Iron acts as an essential cofactor for a range of cellular redox reactions involved in photosynthesis and respiration. Chloroplasts require iron for metabolic reactions including photosynthetic electron transport and chlorophyll biosynthesis. In mitochondria, iron is required for the synthesis of iron–sulphur clusters and for proper function of the respiratory electron transport chain. Iron deficiency can lead to chlorosis of younger leaves, which may in part be due to reduced chlorophyll synthesis.
From the high iron content of soils it is clear that any problems of iron deficiency in crops must be due to iron availability. Within the normal pH range of agricultural soils, it has been shown that the likely plant-available iron levels in soils are far below those required by plants. Soil conditions likely to inhibit root development and branching, such as waterlogging and soil compaction, will limit Fe uptake and increase the risk of Fe deficiency.
Given the importance of iron in chlorophyll biosynthesis, it is not surprising that plants which are deficient in iron are chlorotic. Chlorosis occurs in new leaves, whilst older leaves remain green. Iron deficient plants remain erect. In oilseed rape, symptoms of iron deficiency are similar to those symptoms of manganese and magnesium deficiency. However, in contrast to magnesium deficiency, where the plants first show symptoms in the older leaves, a lack of iron first appears on the young leaves. This is also true of manganese deficiency, which can make diagnosis difficult.