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

Lithium (Li+) is known to disrupt the development of several different organisms, presumably through the inhibition of Li+-sensitive enzymes such as the 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 germinating tomato seedlings. It was found that an increase in cell size, termed hypertrophy, results from application of LiCl but not other tested salts. Hypertrophic growth was found to consist of greatly enlarged cells that originate from within the cortex of the seedling stem. Measurements of 44 elements within the hypertrophic tissue indicated that only Li+ accumulated in a pattern consistent with the observed alterations in stem growth. We found that in response to Li+, the IMP activity and levels of the three isoforms of IMP were down regulated. These results suggest that down regulation of IMP via Li+ is involved in the process of hypertrophic growth.