Everyone loves receiving a beautiful bouquet of fresh flowers, but making sure they stay vibrant on their way to your vase is a challenging task. A major cause for the deterioration of cut flowers is a gaseous molecule called ethylene, a plant hormone that causes flowers to wilt and fade and accelerates the drop of buds, petals, and leaves (Figure 1). In the floriculture industry, ethylene’s effects can significantly reduce the quality and longevity of cut flowers during storage and transport. AFE-funded researchers at the University of Texas at Arlington have been hard at work trying to find a way to inhibit ethylene’s adverse effects, and recent discoveries may offer promising alternatives to the methods currently in use.
Current Solutions and Their Drawbacks
Two treatments are commonly used to block ethylene’s effects: 1-methylcyclopropene (1-MCP) and silver thiosulfate (STS). They are very effective, but both have their drawbacks. 1-MCP is a reactive gas that is difficult to handle and requires enclosed areas for application. STS contains heavy metals, which raises environmental and disposal concerns, especially when used in large quantities. It is also light sensitive and must be prepared just prior to use, which can be inconvenient.
1-MCP belongs to a family of compounds called cyclopropenes, which are potent ethylene inhibitors. (The parent cyclopropene is a tiny, triangular molecule made up of three carbon atoms and four hydrogen atoms.) Cyclopropenes like 1-MCP have a similar structural feature to ethylene, which allows them to bind to the ethylene receptor sites in plant cells without eliciting the ethylene response, thus preventing ethylene from exerting its effects on plant tissues. (This is called competitive inhibition.)
Silver thiosulfate contains silver ions (Ag+) that can alter ethylene receptors in plants. These receptors are proteins located on the surface of plant cells, which are responsible for sensing and responding to ethylene. By interfering with these receptors, the silver ions block ethylene from interacting with them. As a result, the plant cells do not receive the ethylene signal, and the associated ethylene effects are not initiated. STS can also reduce the overall production of ethylene in plants by inhibiting the activity of the enzyme that is a precursor to ethylene.
The Search for Better Ethylene Inhibitors
Dr. Rasika Dias and his team at The University of Texas at Arlington are working to develop user-friendly chemicals that can be used in the cut flower industry to counteract ethylene’s negative effects. They are also creating simple laboratory models of ethylene binding sites in plants to test potential alternatives to 1-MCP more conveniently, and to better understand how 1-MCP works on ethylene binding sites.
The research team has synthesized several non-volatile 1-MCP alternatives, which were tested for anti-ethylene activity using fresh carnations. Some of these alternatives displayed good water solubility compared to 1-MCP and were more convenient to use. Two of the tested cyclopropene alternatives showed reasonable anti-ethylene activity, while a third reactive carbon-centered reagent displayed very strong anti-ethylene activity. These exciting findings represent a new approach to designing ethylene antagonists.
The team also managed to create four isolable molecules that feature copper-ethylene bonds, which they believe can serve as laboratory models for the copper-ethylene binding site in plants (figure 2). Copper ions are essential for the function of ethylene receptors in plants, which have copper centers. Furthermore, they were the first to isolate molecules that show copper-cyclopropene bonds, providing insights into the likely interaction between ethylene-binding sites in plants and 1-MCP.
These discoveries have the potential to greatly benefit the floriculture industry. The identified 1-MCP alternatives could be formulated into products for controlling ethylene’s adverse effects on crops, while synthetic “ethylene binding site” models can speed up the screening of new anti-ethylene products. The structures of molecules that provide insights into 1-MCP action in plants can also be useful for developing better and more effective anti-ethylene reagents.
To read the full research report and additional articles on protecting crops from ethylene damage, click here. Additionally, you can learn more about postharvest handling recommendations for cut flowers from our June Grow Pro Webinar – watch the recording here.
By Laura Barth and Dr. Rasika Dias