Remedying the iron-deficient maize plants grown at lower than the optimal temperature and irradiance by new synthetic macromolecular iron-chelating agents

The efficacy of Fe3+ complexes of polyethers having chelating terminal 8-quinolinol (8QOH) residues for remedying the iron-deficient maize plants at temperatures of 20/16°C and photosynthetic photon flux density (PPFD) 500-600 μmol m-2 s-1 was evaluated by their effect on the fresh and dry weight, pigment content (total chlorophyll and carotenoids), chlorophyll fluorescence, and photosynthetic activity of maize plants. In order to estimate the effect of the oligomer nature of the polyethers with 8QOH group attached to the oxyethylene chain at different positions of aromatic ring, tests on chlorotic plants were also performed with Fe3+ complexes of low-molecular-weight ligand 8QOH, and mixtures of commercial polyethers with isopropylamino end-groups (Jeffamines ED) and 8QOH (Jeff/8QOH). The efficacy of Fe3+ chelates of synthetic chelator ethylenediaminetetraacetic acid and FeCl3 · 6H2O for remedying the chlorotic maize plants under the same conditions was also tested. At temperatures of 20/16 °C and PPFD 500-600 1J.mol m-2 s-1 , the Fe3+ chelates of polymers with 8QOH groups attached at 5-position were the most effective for remedying the iron-deficient maize plants compared to the other tested Fe3+ complexes. It was found that the plant remedy process was sensitive to lowering of the temperature and PPFD. The remedy of chlorotic maize plants supplied with investigated Fe3+ complexes at 20/16 °C (day/night) and PPFD 500-600 μmol m-2 s-1 retarded 4-fold compared to that observed at 30/25 °C and PPFD 1100-1300 μmol m-2 s-1. We concluded that the longer period for remedying the iron-deficient maize plants at lower than the optimal temperature and PPFD is probably due to the fact that, under these conditions, the amount of DMA released from roots is several times lower, and the efficiency of the high-affinity system for uptake of Fe3+-PS is decreased as compared to that at optimal temperature and PPFD.