Ca. Sacksteder et al., The proton to electron stoichiometry of steady-state photosynthesis in living plants: A proton-pumping Q cycle is continuously engaged, P NAS US, 97(26), 2000, pp. 14283-14288
Citations number
88
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
A noninvasive technique is introduced with which relative proton to electro
n stoichiometries (H+/e(-) ratios) for photosynthetic electron transfer can
be obtained from leaves of living plants under steady-state illumination,
Both electron and proton transfer fluxes were estimated by a modification o
f our previously reported dark-interval relaxation kinetics (DIRK) analysis
, in which processes that occur upon rapid shuttering of the actinic light
are analyzed. Rates of turnover of linear electron transfer through the cyt
ochrome (cyt) b(6)f complex were estimated by measuring the DIRK signals as
sociated with reduction of cyt f and P-700 The rates of proton pumping thro
ugh the electron transfer chain and the CF0-CF1 ATP synthase (ATPase) were
estimated by measuring the DIRK signals associated with the electrochromic
shifting of pigments in the light-harvesting complexes, Electron transfer f
luxes were also estimated by analysis of saturation pulse-induced changes i
n chlorophyll a fluorescence yield. It was shown that the H+/e(-) ratio, wi
th respect to both cyt b(6)f complex and photosystem (PS) II turnover, was
constant under low to saturating illumination in intact tobacco leaves. Bec
ause a H+/e(-) ratio of 3 at a low light is generally accepted, we infer th
at this ratio is maintained under conditions of normal (unstressed) photosy
nthesis, implying a continuously engaged, proton-pumping Q cycle at the cyt
b(6)f complex.