Factors Affecting the Distribution of Iron in Plants

Abstract

I. IntroductionThe influence of acid and alkaline reactions of the growth medium on iron relationships in plants has been known, or at least suspected, for over a century. The internal conditions of the plant in their relation to iron metabolism and chlorophyll production are not at all well understood. A number of investigations (22,23,20,18,16,14,10,3,1) have been carried out in which the general conclusion is that the reaction of the growth medium governs, to a large extent, the quantities of iron available to the plant. These observations are in keeping with the results obtained by PATTEN and MAINs (24). Working with HCl solutions containing definite concentrations of iron, they found that, beginning with a pH of 3.5, iron was precipitated in increasing amounts up to pH 6.0, above which point practically no iron remained in solution. This was accomplished by adding, in separate experiments, ammonium hydroxide, sodium hydroxide, and hydrogen sulphide to the hydrochloric acid solutions containing definite quantities of iron. The range of iron precipitation under these conditions thus extends from pH 3.5 as the lower limit to pH 6.0 as the upper limit.All of this work deals with the influence of the reaction of the growth medium on the availability of iron. Very little has been said regarding the possible influence of internal reactions on the availability and mobility of iron within the plant. Investigations (21,12,13,17) in which actual quantitative measurements were employed in determining iron in the plant tissues generally indicate that plants chlorotic from lack of available iron contain as much, or more, total iron per unit weight of tissue than do normal green plants of the same species. From this it follows that certain internal conditions may render unavailable to the chlorophyllous cells the iron already in the plant.INGALLS and SHIVE (15) found that not only does the H-ion concentration of plant tissue fluids fluctuate over a 24-hour day and night period, but that the soluble (filterable) iron content also fluctuates, and, in most cases, is directly proportional to the H-ion concentration of the respective tissue fluids. The pH of fleshy succulents fluctuates much more than does that of thin-leaved or non-succulent forms, the H-ion concentration in all

Mechanism of iron uptake by plants

“…The young lateral toots were the principal sites of Fe'* reduction in Fe-cfficient soybean (Ambler el at., 1971;Brown, 1972) and tomato , Reduction sites were detertnined hy transferritig Fe-stressed T3238fer (Fe-inefficient) and T3238FER (Fe-efficient) tomatoes to nutrient solutions containing FeHEDTA (Fe-hydroxyethylethylenediamlnetriacetic aeid) and K3Fe(CN)6 (Biown & Ambler, 1974), A blue precipitate, Prussian Blue, appeared in the epidermal areas of the T3238FFR root, but not in T3238fer root, where Fe^'^was reduced by the root (Fig, 6a), If the Fe-efficient roots were given Fe as FeHEDTA for 20 h, then taken out of the nutrient solutions, rinsed free of FeHEDTA, and plaeed in nutrient solutions containing Prussian Blue formed throughout the protoxylem of the young lateral roots up to the junction witli the metaxylem (Fig, 6b) (Ambler et at., 1971), Most of the Fe'* was reduced in areas of the root accessible to BPDS (bathophenanthrolinedisulfonate), a relatively strong chelator of Fe^* , This was established by adding BPDS to the nutrient solutions, 10% in excess of Fe'*, As the Fe'* was redticed, most of it was trapped in solution as Fe^*BPDS3 and was not transported to die plant top (Brown & Chaney, 1971), (4), Iron transported as iron citrate. Citric aeid chelates Fe and can keep it soluble in an external solution (Rogers & Shive, 1932), Citrate may function sitnilarly inside the plant. Iron-deficient plants usually cotitaln tnore citric and malic acids thati normal green plants (DeKock & Morrison, 1958;Iljin, 1951;1952), When Fe-defieiency stress was induced in plants by litniting the Fe supply, or when Zn, azide and arsenate were used to induce Fe stress (Brown & Tiffin, 1965;Brown & Chaney, 1971), a striking telationship existed between Fe and citrate transported in the xylem exudate (Fig, 7), When Fe increased, the citrate Increased; a decrease in Fe was paralleled by a decrease in citrate.…”

The Relationship Between Nickel Toxicity and Iron Supply

“…Thorne & Wallace (1944), however, consider that the total-iron content may be significant if measured on the basis of leaf area rather than of dry matter. Soluble fractions of the iron content appear to be of more value in determining iron availability ; the water-soluble iron content, for example, has been successfully used by Nicholas (1950), the iron content of the expressed sap by Rogers & Shive (1932), and the iron soluble in 0.5 N hydrochloric acid by Lindner & Harley (1944).…”

Iron Transport in Pea Plants

“…Attention has focused on chlorosis, which has frequently been ascribed to iron immobilization or inactivation rather than to iron deficiency (5,6,30,31,32). However, recent evidence shows a clear relationship between total iron content and chlorophyll content (2,20,21,29).…”