Abstract—A significant positive correlation between carbon isotope ratio (δ13C, ‰) and total chlorophyll concentration [Chl] was observed in field-grown soybean (Glycine max L.) and Maize ( Zea mays, L.) leaves with varying Chl levels. Leaf δ13C values became less negative by up to 4.5‰ with increasing Chl levels from 40 to 500 μmol m-2 in soybean whereas in maize, the same values became more negative (~1‰). The trend towards decreased leaf carbon isotope fractionation with increased Chl levels in soybean and maize suggests an enhanced carboxylation capacity in these leaves. Soybean leaves showed a linear increase in GAPDH activity with increase in leaf [Chl] suggesting an enhanced Ribulose -1,5- bisphosphate (RuBP) pool size. Levels of Ribulosebisphosphate carboxylase (Rubisco) also increased in concert with leaf Chl levels. Less negative δ¹³C values in these leaves with increasing [Chl] is thus due to an enhanced carboxylation capacity, resulting from a larger RuBP pool size and increased Rubisco levels. Gas exchange studies of these leaves also indicated a correlation between Chl content and net photosynthetic rate. Results from this study demonstrate that leaf Chl provides a major molecular basis influencing leaf carbon isotope discrimination by regulating carboxylation strength.

Index Terms—Carbon isotope discrimination, chlorophyll, photosynthesis, ribulose 1, 5-bisphosphate carboxylase/oxygenase.

M. Soundararajan is with the Department of Biochemistry, University of Nebraska, Lincoln, NE 68588-0664, USA. (Phone: 402-472-9802; fax: 402-472-7842; e-mail: msoundararajan1@unl.edu).

Cite: Madhavan Soundararajan, "Leaf Chlorophyll Levels Influence Carbon Isotope Discrimination in Soybean and Maize," International Journal of Bioscience, Biochemistry and Bioinformatics vol. 2, no. 3, pp. 207-211, 2012.