Photosynthesis is a vital process for seed productivity. It occurs in the leaves and provides developing seeds with the necessary nutrients. Moreover, many crops require photochemical reactions inside the seeds for proper development. The present study aimed to investigate Pisum sativum L. seeds at the middle stage of maturation, which is characterized by the active synthesis of nutrient reserves. Embryonic photosynthesis represents a crucial process to produce cells’ NADP(H) and ATP, which are necessary to convert sucrose into reserve biopolymers. However, it remains unclear how the pea embryo, covered by a coat and pericarp, receives sufficient light to provide energy for photochemical reactions. Recent studies have demonstrated that the photosynthetically active radiation reaching the developing pea embryo has a high proportion of green light. In addition, green light can be utilized in foliar photosynthesis by plants cultivated in shaded conditions. Here, we addressed the role of green light in seed development. Pea plants were cultivated under red and blue (RB) LEDs or red, green, and blue (RGB) LEDs. A Chl a fluorescence transient based on OJIP kinetics was detected at the periphery of the cotyledons isolated from developing seeds. Our findings showed that the addition of green light resulted in an increase in photochemical activity. Furthermore, the mature seeds that developed in the RGB module had a significantly higher weight and more storage proteins. Using a metabolomics approach, we also detected significant differences in the levels of organic acids, carbohydrates, nucleotide monophosphates, and nitrogenous substances between the RB and RGB conditions. Under RGB light, the cotyledons contained more ornithine, tryptophan, arginine, and aspartic acid. These changes indicate an impact of green light on the ornithine–urea cycle and polyamine biosynthesis. These results allow for a deeper understanding of the photochemical processes in embryos of developing seeds grown under a low light intensity. The photosynthetic system in the embryo cell adapts to the shade conditions by using green light.

In addition to leaves, photosynthesis can occur in other green plant organs, including developing seeds of many crops. While the majority of studies examining photosynthesis are concentrated on the leaf level, the role of other green tissues in the production of total photoassimilates has been largely overlooked. The present work studies the photosynthetic behavior of leaves and non-foliar (pericarps, coats, and cotyledons) organs of pea (Pisum sativum L.) plants at the middle stage of seed maturation. The Chl a fluorescence transient was examined based on OJIP kinetics using the FluorPen FP 110. A discrepancy was observed between the performance index (PI_ABS) for foliar and non-foliar plant tissues, with the highest level noted in the leaves. The number of absorbed photons (ABS) and captured energy flow (TRo) per reaction center (RC) were elevated in the non-foliar tissues, which resulted in a faster reduction in Q_A. Conversely, the energy dissipation flux per RC (DIo/RC and PHI_Do) indicated an increase in the overall dissipation potential of active reaction centers of photosystem II. This phenomenon was attributed to the presence of a higher number of inactive RCs in tissues that had developed under low light intensity. Furthermore, the expression of genes associated with proteins and enzymes that regulate ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo) activity was observed, including chaperonins Cpn60α and Cpn60β, RuBisCO activase, as well as phosphoribulokinase. The expression of these genes was found to differ between foliar and non-foliar tissues, indicating that the activation state of RuBisCO may be modified in response to light intensity. Overall, the present study provides insights into the mechanisms by which non-foliar green tissues of plants adapt to efficient light capture and utilization under low light conditions.

Zinc excess (Zn stress) could lead to deleterious effects in plants such as enhanced ROS production, inhibition of photosynthetic machinery, and impairment of nutrient uptake. Hence, we aimed to investigate the complexity of metabolic responses to Zn stress in Amaranthus caudatus young and mature leaves, as well as in roots by means of proteomics. Our previous metabolomics research has indicated potential involvement of gluconate and salicylate in Zn tolerance mechanisms. However, proteomics study of metabolic adjustments underlying Zn stress tolerance can give additional insight to the issue, as a lot of enzymes are known to be affected by the excess of transitional metals. The results obtained through bottom-up proteomics were complementary to our earlier metabolomics data and, furthermore, enlightened other important details in the metabolic response of A. caudatus plants to the applied Zn stress. In particular, the significant involvement of redox-related enzymes was shown, especially for the roots, and their possible interactions with salicylate and jasmonate signaling could be proposed. Furthermore, Zn²⁺-induced changes in roots and young leaves strongly affected sugar metabolism, enhanced protein quality control system, while mature leaves were characterized by remarkable decrease in subunits of photosynthetic electron transport complexes. Thus, this work emphasizes massive metabolic reprogramming aimed to reinforce root defense responses while supporting young leaves with sugar metabolites. Mass spectrometry proteomics data are available via ProteomeXchange with identifier PXD069557.