Promotion and Inhibition of Iron Accumulation in Soybean Plants

Abstract

Plants of four soybean (Glycine max L. Merrill) genotypes differing in their ability to accumulate iron were studied. The efficient genotypes were Hawkeye (HA) and A62-9 (E-9), and the inefficient ones were PI-54619-5-1 (PI) and A62-10 (1-10). When plants of opposite efficiency were grown in the same solution, iron accumulation decreased in the primary leaves of efficient plants, but it was unaffected or slightly reduced in the leaves of inefficient plants.Absorption of iron during a 24-hour period by 17-day-old plants indicated that solutions in which either HA or PI plants had been previously cultured contained a heat-labile factor which increased iron accumulation by iron-stressed HA plants. Also, it was found that HA plants from mixed culture accumulated about 50% less iron than HA plants grown in pure culture, independent of the absorption solution used. The conditions described, therefore, may either stimulate or inhibit iron accumulation in efficient soybean plants.The superior ability of efficient soybean genotypes to accumulate iron has been attributed to the greater reducing capacity of their roots than that of inefficient genotypes (4, 5). Inhibitory factors may also be involved, since it has been shown (6, 7) that iron accumulation by HA plants was reduced when these plants were grown in mixed culture with PI plants. Also, certain compounds indigenous to plant cells-i.e., citrate, riboflavin 5-phosphate, and glycine-inhibit iron accumulation by HA plants (7).The purpose of this investigation was to study iron accumulation by soybean plants grown alone and in mixed culture and to evaluate the influence of nutrient solution composition and mixed culture on iron accumulation by iron-stressed plants. MATERALIS AND METHODSTwo efficient soybean genotypes-Hawkeye (HA) and E62-9 (E-9)-and two inefficient genotypes-PI-54619-5-1 (PI) and A62-10 (1-10)-were grown in a growth chamber as described previously (6). Seeds of the four genotypes were allowed to germinate in a plastic tray of distilled water. After 4 lays seedlings with protruding radicles were selected and transferred to a perforated Plexiglass disk suspended over aerated nutrient solu- tion containing all essential elements except iron. Freshly prepared nutrient solution used for culturing plants had the following composition in millimoles per liter: Ca(N03)2.4H20, 0.63; Mg(NO3)2.6H20, 0.14; K21HPO4, 0.22; NH4NO3, 0.11; KNO3, 0.03; (NH4)ZS04, 0.07, and in ymoles per liter: MnCl2.4H20, 1.18; ZnSO4.7H20, 0.31; CuS04-5H20, 0.08; H3B03, 3.29; Na2MoO4.2H20, 0.05. In all instances the pH of the nutrient solution decreased from initial values of about 7.5 to about 4.2 during the 7-day absorption period (6).To study the effect of one genotype on iron absorption by the other, plants were grown in mixed culture for a 7-day absorption period in freshly prepared nutrient solutions containing 1.1, 5.6, or 11.1 /LM chelated iron (FeEDDHA) labeled with 2.22 lc of 59Fe per liter. In all instances 16 plants were grown in 9 liters of solution. One mixed cultur...

The Effect of Micro‐organisms on the Absorption of Manganese by Plants

“…Interest also attaches to the results of Engstrom and Howard (1970) who, in experiments carried out under non-sterile conditions, showed that the absorption of iron by soybean plants deficient in that element, was stimulated by transferring them to culture solution in which iron sufficient plants had previously been grown. None the less, the present results appear to conflict with those of Bromfield (1958) who grew oats under sterile and non-sterile conditions enclosed in boiling tubes with manganese supplied as the sulphate, a microbiologically produced oxide or a chemically prepared yMNOj.…”