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Out of 750,000 known plants in the world, a major part are medicinal and aromatic plants – a source of raw material for folk and documented systems of medicines worldwide. The folk and documented medicine in India use about 6,000 plants, although, less than 50 species have been scientifically studied and cultivated to any sizeable extent. The main factor behind the slow pace of domestication of medicinal plants is the absence of knowledge on cultivation practices and lack of suitable technology. About 90% of the medicinal plants for trade are harvested from the wild and the demand for traditional medicinal plants is increasing rapidly. Continuous exploitation of several medicinal plant species from the wild has resulted in their population decline. Hence, an effective strategy is needed for their sustainable utilization and conservation. Cultivation is the most effective way of conservation. Cultivation can also ensure production of standardized raw materials. Thereby, enhances the quality of the manufactured products. The methods and techniques of modern chemical agriculture cannot be adopted for the cultivation of medicinal plants as they should be free from harmful residues. Pesticides and other harmful chemicals have been detected in some herbal products. Hence, to ensure a safe, residue-free and reliable material for use in herbal drug industry, there is an urgent need to adopt strategies for cultivation of medicinal plants that are consistent with principles of good agricultural practices.
Pot culture experiments were conducted to assess the extent of growth, photosynthetic efficiency and nitrogen assimilation of chicory (Cichorium intybus L.) as affected by NaCl and CaCl₂ alone as well as in combination. Six treatments, i.e., 80 mM and 160 mM NaCl, 5 mM and 10 mM CaCl₂ and 80 mM + 10 mM and 160 mM + 10 mM of NaCl + CaCl₂ were given to the growing plants separately at three developmental stages, viz., the pre-flowering (30 DAS), flowering (120 DAS) and post-flowering (150 DAS) stages. Each NaCl treatment caused a significant reduction in total plant biomass, photosynthetic rate, stomatal conductance, total chlorophyll content, soluble protein content, NR activity and nitrogen content, although nitrate content increased. On the contrary CaCl₂ treatment gave a favorable effect, compared to the control. The effect of combined treatments was similar to that of NaCl but less in magnitude. Thus, the application of CaCl₂ may mitigate the adverse effect caused by NaCl.
In vivo modulation of HMG-CoA reductase (HMGR) activity and its impact on artemisinin biosynthesis as well as accumulation were studied through exogenous supply of labeled HMG-CoA (substrate), labeled MVA (the product), and mevinolin (the competitive inhibitor) using twigs of Artemisia annua L. plants collected at the preflowering stage. By increasing the concentration (2–16 µM) of HMG-CoA (3-¹⁴C), incorporation of labeled carbon into artemisinin was enhanced from 7.5 to 17.3 nmol (up to 130%). The incorporation of label (¹⁴C) into MVA and artemisinin was inhibited up to 87.5 and 82.9%, respectively, in the presence of 200 µM mevinolin in incubation medium containing 12 µM HMG-CoA (3-¹⁴C). Interestingly, by increasing the concentration of MVA (2-¹⁴C) from 2 to 18 µM, incorporation of label (¹⁴C) into artemisinin was enhanced from 10.5 to 35 nmol (up to 233%). When HMG-CoA (3-¹⁴C) concentration was increased from 12 to 28 µM in the presence of 150 µM mevinolin, the inhibitions in the incorporation of label (¹⁴C) into MVA and artemisinin were, however, reversed and the labels were found to approach their values in twigs fed with 12 µM HMG-CoA (3-¹⁴C) without mevinolin. In another experiment, 14.2% inhibition in artemisinin accumulation was observed in twigs in the presence of 175 µM fosmidomycin, the competitive inhibitor of 1-deoxy-D-xylulose 5-phosphate reductase (DXR). HMG-CoA reductase activity and artemisinin accumulation were also increased by 18.6 to 24.5% and 30.7 to 38.4%, respectively, after 12 h of treatment, when growth hormones IAA (100 ppm), GA₃ (100 ppm) and IAA + GA₃ (50 + 50 ppm) were sprayed on A. annua plants at the pre-flowering stage. The results obtained in this study, hence, demonstrate that the mevalonate pathway is the major contributor of carbon supply to artemisinin biosynthesis and HMGR limits artemisinin synthesis and its accumulation in A. annua plants.
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