REGULATION OF Fe DEFICIENCY RESPONSES IN WT PEA AND SOME OF ITS MUTANTS (BRZ AND DGL) - Pisum Sativum - page 9

experiments and found that enhanced ferric reductase activity was higher in
the brz /Sp combination than in the Sp/ brz one, which suggests that the brz
mutation is related to shoots. We think this needs further clarification. In
relation to the dgl mutation, Grusak and Pezeshgi [18] showed, by grafting dgl
onto its wild type DGV ( dgl /DGV), that the ferric reductase activity of the
grafted plants was up-regulated in relation to the DGV/DGV combination,
which suggests that the dgl mutation is related to shoots. The authors
explained the above results by suggesting that the dgl shoots transmit a signal
compound that acts as a promoter of Fe responses in the DGV roots [18].
Now, these results can also be explained by considering that the dgl mutant is
impaired in the movement of a Fe-related repressive signal from leaves to
roots through the phloem: when the dgl mutant is sprayed with Fe in its leaves,
the Fe responses are not repressed as occurred in the wt cultivar „Sparkle‟ [49].
In addition to the experiments trying to associate the brz and dgl mutations
with either roots or shoots, there are also some experimental results showing
that both mutants have alterations related, either directly or indirectly, to
ethylene, the plant hormone that plays a key role in the activation of Fe
Figure 1. Effects of the ethylene inhibitors Co (cobalt) and AOA (amino-oxyacetic
acid) on the expression of the Fe acquisition genes PsFRO1 and PsRIT1 and on the
ferric reductase activity (FRA) in roots of the pea brz and dgl mutants. Plants (16-d-
old) were grown in nutrient solution with 3 µM Fe-EDDHA. CoSO 4 (10 µM) or AOA
(20 µM) was applied to some of the plants during the last 24h. FRA and gene
expression were determined as in [5].