JXB Advance Access published online on April 24, 2008
Journal of Experimental Botany, doi:10.1093/jxb/ern020
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RESEARCH PAPER |
Occurrence and forms of Kranz anatomy in photosynthetic organs and characterization of NAD-ME subtype C4 photosynthesis in Blepharis ciliaris (L.) B. L. Burtt (Acanthaceae)
1Department of Plant Sciences, School of Biology, College of Science, University of Tehran, PO Box 14155-6455, Tehran, Iran
2Department of Biology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada
3School of Biological Sciences, Washington State University, Pullman, Washington, WA 99164-4236, USA
* To whom correspondence should be addressed. E-mail: akhani{at}khayam.ut.ac.in; edwardsg{at}wsu.edu
Blepharis (Acanthaceae) is an Afroasiatic genus comprising 129 species which occur in arid and semi-arid habitats. This is the only genus in the family which is reported to have some C4 species. Blepharis ciliaris (L.) B. L. Burtt. is a semi-desert species with distribution in Iran, Oman, and Pakistan. Its form of photosynthesis was investigated by studying different organs. C4-type carbon isotope composition, the presence of atriplicoid type Kranz anatomy, and compartmentation of starch all indicate performance of C4 photosynthesis in cotyledons, leaves, and the lamina part of bracts. A continuous layer of distinctive bundle sheath cells (Kranz cells) encircle the vascular bundles in cotyledons and the lateral vascular bundles in leaves. In older leaves, there is extensive development of ground tissue in the midrib and the Kranz tissue becomes interrupted on the abaxial side, and then becomes completely absent in the mature leaf base. Cotyledons have 5–6 layers, and leaves 2–3 layers, of spongy chlorenchyma beneath the veins near the adaxial side of the leaf, indicating bifacial organization of chlorenchyma. As the plant matures, bracts and spines develop and contribute to carbon assimilation through an unusual arrangement of Kranz anatomy which depends on morphology and exposure to light. Stems do not contribute to carbon assimilation, as they lack chlorenchyma tissue and Kranz anatomy. Analysis of C4 acid decarboxylases by western blot indicates B. ciliaris is an NAD-malic enzyme type C4 species, which is consistent with the Kranz cells having chloroplasts with well-developed grana and abundant mitochondria.
Key words: Acanthaceae, Blepharis, C4 plants, desert adaptation, Kranz anatomy, NAD-ME type, photosynthetic enzymes
Received 17 October 2007; Revised 14 December 2007 Accepted 16 January 2008