Export patterns of 14C-assimilates from source leaves of C3, C3C4 intermediate, and C4 Panicum and Flaveria species during light and dark periods
Source leaves of Panicum and Flaveria C3, C3C4 intermediate, and C4 species were fed 14CO2 in the mid-afternoon. Immediate export, calculated when isotopic equilibrium existed between 14CO2 and the 14C translocates, was compared with 14C export during the feed period, and both were compared with subsequent 14C export of primary reserves during daytimenighttime chase periods. Sugars and starch supported export in all species. In addition, regardless of differences in partitioning into starch and sugars during labelling, similar photosynthesis, immediate export, and daily export occurred in some Panicum C4 species. Within both genera, C4 types fixed and exported the most carbon. The Panicum "type I" C3C4 intermediates behaved in an "intermediate" manner with respect to both export during photosynthesis and daily. In contrast, compared with C3 and C4 species within the Flaveria, "type II" C3C4 intermediates had the lowest initial export during the feed period and total 14C export by the next morning. In spite of the plasticity in carbohydrate storage, export in all species was greater in the light than in the dark. Interestingly, daily 14C export correlated better with immediate export rates than with photosynthesis or other parameters of leaf function.Key words: C export, C partitioning, C3C4 intermediates, Flaveria, Panicum, photosynthesis.