Hormone Clue To Root Growth

Now an international group of scientists, led by the Centre for Plant Integrative Biology at The University of Nottingham, has shed light on how a plant hormone is crucial in controlling the growth of plant roots.

Plant growth is driven by an increase in two factors: the number of cells, and their size. It is already known that the plant hormone gibberellin controls how root cells elongate as the root grows in the model plant Arabidopsis thaliana. Now a paper appearing in Current Biology describes for first time how this hormone also regulates the number of cells in the root in order to control root growth.

Gibberellin normally acts by signaling the removal of proteins which repress growth, and so promotes root cell production. The new research shows that mutant plants that do not produce gibberellin are unable to increase their cell production rate and the size of the root meristem, the zone of cell proliferation.

Plants in which the cells in the meristem were made to express a mutant version of the growth-repressing protein GAI not degraded by gibberellin showed disrupted cell proliferation. Expressing this mutant form, gai, in only one tissue, the endodermis (the innermost layer of the root cortex of a plant), was sufficient to stop the meristem enlarging. In effect, the rate of expansion of dividing endodermal cells dictates the equivalent rate in other tissues.

This research was headed by Dr Susana Ubeda-Tomás and Professor Malcolm Bennett of the Centre for Plant Integrative Biology, in collaboration with scientists in Nottingham, Cambridge, Edinburgh, Spain, Belgium and Sweden.

Professor Malcolm Bennett, Biology Director for the Centre for Plant Integrative Biology and Professor of Plant Sciences in the Division of Plant and Crop Sciences, said: “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.

“Understanding precisely how hormones regulate plant growth is one of the key areas of fundamental plant biology which will underpin crop improvements in the future.”