Iron in the Leaves and Chloroplasts of Some Plants in Relation to Their Chlorophyll Content.

That lime-induced chlorosis can be alleviated by the application of iron salts has been recognized for a hundred years. As early as 1845, GRIS (8) treated chlorotic plants with iron and obtained positive results; his experiments have been repeatedly confirmed. Opinions differ widely, however, as to the comparative amount and state of iron in chlorotic leaves. Various investigators have presented evidence indicating that more, the same, or less iron is present in chlorotic than in green leaves. Those who have reported the first two conditions have, in general, explained chlorosis as an immobilization or inactivation of iron which occurs mainly, or at least to a greater extent, in chlorotic leaves than in green ones. Of the more recent workers, WALLACE (20) and VIDAL (19) found no relation between total iron and chlorophyll content in lime-induced chlorosis, but GILE and CARRERO (5) and CHAPMAN (2) did. OLSEN (13) was unable to relate total iron to chlorophyll content in plants grown in iron-deficient culture solution whereas SCHOLZ was able to find such a relationship. Both MOORE (12) and GRIESSMEYER (7) demonstrated the qualitative presence of iron in chloroplasts by employing staining reactions. LEIBICH (10) found up to 82 per cent. of the leaf iron in the chloroplasts of spinach. HIL and LEHMANN (9) found the isolated chloroplasts of Claytonia to contain four times as much iron as would be expected were the iron equally distributed throughout the leaf. That the iron in the leaf is not all in the same chemical combination and does not all perform the same function seems indicated by the necessity of iron for non-green plants and the presence of iron containing enzymes in all plants. Hence it is probable that only a fraction of the leaf iron is closely related to chlorophyll formation. Although PARSCHE. (15) found only a poor correlation between total iron and chlorophyll, he did find that the water soluble (filterable) iron was, as a rule, higher in green leaves. OSERKOWSKY (14), working with pear, apricot, and peach leaves, developed a method for determining a fraction of iron which was proportional to the chlorophyll content. His method consisted of extracting the dried leaf material with 1.0N hydrochloric acid. He then plotted this acid-soluble iron against the chlorophyll content and obtained a straight line which, when extrapolated, intersected the iron axis at some point other than the origin. The difference beween the iron axis intercept and the acid-soluble iron for a given sample represented the amount of iron directly proportional to the chlorophyll. OSERKOWSKY called this "active iron" by which he 233