Potassium effect on iron stress in tomato. I. The effect on pH, Fe‐reductase and chlorophyll

Seedlings of Fe‐efficient tomato plants were cultured in nutrient solutions with two concentrations of Fe and K. The pH of the nutrient solution increased initially in all treatments. A subsequent drop in pH of the nutrient solution to 4.4 occurred only in the low Fe, normal K treatment. Ferric iron reduction by root samples was markedly increased only in those producing a decrease in pH of nutrient solution. Most “Fe‐reductant” was released from the swollen elongation zones of young roots. Chlorophyll content in young leaves (after a pH Fe‐stress response) was greater with normal K versus low K for both normal and low iron treatments. Iron‐stressed plants accumulated more K/g dry weight, especially in the roots, than with normal Fe supply.