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)

• Published in: Journal of experimental botany 2008, Vol.59 (7), p.1755-1765
• Main Authors: Akhani, Hossein, Ghasemkhani, Maraym, Chuong, Simon D.X, Edwards, Gerald E
• Format: Article
• Language: English
• Subjects: Acanthaceae; Acanthaceae - anatomy & histology; Acanthaceae - metabolism; Blepharis; C4 plants; Cotyledon - anatomy & histology; Cotyledon - physiology; desert adaptation; Desert Climate; Ecosystem; Hot Temperature; Kranz anatomy; Malate Dehydrogenase - metabolism; NAD-ME type; Photosynthesis - physiology; photosynthetic enzymes; Plant Leaves - anatomy & histology; Plant Leaves - physiology; Plant Stems - anatomy & histology
• ISSN: 0022-0957; 1460-2431
• DOI: 10.1093/jxb/ern020

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.