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The two most important growth hormones of plants, so far considered antagonists, also work synergistically. The activities of auxin and cytokinin, key molecules for plant growth and the formation of organs, such as leaves and buds, are in fact more closely interwoven than previously assumed. Scientists from Heidelberg, Tbingen (Germany) and Umea (Sweden) made this surprising discovery in a series of complex experiments using thale cress (Arabidopsis thaliana), a biological reference organism. The international team of researchers, led by Jan Lohmann, stem cell biologist at Heidelberg University, have now published their results in the scientific journal "Nature". (Nature, 24. Juni 2010)
All the above-ground parts of a plant leaves, buds, stems and seeds ultimately arise from a small tissue at the shoot tip, which contains totipotent stem cells. Since plant stem cells remain active over the entire life of the organism, plants, unlike animals, are able to grow and develop new organs over many decades. On the periphery of the tip, auxin triggers cells to leave the pool of stem cells, differentiate and form organs like leaves and buds. Cytokinin stimulates stem cells to divide and proliferate; it maintains the number of cells and thus the plant's growth potential.
Some of the genetic factors involved in cytokinin's effect on plant growth were already known. In the thale cress experiments, which concentrated on the growth zone at the tip of the shoot, Lohmann and his team now studied the role of auxin in the interplay of the two hormones. It turns out that auxin directly interferes with a feedback loop involving two genes activated by cytokinin ARR7 and ARR15 which limit the effect of cytokinin. Auxin suppresses these two genes, thereby boosting the effect of cytokinin.'/>"/>
|Contact: Jan Lohmann|