BIOCHEMISTRY OF PHOTOSYNTHESIS IN SPECIES OF TRITICUM OF DIFFERING PLOIDY

Illuminated flag leaves of Triticum monococcum(2X), T. urartu(2X), T. dicoccum(4X), T. dicoccoides(4X), and T. aestivum(6X) were exposed to (14)CO(2) for 10 seconds and subsequently allowed to continue photosynthesis in the ambient air for periods of up to 2 minutes. The relative distribution of (14)C among water-soluble products in the leaves was similar for each species at each sampling time. After the 10-second pulse of (14)CO(2), radioactivity was mainly in phosphate esters with less than 5% in C(4) acids. Subsequently, radioactivity increased in sucrose, glycine, and serine at the expense of that in phosphate esters. By 2 minutes, between 18% and 29% of the (14)C was in glycine plus serine. The results suggest rapid photorespiration in all species and an absence of C(4) photosynthesis.d-Ribulose 1,5-bisphosphate carboxylase (EC 4.1.1.39) was partly purified from seedling leaves of each of the five Triticum species. Each preparation was assayed for simultaneous carboxylase and oxygenase activities in 2.1 millimolar NaHCO(3) and 265 micromolar O(2) at pH 8.2 and 25 degrees C. The mean ratio of carboxylase to oxygenase activities was 6.11 +/- 0.16 (standard error); differences between values for different species were not statistically significant. The results do not explain the faster rates of photosynthesis per unit leaf area reported for diploid and tetraploid species of Triticum compared to the hexaploid.