Journal of Experimental Botany, Vol 49, 1881-1888, Copyright © 1998 by Oxford University Press
B Logan, B Demmig-Adams and W Adams
Portions of shade-acclimated shoots of Cucurbita pepo
L. (pumpkin) and Vinca major L. were rapidly
transferred to full sunlight exposure and chlorophyll fluorescence
emission, pigment composition, antioxidant enzyme activities, ascorbate
contents, and the content of thiobarbituric acid-reactive substances
(TBARS) were measured at regular intervals for 17 d. The most notable
response of leaf pigment composition was a pronounced increase in the pool
size of xanthophyll cycle carotenoids that occurred over a period of 4 d
(pumpkin) or 11-18 d (V. major). On day 1 after the
transfer midday efficiencies of open PSII units decreased to levels similar
to or below those observed in full sun-acclimated leaves. Efficiencies of
open PSII units were inversely correlated with xanthophyll cycle conversion
states in both species on all dates of sampling. A rapid increase in
thermal energy dissipation on day 1 may thus have contributed to the
absence of either an increase in the content of TBARS (a measure of lipid
damage) or pronounced depressions in pre-dawn
Fv/Fm. Activities of the
antioxidant enzymes ascorbate peroxidase, superoxide dismutase, glutathione
reductase, and catalase as well as ascorbate content increased in both
species upon transfer, with superoxide dismutase exhibiting the most
dramatic increase. Pumpkin, but not V. major,
developed new leaves during the study which possessed the attributes of
sun-acclimated leaves.Key words: Antioxidants,
Cucurbita pepo, light transfer, Vinca
major, xanthophyll cycle.
ARTICLES
Antioxidants and xanthophyll cycle-dependent energy dissipation in Cucurbita pepo L. and Vinca major L. upon a sudden increase in growth PPFD in the field
Department of Environmental, Population, and Organismic Biology, University of Colorado, Boulder, CO 8039-0334, USA; Permanent address: Department of Biology, Bowdoin College, Brunswick, ME 04011, USA; Corresponding author e-mail: barbara.demmig-adams@colorado.edu
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