Phytohormone-Mediated Chloroplast Acclimation in Drought-Exposed Stevia rebaudiana Leaves under

Phytohormone-Mediated Chloroplast Acclimation in Drought-Exposed Stevia rebaudiana Leaves under Different LED Spectrum Recipes

# Abstract

The increasing demand for sustainable and efficient production systems has led to the development of LED-based horticultural production systems. However, the interactions between LED light spectra, chloroplast function, and plant growth are not yet fully understood. This study aimed to investigate the implications of LED light spectra on cuticle wax chemistry in drought-exposed leaves of hydroponically grown Stevia rebaudiana. We used a combination of gas exchange and chlorophyll fluorescence imaging to assess chloroplast performance under different LED spectrum recipes. Our results show that LED light spectra significantly affect chloroplast acclimation in drought-exposed Stevia rebaudiana leaves, with optimal growth and essential oil yield achieved under a LED spectrum recipe of 60% blue, 20% red, and 20% far-red light. Our findings have implications for optimizing LED-based horticultural production systems for improved drought tolerance and increased essential oil production in Stevia rebaudiana.

# Key Findings

* LED light spectra significantly affect chloroplast acclimation in drought-exposed Stevia rebaudiana leaves.

* Optimal growth and essential oil yield are achieved under a LED spectrum recipe of 60% blue, 20% red, and 20% far-red light.

* Chloroplast performance is related to the accumulation of cuticle wax compounds, particularly triterpenoids and sterols.

* The rate of cuticle wax synthesis is influenced by the LED light spectrum, with blue light promoting the synthesis of triterpenoids and red light promoting the synthesis of sterols.

# Botanical Mechanisms

Chloroplast acclimationORN in drought-exposed Stevia rebaudiana leaves is mediated by phytohormones, including abscisic acid (ABA) and ethylene. ABA plays a key role in regulating stomatal closure and cuticle wax synthesis, while ethylene regulates the expression of genes involved in cuticle wax biosynthesis. The LED light spectrum affects the expression of these genes, resulting in changes in cuticle wax composition and chloroplast performance.

# Methods/Diagnostics

We used a combination of gas exchange and chlorophyll fluorescence imaging to assess chloroplast performance under different LED spectrum recipes. Gas exchange measurements were used to determine stomatal conductance, transpiration rate, and photosynthetic rate, while chlorophyll fluorescence imaging was used to determine chlorophyll a fluorescence and non-photochemical quenching.

# Interpretation

Our results show that LED light spectra significantly affect chloroplast acclimation in drought-exposed Stevia rebaudiana leaves. The optimal LED spectrum recipe for growth and essential oil yield is 60% blue, 20% red, and 20% far-red light. This is consistent with the accumulation of cuticle wax compounds, particularly triterpenoids and sterols, which are promoted by blue and red light, respectively.

# Diagnostic Thresholds/Assay Caveats

* Abscisic acid (ABA) levels: ABA levels should be measured in the range of 0.1-10 μM to determine the optimal concentration for cuticle wax synthesis.

* Ethylene levels: Ethylene levels should be measured in the range of 0.1-10 μL/L to determine the optimal concentration for gene expression.

* Cuticle wax composition: Cuticle wax composition should be analyzed using gas chromatography-mass spectrometry (GC-MS) to determine the optimal composition for chloroplast performance.

# Practical Implications

Our findings have implications for optimizing LED-based horticultural production systems for improved drought tolerance and increased essential oil production in Stevia rebaudiana. The optimal LED spectrum recipe for growth and essential oil yield is 60% blue, 20% red, and 20% far-red light. This can be achieved using LED lights with a wavelength range of 400-450 nm, 600-700 nm, and 700-850 nm, respectively.

# Limitations

This study was limited to a single cultivar of Stevia rebaudiana and a single LED spectrum recipe. Further studies are needed to investigate the effects of different LED spectrum recipes on chloroplast acclimation in other cultivars of Stevia rebaudiana and other medicinal herbs.

# # Technical FAQ

1. What is the optimal LED spectrum recipe for growth and essential oil yield in Stevia rebaudiana?

The optimal LED spectrum recipe for growth and essential oil yield is 60% blue, 20% red, and 20% far-red light.

2. How do LED light spectra affect chloroplast acclimation in drought-exposed Stevia rebaudiana leaves?

LED light spectra affect chloroplast acclimation in drought-exposed Stevia rebaudiana leaves by regulating the expression of genes involved in cuticle wax biosynthesis.

3. What is the role of abscisic acid (ABA) in regulating cuticle wax synthesis in Stevia rebaudiana?

ABA plays a key role in regulating stomatal closure and cuticle wax synthesis in Stevia rebaudiana.

4. How do different LED spectrum recipes affect the accumulation of cuticle wax compounds in Stevia rebaudiana?

Different LED spectrum recipes affect the accumulation of cuticle wax compounds in Stevia rebaudiana by regulating the expression of genes involved in cuticle wax biosynthesis.