Impact of varying light intensities on morphology, phytochemistry, volatile compounds, and gene expression in Thymus vulgaris L

Abstract

Light is a crucial factor in plant growth and development. Plants exposed to light stress experience various effects on their growth. This research was conducted to investigate the effects of different light intensities on morpho-physiological traits, phytochemical compounds, and gene expression related to the biosynthesis of voletile in Thymus vulgaris L. The results demonstrated that light intensity (20, 50, 70 and 100%) had a significant impact on morpho-physiological characteristics, pigments content, antioxidant enzymes activities, as well as the content of MDA, H2O2, anthocyanin, thymol, carvacrol, phenols, flavonoids, essential oils, and monoterpenes. Moreover, the expression of the biosynthesis genes of monoterpene compounds was significantly influenced by light intensity. While an increase in light intensity led to higher leaf count (164.6%) and biomass (33.5%), it was accompanied by a decrease in leaf area, stem length, and internode length. The highest levels of chlorophyll a (4.92 mgg-1 FW) and b (1.75 mgg-1 FW), carotenoids (907.31 µ Mg-1FW), MDA (9.93 µ Mg-1FW), anthocyanin, SOD (29.62 Umg - 1 Protein), thymol (41.2%), and carvacrol (4.46%) were observed at 70% treatment and decreased as light intensity increased. Also, H2O2, catalase and polyphenol oxidase activities, phenols, flavonoids, essential oils, and monoterpenes increased with higher light intensity, with the highest H2O2 concentration recorded at 100% (4.43 fold). Importantly, key genes involved in monoterpene biosynthesis, including DXR, TPS, CYP71D178, and CYP71D179, exhibited significantly enhanced expression under full light conditions compared to other light intensities. In conclusion, increased light intensity stimulated the elevation of oxidative indicators, antioxidant activity and enhancing the expression of genes involved in phytochemical compound biosynthesis and consequently leading to the accumulation of volatile compounds in Thymus vulgaris L. Future research will focus on investigating the combined effects of various abiotic stresses at the field level and extending the stress duration to evaluate potential additive effects.

Fig 1. Environmental conditions during the growth period of Thymus vulgaris recorded on different days after treatments (DAT).

(A) Light intensity (μmol m^-2 s^-1), (B) Temperatures at 9:00, 12:00, and 18:00 (ºC).

Fig 2. Alterations in the activity of antioxidant enzymes (U mg ^− 1 Protein) of T. vulgaris in response to different light intensities (20%, 50%, 70% and 100%).

Fig 3. Heat map diagram illustrating the expression levels of genes involved in the thymol biosynthetic pathway in response to different light intensities in T. vulgaris.

Error bars indicate the standard deviation.

Fig 4. Principal Component Analysis (PCA) of studied traits in Thymus vulgaris.

(A): Loading Plot, (B): Component Plot. TSC: Total sugar content, CYP178:CYP71D178, CYP179: CYP71D179, pCymen: P-Cymen, gTerpinene: γ-terpinene, POD: Peroxidase, CAT: Catalase, MDA: Malondialdehyde, SOD: super oxiddismotase, PPO: Polyphenol oxidase, Chla: Chlorophyll a, Chlb: Chlorophyll b, CAR: Carotenoids, TFC: Total flavonoid content, ACN: Anthocyanin, BI: Biomass index, LN: Leaf number, IN: Internode number, LA: Leaf area, SM: Stem length, TPC: Total phenol content, EO: Essential oil, MTs: Monoterpenes, SQTs: Sesquiterpenes.

Fig 5. Pearson correlation between different traits in the T. vulgaris.

CYP178: CYP71D178, CYP179: CYP71D179, EO: essential oil, BI: biomass index, LN: leaf number, IN: internode length, LA: leaf area, SL: stem number, CAT: catalase, POD: polyphenoloxidase, SOD: super oxiddismotase, MDA: malondialdehyde, TPC: total phenol content, TFC: total flavonoid content.