Differential response of dicotyledonous plants to potassium‐deficiency stress: Iron‐stress response mechanism

Abstract

Iron‐efficient tomato and soybean, when subjected to Fe‐deficiency stress, required K before the Fe‐stress response mechanism would function, ie, would (a) release H ions and reductants from their roots and (b) reduce Fe³⁺ to Fe²⁺ in their roots. In previous studies with tomato and soybean, H ion release ceased after Fe was made available to the plant. Muskmelon differed from tomatoes and soybeans in that H ion release was sustained even after Fe was made available. This study was conducted to determine if muskmelon also differs from soybean and tomato plants in its Fe‐K relationship. Muskmelon was grown in hydroponic solutions at varying levels of K in combination with low or no Fe and also in various combinations of Na or Rb (as substitutes for K). Hydrogen ion release and reduction of Fe³⁺ at the roots as well as chlorosis ratings and leaf Fe concentrations were determined. Potassium‐deficiency stress did not prevent hydrogen ion release by muskmelon roots as had been previously observed in tomato and soybean. Adequate levels of K were, however, essential to maximizing the reduction of Fe³⁺ to Fe²⁺ at the root. Hydrogen ion release was enough of a response to maintain leaf Fe above 50 μg/g even when Fe³⁺ reduction was low without solution K. Neither Na nor Rb substituted for K in enhancing Fe³⁺ reduction in muskmelon. Potassium does appear to have a specific role in the Fe‐stress response mechanism of dicotyledonous plants when subjected to Fe‐deficiency stress. Muskmelon could potentially serve in future studies directed toward defining the genetic differences in dicotyledenous species.