Pretreatment with nano-silver extends the post-harvest longevity of gladiolus cut flowers by reducing free water mobility

The water content of cut flowers is a significant factor in their post-harvest quality. In this study, we examine the efficacy of silver nanoparticles (NS) on the longevity of cut gladiolus, with a focus on water state and distribution. We used Low-field nuclear magnetic resonance (LF-NMR) technology to identify three water fractions with different transverse relaxation times (T2) values: bound water T21 (<10 ms), intermediate immobilized water T22 (10–100 ms), and the slowest component free water T23 (>10 ms). During the opening process, T23 increased at stages 2 and 3 and then decreased, T22 decreased slowly, and T21 remained unchanged. Free water values were consistently higher than bound water and immobilized water and reached their maximum from stage 2 until stage 4, when the petals were extended and began to wilt. The vascular bundles responsible for transporting water had higher water content, as detected by proton density-weighted magnetic resonance imaging (MRI). Bound water and free water with NS pretreatments in bracts were initially lower but then two days later the signal amplitude of each water state exceeded those of the control, indicating that the treatment enhanced the water-holding capacity over time. Furthermore, NS pretreatments reduced the free water mobility of the cut flowers and inhibited stem decay. Additionally, we found that NS can enter the stem and are primarily transported upward along the xylem with water using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) technology. Overall, our findings indicate that NS pretreatment reduces free water in gladiolus cut flowers, enhancing their water retention and prolonging their vase life.