Abstract
Ethylene is the most important factor playing roles in senescence and deterioration of harvested crops including cut flowers. Brassinosteroids (BRs), as natural phytohormones, have been reported to differently modulate ethylene production and related senescence processes in different crops. This study was carried out to determine the effects of different levels of 24-epibrassinolide (EBL) on ACC oxidase enzyme activity, the final enzyme in ethylene biosynthesis pathway, vase life, and senescence rate in lisianthus cut flowers. Harvested flowers were treated with EBL (at 0, 3, 6, and 9 µmol/L) and kept at 25 °C for 15 days. The ACC oxidase activity, water absorption, malondialdehyde (MDA) production and vase solution absorption rates, chlorophyll and anthocyanin contents, and the vase life of the flowers were evaluated during and at the end of storage. EBL at 3 µmol/L significantly (p ≤ 0.01) enhanced the flower vase life by decreasing the ACC oxidase activity, MDA production and senescence rates, and enhancing chlorophyll and anthocyanin biosynthesis and accumulation, relative water content, and vase solution absorption rates. By increasing the concentration, EBL negatively affected the flower vase life and postharvest quality probably via enhancing the ACC oxidase enzyme activity and subsequent ethylene production. EBL at 6 and 9 µmol/L and in a concentration dependent manner, enhanced the ACC oxidase activity and MDA production rate and decreased chlorophyll and anthocyanin accumulation and water absorption rate. The results indicate that the effects of brassinosteroids on ethylene production and physiology of lisianthus cut flowers is highly dose dependent.
Highlights
The conversion of SAM to ACC has been considered as the rate-limiting step in ethylene biosynthesis pathway, recent studies show that in some cases ACC oxidase plays an important role in the regulation of ethylene biosynthesis pathway [15,21]
Our results demonstrate that the higher levels of BRs may enhance the ethylene biosynthesis via enhancing the ACC oxidase activity in cut flowers and harvest crops, while at very low levels decrease ethylene production and related senescence processes
From the results of this study, we can conclude that EBL as a common brassinosteroid modulates the physiological responses of lisianthus cut flowers resulting in an enhanced or decreased vase life depending on the concentration used
Summary
Lisianthus (Eustoma grandiflorum), is an attractive and popular potted and cut flower that is becoming one of the most highly valued cut flowers in local and international markets [1]. Flowers are fast living organs of the plants with a high metabolic activity making them very susceptible to postharvest losses [4]. For this reason, the vase life is a commercial attribute determining the flexibility of the market at any time and an important indicator for cut flowers value. Similar to most other cut flowers, lisianthus has a relatively short vase life and extending the vase life of the flower is a major concern for the producers [3,5]
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