Regulation of Photosynthetic Induction State in High- and Low-Light-Grown Soybean and Alocasia macrorrhiza (L.) G. Don.

Alocasia (Alocasia macrorrhiza [L.] G. Don) and soybean (Glycine max [L.]) were grown under high or low photon flux density (PFD) conditions to achieve a range of photosynthetic capacities and light-adaptation modes. The CO2 assimilation rate and in vivo linear electron transport rate (Jf) were determined over a range of PFDs and under saturating 1-s-duration lightflecks applied at a range of frequencies. At the same mean PFD, the assimilation rate and the Jf were lower under the lightfleck regimes than under constant light. The activation state of two, key enzymes of the photosynthetic carbon reduction cycle pathway, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and fructose-1,6-bisphosphatase, and the photosynthetic induction states (ISs) were also found to be lower under flashing as compared to continuous PFD. Under all conditions, the IS measured 120 s after an increase in PFD to constant and saturating values was highly correlated with the Rubisco activation state and stomatal conductances established in the light regime before the increase. Both the fructose-1,6-bisphosphatase and Rubisco activities established in a particular light regime were highly correlated with the mean Jf in that regime. The relationships between enzyme activation state and Jf and between IS and enzyme activation state were similar in soybean and Alocasia and were not affected either by growth-light regime, and hence photosynthetic capacity, or by flashing versus constant PFD. The common relationship between the linear Jf and the activation state of key enzymes suggests that electron transport may be the determinant of the signal regulating IS, at least to the extent that the IS is controlled by the activation state of key stromal enzymes.