SIGNALING MOLECULES
The number and kinds of hormone-like signaling molecules are an active area of research, with new discoveries being made all the time.

Brassinolides are steroid molecules that may function in cell division and cell elongation. They are also involved in light-mediated gene expression, flower development, and leaf senescence.

Other signaling molecules function in defensive response of plants to infections and wounds. Salicylic acid is similar in structure to aspirin. It appears to be produced by plants as a defense against insect pests and viruses; it also appears to promote wound healing.

Systemin aids in defense against insect herbivores and disease organisms.

Oligosaccharins are carbohydrates that stimulate cells to produce antimicrobial compounds that limit the spread of disease organisms. Oligosaccharins may also be involved in aspects of normal cell growth and development.

Jasmonates are lipid-based molecules produced in response to insect infestations, providing the plant with resistance to the insect pests. Jasmonates also affect pollen development, root growth, fruit ripening, and senescence.