Organic acid synthesis and release of hydrogen ions in response to Fe deficiency stress of mono‐ and dicotyledonous plant species

Abstract

Abstract Comparing three mono‐ and dicotyledonous plant species (barley, oat, millet; pea, sugar beet, bean) it will be shown that under Fe stress conditions monocots do not lower the pH of the nutrient solution if nitrate is the only form of nitrogen supplied, whereas dicots do. During the iron stress‐induced H+ excretion there is a striking increase in organic acids (particularly citrate and malate) in the roots of dicots. Therefore, it is proposed that these acids could be the source of hydrogen ions released by the roots. When severe chlorosis has developed the organic acid content of the monocots is raised too, but without any drop of the nutrient solution pH. The results are discussed in relation to a possible involvement of growth regulators and differences between the NO3 assimilation rate in roots of mono‐ and dicotyledonous plant species.