High concentrations of what substance promote ethylene synthesis and act as a defoliant?

The correct answer is that high concentrations of cytokinins promote ethylene synthesis and act as a defoliant. Cytokinins are a class of plant hormones that play a crucial role in cell division and growth, but they also significantly influence the development of leaves and flowers. When used in high concentrations, cytokinins can enhance the production of ethylene, which is a gaseous plant hormone associated with the ripening of fruits and the abscission (or shedding) of leaves.

In the context of defoliation, ethylene is vital because it initiates the process by which plants shed leaves, making it an essential factor in crop management, particularly in cotton production where defoliation is sometimes necessary before harvest. By promoting ethylene synthesis, cytokinins indirectly support this process, ensuring a timely and efficient removal of leaves.

While auxins are also involved in the growth and development processes, including defoliation, they do not primarily promote ethylene synthesis to the same extent as cytokinins in high concentrations. Gibberellins primarily affect plant growth and elongation, and while they can influence the timing of flowering or fruiting, they do not facilitate high levels of ethylene production as their main action. Abscisic