Nitric oxide (NO) production and amino acid metabolism modulation, in particular abscisic acid (ABA)-dependent proline accumulation, are stimulated in planta by most abiotic stresses. However, the relationship between NO production and proline accumulation under abiotic stress is still poorly understood, especially in the early phases of plant development. To unravel this question, this work investigated the tight relationship between NO production and proline metabolism under water-deficit stress during seedling establishment. Endogenous nitrate reductase-dependent NO production in Medicago truncatula seedlings increased in a time-dependent manner after short-term water-deficit stress. This water-deficit-induced endogenous NO accumulation was mediated through a ABA-dependent pathway and accompanied by an inhibition of seed germination, a loss of water content, and a decrease in elongation of embryo axes. Interestingly, a treatment with a specific NO scavenger (cPTIO) alleviated these water-deficit detrimental effects. However, the content of total amino acids, in particular glutamate and proline, as well as the expression of genes encoding enzymes of synthesis and degradation of proline were not affected by cPTIO treatment under water-deficit stress. Under normal conditions, exogenous NO donor stimulated neither the expression of P5CS2 nor the proline content, as observed after PEG treatment. These results strongly suggest that the modulation of proline metabolism is independent of NO production under short-term water-deficit stress during seedling establishment.

Zinc oxide (ZnO) and iron oxide (IO) nanoparticles have been identified as promising candidates for biomedical applications, based on their unique physicochemical properties. The association of these nanoparticles in a single system creates a bimodal entity, allowing the excellent luminescent properties of ZnO quantum dots to be combined with the contrast agent of IO for magnetic resonance imaging (MRI). The present study focuses on the luminescent and MRI properties of a new poly(lactic-co-glycolic acid) (PLGA) nanocarrier system formulation containing ZnO NPs and IO NPs in different nominal ratios. Microscopic analysis (TEM and SEM) reveals a circular morphology with IO and ZnO NPs. The average diameter of the particles was determined to be 220 nm, as measured by DLS. The luminescence results indicate that the PLGA system shows strong emission in the visible range, and the MRI analysis shows a high r2 relaxivity of 171 mM⁻¹ s⁻¹ at 7T. The optimized formulation, exhibiting a molar ratio of Fe:Zn ranging from 1:10 to 1:13 (mol:mol), demonstrates superior fluorescence and MRI performance, underscoring the significance of nanoparticle composition in bimodal imaging applications. The systems evaluated demonstrate no toxicity in the THP-1 cells for doses of up to 128 µg mL⁻¹, with efficient labeling after 4 h of incubation, yielding images of strong luminescence and T2 contrast. The PLGA:ZnO:IO system demonstrates considerable potential as a bimodal platform for diagnostic imaging.