Submitted to: Iron Nutrition and Interactions in Plants Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 7/1/1997
Publication Date: N/A
Interpretive Summary: Interpretive Summary not needed for this 115.
Technical Abstract: A kinetic analysis of Fe2+ and Zn2+ membrane transport into leaf cells was conducted using the argenteum mutant of pea (Pisum sativum L.). Leaf disks with the abaxial epidermis removed were vacuum-infiltrated in a pre-treatment solution containing 5 mM MES-TRIS (pH 5.0), 0.2 mM Ca SO4, 250 mM mannitol, and the same concentration of Fe2+ or Zn2+ as the subsequent uptake media. Uptake media contained 1 uCi of either 65Zn2+ or 59Fe2+ (59Fe3+ was reduced with sodium dithionite and was maintained as Fe2+ using ascorbate). Uptake was conducted for various time periods up to 40 min; disks were desorbed of apoplastic tracer using pre-treatment media containing 1 mM LaCl3. Uptake of Fe2+ and Zn2+ was linear for periods of 5 to 40 min. Concentration-dependent uptake of Fe2+ and Zn2+ demonstrated biphasic kinetics that could be separated into two components: a high affinity saturating system and a linear component. Lineweaver-Burke reciprocal analysis of the transformed data revealed that the high-affinit transporter for Fe2+ had a Vmax of 12 pmol Fe2+ mm-2 20 min-1 and a Km of 15 uM; this transporter was insensitive to metabolic inhibitors (CCCP and vanadate) and competing cations. The Vmax and Km of the Zn2+ high-affinity transporter were 15 pmol Zn2+ mm-2 20 min-1 and 41 uM, respectively; this transporter was sensitive to equimolar concentrations of Ni2+ or Cd2+. The linear transport component for each ion did not saturate up to 1 mM Fe2+ or Zn2+. Influx of both Fe2+ and Zn2+ (500 uM metal) was severely inhibited by La3+, but was insensitive to metabolic inhibitors (CCCP and vanadate). We conclude that Fe2+ and Zn2+ influx at low concentrations occurs via specific high-affinity carriers; at concentrations >100uM, influx for both ions may occur via the same system.