How do chemical compounds in legumes help defend the plants from animals?

Legumes within the order Fabales produce a variety of secondary chemical compounds that serve as a primary defense mechanism against predators. These substances, which are often physiologically active or poisonous, help protect the plant by deterring herbivory.12

The chemical defenses found in legumes include:

• Alkaloids: These are commonly used by plants to deter predators and can be toxic to livestock, such as the toxins found in Astragalus (locoweed).12
• Nonprotein amino acids: Compounds like canavanine and mimosine can disrupt animal health, potentially causing neural diseases or inhibiting hair and wool growth in livestock.12
• Flavonoids and Tannins: These compounds contribute to the plant's chemical arsenal against consumption.12
• Phytohemagglutinin: Found in many legume seeds, this protein is toxic to some animals and can cause agglutination of blood cells.2
• Rotenone: Abundant in the roots and stems of certain species, this compound is toxic to various organisms, including fish.2

These chemicals often function by being distasteful or by causing illness, forcing predators to learn to associate specific flavors with negative physiological effects.32