Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 23, 1995
Publication Date: N/A
Interpretive Summary: This research was conducted to determine the effect of soil acidity (pH) on growth, development and alkaloid content of two cultivated Erythroxylum species (Erythroxylum coca and Erythroxylum novo. novogranatense) from which cocaine is extracted. A naturally acidic (pH 4.7) Maryland soil was adjusted to provide 7 pH levels which ranged from 3.5 through 7.0. Optimal growth for E. coca occurred at pH 3.5, and for E. novo. novogranatense at pH 4.7 through 6.0. The pH extreme for E. coca was 6.5 and for E. novo. novogranatense 3.5 and 6.5. Cocaine content in leaves of E. coca from pH 3.5 through 6.0 was independent of biomass accumulation. Leaves of E. coca grown in soil at pH 3.5 through 6.0 had higher concentrations of cocaine than those of E. novo. novogranatense. Other alkaloids were lower in concentration. Leaves of E. novo. novograna-tense grown at soil pH 4.7 through 6.0, contained more trans- and cis-cinnamoylcocaine than those of E. coca; however, methyl ecgonine was the most abundant alkaloid. The results of the current study are important to plant and soil scientists conducting research on plant-soil inter-actions at low pH, the pharmaceutical industry, medicinal plant researchers, food and flavor industry, Drug Enforcement Agency, Food and Drug Agency, National Institutes of Health, CNC and CIA, in that it showed how soil pH levels influenced and/or affected plant dry weight and alkaloid buildup in two cultivated species of Erythroxylum, and classified the species in terms of their growth and development in pH soils where E. coca was aluminum tolerant and E. novo. novogranatense iron efficient.
Technical Abstract: In the current study Erythroxylum coca var. coca Lam. (E. coca) and Erythroxylum novogranatense var. novogranatense (Morris) Hieron (E. novo. novogranatense) were grown in greenhouse pots of Monmouth soil (clayey, mixed mesic, typic Hapludult, original pH 4.7) over a pH range of 3.5 through 7.0, to determine patterns for biomass accumulation and alkaloid content in leaves. Optimal growth for E. coca occurred at pH 3.5, and for E. novo. novogranatense at pH 4.7 through 6.0. The pH extreme (sub-optimal biomass accumulation, above and below optimal pH) for E. coca was 6.5 and for E. novo. novogranatense </= 3.5 and >/= 6.5. Hence, E. coca is termed a calcifuge (Al-tolerant) while E. novo. novogranatense, a calcicole (Fe-efficient). Increases in leaf alkaloid content observed at the pH extremes for E. coca and E. novo. novogranatense appeared to be caused by plant stress. E. novo. novogranatense was more tolerant to the high pH extreme than E. coca. Concentration of cocaine by E. coca was independent of biomass accumulation. Leaves of E. coca grown in soil at pH 3.5 through 6.0 had higher concentrations of cocaine than those of E. novo. novogranatense. Conversely, leaves of E. novo. novogranatense contained more trans- and cis-cinnamoyl-cocaine and methyl ecgonine than those of E. coca. The least abundant alkaloid observed in E. coca and E. novo. novogranatense was tropinone (low or non-detectable). Of the eight alkaloids monitored in leaves of E. novo. novogranatense grown in soils at the various pH levels, methyl ecgonine was the most abundant.