Beyond the Red-Blue Paradigm: The Role of Green Light in Pod and Seed Tissues of Pea (Pisum sativum L.) Plants

Our study demonstrates that green light influences photosynthetic efficiency of leaves, pericarps, seed coats and cotyledons, driving tissue-specific light adaptations in Pisum sativum L. plants. Unlike leaves, pericarps and seed coats, cotyledons developed specialized traits, including higher chlorophyll b and carotenoids content and greater electron transport turnover, thus optimizing photosynthetic function in light-limited environment. The supplement of green light to blue and red light enhanced chlorophylls and carotenoids in cotyledons while suppressing their level in leaves and leaving them unchanged in pericarps and seed coats. Analysis of OJIP chlorophyll fluorescence kinetics using PAM-fluorometry revealed that fluorescence intensity at the J-step increased from ~0.7 in leaves to ~0.9 in cotyledons with an increase of the normalized total area above the OJIP transient (Sm) up to 12.7-fold in the adaxial region of cotyledons. Green light supplement enhanced Sm in leaves (1.2-fold), seed coats (1.7-fold) and the abaxial region of cotyledons (1.8-fold). The photosynthetic performance (PIABS) was significantly lower in cotyledons, but green light mitigated this decline from 9-fold to 3-fold. This was associated with a 1.4-fold increase in photon flux absorbed by antenna pigments (ABS/RC), 1.5-fold improved quantum yield of photochemistry (PHI_Po) and 1.2-fold reduced energy dissipation (DIo/RC). Molecularly, green light upregulates the expression of genes encoding the Rubisco chaperonin Cpn60α in leaves and cotyledons, without affecting Cpn60β, Rubisco activase (RCA), and phosphoribulokinase (PRK). These findings redefine green light as an active participant in photosynthesis, particularly in tissues of developing pods and seeds and opens new research avenues in wavelength-dependent signaling during plant development.