The mechanism of starch content increase in grain of autotetraploid rice (Oryza sativa L.)

Net photosynthetic rate (PN), photorespiration (PR), chlorophyll (Chl) content, Chl fluorescence parameters, starch accumulation, and related key enzyme activities were determined during the grain-filling stage in two autotetraploid lines and corresponding diploid rice lines. The results showed that autotetraploid rice lines had a higher Chl content, PN, electron transport rate, maximum photochemical efficiency of PSII, actual photochemical efficiency of PSII, and lower PR in leaves than that in corresponding diploid rice lines during the grain-filling stage. It indicated that autotetraploid rice line had a high photosynthetic capacity and high light-utilization efficiency. The activities of ADP-glucose pyrophosphorylase, soluble starch synthase, and starch-branching enzyme in grains of autotetraploid rice lines were higher than those in grains of corresponding diploid rice lines during the grain-filling stage. Therefore, autotetraploid rice lines were more efficient than corresponding diploid rice lines in converting photosynthetic products into starch.