Plant Physiol, February 2001, Vol. 125, pp. 1094-1102
Subcellular Compartmentation of the Diterpene Carnosic Acid and
Its Derivatives in the Leaves of Rosemary1
Sergi
Munné-Bosch and
Leonor
Alegre*
Departament de Biologia Vegetal, Facultat de Biologia, Universitat
de Barcelona, Avinguda Diagonal 645, 08028 Barcelona,
Spain
The potent antioxidant properties of rosemary (Rosmarinus
officinalis) extracts have been attributed to its major
diterpene, carnosic acid. Carnosic acid has received considerable
attention in food science and biomedicine, but little is known about
its function in the plant in vivo. We recently found that highly
oxidized diterpenes increase in rosemary plants exposed to drought and high light stress as a result of the antioxidant activity of carnosic acid (S. Munné-Bosch, K. Schwarz, L. Alegre [1999] Plant
Physiol 121: 1047-1052). To elucidate the significance of the
antioxidant function of carnosic acid in vivo we measured the relative
amounts of carnosic acid and its metabolites in different compartments of rosemary leaves. Subcellular localization studies show that carnosic
acid protects chloroplasts from oxidative stress in vivo by following a
highly regulated compartmentation of oxidation products. Carnosic acid
scavenges free radicals within the chloroplasts, giving rise to
diterpene alcohols, mainly isorosmanol. This oxidation product is
O-methylated within the chloroplasts, and the resulting form, 11,12-di-O-methylisorosmanol, is transferred to
the plasma membrane. This appears to represent a mechanism of a way out
for free radicals from chloroplasts. Carnosic acid also undergoes direct O-methylation within the chloroplasts, and its
derived product, 12-O-methylcarnosic acid, accumulates
in the plasma membrane. O-methylated diterpenes do not
display antioxidant activity, but they may influence the stability of
the plasma membrane. This study shows the relevance of the
compartmentation of carnosic acid metabolism to the protection of
rosemary plants from oxidative stress in vivo.
1
This work was supported by the Programa
Sectorial de Promoción General del Conocimiento (grant nos.
DGICYT PB96-1257 and BOS2000-0560).
*
Corresponding author; e-mail leonor{at}porthos.bio.ub.es; fax
34-93-411-28-42.
© 2001 American Society of Plant Physiologists
