Root Growth (image) University of Helsinki Caption Cell division in the root meristem is maintained by PLETHORA transcription factors solely transcribed in the stem cells. Outside the stem cells the amount of PLETHORA protein in the cells halves each time the cells divide. In the end there is so little PLETHORA left in the cells that they cannot stay in the dividing mode and start to elongate and differentiate. Credit Ari Pekka Mähönen group, Institute of Biotechnology Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.