Plants can experience uncontrolled cell division, leading to abnormal growths, but they do not get cancer in the same way animals do. The defining feature of malignant cancer in animals is its ability to metastasize, or spread to other parts of the body, which plant growths cannot do. This fundamental difference means that while these growths can sometimes harm a plant, they are rarely fatal. The reasons for this are rooted in the basic biology and structure of plant cells and tissues.
Uncontrolled Growth in Plants
Uncontrolled cell division in plants manifests as abnormal swellings known as galls, burls, or tumors. These growths result from cells dividing more rapidly than normal (hyperplasia) or enlarging excessively (hypertrophy). They can appear on nearly any part of the plant, including the trunk, branches, leaves, and roots, varying widely in size and shape.
Galls are often specific in their appearance, sometimes resembling intricate structures, while burls are large, woody, hemispherical swellings on a trunk or branch. Burls are often covered in bark and may even sprout new buds. Crown galls specifically refer to tumors that form near the ground on the stem or roots. These growths are composed of the plant’s own cells prompted into disorganized growth.
Triggers for Plant Tumors and Galls
The primary triggers for these growths are typically external factors rather than spontaneous genetic mutations. Infections from bacteria, fungi, viruses, and even insects are the most common culprits. The bacterium Agrobacterium tumefaciens is a well-known cause of a disease called crown gall. This soil-dwelling bacterium enters a plant through a wound, often near the roots or the base of the stem.
Once inside, Agrobacterium tumefaciens inserts a piece of its own DNA into the plant’s genome. This transferred genetic material overrides the plant’s normal cellular controls, causing the cells to produce growth hormones at an uncontrolled rate. This leads to rapid cell division and the formation of a visible tumor. Fungi and insects can also induce gall formation, typically by injecting chemicals that disrupt normal plant development to create shelter or a food source.
Why Plant Tumors Are Not True Cancer
The fundamental reason plant tumors do not spread is the rigid cell wall that encases every plant cell. This structure, composed mainly of cellulose, provides support and locks each cell into a fixed position within the plant’s tissue. Unlike animal cells, which are more mobile, plant cells cannot break away from a primary tumor and travel to distant locations to establish secondary growths.
Furthermore, plants lack the complex circulatory systems that facilitate the spread of cancer in animals. Animals have blood and lymphatic vessels that can act as highways, transporting cancerous cells throughout the body. Plants transport water and nutrients through xylem and phloem, but this system is not conducive to cell migration. The combination of rigid cell walls and this transport system means that plant growths remain localized.