Using ATR-FTIR Spectroscopy to Study Heat Stress on Leaf Cuticles of Field Pea Cultivars.

Heat stress due to climate change is a threat to field pea (Pisum sativum) production in western Canada and globally. To characterize the effects of heat stress and cultivars on leaf cuticles, eleven cultivars (03H107P-04HO2026, CDC 40-10,CDC Golden, CDC Sage, CDC Vienna, Kaspa, MFR043, Naparnyk, Rally, TMP15121, TMP15213) were grown under control condition (24/18 °C day/night) and heat stress (35/18 °C day/night). Mid infrared (mid-IR) attenuated total reflectance (ATR) - Fourier transform infrared (FTIR) spectroscopy with uni- and multivariate spectral analyses were used to investigate chemical-structural features of adaxial leaf cuticles. For spectra, integrated area of characteristic peaks and peak area ratios were used. The eleven cultivars showed significant spectral differences in the integrated area of the CH₃ peak (ca. 2954 cm^-1), asymmetrical and symmetrical CH₂ peaks (ca. 2918 cm^-1 and ca. 2848 cm^-1), the ester carbonyl peak (ca. 1736 cm^-1), and the peak area ratio of CH₂ to CH₃, indicating chemical-structural diversity of cuticular waxes, cutin, cutan, and phenolic compounds. CDC Vienna exhibited the largest amount of total lipid compounds among these eleven cultivars, while CDC Sage had the smallest amount. Heat stress caused chemical modifications of leaf cuticles in CDC 40-10, CDC Golden, CDC Sage, Naparnyk and TMP15213, which were characterized by significant changes in their integrated ester carbonyl peak area and peak area ratio of CH₂ to CH₃. This study indicated considerable diversity in chemical-structural makeup of leaf cuticles within commercially available pea cultivars. These cultivars responded differently to the unexpected high growth temperature, revealing diverse potential to fight against heat stress. The ATR-FTIR spectral technique can therefore be further used as a medium-throughput approach for rapid screening of superior cultivars for heat tolerance.