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Environmental and Stress Physiology

Autotrophy in Maize Husk Leaves ¹

Evaluation Using Natural Abundance of Stable Isotopes

Botany Department and Phytotron, Duke University, Durham, North Carolina 27706

The natural abundance of carbon and hydrogen isotopic composition, expressed as a ¹³C value of plant dry matter and cellulose in the hypsophylls (husk leaves) of maize (Zea mays L.) was measured and compared with that of leaves and cobs. The ¹³C values of outer hypsophylls were usually 2 to 3% more negative than leaves or other tissues, and became more negative with increasing chlorophyll content, indicating significant local C₃ pathway fixation of CO₂ in the outer hypsophylls. The D values indicated a significant part of hypsophyll cellulose was derived from heterotrophic sources (sucrose from C₄ photosynthesis in other tissues). Isotopic mass balance calculations allowed quantitative estimation of these carbon sources and, in the samples examined, about 16% of hypsophyll cellulose was derived from local C₃ photosynthesis, about 62% from local C₄ photosynthesis, and about 22% from sucrose imported from other leaves.

³ Present address: Research School of Biological Sciences, Australian National University, Box 475 Canberra A.C.T. 2601, Australia.

¹ Research supported in part by grants from the U.S. Department of Energy, Division of Energy Biosciences, grant DE-FG05-89ER 14005 to B.O., and from Duke University. We are grateful to the North Carolina Biotechnology Center for a grant toward purchase of the VG-SIRA mass spectrometer.

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