Bicarbonate inhibits Fe?stress response and Fe uptake?translocation of chlorosis?susceptible soybean cultivars

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Abstract
Effects of HCO‐ 3 on three chlorosis‐resistant (A2, Clark, Hawkeye) and three chlorosis‐susceptible (Anoka, Wayne, Hark) soybean cultivars (Glycine max (L.) Merr.) were tested to determine how HCO‐ 3 induces differential Fe‐chlorosis. Effects on regulation of Fe‐stress response were measured by conditioning the plants 8 days with low Fe and 0 or 10 mM HCO‐ 3 before a 24 hour assay of 59Fe uptake‐trans location from 20 μM 59feddhA; the assay solution contained CaCO3 but no added HCO‐ 3. Conditioning with added HCO‐ 3 caused increased 59Fe movement to shoots of resistant cultivars, but decreased it for susceptible cultivars. Direct effects of HCO‐ 3 on 59Fe uptake‐trans location were tested using plants conditioned with 0 Fe and 0 HCO‐ 3. Iron uptake (59Fe) assays were conducted for 72 hour with 0 and 10 mM HCO‐ 3 treatments. HCO‐ 3 reduced 59Fe movement to shoots to 31% of the control for resistant cultivars, and 17% for susceptible cultivars. Translocation of 59Fe (shoots & whole plant) was significantly lower in susceptible than resistant cultivars (roots rinsed, but not desorbed). Thus HCO‐ 3 reduces Fe‐stress response and Fe‐translocation in chlorosis‐susceptible soybean cultivars. However, HCO‐ 3 inhibition of Fe‐stress response was the major source of cultivar difference.