Absence of nicotianamine synthase activity in the tomato mutant 'chloronerva'

Nicotianamine is proposed to play a key role in iron (Fe) metabolism in plants. In graminaceous plants nicotianamine is the precursor for phytosiderophores, and the activity of the nicotianamine synthase is strongly enhanced under Fe deficiency. The tomato mutant 'chloronerva' (Lycopersicon esculentum Mill. cv. chloronerva) lacks nicotianamine and has a disturbed Fe homeostasis. Our objective was to compare nicotianamine synthase activity of the mutant 'chloronerva' with the wild form ('Bonner Beste'). In contrast to the wild form which as high nicotianamine synthase activity, no activity of the enzyme could be detected in roots or shoots of 'chloronerva', regardless of the iron nutritional status of the plants. This finding might allow comparison of promoter regions of the genes of 'chloronerva', 'Bonner Beste', and graminaceous species to clarify the regulatory mechanism of gene expression by the Fe nutritional status in graminaceous species.