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First published online May 28, 2009; doi:10.3732/ajb.0800224 American Journal of Botany 96: 1222-1235 (2009) © 2009 Botanical Society of America, Inc.

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Grasses of different C₄ subtypes reveal leaf traits related to drought tolerance in their natural habitats: Changes in structure, water potential, and amino acid content¹

² Centro de Engenharia Biológica (CEB) and Departamento de Biologia Vegetal, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal ³ Department of Plant Sciences, Centre for Crop Genetic Improvement, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK ⁴ Centro de Biotecnologia Vegetal (CBV-IBB) and Departamento de Biologia Vegetal, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal ⁵ Department of Biomathematics and Bioinformatics, Centre for Mathematical and Computational Biology, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK

ABSTRACT

Three grasses (Poaceae) of different C₄ subtypes, Paspalum dilatatum (NADP-malic enzyme [ME]), Cynodon dactylon (NAD-ME) and Zoysia japonica (phosphoenolpyruvate carboxykinase), occur in natural habitats that differ in annual rainfall. Their leaf characteristics were studied to identify traits related to drought tolerance. Plants were grown in pots, and water deficit was gradually induced by withholding water. Leaves of Z. japonica had the greatest and P. dilatatum the lowest relative dry matter content. Transverse sections of leaves that developed during the water deficit showed little change compared to control leaves, consistent with low phenotypic plasticity. Anatomical features distinguished the three species, with xeromorphic characteristics most strongly represented in Z. japonica. The leaf relative water content (RWC) decreased with the soil water content similarly for the three grasses. However, at 80% RWC, the leaf water potential was –3.1 MPa for Z. japonica and only –1.3 MPa for P. dilatatum and C. dactylon. Soluble amino acids, especially proline, increased as RWC decreased in leaves of C. dactylon and Z. japonica. Phenylalanine, valine, leucine, and isoleucine increased more in Z. japonica than in the other two species. The results provide evidence that C. dactylon and, especially, Z. japonica have evolved leaf traits better suited to arid habitats.

Key Words: C₄ grasses • Cynodon dactylon • drought stress • leaf anatomy • Paspalum dilatatum • Poaceae • water deficit • Zoysia japonica

Received for publication 3 July 2008. Accepted for publication 3 March 2009.

FOOTNOTES

¹ The authors thank Dr. S. Dufour, Rothamsted Research, for help and advice on analytical chemistry, and C. Oliveira, Olive Design, for help on quantitative analysis of leaf anatomy. A.E.C.-S. acknowledges Fundação para a Ciência e a Tecnologia for financial support (Grant SFRH/BD/13730/2003). Rothamsted Research is a grant-aided Institute of The Biotechnology and Biological Sciences Research Council.

⁶ Author for correspondence (e-mail: elizabete.carmosilva{at}gmail.com)

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