Maize (
Zea mays L.) is one of the most representative C
4 plants. However, several reports have suggested the occurrence of C
3 photosynthesis in this C
4 plant. We examined the photosynthetic characteristics of the coleoptiles, as well as the first, the second, and the third leaves of maize seedlings at their maturities. All the foliage leaves examined, including the first leaf sheath, exhibited representative Kranz anatomy, low CO
2 compensation point, and expression of genes for enzymes involved in the C
4-dicarboxylic acid cycle. In contrast, coleoptiles showed no Kranz anatomy and extremely high CO
2 compensation point. The expression of C
4-specific genes in the coleoptiles was hampered at various levels. These results strongly suggest that the maize coleoptiles do not perform typical C
4 photosynthesis.
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