Maintaining the Postharvest Quality and Reducing the Browning of Narcissus cv. ‘Shahla-e-Shiraz’ Cut Flowers Using Sodium Nitroprusside

Introduction Narcissus (Narcissus tazetta) has high demand in flora markets due to its beauty, having a multi-floret flowerhead and delicate fragrance. The appearance quality and vase life of cut flowers decreased after harvest due to flower senescence, loss of petals turgor, reduced water absorption, transpiration, fresh weight loss, and reduced water potential which reduces the economic and ornamental value of flowers at the consumer. One of the important reasons for the poor postharvest quality of Narcissus tazetta is the loss of turgor and their high sensitivity to browning of the petals. Browning mechanisms are chemically divided into enzymatic and non-enzymatic browning reactions. Enzymatic browning, which causes important reactions and discoloration, is one of the important factors affecting the quality and shelf life of fresh produce. Previous studies have shown that the activity of polyphenol oxidase (PPO) and peroxidase (POD) is positively correlated with browning during the postharvest storage of fruits and vegetables. Nitric oxide (NO) is recognized as a biological messenger in plants. It is a highly reactive gaseous free radical. Optimum NO levels could delay the climacteric phase of many tropical fruits and prolong the post-harvest shelf life of a wide range of horticultural crops by preventing ripening and senescence. Nitric oxide also could prevent the activity of PPO, phenylalanine ammonialyase (PAL) and POD, and keep the highest activity of superoxide dismutase (SOD).Materials and MethodsNarcissus (Narcissus tazetta L. cv. Shahla e-Shiraz) cut flowers at their commercial maturity stage (Goose-neck) were harvested from a production field in Farse province and. then they were transported to the laboratory. Healthy and uniform cut flowers with the same number of buds, a similar size and growth status were selected. Cut flowers were subjected to pulsed treatment of sodium nitroprusside for 24 hours on two levels (25 and 50 μM) and then kept in containers. Samples were stored at 20 ± 2 °C, relative humidity of 70-60%, with light cycle of 12 hours light and 12 hours dark. In this experiment, various physiological and biochemical indices including apparent quality (wilting index), cell membrane stability index (%), petal relative water content (%), color index and browning using a colorimeter, relative weight using digital scale (g), flower diameter, PPO and POD were examined. Results and DiscussionSodium nitroprusside treatment reduced the browning process by reducing the activity of POD and PPO enzymes. The effect of sodium nitroprusside was concentration-dependent. Sodium nitroprusside maintains membrane stability by protecting the membrane and preventing lipoxygenase activity and scavenging free radicals that have attacked the membrane. Sodium nitroprusside-maintained flower diameter due to its role in eliminating free radicals, delaying the aging process and maintaining flower quality. Discoloration and browning reactions of cut flowers reduce their appearance quality, leading to economic loss. The browning of the petals due to senescence is one of the important factors limiting the vase life of narcissus. It has been shown that PPO and POD are the key enzymes for the oxidation of the phenolic substrate (especially simple phenols) and the production of the brown compounds. It has also been suggested that the stability index of the cell membrane, which represents the ion leakage of the tissues, is diminished extremely as the longevity is increased. Another effective factor in determining the quality and vase life of cut flowers is the water-holding ability and water balance of the cut flowers petals. Changes in the cut flower fresh weight could also be regarded as one of the most important postharvest physiological disorders that affected the quality, vase life and commercial value of the cut flowers. Fresh weight loss, which is one of the most important reasons for the wilting of the flowers, is due to the less water uptake and more respiration rate.Conclusion Sodium nitroprusside treatment maintained the quality of Narcissus tazetta L. cv. Shahla e-Shiraz by increasing the relative water content of the petals and maintaining the cell stability index, as well as reducing the activity of browning enzymes (PPO and POD).Of course, the concentration used was very important.The best results were observed at lower concentrations (25 μM) of sodium nitroprusside.