Alkaloids as Growth Stimulators and Inhibitors

The best known example of an alkaloid which inhibits ceU division in plants is colchicine. Added in minute amounts, this alkaloid interferes with the formation of the cell carokinetic spindle instead of a division of the cell into two daughter cells, a restitutive cell is formed with a doubled set of chromosomes. The alkaloid, while very active on cells of most species of plants, produces no effects in Colchicum autumnale, the most common source of this compound. Alkaloids of Senecio and Crotalaria can cause chromosome breakage in a number of organisms, mostly animals, but are 

Compound d Surface in transverse section, mm Percent inhibition  

Additions to incubation medium Incubation medium Seed homogenate Incubation medium Seed homogenate  

In a preliminary experiment, it was shown that [7- C] nicotinic acid was significantly incorporated into both ricinine and N-demethylricinine during the first day of germination, which indicated that alkaloid biosynthesis is one of the earliest metabolic processes initiated with growth and differentiation in R. communis. 

Experiments performed on the nicotinic acid-ricinine relationship in sterile cultures of R, communis established clearly that (1) the relationship exists, and (2) the metabolism of ricinine can be spared by the presence of higher concentrations of nicotinic acid than normally found in the tissue (Waller and Nakazawa, 1963). This sparing action of nicotinic acid on ricinine utilization suggests a vitamin-alkaloid metabolic relationship not previously found in a plant system. 

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