GROWTH AND CHEMICAL COMPOSITION OF ANANAS COMOSUS (L.) MERR., IN SOLUTION CULTURES WITH DIFFERENT IRON-MANGANESE RATIOS

Abstract

Pineapple plants grown in soln. cultures with different concns. of Fe (0.05, 0.5 and 5[mu] g.) and Mn (0.05, 0.5, 5 and 50 [mu]g.) in various combinations and supplied with equal amts. of all essential elements and N as nitrate or ammonium salts developed under the various conditions as follows: Most satisfactory growth, as measured by plant wts. was obtained in culture 7 with 0.5.[mu]g. of Fe and 5 [mu]g. of Mn. The cultures with 0.05 [mu]g. Fe and 0.05 [mu]g. Mn or with 0.05 [mu]g. Fe and 50 [mu]g. Mn produced smaller plant wts. presumably because of Fe and Mn deficiency for the former or Mn toxicity for the latter. The plants of cultures minus-Fe failed to produce fruits and most died. The concns. of both Fe and Mn increased in the tissues in proportion with the amts. in the nutrient soln. of the cultures supplied with nitrates. In the cultures supplied with ammonium similar concns. of Mn in the tissues were only half as great as those of the nitrate cultures, due presumably to antagonism between Mn++ and NHt. Iron concns. were greater in the tissues of the ammonium than of the nitrate cultures. Certain amts. of Fe and Mn in the leaf tissues were in combination with definite protein fractions; the amts. of protein increasing with Fe but decreasing with Mn. The tissues of the high-Mn cultures contained more Mg than of the low-Mn cultures; but other elements, such as K, Ca and P, were taken up from the nutrient soln. at approx. equal rates by high-Mn or low-Mn cultures. Sugars and starch were high in cultures with good growth and ample chlorophyll, but starch was not proportionally related to sugar in all cultures. In cultures suppled with Fe, ascorbic acid was higher in those with low-Mn than with high-Mn. But in the minus-Fe and high-Mn cultures ascorbic acid accumulated in the young leaves. This condition was explained as resulting from lower rates of utilization due to decreased rates of plant growth. The development of plant chlorosis from high Mn is explained by the hypothesis of biochemical antagonism of homologous substances, whereby Mn is presumably substituted for Fe in proto-porphyrin 9, the chlorophyll precursor, thereby inactivating the latter for subsequent conversion to chlorophyll.