Which of the following is NOT considered a plant hormone that can act as a plant growth regulator?

Anthocyanins are pigments found in many plants that are responsible for red, purple, and blue colors in flowers, fruits, and leaves. They play a role in attracting pollinators and can provide some protection against ultraviolet light and environmental stress. However, they do not function as hormones or growth regulators in plants.

In contrast, auxins, gibberellins, and cytokinins are indeed classified as plant hormones. Auxins primarily promote cell elongation and are involved in processes such as rooting and the growth of stems. Gibberellins stimulate stem elongation, seed germination, and flowering, while cytokinins promote cell division and are influential in shoot and root development. Each of these hormones has specific mechanisms of action that affect plant growth and development, making them vital to understanding plant physiology and horticulture.