Light spectra manipulation stimulates growth, specialized metabolites and nutritional quality in Anethum graveolens.

Light-Emitting Diodes (LED) play a major role in manipulating light spectra that helps in regulating the growth and specialized metabolite synthesis relevant to the plant defence system. In this study, we assessed photosynthetic performance, phytonutrients, and anatomical variations of an aromatic herb Anethum graveolens (also known as dill), grown under various combinations of LED lights viz. red (100R:0B), red:blue (50R:50B); blue (0R:100B) and warm white (WW, served as control). Exposure to 0R:100B LED lights led to the tallest stem height, whereas, the number of leaves were highest under 50R:50B LED lights. The photosynthetic performance was observed to be highest under 50R:50B LED lights. HPLC analysis revealed chlorogenic acid and rosmarinic acid as the major phenolic compounds accumulated under different spectral irradiations. The highest chlorogenic acid content was observed in 50R:50B LED treated dill plants, while 100R:0B light showed the highest accumulation of rosmarinic acid. Dill plants grown under 50R:50B light displayed a relatively higher content of volatile compounds including, myristicin (phenylpropene), psi-limonene, and α-phellandrene (monoterpenoids). Expression analyses of candidate genes of phenylpropanoid and monoterpenoid biosynthetic pathways showed good correlations with the enhanced phenolic compounds and monoterpenes detected under appropriate light treatments. Further, the stem anatomy revealed higher vascularization under the influence of 0R:100B LED lights, whereas, intense histochemical localization of specialized metabolites could be correlated with enhanced accumulation of phenolic compounds and terpenoids observed in this study. Taken together, these studies suggest that proper combinations of blue and red spectra of light could play important role to augment the growth and phytochemical characteristics of dill, thus improving its value addition in the food industry.

Spectral Light Treatment Influenced Morpho-Physiological Properties and Carvacrol Accumulation in Indian Borage.

Light emitting diodes (LEDs) as an alternative light source for plants had shown to enhance the plant material quality. Indian borage or Plectranthus amboinicus (Lour.) Spreng, a medicinal herb produces carvacrol as the major volatile organic compound (VOC). Histolocalization of VOCs and expression pattern of the terpenoid biosynthesis genes after spectral light treatment is not yet reported in P. amboinicus. This work investigated the morpho-physiological, biochemical and transcriptional responses towards red, green, blue, warm white and red-blue (RB, 1:1) LEDs treatment at 40 ± 5 µmol m-2 s-1 light intensity after 40 days. Maximal growth index (GI), leaf fresh weight and dry weight were obtained in RB (1:1) treated plants. There was one-fold increase in phenolics content and 2.5-fold increase in antioxidant activity in comparison to warm white. High quantity of terpenes and phenolics deposition were observed in the glandular trichomes of RB (1:1). Maximum carvacrol accumulation (14.45 µmol g-1 FW) was also detected in RB (1:1). The transcript levels of early terpene biosynthesis genes PaDXS, PaDXR, PaHMGR and cytochrome P450 monooxygenase genes, PaCYP1 and PaCYP9 were highly upregulated in RB (1:1) and green. The overall results suggest RB (1:1) as the better lighting option amongst the studied spectral lights for obtaining maximum phytochemicals in P. amboinicus. Work is being continued with different spectral ratios of red and blue LED lights to maximize phytochemical accumulation, the outcome of which will be reported elsewhere in near future. Supplementary Information: The online version contains supplementary material available at 10.1007/s00344-023-11028-6.

Temporal accumulation of pigments during colour transformation from white to red in Combretum indicum (L.) DeFilipps (syn. Quisqualis indica L.) flowers.

This study focuses on the identification of major anthocyanin following its temporal accumulation in colour changing flowers of Combretum indicum (L.) DeFilipps (syn. Quisqualis indica L.). Separation and identification of pigments governing changes in floral colour were performed using HPLC-DAD. Comparison of chromatographic runs with retention time and UV-Vis spectra of authentic standards determined cyanidin 3-O-glucoside as the major anthocyanin accumulating in the petals. Acid hydrolysis of anthocyanin extracts further confirmed cyanidin as the major anthocyanidin in floral tissue. Light microscopic studies revealed gradual accumulation of pigments in the epidermal and hypodermal cell layers of petals. Antioxidant potentials of floral extracts in ethanol, methanol, water and ethyl acetate were determined by DPPH assay where methanolic extracts showed highest free-radical scavenging capacity, and petals of red stage showed maximum activity. Antioxidative potentials measured in terms of FRAP and ABTS also indicated similar results showing highest activity in the red stage.