PLANT PHYSIOLOGY , Vol 111, Issue 3 747-753, Copyright © 1996 by American Society of Plant Biologists
|
BIOCHEMISTRY AND ENZYMOLOGY |
Biosynthesis of Caffeine in Leaves of Coffee
H. Ashihara, A. M. Monteiro, F. M. Gillies and A. Crozier
Department of Biology, Faculty of Science, Ochanomizu University, Otsuka, Bunkyo-ku, Tokyo 112, Japan (H.A.)
The levels of endogenous caffeine and theobromine were much higher in buds
and young leaves of Coffea arabica L. cv Kent than in fully developed
leaves. Biosynthesis of caffeine from 14C-labeled adenine, guanine,
xanthosine, and theobromine was observed, whereas other studies (H.
Ashihara, A.M. Monteiro, T. Moritz, F.M. Gillies, A. Crozier [1996] Planta
198: 334-339) have indicated that there is no detectable incorporation of
label into caffeine when theophylline and xanthine are used as substrates
for in vivo feeds with leaves of C. arabica. The capacity for caffeine
biosynthesis, especially from guanine and xanthosine, was reduced markedly
in both fully developed mature and aged leaves. Data obtained in
pulse-chase experiments with young leaves indicate the operation of an AMP
-> IMP -> xanthosine 5[prime]-monophosphate (or GMP -> guanosine)
-> xanthosine -> 7-methylxanthosine -> 7-methylxanthine ->
theobromine -> caffeine pathway. The data obtained provide strong
evidence against proposals by G.M. Nazario and C.J. Lovatt ([1993] Plant
Physiol 103: 1203-1210) concerning the independence of caffeine and
theobromine biosynthesis pathways and the role of xanthine as a key
intermediate in caffeine biosynthesis.
