Question

Gaseous hormones are able to enter cells without requiring special membrane transporter. Which of the major plant hormones is a diffusible gas? a. auxin d. ethylene b. gibberellin e. abscisic acid c. cytokinin

Short answer

The major plant hormone which is a diffusible gas is ethylene.

Step-by-step solution

Understanding Plant Hormones

There are different kinds of plant hormones having diverse characteristics. Some are solid, some are liquid and some are gaseous. The gaseous ones can diffuse quickly and do not require a special membrane transporter to enter the cells.

Identifying the Gaseous Plant Hormone

Among the given options (auxin, ethylene, gibberellin, abscisic acid, cytokinin), only ethylene is a gaseous plant hormone. It can diffuse easily across membranes and does not require a specific transporter.

Key concepts

Ethylene

As a simple hydrocarbon with the chemical formula C₂H₄, ethylene plays a crucial role in the life cycle of plants. It is unique among plant hormones because it is a gas at biological temperatures. This quality allows ethylene to diffuse freely through the air and plant tissues, enabling it to act over both short and long distances.

Ethylene is involved in various plant processes, including leaf abscission, fruit ripening, and the response to stress conditions such as drought, flooding, and mechanical injury. Its synthesis can be triggered by internal developmental signals or external environmental factors. Given its gaseous nature, ethylene's effective transmission doesn't rely on any dedicated transport system, which contrasts with the majority of other plant hormones that require specific transport mechanisms to move within the plant.

Hormone Transport in Plants

Transporting hormones within a plant is key to ensuring growth, development, and responses to the environment are regulated effectively. Unlike animals, plants do not have an organ system designed for hormone circulation. Instead, they rely on a combination of processes, including diffusion, active transport, and vascular transport.

These transport methods are influenced by hormone solubility. Water-soluble hormones, such as auxin, often require active transport via protein carriers or are moved through vascular tissues like phloem and xylem. Lipid-soluble hormones, however, can typically diffuse across cell membranes. The movement of hormones can result in localized effects on specific tissues or widespread impacts throughout the plant, depending on the hormone's nature and the plant's needs.

Gaseous Plant Hormones

In the realm of plant biology, gaseous hormones are a rarity, with ethylene being the prime example. The ability to exist as a gas under normal atmospheric conditions confers upon ethylene a distinctive set of characteristics and a mode of action that is different from other, non-gaseous plant hormones.

Gaseous hormones like ethylene do not require specialized transporters to move into plant cells. This characteristic allows for rapid and uniform distribution within the plant, as well as between plants, providing an efficient communication medium. Gaseous hormones can be quickly released into the environment in response to stress, signaling to neighboring plants and initiating defensive mechanisms.

Plant Biology

The study of plant biology encompasses the exploration of plant life at the cellular, genetic, and ecological levels. Hormones are among the most crucial aspects to understand because they influence every phase of a plant's life cycle—from germination to death. These bioactive compounds help plants adapt to their environmental challenges and regulate their growth and development.

In plant biology, understanding how hormones like ethylene function is essential for applications ranging from agriculture to conservation. Knowing how plant hormones are transported and act can lead to breakthroughs in improving crop yields, creating stress-resistant plants, and even in preventing the premature spoiling of produce during storage and transportation.