PLANT PHYSIOLOGY , Vol 108, Issue 2 721-726, Copyright © 1995 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
An Investigation of the Sustained Component of Nonphotochemical Quenching of Chlorophyll Fluorescence in Isolated Chloroplasts and Leaves of Spinach
A. V. Ruban and P. Horton
Robert Hill Institute, Department of Molecular Biology and Biotechnology, University of Sheffield, P.O. Box 594, Western Bank, Sheffield S10 2UH, United Kingdom
The slowly reversible component of nonphotochemical quenching of Chl
fluorescence, ql, has been investigated in intact leaves and chloroplasts
of spinach (Spinacia oleracea). In leaves, between 50 and 100% of ql
(defined as the quenching that remained after at least 10 min of dark
adaptation of a previously illuminated leaf) is instantly reversible when
leaves were infiltrated with nigericin. Chloroplasts isolated from leaves
in which ql had been induced by prior illumination retained the same level
of quenching. No pH gradient, as measured by quenching of 9-aminoacridine
fluorescence, was present. However, addition of nigericin caused a partial
removal of ql, as observed in whole leaves. It is concluded that ql is not
related to a persistence of a bulk phase pH gradient in darkness but to a
structural change in the thylakoid that can be reversed by addition of
nigericin. The relationship between these observations and the hypothesis
that nonphotochemical quenching of chlorophyll fluorescence results from
protonation of light-harvesting complex of photosystem II components is
discussed.
