Comparison between tumors in plants and human beings: Mechanisms of tumor development and therapy with secondary plant metabolites.

Background: Human tumors are still a major threat to human health and plant tumors negatively affect agricultural yields. Both areas of research are developing largely independent of each other. Treatment of both plant and human tumors remains unsatisfactory and novel therapy options are urgently needed.

Generation and possible roles of NO in plant roots and their apoplastic space.

In recent years, three different enzymatic pathways and a few non-enzymatic reactions have been proposed for the generation of NO in plant roots. Two of the enzymatic pathways are located in the cytosol of the plant cells, whereas the third is exclusively located in the root plasma membrane facing the apoplast from where it seems to interact with nitrate metabolism by producing signals. A response of the NO pathways to external nitrate concentrations by preventing excess nitrate nutrition, particularly in the apoplast, as well as a regulatory role in root morphogenesis of NO in interaction with plant hormones is suggested.