastewater treatment into hydroponic plant production . In a wastewater hydroponic system, nutrients generated from wastewater treatment through physical and microbial degradation are absorbed by plants. Using such synergies offer several advantages over other bioremediation/phytoremediation techniques such as constructed wetlands by producing value-added crops . As a wastewater-based hydroponic technology, it requires less area, it is inexpensive and can be implemented onsite . The hydroponic component serves as a secondary or tertiary treatment step for wastewater treatment thus minimizing the requirements for further purification of wastewater to levels acceptable for disposal standards. Hence, linking the two systems may offer sustainable options in which renewable resources such as water and nutrients recovered from domestic wastewater can be used for crop production. This will reduce energy and input costs which are commonly involved in conventional wastewater treatment plants and commercial hydroponic crop production systems, respectively . The use of wastewater effluents as nutrient sources for hydroponic channel crop production has been widely used as a form of domestic wastewater disposal . This practice has been recognised as one of the sustainable methods for wastewater management. Several studies have shown the potential of different types of wastewater as a source of fertilizer and irrigation water for the cultivation of green plants in the hydroponic system . In these studies, a number of crop species, including leafy vegetables , fruit crops and ornamental plants grown in hydroponic system have been reported to be suitable for wastewater hydroponic system. Results from these studies showed variation in nutrients removal, yield/biomass production and crop quality when compared to either conventional wastewater treatment or commercial hydroponic crop production system .
This variation is caused by a number of factors including, crop selection in terms of adaptability to grow in hydroponic systems and their tolerance to grow under wastewater of different qualities, the source and composition of wastewater used for agricultural irrigation and fertilization . The method of wastewater treatment before reuse is also reported to have an effect on crop performance irrigated with wastewater. Decentralised wastewater treatment systems which involve the combination of treatment and disposal of wastewater has gained attention in recent years . Such an approach allows for the reuse of treated wastewater within the source of generation and is designed to operate at a small-scale level, thereby offering sustainable opportunities for wastewater treatment especially for developing countries . This system involves a number of treatment stages/processes for the breakdown of waste fractions in a wastewater treatment plant. Among those processes, anaerobic digestion is regarded as the most important component of the DEWATS system due to its low requirement on energy inputs, low sludge production and the opportunity to recover nutrients from the effluents produced . This high nutrient load of wastewater generated through anaerobic digestion has prompted its use for agriculture, including the hydroponic cultivation of crops. Generally, higher plants require both macro and micro-nutrients to grow and reproduce to their full potential. The most essential elements required in sufficient amounts for tomato cultivation include, N, P, K, Ca, Mg, Fe, Zn. The demand for these nutrients is known to be higher in hydroponically grown crops compared to their field-grown counterparts. This is because field produced crops source a portion of their nutrients supply from the soil, whereas, in hydroponic production system, the nutrient requirements of the crop are fulfilled by the nutrient solution . Integrated wastewater treatment and hydroponic plant production systems that solely depend on wastewater to supply nutrients for tomato plants have been reported to be deficient in nutrients such as nitrogen, phosphorus, potassium and calcium .
This is attributed to the low content of nutrients such as N, P, K, Ca and Mg in wastewater effluents. In addition, the complex nature of tomato plants in terms of nutrient management which is highly variable than leafy vegetables are also known to be the limiting factor for growth and yield performance in wastewater hydroponic systems. The nutrient demand of tomatoes changes as the plants grow from germination, vegetative to the reproductive stage . From germination to first flower development, N, P, K are the most critical nutrients required by the plants while, K, Ca, Mg, Zn and Mn are required in sufficient amounts during fruit set. Most investigations have shown that the plant nitrogen content decreased significantly when digestates from organic manure were used as an alternative to mineral fertilizers under hydroponic systems , as well as in pot experiments . The reduction in N content has been related to differences in the composition of the digestate. However, NH4þ is known to be the dominant source of N for domestic wastewater hence its conversion to nitrate is required for hydroponically grown tomatoes . This is necessary because of the high sensitivity of tomatoes to high NH4þ –N levels. The low content and unavailability of Mg and P in wastewater effluents as a result of struvite formation and precipitation during anaerobic digestion were also reported to be the growth-limiting factor for hydroponically grown tomatoes . However, other studies have reported that supplementation of wastewater with deficient nutrients improved plant growth in hydroponically grown plants. The addition of P and micro-nutrients particularly, iron increased the shoot biomass of lettuce .