Contents of carbon-assimilating enzymes in leaves of maize hybrids released between 1936 and 1976

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Abstract
Changes in the contents of soluble protein, ribulose-1,5-bisphosphate carboxylase/ oxygenase (RuBisCO), phosphoenolpyruvate carboxylase (PEPC), and pyruvate, P1 dikinase (PPDK) in newly developed leaves and in the fully developed second leaf from the top as well as the grain yield were studied in maize (Zea mays L.) hybrids released from 1936 to 1976 and an open-pollinated variety developed in 1930. Contents of soluble protein, PEPC, and PPDK in the newly developed leaves of plants on the active growth stage did not differ among the cultivars including an open-pollinated variety. By contrast, the content of RuBisCO tended to decrease in the more recently released cultivars. At the early ripening stage, the content of soluble protein in the fully developed second leaf from the top varied among the cultivars, indicating different degrees of senescence. The content of soluble protein in the second leaf generally tended to be higher in the hybrids released in the 1960s than in those released before or more recently and in an open-pollinated variety. Pattern of fluctuation of the contents of RuBisCO, PEPC, and PPDK among the cultivars was almost similar to that of the contents of soluble protein. The grain yield in the hybrids was obviously higher than that in an open-pollinated variety and appeared to fluctuate with an almost similar pattern to that of soluble protein and carbon assimilating enzymes in the second leaf.