Li+ induces hypertrophy and down regulation of myo-inositol monophosphatase in tomato

Lithium (Li+) is known to disrupt the development of several different orga nisms, presumably through the inhibition of Li+-sensitive enzymes such as t he myo-inositol monophosphatase (IMP) enzyme. In animal cells, decreases in IMP activity result in down regulation of phosphatidylinositol signaling, which can alter development. We characterized the effects of Li+ on germina ting tomato seedlings. It was found that an increase in cell size, termed h ypertrophy, results from application of LiCl but not other tested salts. Hy pertrophic growth was found to consist of greatly enlarged cells that origi nate from within the cortex of the seedling stem. Measurements of 44 elemen ts within the hypertrophic tissue indicated that only Li+ accumulated in a pattern consistent with the observed alterations in stem growth. We found t hat in response to Li+, the IMP activity and levels of the three isoforms o f IMP were down regulated. These results suggest that down regulation of IM P via Li+ is involved in the process of hypertrophic growth.