Postharvest Application of Salicylic Acid, Sodium Nitroprusside, and Spermidine Modulates Senescence in Cut Eustoma grandiflorum (Lisianthus)

Postharvest senescence poses a significant challenge for the commercialization of cut flowers, making it difficult for florists to sustain quality and prolong the vase life of their flowers. Among the most sought-after cut flowers, cut Eustoma grandiflorum ‘Mariachi Blue’ exhibits considerable variation in postharvest longevity across different cultivars. The onset of postharvest senescence adversely affects several physiological and biochemical processes, leading to water loss from senescent tissues, electrolyte leakage, elevated levels of reactive oxygen species (ROS), altered membrane fluidity, degradation of nucleic acids, and decreased concentrations of carbohydrates and proteins. Recent studies underscore the vital roles of salicylic acid (SA), polyamines, and nitric oxide in mitigating postharvest losses in floral systems. In this study, cut flowers of Eustoma grandiflorum ‘Mariachi Blue’ were placed in vase solutions supplemented with varying concentrations of SA (0.5, 1, and 2 mM), spermidine (Sp) (0.5, 1, and 2 mM), and sodium nitroprusside (SNP) (20, 40, and 60 µM). All three treatments significantly extended the vase life of the flowers while reducing the depletion of soluble sugars and proteins in the petals. Additionally, they enhanced antioxidant activity by increasing the levels of key antioxidant enzymes, including ascorbate peroxidase (APX) and guaiacol peroxidase (GPX). SA at 2 mM, Sp at 1 mM, and SNP at 20 µM significantly enhanced antioxidant defenses, which contributed to extending the vase life of Lisianthus flowers by an additional 5 to 7 days compared to controls. Comparative analysis showed that SA, spermidine (Sp), and sodium nitroprusside (SNP) applied at varying concentrations significantly prolonged the vase life of cut Eustoma grandiflorum ‘Mariachi Blue’ flowers. These treatments reduced the depletion of soluble sugars and proteins in petals and enhanced antioxidant activity by increasing key antioxidant enzymes such as APX and GPX. Specifically, SA at 2 mM, Sp at 1 mM, and SNP at 20 µM exhibited the strongest antioxidant defense, resulting in an extension of vase life by 5 to 7 days compared to controls. Overall, the applied plant growth regulators are effective in prolonging the freshness and postharvest quality of cut Lisianthus flowers.