Plant Physiol, April 2003, Vol. 131, pp. 1816-1825
Drought-Induced Changes in the Redox State of 
-Tocopherol,
Ascorbate, and the Diterpene Carnosic Acid in Chloroplasts of
Labiatae Species Differing in Carnosic Acid
Contents1
Sergi
Munné-Bosch* and
Leonor
Alegre
Departament de Biologia Vegetal, Facultat de Biologia, Universitat
de Barcelona, Avinguda Diagonal 645, E-08028 Barcelona, Spain
To assess antioxidative protection by carnosic acid (CA) in
combination with that of other low-molecular weight
(Mr) antioxidants (
-tocopherol [-T]
and ascorbate [Asc]) in chloroplasts, we measured endogenous
concentrations of these antioxidants, their redox states, and other
indicators of oxidative stress in chloroplasts of three Labiatae
species, differing in their CA contents, exposed to drought stress in
the field. Damage to the photosynthetic apparatus was observed neither
in CA-containing species (rosemary [Rosmarinus officinalis]) and sage [Salvia officinalis])
nor in CA-free species (lemon balm [Melissa
officinalis]) at relative leaf water contents between 86% and
58%, as indicated by constant maximum efficiency of photosystem II
photochemistry ratios and malondialdehyde levels in chloroplasts. The
three species showed significant increases in -T, a shift of the
redox state of -T toward its reduced state, and increased Asc levels
in chloroplasts under stress. Lemon balm showed the highest increases
in -T and Asc in chloroplasts under stress, which might compensate
for the lack of CA. Besides, whereas in rosemary and sage, the redox
state of CA was shifted toward its oxidized state and the redox state
of Asc was kept constant, lemon balm displayed a shift of the redox
state of Asc toward its oxidized state under stress. In vitro
experiments showed that both CA and Asc protect -T and
photosynthetic membranes against oxidative damage. These results are
consistent with the contention that CA, in combination with other
low-Mr antioxidants, helps to prevent
oxidative damage in chloroplasts of water-stressed plants, and they
show functional interdependence among different low-Mr antioxidants in chloroplasts.
1
This study was supported by the Ministerio de
Ciencia y Tecnología (project no. MCYT BOS 2000-0560).
*
Corresponding author; e-mail smunne{at}ub.edu; fax
34- 934112842.
© 2003 American Society of Plant Biologists
