Unravelling Compositional Changes in Field Pea Leaf Cuticles Under Heat Stress Using Synchrotron-Based Fourier Transform Mid-Infrared Spectroscopy

Plant leaf cuticle, a heterogeneous and lipophilic membrane, is an interface between the plant and its aerial environment and protects plants against abiotic and biotic stresses. This study used synchrotron-based Fourier transform mid infrared (sFTIR) spectroscopy to evaluate the effect of heat stress on the compositional changes of leaf cuticles in field pea (Pisum sativum). The results showed that oxidative stress was associated with heat stress. A new peak at 1721 cm⁻¹ was observed in the heat-stressed leaf cuticles, and it was not found in the control leaf samples; this peak arises from the carbonyl stretching (C=O) from the aldehyde of 4-Hydroxynonenal (4-HNE) which is an adduct of the lipid peroxidation chain reaction. Heat stress reduced the amounts of phenolic compounds in leaf cuticles, indicated by the reduction of the integrated band area in the region of 1650–1500 cm⁻¹. Substantial spectral variations between the control and heat-stressed leaf cuticles were revealed using Principal Component Analysis (PCA). The spectral information showed the compositional changes in waxes, cutin, cutan, phenolic compounds and polysaccharides may be due to heat stress. This study provides important information for rapid understanding of the compositional changes of leaf cuticles under environmental stresses and may significantly contribute to routine screening for resistant pea genotypes to heat stress.