Translocation of copper and other micronutrients in tomato plants (Lycopersicon esculentum Mill.): nicotianamine-stimulated copper transport in the xylem

Abstract

The influence of the endogenous micronutrient chelator, nicotianamine (NA), and of Cu nutrition on the distribution of Cu, Fe, Mn, Zn, and NA was investigated in eight different shoot organs, roots, and in xylem exudates of the NA-containing tomato wild type Lycopersicon esculentum Mill. cv. Bonner Beste and its NA-less mutant chloronerva. Contrary to the other heavy metals, copper transport in the xylem was inefficient in the mutant and was enhanced by an application of NA to the roots or leaves in proportion to the applied NA concentration. Also, with NA application, the Cu concentration in mutant roots decreased significantly, and increased in the shoot. Fe and Mn transport in the xylem was greater in the mutant than in the wild type, and was decreased in the mutant by the application of NA to the leaves. Zn transport in the xylem was the same in both genotypes and was unaffected by NA application. After application of NA to leaves and roots of the mutant it was possible to detect NA in the xylem exudate (up to 2nmol NA(g−1 root FWh−1). High Cu supply (3 μM) resulted in higher Cu and Mn concentrations in all organs of the wild type as compared to mutant organs, but Fe concentrations were not influenced. Under high Cu supply (3μM) the NA concentrations of roots and the three youngest leaves of the wild type were higher than under normal Cu supply (0.3 μM). The highest concentrations were found in the shoot apex under both Cu conditions (up to 361 nmol NAg−1 FW). It is concluded from our experiments and from the high stability constant of the NA-Cu-complex (log K= 18.6) that NA is involved in Cu translocation whereas for the translocation of Fe, Mn, and Zn, NA is not essential.