Similar but Distinctive Strategies: How Peas and Beans Adapt Their Thylakoid Membranes to Low-Light Conditions

Plants adapt their photosynthetic apparatus to optimize energy capture under varying light conditions. This study investigates how species-specific thylakoid membrane organization influences low-light (LL) adaptation in peas and beans, two closely related plants that display distinct membrane architectures under moderate-light (ML) conditions. Despite their differences, both species exhibited convergent ultrastructural modifications when grown under LL, primarily through increased grana size. These structural changes were accompanied by similar proportional increases in light-harvesting complex II (LHCII) proteins and lutein content in both species. However, significant species-specific adaptations were also recognized. LL-grown beans showed higher PSII core protein phosphorylation, increased LHCII aggregation, an elevated MGDG/DGDG ratio, and a reduced neoxanthin contribution to the total carotenoid pool compared with LL-grown peas, which did not exhibit light-dependent changes in these parameters. In contrast, LL-grown peas showed a decreased total protein aggregation, which suggests an increased membrane fluidity in pea plants growing in LL compared with ML conditions, probably securing protein mobility, which is beneficial in limited light environments. These molecular differences resulted in a superior acclimatory capacity in peas, which maintained higher photochemical efficiency under increasing light intensities compared to beans. Notably, peas lacked typical LL stress symptoms and grew more similarly to their ML counterparts than beans did. Our findings highlight the importance of species-specific membrane properties in determining adaptation potential to LL environments. These insights are valuable for selecting and breeding plants that are better suited for controlled-environment agriculture, where artificial lighting is often limited by economic and technical constraints.