SHOOT-TO-ROOT SIGNAL TRANSMISSION REGULATES ROOT FE(III) REDUCTASE-ACTIVITY IN THE DGL MUTANT OF PEA

To understand the root, shoot, and Fe-nutritional factors that regulat e root Fe-acquisition processes in dicotyledonous plants, Fe(III) redu ction and net proton efflux were quantified in root systems of an Fe-h yperaccumulating mutant (dgl) and a parental (cv Dippes Gelbe Viktoria [DGV]) genotype of pea (Pisum sativum). Plants were grown with (+Fe t reated) or without (-Fe treated) added III)-N,N'-ethylenebis[2-(2-hydr oxyphenyl)-glycine] (2 mu M); root Fe(III) reduction was measured in s olutions containing growth nutrients, 0.1 mM Fe(III)-ethylenediaminete traacetic acid, and 0.1 mM Na-2-bathophenanthrolinedisulfonic acid. Da ily measurements of Fe(III) reduction (d 10-20) revealed initially low rates in +Fe-treated and -Fe-treated dgl, followed by a nearly 5-fold stimulation in rates by d 15 for both growth types. In DGV, root Fe(I II) reductase activity increased only minimally by d 20 in +Fe-treated plants and about 3-fold in -Fe-treated plants, beginning on d 15. Net proton efflux was enhanced in roots of -Fe-treated DGV and both dgl g rowth types, relative to +Fe-treated DGV. In dgl the enhanced proton e fflux occurred prior to the increase in root Fe(III) reductase activit y. Reductase studies using plants with reciprocal shoot:root grafts de monstrated that shoot expression of the dgl gene leads to the generati on of a transmissible signal that enhances Fe(III) reductase activity in roots. The dgl gene product may alter or interfere with a normal co mponent of a signal transduction mechanism regulating re homeostasis i n plants.