Inhibition of iron‐stress reactions in sunflower by bicarbonate

Abstract

In pot culture experiments using a calcareous soil the growth rate of sunflowers was depressed by latent iron deficiency. Iron‐stress reactions, reflected by enhanced uptake rate of Fe‐59 after short‐term supply of 59FeEDDHA were observed under these conditions. These reactions, however, were delayed and much less distinct than those observed under latent iron deficiency in water culture experiments. Addition of MgCO3 to this soil increased the iron deficiency of the plants and caused chlorosis, but prevented these iron‐stress reactions. In contrast to the soil experiments, distinct iron‐stress reactions could be observed with latent iron‐deficiency in sand culture experiments in which varied amounts of inorganic Fe‐III were supplied. These reactions were only observed, however, in absence of bicarbonate. Even 4 meq bicarbonate severely inhibited these iron‐stress reactions which were almost totally inhibited at 10 meq bicarbonate. Bicarbonate depressed both short‐term uptake of Fe‐59 as well as total iron content of the leaves. There was no evidence for an additional “inactivation” of iron within the leaves due to bicarbonate treatment. Bicarbonate also strongly depressed the manganese content of the young leaves. The results demonstrate that the regulatory mechanism of so‐called “iron‐efficient” plant species like sunflower under iron‐stress ‐ increase in H+ efflux and reducing capacity of the roots and thus enhanced uptake of iron (and manganese) ‐ is severely inhibited or even blocked by high bicarbonate concentrations. “Lime chlorosis”, caused by high bicarbonate concentrations on calcareous substrates is therefore also widespread in so‐called “iron‐efficient” species.

Influence of increasing bicarbonate concentrations on plant growth, organic acid accumulation in roots and iron uptake by barley, sorghum, and maize

“…It has been demonstrated previously by many authors that bicarbonate in the rooting medium decreases Fe accumulation in the shoots (Venkat Raju and Downloaded by [Northeastern University] at 03:46 08 January 2015 Marschner, 1981;Inskeep and Bloom, 1986). Our results fully confirm these findings (Table 1 ).…”

Effect of phosphate on regulation of Fe‐stress response in soybean and peanut

“…In view of these recent observations on a direct role of bicarbonate, further research is needed to characterize regulation of Fe-stressresponse. Much research has indicated an important role for bicarbonate in lime-induced chlorosis of dicotyledonous plants (Wadleigh and Brown, 1952;Porter and Thorne, 1955;Rutland and Bukovac, 1971;Boxma, 1972;Venkatraju and Marschner, 1981). Many aspects of Fe-stress-response were Illustrated in these screening experiments.…”

FeEDDHA-facilitated Fe uptake in relation to the behaviour of FeEDDHA components in the soil-plant system as a function of time and dosage

“…Elevated bicarbonate concentrations and high pH have been identified as the main soil conditions explaining the incidence of Fe chlorosis (Boxma 1972;Mengel et al 1984;Shi et al 1993). Under such conditions, the solubility of Fe(hydr)oxides is low (Lindsay 1979) and Fe uptake mechanisms become impaired (Marschner 1995;Venkatraju and Marschner 1981) or Fe becomes inactivated inside the leaf's apoplast (Mengel 1994).…”