Abstract
BACKGROUND: Light is essential for producing high-quality plants. The advancement of light-emitting diode technology has unlocked new opportunities for growing plants in controlled settings. In this study, the effects of light-emitting diodes priming and drought stress on some physiological and biochemical parameters were studied in two Melissa officinalis genotypes (Ilam and Isfahan) one and three weeks after drought stress. The experiments were conducted in a factorial arrangement within a completely randomized design with three replications. RESULTS: Drought stress reduced growth indicators such as fresh and dry weights of aerial parts, leaf number, and relative water content. Light-emitting diode priming relieved such reductions in both genotypes. The accumulation of phenolic compounds, anthocyanin, and levels of proline, along with the activity of the enzyme phenylalanine ammonia-lyase, increased under drought stress, with the maximum increase achieved under red + blue and blue light-emitting diode light-primed plants. Especially in the Ilam genotype, phenylalanine ammonia-lyase enzyme activities and the accumulation of phenolic compounds were remarkably enhanced by the use of red + blue light-emitting diode light. Also, abscisic acid showed higher values under drought stress and the highest in pre-treatments with red + blue and red light-emitting diodes. CONCLUSION: The effects of different treatments on the physiological indices showed that drought tolerance in Melissa officinalis was improved due to the priming of red + blue light-emitting diode in both genotypes. Thus, our results emphasized the use of light-emitting diode priming as a useful method to enhance the drought resistance of medicinal plants.