Phytochemical, physiological and morphological alterations in Hyssopus officinalis L. as affected by light emitting diodes (LEDs) and water deficit

In this study the effect of different light emitting diodes (LEDs) was investigated on the morphological, physiological, and biochemical characteristics of hyssop (Hyssopus officinalis L.) under different irrigation regiems. The experiment was performed in a completely randomized design with three replications. The different treatments included the natural light of the greenhouse (C), 100 % white (W), 100 % red (R), 100 % blue (B), and 75 % red + 25 % blue light (RB). Two levels of 90 % field capacity irrigation (control) and 70 % field capacity irrigation (low irrigation) were also used in this research. The results indicated that low irrigation led to a reduction in the wet and dry weight of shoots, canopy area, and relative water content (RWC) as compared with control irrigation. Photosynthetic pigments and most of the physiological traits, along with electrolyte leakage (EL), increased under low irrigation. Among various LED light spectra, R-light and B-light exhibited the highest shoot length and leaf width, respectively. The RB-light enhanced most of the investigated traits, such as developmental and physiological traits, and the percentage of essential oil under low irrigation compared with other light spectra. The RB-light significantly increased phenol and flavonoid content by 92 % and 121 %, respectively, compared with C-light and resulted in a 2.5 times increase in essential oil percentage. Based on GC-MS analysis, 3-pinanone, caryophyllene, germacrene-D, elemol were the most abundant components. Elemol showed the highest amount (45 %) in RB-light condition. It appears that the RB-light could elevate plant resistance to low irrigation, improve plant performance, and increase the plant essential oil production.