Photosynthesis in Tall Fescue : IV. Carbon Assimilation Pattern in two Genotypes of Tall Fescue Differing in Net Photosynthesis Rates |
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| Authors: | Wong J H Randall D D Nelson C J |
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| Affiliation: | Department of Biochemistry, University of Missouri, Columbia, Missouri 65211. |
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| Abstract: | We previously reported that the net photosynthetic rate of a decaploid genotype (I-16-2) of tall fescue (Festuca arundinacea Schreb.) was 32 to 41 versus 22 milligrams CO2 per square decimeter per hour in a hexaploid genotype (V6-802) (Randall, Nelson, Asay Plant Physiol 59: 38-41). The high rate was later correlated with increases in total ribulose 1,5-bisphosphate carboxylase protein (17%) and activity (27%) (Joseph, Randall, Nelson Plant Physiol 68: 894-898). This report characterizes photosynthesis with respect to light saturation and early products of photosynthesis in an attempt to identify regulatory metabolic site(s) in these two genotypes. Analysis of the early products of photosynthesis indicated that both genotypes fixed CO2 via the Calvin-Benson cycle with phosphoglyceric acid as the initial primary product. Both genotypes had similar 14C-labeled intermediates. Sucrose was the primary sink of 14CO2 assimilation. After 10 min of 14CO2 assimilation with attached leaves, sucrose accounted for 89% (decaploid) and 81% (hexaploid) of the total 14C incorporated. In 10 min, this amounted to 1.3 (decaploid) and 0.8 (hexaploid) μmol [14C]sucrose formed g fresh weight−1 and reflected the observed differences in photosynthetic rates. There was limited labeling of starch (1%) and fructan (1%). Results of total nonstructural carbohydrates and Pi analysis also demonstrated sucrose was the predominant carbohydrate in fescue leaves. Quantitative differences in sucrose and Pi between the two genotypes may reflect changes in partitioning and this possibility is discussed. |
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