Redox and thylakoid membrane proteomic analysis reveals the Momordica (Momordica charantia L.) rootstock-induced photoprotection of cucumber leaves under short-term heat stress

Abstract Heat stress adversely affects plant physiological and metabolic processes and is considered an important constraint on crop growth and productivity in agriculture worldwide. Grafting techniques are capable of mitigating various stresses. Here, compared with self-grafted cucumbers subjected to 42 °C heat stress for 24 h, we found that Momordica-grafted cucumbers exhibited higher cytomembrane thermostability, less photoinhibition reflected by their chlorophyll fluorescence, and a reduction in oxidative stress. To better understand the mechanism, optimized Blue-Native/SDS-PAGE two-dimensional electrophoresis (2-DE) was firstly applied to entire thylakoid membrane of grafted cucumbers, and 25 significantly differential accumulated protein spots were identified by MALDI-TOF/TOF MS analysis. The proteomic analysis revealed that high temperatures suppressed the accumulation of 13 proteins in self-grafted cucumbers, while Momordica rootstock stimulated the accumulation of 12 of these proteins. The transcriptional analysis indicated that grafting onto Momordica significantly increased the expression of genes that encode the photosystem II subunit S (PsbS) and minor light-harvesting complexes (CP24, CP26 and CP29.1), which are closely associated with non-photochemical quenching (NPQ) after heat shock. Immunoblotting for PsbS corroborated the Momordica-induced acceleration of heat dissipation. Taken together, Momordica rootstock alleviated heat-induced photoinhibition by maintaining intracellular redox homeostasis, stabilizing the protein library of the thylakoid membrane and modulating NPQ in the scions.