University of Isfahan Journal of Plant Biological Sciences 3041-9603 17 3 2025 09 23 Effect of LED Light Spectra and Rhizobium rhizogenes Strains on the Growth and Physiological Characteristics of German Chamomile (Matrocaria chamomilla L.) Effect of LED Light Spectra and Rhizobium rhizogenes Strains on the Growth and Physiological Characteristics of German Chamomile (Matrocaria chamomilla L.) 47 66 29929 10.22108/ijpb.2025.144603.1402 FA Nastaran Maham Department of Horticultural Sciences, Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili, Ardabil, Iran Esmaeil Chamani Department of Horticultural Sciences, Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili, Ardabil, Iran Mehdi Mohebodini Department of Horticultural Sciences, Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili, Ardabil, Iran Asghar Estaji Department of Horticultural Sciences, Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili, Ardabil, Iran Roza Shahbazi Department of Horticultural Sciences, Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili, Ardabil, Iran Journal Article 2025 03 11 This study investigated the individual and combined effects of LED light spectra and Rhizobium rhizogenes strains on the growth and physiological attributes of German chamomile (Matricaria chamomilla L.). A factorial experiment with three replications was conducted under controlled conditions. Plantlets inoculated with bacterial strains A4 or ATCC15834 were exposed to seven light regimes: monochromatic white (W100), red (R100), blue (B100), and red–blue combinations (R80B20, R60B40, R40B60, R20B80). The interaction between the bacterial strain and the light spectrum significantly affected most of the measured parameters. The A4 strain under red light (R100) produced the longest shoots (19.5 mm), whereas ATCC15834, combined with R40B60, generated the longest roots (90.9 mm). Maximum shoot and root fresh weights (2342 and 3887 mg, respectively) were obtained from A4 under R20B80 light. From a physiological perspective, A4 under R80B20 light resulted in the highest chlorophyll a content, while ATCC15834 under R40B60 produced the greatest chlorophyll b and carotenoid levels (21.26 mg g-1 FW). The R60B40 spectrum enhanced flavonoid biosynthesis, and A4 under R100 exhibited the strongest antioxidant activity (14.71% DPPH inhibition). These findings demonstrate that combining specific bacterial strains with optimized light spectra can significantly enhance chamomile growth and its medicinal value. Introduction German chamomile, a member of the Asteraceae family, is a well-known medicinal herb valued for its essential oils and flavonoids, which possess antioxidant, anti-inflammatory, and antimicrobial properties. However, sustainable production faces challenges due to agricultural limitations and overexploitation. In vitro culture, integrated with elicitor-based strategies, offers an effective means to conserve germplasm and enhance bioactive metabolite production. Among elicitors, Light-Emitting Diodes (LEDs) enable precise spectral manipulation, with red and blue wavelengths particularly efficient at regulating photosynthesis and secondary metabolism. Similarly, Rhizobium rhizogenes acts as a biological elicitor, stimulating root induction and enhancing metabolite accumulation through phytohormonal interactions. This research aimed to explore the synergistic influence of LED spectra and R. rhizogenes strains on morpho-physiological traits and secondary metabolite biosynthesis in German chamomile. Materials and Methods The experiment was performed during 2022–2023 in the tissue culture laboratory of the University of Mohaghegh Ardabili, Iran. Chamomile seeds were surface-sterilised using liquid soap, 70% ethanol, and 3% sodium hypochlorite, then rinsed with sterile distilled water. Sterilized seeds were germinated on solid MS medium. After eight weeks, uniform seedlings were inoculated at the crown with R. rhizogenes strains A4 or ATCC15834. Following 48 hours of co-cultivation in darkness, plantlets were transferred to MS medium supplemented with 500 mg L-1 cefotaxime. They were subsequently exposed toseven LED treatments (90 µmol m-2 s-1) for 6 weeks. Growth and physiological parameters were recorded, and data were analyzed by factorial ANOVA followed by Duncan’s test (P ≤ 0.01). Results and Discussion Analysis of variance revealed that the interaction between LED light spectra and Rhizobium rhizogenes strains significantly (P ≤ 0.01) influenced the morpho-physiological profile of German chamomile plantlets. Morphological Development The evaluation of growth parameters revealed that the most significant synergy for biomass accumulation was observed between the A4 bacterial strain and the R20B80 light regime. This specific combination yielded the highest shoot fresh weight (2342 mg), underscoring its superior efficacy in enhancing aerial biomass production. Secondary Metabolite Production The production of pharmaceutically valuable secondary metabolites was markedly affected by the treatments. The synthesis of total phenolics exhibited a complex, spectrum-dependent pattern. The R20B80 treatment, when combined with bacterial inoculation, resulted in a significant increase in phenolic content compared to the non-inoculated control under the same light, indicating an apparent bacterial elicitation effect under this specific spectrum. Antioxidant Capacity The antioxidant capacity, a critical functional property derived from secondary metabolites, was most potently enhanced in plantlets inoculated with the A4 strain and cultivated under monochromatic red light (R100), resulting in the highest DPPH radical scavenging activity (14.71% inhibition). This confirms that the A4 strain and red light are the most effective combination for enhancing the plant's functional antioxidant defense. In summary, this study demonstrates that the strategic combination of LED light spectra and specific bacterial strains can effectively steer both the growth and the metabolic profile of German chamomile. The A4 strain, particularly under the R20B80 spectrum, proved highly effective at enhancing biomass and phenolic content, while its combination with red light (R100) optimally boosted antioxidant capacity. Conclusion This study demonstrates that tailored combinations of LED light spectra and R. rhizogenes strains, particularly the A4 strain with R20B80 and R100 light, can simultaneously enhance growth and the production of valuable bioactive compounds in German chamomile. This approach provides a sustainable strategy for optimizing the pharmaceutical quality of chamomile under controlled conditions. This study investigated the individual and combined effects of LED light spectra and Rhizobium rhizogenes strains on the growth and physiological attributes of German chamomile (Matricaria chamomilla L.). A factorial experiment with three replications was conducted under controlled conditions. Plantlets inoculated with bacterial strains A4 or ATCC15834 were exposed to seven light regimes: monochromatic white (W100), red (R100), blue (B100), and red–blue combinations (R80B20, R60B40, R40B60, R20B80). The interaction between the bacterial strain and the light spectrum significantly affected most of the measured parameters. The A4 strain under red light (R100) produced the longest shoots (19.5 mm), whereas ATCC15834, combined with R40B60, generated the longest roots (90.9 mm). Maximum shoot and root fresh weights (2342 and 3887 mg, respectively) were obtained from A4 under R20B80 light. From a physiological perspective, A4 under R80B20 light resulted in the highest chlorophyll a content, while ATCC15834 under R40B60 produced the greatest chlorophyll b and carotenoid levels (21.26 mg g-1 FW). The R60B40 spectrum enhanced flavonoid biosynthesis, and A4 under R100 exhibited the strongest antioxidant activity (14.71% DPPH inhibition). These findings demonstrate that combining specific bacterial strains with optimized light spectra can significantly enhance chamomile growth and its medicinal value. Introduction German chamomile, a member of the Asteraceae family, is a well-known medicinal herb valued for its essential oils and flavonoids, which possess antioxidant, anti-inflammatory, and antimicrobial properties. However, sustainable production faces challenges due to agricultural limitations and overexploitation. In vitro culture, integrated with elicitor-based strategies, offers an effective means to conserve germplasm and enhance bioactive metabolite production. Among elicitors, Light-Emitting Diodes (LEDs) enable precise spectral manipulation, with red and blue wavelengths particularly efficient at regulating photosynthesis and secondary metabolism. Similarly, Rhizobium rhizogenes acts as a biological elicitor, stimulating root induction and enhancing metabolite accumulation through phytohormonal interactions. This research aimed to explore the synergistic influence of LED spectra and R. rhizogenes strains on morpho-physiological traits and secondary metabolite biosynthesis in German chamomile. Materials and Methods The experiment was performed during 2022–2023 in the tissue culture laboratory of the University of Mohaghegh Ardabili, Iran. Chamomile seeds were surface-sterilised using liquid soap, 70% ethanol, and 3% sodium hypochlorite, then rinsed with sterile distilled water. Sterilized seeds were germinated on solid MS medium. After eight weeks, uniform seedlings were inoculated at the crown with R. rhizogenes strains A4 or ATCC15834. Following 48 hours of co-cultivation in darkness, plantlets were transferred to MS medium supplemented with 500 mg L-1 cefotaxime. They were subsequently exposed toseven LED treatments (90 µmol m-2 s-1) for 6 weeks. Growth and physiological parameters were recorded, and data were analyzed by factorial ANOVA followed by Duncan’s test (P ≤ 0.01). Results and Discussion Analysis of variance revealed that the interaction between LED light spectra and Rhizobium rhizogenes strains significantly (P ≤ 0.01) influenced the morpho-physiological profile of German chamomile plantlets. Morphological Development The evaluation of growth parameters revealed that the most significant synergy for biomass accumulation was observed between the A4 bacterial strain and the R20B80 light regime. This specific combination yielded the highest shoot fresh weight (2342 mg), underscoring its superior efficacy in enhancing aerial biomass production. Secondary Metabolite Production The production of pharmaceutically valuable secondary metabolites was markedly affected by the treatments. The synthesis of total phenolics exhibited a complex, spectrum-dependent pattern. The R20B80 treatment, when combined with bacterial inoculation, resulted in a significant increase in phenolic content compared to the non-inoculated control under the same light, indicating an apparent bacterial elicitation effect under this specific spectrum. Antioxidant Capacity The antioxidant capacity, a critical functional property derived from secondary metabolites, was most potently enhanced in plantlets inoculated with the A4 strain and cultivated under monochromatic red light (R100), resulting in the highest DPPH radical scavenging activity (14.71% inhibition). This confirms that the A4 strain and red light are the most effective combination for enhancing the plant's functional antioxidant defense. In summary, this study demonstrates that the strategic combination of LED light spectra and specific bacterial strains can effectively steer both the growth and the metabolic profile of German chamomile. The A4 strain, particularly under the R20B80 spectrum, proved highly effective at enhancing biomass and phenolic content, while its combination with red light (R100) optimally boosted antioxidant capacity. Conclusion This study demonstrates that tailored combinations of LED light spectra and R. rhizogenes strains, particularly the A4 strain with R20B80 and R100 light, can simultaneously enhance growth and the production of valuable bioactive compounds in German chamomile. This approach provides a sustainable strategy for optimizing the pharmaceutical quality of chamomile under controlled conditions.

https://ijpb.ui.ac.ir/article_29929_9ba0ace21e45e57aea0c337f243e7899.pdf