Physiology and Molecular Biology of Stress ... - KHAM PHA MOI

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T.D. Sharkey and S.M. Schrader
of an increased pH gradient (Horton et al., 1996). Further, ATP levels, which are dependent
on an energized thylakoid membrane, were higher in isolated chloroplasts (Weis,
1981a) and did not change in whole leaves (Schrader et al., 2004) under heat stress.
3.3.3. The Role of Membrane-Bound Reactions
Early studies of high temperature stress on photosynthesis noted a decline in oxygen
evolution in isolated chloroplasts (Holt and French, 1946). Katoh and San Pietro (1967)
ascribed this heat effect on O 2
evolution to the water splitting complex of PSII, showing
that NADP photoreduction could be restored using ascorbate as an artificial electron
donor that substituted for the water splitting complex. Later, the heat inactivation of O 2
evolution was associated with the release of Mn from PSII (Cheniae and Martin, 1970;
Kimimura and Katoh, 1972; Wydrzynski and Sauer, 1980) and the release of the 18, 24,
and 33 kDa proteins from the thylakoid membranes which are associated with the water
splitting complex on the luminal surface of PSII (Figure 2) (Yamamoto and Nishimura,
1983; Nash et al., 1985).
Figure 2. Photosynthetic electron transport and processes that can be affected by high
temperature stress (Light arrows indicate electron transport paths, heavy arrows indicate
changes that can occur in response to heat)