Researchers at the Department of Plant Pathology at the University of California Davis have discovered that plants have an immune system that helps them fight off infections. Unlike humans, plants don’t make antibodies and can’t fight off the same bug more quickly months or years later. However, plant cells can identify pathogens and react to them, often by producing a burst of reactive oxygen which is toxic to bacteria or fungi. Cells around an infected site will go into programmed cell death to seal off the disease.