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Articles

Variation in Amounts of Pyruvate, Orthophosphate Dikinase, and Some Other Enzymes of the C₄ Pathway in Some Wheat Species ¹

Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720

First leaves and flag leaves of the wheat species Triticum aestivum cv Anza (6x), T. boeoticum Boiss (2x) L. were examined for content of pyruvate, orthophosphate dikinase (PPDK), phosphoenolpyruvate carboxylase (PEPC), and ribulose 1,5-bisphosphate carboxylase (RuBPC) by protein blot analyses using antibodies to maize leaf enzymes and by activity assays. In agreement with previous reports, the amount of RuBPC per mesophyll cell was about 3 times more in the hexaploid species, T. aestivum, than in the diploid species, T. boeoticum, both in first leaves and in flag leaves. In contrast, the level of PPDK polypeptide was nearly 3-fold higher per unit leaf area in the first leaf and 63% higher in the flag leaf of this diploid species compared to this hexaploid species. There was no significant difference in the levels of polypeptide and enzyme activity of PEPC between diploid and hexaploid wheat. Despite this significantly greater level of PPDK in the diploid species, the actual amount of PPDK could still supply only a limited amount of the enzyme activity necessary to provide phosphoenolpyruvate (PEP) for any putative intracellular C₄ carbon shuttle providing carbon to RuBPC. Thus, this difference in enzyme amount could not by itself account for the reported high rates of net photosynthesis at high light intensity in T. boeoticum. Together with reported anatomical differences between the diploid and hexaploid species, however, this biochemical difference may be of physiological importance.

¹ Supported by the Office of Energy Research, Office of Basic Energy Sciences, Biological Energy Research Division of the United States Department of Energy under Contract No. DE-AC03-76 SF00098.