Biochemistry of Photosynthesis in Species of Triticum of Differing Ploidy

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Abstract
Illuminated flag leaves of Triticum monococcum(2X), T. urartu(2X), T. dicoccum(4X), T. dicoccoides(4X), and T. aestivum(6X) were exposed to 14CO2 for 10 seconds and subsequently allowed to continue photosynthesis in the ambient air for periods of up to 2 minutes. The relative distribution of 14C among water-soluble products in the leaves was similar for each species at each sampling time. After the 10-second pulse of 14CO2, radioactivity was mainly in phosphate esters with less than 5% in C4 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 14C was in glycine plus serine. The results suggest rapid photorespiration in all species and an absence of C4 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 NaHCO3 and 265 micromolar O2 at pH 8.2 and 25°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.