Investigations on the growth and metabolism of cultured explants of Daucus carota : II. Effects of iron, molybdenum and manganese on metabolism.

Knowing that the element Fe essentially triggers the action of the coconut milk stimulus for the growth of carrot explants and thereafter interacts with added Mo and Mn, the effects of these trace elements on growth (fresh and dry weight) and metabolism of both nitrogenous and nitrogen-free metabolites have been determined. An outstanding effect of Fe is to determine the level of protein synthesized, and the combination of Mo with Fe increases both protein and the content of non-protein nitrogen compounds. The role of Mn seems to reside in the mobilization of the soluble (non-protein) nitrogen compounds but its effects, which tend to compete with Fe in combination with Mo, tend to divert these compounds from protein synthesis. The element Fe appears again as a key element which determines the linkage between the use of carbon from carbohydrate and its entry into nitrogen metabolism: this has been shown by the use of (14)C-fructose as the source. Whereas Fe promotes the use of (14)C from fructose and directs it into protein, neither Mo nor Mn could achieve this either separately or in combination. The paper presents both the individual effects due to the trace elements and their interactions when supplied in combination. Stress is laid upon the need to consider the effects which are due to the inorganic elements in combination with the componenents of such growth-promoting systems as those present in coconut milk. These interactions are illustrated by polygonal diagrams (Figs. 3, 4 and 5). The point is made that any of several single entities of such an interacting complex may be in a given case rendered limiting, and the consequences of this fact for the concept of kinins or cell division factors are outlined. Any concept that requires cell division to be mediated solely by a given kind of chemical substance, or cell-division factor, would on the evidence here given present problems.