(1) Background: In recent years, the use of light emitting diodes (LEDs) for plant production purposes has expanded. However, LEDs’ effect on seed germination and early seedling growth has been scarcely documented. (2) Methods: In this work, the effect of monochromatic red light (RL, 100 µmol m−2 s−1) for up to 60 min applied to seeds of pea and melon was analyzed in terms of seedling growth and antioxidant enzymes levels. An experimental LED chamber coupled to an electronic control system was developed for this purpose. (3) Results: RL did not alter the germination rate, but significantly improved the early seedling growth. Pea and melon seedlings showed the highest increase in fresh weight and length upon 15 min RL treatment of the seeds, whereas longer exposure times decreased seedling growth. Interestingly, RL favored the development of secondary roots in both species, which could favor the nutrition and water uptake by the seedling. The ability of the seedlings to respond to a hypothetical LED irradiance-induced oxidative stress was reflected differently on the antioxidant system of pea and melon. (4) Conclusions: These findings can be relevant for designing seed priming treatments to improve plant vigor, thus enhancing the productivity of important crop plants.

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Red LED light (R LED) is an efficient tool to improve seed germination and plant growth under controlled environments since it is more readily absorbed by photoreceptors’ phytochromes compared to other wavelengths of the spectrum. In this work, the effect of R LED on the radicle emergence and growth (Phase III of germination) of pepper seeds was evaluated. Thus, the impact of R LED on water transport through different intrinsic membrane proteins, via aquaporin (AQP) isoforms, was determined. In addition, the remobilization of distinct metabolites such as amino acids, sugars, organic acids, and hormones was analysed. R LED induced a higher germination speed index, regulated by an increased water uptake. PIP2;3 and PIP2;5 aquaporin isoforms were highly expressed and could contribute to a faster and more effective hydration of embryo tissues, leading to a reduction of the germination time. By contrast, TIP1;7, TIP1;8, TIP3;1 and TIP3;2 gene expressions were reduced in R LED-treated seeds, pointing to a lower need for protein remobilization. NIP4;5 and XIP1;1 were also involved in radicle growth but their role needs to be elucidated. In addition, R LED induced changes in amino acids and organic acids as well as sugars. Therefore, an advanced metabolome oriented to a higher energetic metabolism was observed, conditioning better seed germination performance together with a rapid water flux.

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