What role does abscisic acid play in plants?

Abscisic acid (ABA) plays a significant role in plant physiology, particularly in response to environmental stress. One of its primary functions is to signal the plant to conserve water during times of drought or when soil moisture levels are low. When plants experience drought stress, ABA levels increase, which triggers responses such as closing stomata (the small pores on leaves) to reduce water loss through transpiration. In this way, ABA acts as a signaling molecule that helps plants manage their water supply by essentially communicating their "thirst" to conserve their resources.

This hormone's actions are crucial for plant survival in adverse conditions. In contrast, other options such as promoting cell division, stimulating fruit ripening, or promoting stem elongation are associated with different plant hormones, such as cytokinins, ethylene, and gibberellins, respectively. Therefore, while abscisic acid is focused on stress response and water conservation, the roles highlighted in the other choices pertain to different aspects of plant growth and development.