Researchers Shed Light on Mechanism of Plant Root Growth

An international team of researchers, led by scientists at the University of Nottingham in the UK, has shed light on the molecular underpinnings of root growth by focusing on the phytohormone gibberellin. Plant growth is driven by two factors: cell proliferation and elongation. Gibberellin (GA) has been shown to play a linchpin role in controlling root cell elongation in the model plant Arabidopsis, but it has been unknown whether the hormone also controls root cell proliferation.

The researchers, led by Susana Ubeda-Tomás, in a paper published by Current Biology described for the first time how GA regulates the number of cells in the root in order to control root growth. GA signals the degradation of proteins DELLA, GAI and RGA, which suppress growth. Plants in which the meristems (undifferentiated cells) were made to express a mutant version of the growth-repressing protein GAI showed disrupted cell proliferation. The mutant version of this protein, gai, is not degraded by gibberellin. The scientists found that expressing gai in only one tissue, the endodermis, was sufficient to stop the meristem enlarging.

Malcolm Bennett, co-author of the paper, noted: "We have shown that gibberellin plays a crucial role in controlling the size of the root meristem, and that it is the endodermis which sets the pace for expansion rates in the other tissues."

The paper published by Current Biology is available at http://dx.doi.org/10.1016/j.cub.2009.06.023 For more information, read http://communications.nottingham.ac.uk/News/Article/Hormone-clue-to-root-growth.html