Using radioactively labelled amino acids to investigate repair of photoinactivated photosystem II (PS II) gives only a relative rate of repair, while using chlorophyll fluorescence parameters yields a repair rate coefficient for an undefined, variable location within the leaf tissue. Here, we report on a whole-tissue determination of the rate coefficient of photoinactivation ki, and that of repair kr in cotton leaf discs. The method assays functional PS II via a P700 kinetics area associated with PS I, as induced by a single-turnover, saturating flash superimposed on continuous background far-red light. The P700 kinetics area, directly proportional to the oxygen yield per singleturnover, saturating flash, was used to obtain both ki and kr. The value of ki, directly proportional to irradiance, was slightly higher when CO2 diffusion into the abaxial surface (richer in stomata) was blocked by contact with water. The value of kr, sizable in darkness, changed in the light depending on which surface was blocked by contact with water. When the abaxial surface was blocked, kr first peaked at moderate irradiance and then decreased at high irradiance. When the adaxial surface was blocked, kr first increased at low irradiance, then plateaued, before increasing markedly at high irradiance. At the highest irradiance, kr differed by an order of magnitude between the two orientations, attributable to different extents of oxidative stress affecting repair (Nishiyama et al., EMBO J 20: 5587–5594, 2001). The method is a whole-tissue, convenient determination of the rate coefficient of photoinactivation ki and that of repair kr.
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|Titolo:||Whole-tissue determination of the rate coefﬁcients of photoinactivation and repair of photosystem II in cotton leafdiscs based on ﬂash-induced P700 redox kinetics|
|Data di pubblicazione:||2013|
|Appare nelle tipologie:||1.1 Articolo in rivista|