Effects of Exogenous Gibberellic Acid(3) on Iron and Manganese Plaque Amounts and Iron and Manganese Uptake in Rice

Gibberellins (GA) regulate various components of plant development. Iron and Mn plaque result from oxiding and hydroxiding Fe and Mn, respectively, on the roots of aquatic plant species such as rice (Oryza sativa L.). In this study, we found that exogenous gibberellic acid(3) (GA(3)) spray decreased Fe plaque, but increased Mn plaque, with applications of Kimura B nutrient solution. Similar effects from GA(3), leading to reduced Fe plaque and increased Mn plaque, were also found by scanning electron microscopy and energy dispersive X-ray spectrometric microanalysis. Reduced Fe plaque was observed after applying GA(3) to the groups containing added Fe2+ (17 and 42 mg center dot L-1) and an increasing trend was detected in Mn plaques of the Mn2+ (34 and 84 mg center dot L-1) added treatments. In contrast, an inhibitor of GA(3), uniconazole, reversed the effects of GA(3). The uptake of Fe or Mn in rice plants was enhanced after GA(3) application and Fe or Mn plaque production. Strong synergetic effects of GA(3) application on Fe plaque production were detected. However, no synergetic effects on Mn plaque production were detected.