Role of shoot in regulation of iron deficiency responses in cucumber and bean plants

Abstract

Decapitation of the shoot apex or application to the stem of 2‐chloro‐9‐hydroxyfluorenecarboxylic acid‐(9)‐methylester (CFM), a synthetic inhibitor of polar IAA transport, prevented the increase of Fe³⁺ reductase activity in the roots of Fe deficient bean (Phaseolus vulgaris L., cv. American Supportor) plants. In Fe deficient cucumber (Cucumis sativus L., cv. Xintaimici) plants neither of these treatments inhibited the Fe efficiency response. In a split‐root experiment with cucumber plants, the root half growing in a medium without Fe did not show any Fe efficiency response in spite of very low Fe concentration in the roots. By contrast, in the other half of the roots growing in a medium with Fe supply, the Fe³⁺ reductase activity increased at an early stage of the treatment, although this was obviously a less marked response as compared with roots of Fe deficient plants. Fe concentrations in different parts of the shoot in split‐root cucumber plants were the same as that in control plants supplied with Fe. The results suggest that the shoot plays an important role in regulation of Fe³⁺ reductase activity in roots of Fe deficient plants, but the signal compound may be different in cucumber and bean plants.