Costacurta A, Vanderleyden J
F.A. Janssens Laboratory of Genetics, KU Leuven, Heverlee, Belgium.
Crit Rev Microbiol. 1995;21(1):1-18. doi: 10.3109/10408419509113531.
The plant hormones, auxins and cytokinins, are involved in several stages of plant growth and development such as cell elongation, cell division, tissue differentiation, and apical dominance. The biosynthesis and the underlying mechanism of auxins and cytokinins action are subjects of intense investigation. Not only plants but also microorganisms can synthesize auxins and cytokinins. The role of phytohormone biosynthesis by microorganisms is not fully elucidated: in several cases of pathogenic fungi and bacteria these compounds are involved in pathogenesis on plants; auxin and cytokinin production may also be involved in root growth stimulation by beneficial bacteria and associative symbiosis. The genetic mechanism of auxin biosynthesis and regulation by Pseudomonas, Agrobacterium, Rhizobium, Bradyrhizobium, and Azospirillum, are well studied; in these bacteria several physiological effects have been correlated to the bacterial phytohormones biosynthesis. The pathogenic bacteria Pseudomonas and Agrobacterium produce indole-3-acetic acid via the indole-3-acetamide pathway, for which the genes are plasmid borne. However, they do possess also the indole-3-pyruvic acid pathway, which is chromosomally encoded. In addition, they have genes that can conjugate free auxins or hydrolyze conjugated forms of auxins and cytokinins. In Agrobacterium there are also several genes, located near the auxin and cytokinin biosynthetic genes, that are involved in the regulation of auxins and cytokinins sensibility of the transformed plant tissue. Symbiotic bacteria Rhizobium and Bradyrhizobium synthesize indole-3-acetic acid via indole-3-pyruvic acid; also the genetic determinants for the indole-3-acetamide pathway have been detected, but their activity has not been demonstrated. In the plant growth-promoting bacterium Azospirillum, as in Agrobacterium and Pseudomonas, both the indole-3-pyruvic acid and the indole-3-acetamide pathways are present, although in Azospirillum the indole-3-pyruvic acid pathway is of major significance. In addition, biochemical evidence for a tryptophan-independent indole-3-acetic acid pathway in Azospirillum has been presented.
植物激素生长素和细胞分裂素参与植物生长发育的多个阶段，如细胞伸长、细胞分裂、组织分化和顶端优势。生长素和细胞分裂素的生物合成及其作用的潜在机制是深入研究的课题。不仅植物，微生物也能合成生长素和细胞分裂素。微生物进行植物激素生物合成的作用尚未完全阐明：在一些致病真菌和细菌的情况下，这些化合物参与对植物的致病过程；生长素和细胞分裂素的产生也可能与有益细菌刺激根系生长及联合共生有关。假单胞菌、农杆菌、根瘤菌、慢生根瘤菌和固氮螺菌生长素生物合成和调控的遗传机制已得到充分研究；在这些细菌中，几种生理效应与细菌植物激素的生物合成相关。致病细菌假单胞菌和农杆菌通过吲哚 - 3 - 乙酰胺途径产生吲哚 - 3 - 乙酸，其相关基因位于质粒上。然而，它们也拥有由染色体编码的吲哚 - 3 - 丙酮酸途径。此外，它们具有能够结合游离生长素或水解生长素和细胞分裂素结合形式的基因。在农杆菌中，也有几个位于生长素和细胞分裂素生物合成基因附近的基因，参与调控转化植物组织对生长素和细胞分裂素的敏感性。共生细菌根瘤菌和慢生根瘤菌通过吲哚 - 3 - 丙酮酸合成吲哚 - 3 - 乙酸；也检测到了吲哚 - 3 - 乙酰胺途径的遗传决定因素，但其活性尚未得到证实。在促进植物生长的细菌固氮螺菌中，与农杆菌和假单胞菌一样，吲哚 - 3 - 丙酮酸途径和吲哚 - 3 - 乙酰胺途径都存在，尽管在固氮螺菌中吲哚 - 3 - 丙酮酸途径更为重要。此外，已有证据表明固氮螺菌中存在一条不依赖色氨酸的吲哚 - 3 - 乙酸途径。
