Iron Localization in Pea Plants

Abstract

Iron chlorosis has often been ascribed to iron inactivation, immobilization, or precipitation within the plant (6, 7, 14, 18, 20). This argument has rested on the assumption that there is no correlation between the chlorophyll content and the iron content of chlorotic plants. Since more recent findings do not support this assumption (1, 11, 12, 13), it is difficult to assess suggestions that chlorosis is the result of iron precipitation in xylem elements (14, 18), nodes (10), high-pH tissue such as phloem or bundle sheaths (20), or translocating tissues in general (7,9, 19). If the total iron content of a leaf is related to its chlorophyll content, there is no reason to claim localized regions of high iron represent precipitation or inactivation. Before ascribing chlorosis to iron immobilization, more should be known about some fundamental aspects of its transport and distribution in normal, green plants. A previous study (5) described some of the factors governing iron transport. As a continuation of that study, the localization of absorbed iron was examined by various radioautographic techniques, some of which permitted cellular localization of soluble as well as insoluble iron. These radioautographic results are presented here. While corroborating previous evidence showing the metabolic involvement of root cells in iron transport (5), the radioautographic results shed new light on the cellular distribution of iron in non-chlorotic plants.