Have you got the gall?
Could it be that green mutations are not limited to The Hulk? Plant tumors are caused by insect infestation, bacteria, fungi, or viruses. In animals a tumor is defined as uncontrollable cellular division, generally due to DNA mutation. When localized and harmless, the abnormal growth (neoplasia) is referred to as a benign tumor. A malignant tumor, or cancer, has motility, causing it to metastasize and affect the function and well-being of the individual. Animal cancer cells can travel through the bloodstream and lymphatic system to various other organs of the body, making them difficult to detect and treat, leading to potentially fatal outcomes. Cancerous growths can disable the functionality of critical organs in animals.
Just as in animals, plant cells have intercellular checkpoints which ensure normal cellular growth, death and division. In both, cancer cells do not die, yet continue to grow and divide abnormally. Interestingly, without pathogenic invasion, most plants are exceptionally resistant to neoplasia when compared to animal cells. This resilience can be attributed to the genetically encoded redundancy in their cell cycle regulation. Additionally, plant tumors also do not spread to other parts of the plant because of their rigid cellular walls and lack of circulatory system. Tumor growth in plants is commonly known as gall or burl. Galls contain knots, callus, ingrown bark and stains, whereas, burls are bark-covered and display wildly contorted grain. These tumors can occur on twigs, branches, trunks, roots, or leaves (like seen above) and might be numerous per host. Plant tumors generally remain localized while growing and seldom lead to plant death.
While, plant tumors can reduce vigor and impede certain agricultural practices, burls can produce patterns that are aesthetically desirable. Burl cross-sections can be sold for thousands of dollars for art and furniture making. Burls have even prompted burl burglaries. This avid popularity triggered manufacturers to create burl artificially by binding, burning and grafting trees. These techniques create bulges in trees which resemble burls, but do not result in the appreciable wood figure. Bacterial tumor induction might be the preferable route to create the artistic appearance of natural burls.
The most common gall disease is caused by the bacterium, Agrobacterium tumefaciens, which forms crown galls. More than 600 plants are vulnerable to crown gall. Crown galls form near the root or the stem and have shown stunting and debilitating effects on their hosts, making them susceptible to environmental extremes and parasites. Crown galls have no bacterial content within them, the agrobacterium deposits a plasmid which mutates the DNA of the host cell. This results in unrestricted cellular division and localized growth. Insects have adapted to employ the galls to their benefit; specifically wasps that lay eggs amidst growing gall tissue. The gall tissue protects and feeds the larvae. Not unlike the Hulk, scientists can now employ plasmid transfection to transfer beneficial genes into plants, resulting in genetically engineered superior plants.
The SkyScan 1173 micro-CT is the optimal instrument to scan the galls which formed on the leaf we collected. The systems can handle large samples like the leav and have fine enough pixel density to capture the detail needed to see inside the galls. We used the 1kx1k setting for the scan since most of what we output would be the 3D images. If higher resolution was needed we could have scanned the 2kx2k setting for 8x more pixels. The settings for the scan were: 37kv, 194uA, 58min, 22um.
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