Enhancing biomass and productivity of coumarins and essential oil in ajwain (Trachyspermum ammi) sprouts via laser light treatment

Abstract

Ajwain, Trachyspermum (T.) ammi, is a coumarin-rich, highly nutritive, and medicinally important herb, however, there is not enough data on the efficiency of laser irradiation in inducing such properties. Herein, the effect of seed treatment with laser irradiations [helium-neon (He-Ne, 632 nm, 5 mW) and helium-cadmium (He-Cd, 460 nm, 16.2 mW)] at 500 mJ energy for 5 min on the biomass, photosynthesis, and the metabolism of coumarins, essential oil, and their precursor metabolites in two varieties of ajwain sprouts i.e., Desi and Chakwal was investigated for the first time. Laser irradiation increased sprout biomass accumulation by improving photosynthesis, chlorophyll content, and respiration. Additionally, laser treatment enhanced the metabolism of coumarins and essential oil, which was explained by the increased availability of their precursors (phenylalanine, cinnamic acid, and shikimic acid). There were also increases in the activity of the key enzymes involved in the biogenesis of phenylpropanoid and coumarins, i.e., 3-Deoxy-D-arabino-heptulosonate-7-phosphate synthase (DAHPS), cinnamate-4-hydroxylase (C4H), 4-coumarate: coenzyme A ligase (4CL), and p-coumarate 3-hydroxylase (C3H). Furthermore, laser treatment induced the accumulation of total and individual phenolics and flavonoids. Consequently, laser treatment significantly improved the antibacterial properties of ajwain sprouts against four foodborne pathogens included Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus, and Salmonella spp. Ajwain variety-specific responses to laser light treatment confirmed by principal component analysis (PCA) showed that Desi variety was more responsive. The efficiency of He-Ne was greater than He-Cd laser, which suggests He-Ne laser treatment as a promising approach to boost the production of valuable pigments, coumarins, and essential oils in ajwain sprouts.