|Grusak, Michael - Mike|
Submitted to: Plant Physiology Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 7/1/1997
Publication Date: N/A
Citation: Interpretive Summary: Interpretive Summary not needed for this 115.
Technical Abstract: To better understand how micronutrient metals are processed in and remobilized from leaves we examined the membrane transport kinetics of Fe(II), Zn and Mn into leaf mesophyll cells of the argenteum mutant of pea, using radiolabels. The epidermis of this mutant is loosely attached, thus removal of the epidermis allows access to undamaged cells. Vacuum- infiltrated pre-treated leaf disks were labeled using 5-1000 uM metal, followed by desorption with 1 mM LaCl3. Uptake of Fe(II)(in the presence of ascorbate), Zn and Mn was linear between 5 and 40 min. Concentration dependent uptake for Fe(II) and Zn showed two uptake systems - a high and a low affinity system. Lineweaver-Burke analysis revealed the high-affinity transporter for Fe(II) had a Vmax of 0.6 pmol Fe(II) mm-2 min-1 and a Km of 15 uM whereas the transporter for Zn had a Vmax of 0.75 pmol Zn mm-2 min-1 and a Km of 41 uM; both were relatively insensitive to metabolic inhibitors sand competing cations. The transporter is suggested to be a highly specifi carrier for each cation. The low affinity system did not saturate up to 1000 uM Fe(II) or Zn. Uptake through this system was inhibited by La, moderately sensitive to inhibitors of metabolism, but insensitive to blockers of Ca- and K-channels. We suggest low affinity uptake is via a channel; further work will show the type and specificity of the channel involved. Mn influx showed saturating kinetics. Saturation occurred at approximately 500 uM Mn and transport was inhibited by Ca-channel blockers. Uptake was sensitive to the presence of Cd, Co and Ni. Mn uptake is suggested to occur via an L-type Ca-channel, rather than a specific transporter for Mn. This research was funded in part by USDA-ARS Coop. Agr. No. 58-6250-1-003 and NSF Grant No. IBN-9630341 to M.A.G.