Sensing Iron—A Whole Plant Approach

Abstract

Regulatory mechanisms leading to cellular Fe homeostasis were investigated inPlantago (Plantago lanceolata L.) plants grown hydroponically at different temperature regimes either in the presence or absence of iron. During the experimental period of 6d, growth was not affected by Fe availability, but was decreased by lowering the root zone temperature (RZT) from 24 to 12°C. Cultivating plants at low RZT decreased the reduction activity for ferric chelates in Fe-deficient plants. In the presence of iron, the temperature regime did not affect Fe accumulation by root cells, but decreased translocation of Fe to the shoot, and chlorosis of young leaves was observed at suboptimal RZT. Under these conditions root-mediated reduction of ferric chelates was increased. In cold-treated plants this effect was specific to Fe and could not be evoked by Mn2+and Zn+2additions. Supplementing the medium with the ferrous scavenger ferrozine caused a further enhancement in reduction rates, probably due to mobilization of apoplastic Fe. These results can be explained plausibly if different sites of Fe sensing are postulated and if it is assumed that both the absence and presence of iron could be a signal increasing root reduction activity.