Plant tumors

Schwalm, K. et al., Flavonoid-related regulation of auxin accumulation in Agrobacterium tumefaciens-m.6,v,ct6, plant tumors, Planta, 218, 163, 2003. 

Plant tumors result from uncontrolled hormone production. Crown gall tumors, for example, are due to the infection of plant wounds by certain strains of Agrobacterium. These bacteria carry a large plasmid, the tumor-inducing, or T, plasmid, part of which is incorporated into the plant genome. This DNA encodes several genes that stimu-... 

Figure 6.33. Tumors in Plants. Crown gall, a plant tumor, is caused by a bacterium Agrobacterium tumefaciens) that carries a tumor-inducing plasmid (Ti plasmid). 

The work of many investigators soon showed it to be extremely widespread in plants, and it became clear that it was a fundamental plant hormone (e.g., reviews 530, 655a). Excessive production of indoleacetic acid by parasites is responsible for certain types of plant tumor (e.g., 948). The synthetic plant growth regulators, which are in general substituted phenoxyacetic acids, probably function as indoleacetic acid analogues. 

Tryptophan has been clearly established as the precursor of indoleacetic acids in both plants (e.g., 303, 921, 922) and fungi (e.g., 864), and in plant tumor tissue (e.g., 378, 948). Two routes are possible for indoleacetic acid formation from tryptophan as follows ... 

In this article we refer to the effect of brassinosteroids on plant cell cultures, in particular on plant tumor cells. 

Like all steroids, brassinosteroids derive from a single common precursor mevalonic acid. Some phytohormones are synthesized totally or in part via the isoprenoid pathway, such as absdsic acid, gibberellins and cytokinins. The importance of this biosynthetic pathway in processes involved with cell cycle regulation and tumorigenesis in mammals is well documented. Having in mind the similarities between certain regulatory systems in plants and animals the question arose whether brassinosteroids as putative plant steroid hormones would show a specific effect on plant tumor cells. 

Biosynthesis The biosynthesis from L-Arg and 2-oxo-glutaric acid occurs in plant tumors after infection with Agrobacterium tumefaciens, see also octopine. For synthesis, see Lit. °. 

D-O. is also found in certain plant tumors induced by Agrobacterium tumefaciens. This bacterium induces tumors in dicotyledenous plants by transferring a large bacterial plasmid (called the Tj plasmid) to die eukaryotic cell. In the transformed tissue, the Tj plasmid determines the synthesis of novel amino acids, which serve as specific substrates for the bacterium. These may be d-O. and related compounds (the oc-topine family ), or nopaline and nopalinic acid (the nopaline family ), but not both. [F. Marines D.W.R. White Divergent Transcription and a Remote Operator Play a Role in Control of Expression of a Nopaline Catabolism Promoter in Agrobacterium tumefaciens J. Biol Chem. 270 (1995) 12339-12342]... 

Crown galls are plant tumors that are induced by Agrobacterium tumefaciens. Their occurrence is in no way limited to roots they can occur on any part of the plant (Fig. 139). A precondition is a wound. In the first place it is necessary for the bacteria to penetrate into the plant, but, in addition, the wound leads to a conditioning of the plant cells. For if the bacteria are introduced without injury into the plant no tumor is formed. What this conditioning is, is unknown. At the site of the wound, a wound callus is first formed, as is usual after an injury. Later the tumor grows out of this callus. Wound callus and tumor can be readily distinguished from each other. This is because call divisions in cellus tissue are oriented periclinally, whereas in tumor tissue no orientation at all is to be found. 

Gordon G. Hammes. Enzyme Catalysis and Regulation. 1982 Gunter Kahl and Josef S. Schell (Editors). Molecular Biology of Plant Tumors. 1982... 

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