A novel P700 redox kinetics probe for rapid, non-intrusive and whole-tissue determination of photosystem II functionality, and the stoichiometry of the two photosystems in vivo.

We sought a rapid, non-intrusive, whole-tissue measure of the functional photosystem II (PS II) content in leaves. Summation of electrons, delivered by a single-turnover flash to P700(+) (oxidized PS I primary donor) in continuous background far-red light, gave a parameter S in absorbance units after taking into account an experimentally determined basal electron flux that affects P700 redox kinetics. S was linearly correlated with the functional PS II content measured by the O(2) yield per single-turnover repetitive flash in Arabidopsis thaliana expressing an antisense construct to the PsbO (manganese-stabilizing protein in PS II) proteins of PS II (PsbO mutants).

Antisense reductions in the PsbO protein of photosystem II leads to decreased quantum yield but similar maximal photosynthetic rates.

Photosystem (PS) II is the multisubunit complex which uses light energy to split water, providing the reducing equivalents needed for photosynthesis. The complex is susceptible to damage from environmental stresses such as excess excitation energy and high temperature. This research investigated the in vivo photosynthetic consequences of impairments to PSII in Arabidopsis thaliana (ecotype Columbia) expressing an antisense construct to the PsbO proteins of PSII.

Light and growth temperature alter carbon isotope discrimination and estimated bundle sheath leakiness in C4 grasses and dicots.

We combined measurements of short-term (during gas exchange) and long-term (from plant dry matter) carbon isotope discrimination to estimate CO(2) leakiness from bundle sheath cells in six C(4) species (three grasses and three dicots) as a function of leaf insertion level, growth temperature and short-term irradiance. The two methods for determining leakiness yielded similar results (P > 0.05) for all species except Setaria macrostachya, which may be explained by the leaf of this species not being accommodating to gas exchange.

High temperature acclimation of C4 photosynthesis is linked to changes in photosynthetic biochemistry.

With average global temperatures predicted to increase over the next century, it is important to understand the extent and mechanisms of C4 photosynthetic acclimation to modest increases in growth temperature. To this end, we compared the photosynthetic responses of two C4 grasses (Panicum coloratum and Cenchrus ciliaris) and one C4 dicot (Flaveria bidentis) to growth at moderate (25/20 degrees C, day/night) or high (35/30 degrees C, day/night) temperatures. In all three C4 species, CO2 assimilation rates (A) underwent significant thermal acclimation, such that when compared at growth temperatures, A increased less than what would be expected given the strong response of A to short-term changes in leaf temperature.