Pham, Thi Danh Thom; (1992) Studies of alkaloid metabolism in papaver somniferum l. Doctoral thesis (Ph.D.), University College London.

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Abstract

Six P. somniferum L. cultivars were investigated for quantitative analysis of their alkaloid contents during plant development in the attempt to screen plants with high yields in noscapine and to determine what losses in alkaloid occurred as a result of harvesting the capsule plus 8" stem rather than the whole plant. High temperature sum and sunshine level resulted in high alkaloid content. Two minor alkaloids, oripavine and N- methylnarceine, were successfully isolated during the investigation. Feeding experiments showed tetrahydroberberine, hydrastine, and to a lesser extent berberine, improved noscapine yield. The latex contains a large number of acidic vacuoles in which the alkaloids are found. The vacuoles were separated into two discrete fractions: the 900xg and the 1100xg vacuoles. The two vacuolar populations were assayed over the three-week period of capsule maturation. The 900xg vacuoles contain most of the alkaloids, dopamine and the acids (meconate, sulphate and malate) of the latex. In addition, estimations of the cations K+, Na+, Mg2+, Ca2+ and Cl- were also made. Uptake by the latex vacuoles was specific for the native alkaloids. Both the 900xg and 1100xg vacuolar fractions take up morphine rapidly and effectively. Morphine uptake by the 1100xg vacuoles was more dependent on exogenous ATP and, after uptake of large amounts of alkaloids, both populations were stimulated by exogenous ATP to take up further amounts of alkaloid. Uptake of [35S]-sulphate and L-[U-14C]-malate was continuous and the rate of uptake was much lower than that of morphine and other alkaloids. A correlation between alkaloids and organic acids in the 900xg vacuoles supports the "ion- trap" mechanism proposed for alkaloid sequestration in the poppy latex vacuoles. The young vacuoles (1100xg fraction) which do not contain sufficient organic acids are more dependent on the ATPase- proton pump for the specific and rapid movement of native alkaloids across the vacuolar membrane.

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