Cracking up (IMAGE) John Innes Centre Caption Arabidopsis stem with weakened cell adhesion treated with an inhibitor of the growth hormone brassinosteroid, which slows epidermal growth, causing mechanical stresses and opening cracks as epidermal cells are pulled apart. Credit Rob Kesseler and Robert Bellow. Usage Restrictions No restrictions. License Public Domain 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.