Iron becomes unavailable in pH conditions of 7.0 or more alkaline. Too much copper can interfere with iron uptake. Iron is required for chlorophyll synthesis. Iron is comparatively immobile in the plant, so deficiencies show up in the younger portions of the plant. Utilization of iron is dependent upon pH of nutrient and media and high pH or 7.0 will make iron unavailable.
Iron deficiency inhibits growth and development.
The deficiency shows up as chlorosis, or the loss of chlorophyll of younger tissues. Since both green and yellow pigments are effected, iron deficient leaves first go clear yellow and then white in color. Veins will also lighten in color. Leaves that developed before the deficiency remain green in color. So iron deficiency is common in alkaline soils or media conditions, and in alkaline waters.