Photosynthetic acclimation to elevated CO2 in wheat cultivars

Wheat (T. aestivum) cvs. Kalyansona and Kundan grown under atmospheric (CA) and elevated CO2 concentrations (650-150 cm(3) m(-3) - CE) in open top chambers were examined for net photosynthetic rate (P-N), stomatal limitation (l(S)) of P-N, ribulose-1,5-bisphosphate carboxylase (RuBPC) activity, and saccharide content of the leaves. The P-N values of both CA- and CE-grown plants compared at the same CO2 concentration showed a down regulation under CE at the post-anthesis stage. The negative acclimation of P-N appeared to be due to both stomatal and mesophyll components, and the RuBPC activity got also adjusted. There was a decrease in activation state of RuBPC under CE. In connection with this, an increased accumulation of saccharides in wheat leaf under CE was observed. Kalyansona, owing to its larger sink potential in terms of the number of grains, showed a greater enhancement under CE in both post-ear emergence dry matter production and grain yield. Under CE, this cultivar also showed a lower down regulation of P-N than Kundan.