Zinc (Zn) is considered an essential element with beneficial effects on plant cells; however, as a heavy metal, it may induce adverse effects on plants if its concentration exceeds a threshold. In this work, the effects of short-term and prolonged application of low (25 µM) and high (500 µM) Zn concentrations on pak choi (Brassica rapa L.) plants were evaluated. For this, two experiments were conducted. In the first, the effects of short-term (15 h) and partial foliar application were evaluated, and in the second a long-term (15 day) foliar application was applied. The results indicate that at short-term, Zn may induce a rapid hydraulic signal from the sprayed leaves to the roots, leading to changes in root hydraulic conductance but without effects on the whole-leaf gas exchange parameters. Root accumulation of Zn may prevent leaf damage. The role of different root and leaf aquaporin isoforms in the mediation of this signal is discussed, since significant variations in PIP1 and PIP2 gene expression were observed. In the second experiment, low Zn concentration had a beneficial effect on plant growth and specific aquaporin isoforms were differentially regulated at the transcriptional level in the roots. By contrast, the high Zn concentration had a detrimental effect on growth, with reductions in the root hydraulic conductance, leaf photosynthesis rate and Ca²⁺ uptake in the roots. The abundance of the PIP1 isoforms was significantly increased during this response. Therefore, a 25 µM Zn dose resulted in a positive effect in pak choi growth through an increased root hydraulic conductance.

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.

Light-emitting diode (LED) technology allows for precise spectral tailoring in controlled-environment agriculture, with red light (R; 600–700 nm) acting as a central regulator of plant photophysiology through phytochrome (PHY)-mediated control of photosynthesis, morphology, and metabolic adjustment. This review synthesizes the current knowledge of the benefits and limitations of monochromatic and multichromatic R-containing LED systems under both optimal and saline conditions. Monochromatic R light enhances chlorophyll biosynthesis, carbon assimilation, and biomass accumulation; however, its exclusive application can restrict stomatal regulation, photoprotection, and secondary metabolism due to the absence of blue (B)- and green (G)-light-dependent signaling pathways. In contrast, multichromatic spectra incorporating R—particularly R-B, R-far-red (R-FR), and R-centered multi-spectral combinations with white (W) or G wavelengths—provide broader physiological advantages. These include improved photosystem II efficiency, pigment stability, ion homeostasis, antioxidant defense, and metabolic quality, while also optimizing canopy light distribution and energy use efficiency. Under salinity stress, R-containing spectral combinations consistently outperform monochromatic R by enhancing osmotic adjustment, reducing oxidative damage, and maintaining photosynthetic integrity. Nevertheless, species-specific sensitivity, ratio-dependent responses, and potential risks such as excessive elongation under FR enrichment highlight the need for careful spectral optimization. Despite substantial progress, the mechanisms underlying the integration of PHY signaling with salinity-responsive networks remain insufficiently resolved. Advances in multi-omics approaches and dynamic spectral management will be critical for the development of R-based LED strategies that sustainably enhance crop performance and stress resilience in controlled environments.