# Chloroplast–Thylakoid Organisation Is More Important than Carotenoid Accumulation for Optimum Photosynthetic Quantum Yield and Carbon Gain in Variegated Epipremnum aureum

## TL;DR

Variegated Epipremnum aureum plants show that chloroplast and thylakoid organization, not carotenoid levels, mainly determine photosynthetic efficiency and carbon gain.

## Contribution

The study reveals that structural chloroplast organization is more critical than pigment content for photosynthetic performance in variegated plants.

## Key findings

- Chloroplast–thylakoid organization better predicts CO2 yield and carbon gain than carotenoid accumulation.
- ‘Jade’ leaves have dense chloroplasts and thylakoids, leading to high carbon gain and cool canopies.
- ‘Golden’ maximizes water-use efficiency despite intermediate chloroplast–thylakoid organization.

## Abstract

What are the main findings?
CO2 yield per absorbed photon and carbon gain track chloroplast–thylakoid/grana organisation more than carotenoid accumulation.‘Neon’ overloads fewer photosystem II centres (low quenching, carbon-poor); ‘Jade’ spreads excitation (carbon-rich, cool), while ‘Golden’ maximises water-use efficiency.

CO2 yield per absorbed photon and carbon gain track chloroplast–thylakoid/grana organisation more than carotenoid accumulation.

‘Neon’ overloads fewer photosystem II centres (low quenching, carbon-poor); ‘Jade’ spreads excitation (carbon-rich, cool), while ‘Golden’ maximises water-use efficiency.

What are the implications of the main findings?
Thylakoid abundance sets a structural ceiling for photoprotection and CO2 yield, so pigment ratios alone can be misleading.Hyperspectral, fluorescence and thermal imaging can non-destructively phenotype leaves, linking chloroplast structural state to photosynthetic efficiency, canopy temperature and water-use economy.

Thylakoid abundance sets a structural ceiling for photoprotection and CO2 yield, so pigment ratios alone can be misleading.

Hyperspectral, fluorescence and thermal imaging can non-destructively phenotype leaves, linking chloroplast structural state to photosynthetic efficiency, canopy temperature and water-use economy.

Coloured and variegated leaves are common in shade-tolerant ornamentals. However, it remains unclear whether their photosynthetic performance is determined mainly by pigment abundance or by the organisation of chloroplasts and thylakoids. We tested this in three Epipremnum aureum phenotypes (‘Neon’, ‘Golden’ and ‘Jade’) that share a genetic background but contrast in leaf colour, chloroplast density and thylakoid membrane abundance. Plants were grown in a greenhouse and assessed by hyperspectral and thermal imaging, infrared gas exchange analysis, chlorophyll a fluorescence measurements, and structural, ultrastructural and biochemical analyses. Traits were integrated by principal component analysis, with the quantum yield of CO2 assimilation per absorbed photon (αCO2,abs) as the response variable. ‘Neon’ leaves had high specific leaf area and approximately 55% lower maximum Rubisco carboxylation (VcMAX) and electron transport capacity (JMAX) than ‘Jade’, as well as reduced chloroplast and thylakoid abundance and warmer canopies, despite carotenoid enrichment. JIP-test parameters and fluorescence light–response curves showed high absorption and dissipation per PSII reaction centre, elevated excitation pressure, modest non-photochemical quenching (NPQ), low αCO2,abs, small carbohydrate pools and low intrinsic water-use efficiency. ‘Jade’ leaves developed thick mesophyll with dense chloroplast populations, extensive thylakoid networks, highest NPQ, cool canopies and large carbohydrate reserves, whereas ‘Golden’ leaves combined thin laminae and intermediate chloroplast–thylakoid organisation with early light saturation of CO2 assimilation and the highest intrinsic water-use efficiency. Principal component analysis revealed a structural axis of chloroplast and thylakoid organisation that better predicted αCO2,abs, net carbon gain and canopy temperature than pigment abundance. In variegated E. aureum, ‘photon economy’ is therefore governed primarily by chloroplast and thylakoid membrane organisation and abundance rather than by carotenoid accumulation.