Iron fractions in the apoplast of intact root tips of Zea mays L. seedlings affected by nitrogen form

The effects of ammonium (NH ₄ ⁺ -N) and nitrate (NO ₃ ⁻ -N) were examined on Fe fractions and FeCN (ferricyanide) reductase activity in intact root tips (0–3 cm) of young maize (Zea mays L. cv. Lenz) in solution culture by using short-term experiment under controlled Fe deficiency conditions (containing high HCO ₃ ⁻ concentration in preculture solution). The results showed that Fe(II) concentrations in root tip apoplast of maize were only 20–40 nmol/g FW which accounted for 7%–13% of total Fe. Most of Fe in root tips existed as Fe(III) compounds. Imposition of the roots to NH ₄ ^±N or NO ₃ ^−N for 60 min led to an increase of Fe(II) in root tip apoplast. NH ₄ ^±N led to an increased concentration of Fe(II) and exchangeable Fe (Fe(II) and Fe (III)) in root tips, while NO ₃ ⁻ -N increased FeCN reductase activity. The relationship between pH and Fe fractions, FeCN reductase activity was also discussed.