Basal or innate resistance, hypersensitive response, acquired resistance and RNA silencing are all defense mechanisms used by various types of plants. In addition to these categories, some plants may be poisonous, armed with sharp thorns, or otherwise difficult to feed upon.
Basal resistance is a function of plant cellular sensitivity, according to the American Phytopathological Society. Plant cells can sense the presence of certain bacterial organisms and can promote reactions within the plant that make it harder for those organisms to invade and effect change. All plant cells within the plant fortify themselves against being invaded or tampered with by pathogens or by microbial organisms.
Hypersensitive response is cellular suicide committed on a variable scale, ass stated by the American Phytopathological Society. When plants detect infection, they induce suicide in some of their own cells in order to isolate and starve the infection. This causes part of the plant to die but can protect the bulk of the organism from a full-scale invasion and total destruction.
Acquired resistance occurs only after hypersensitive response takes place. Once plant cells have committed suicide, the plant fortifies itself against invasion and becomes largely impervious to pathogens and other harmful agents. RNA silencing occurs when a plant recognizes a virus and aggressively digests its genetic strands, nullifying it and eventually destroying it entirely by reducing its structure to a state of uselessness.