Diversity in structure and forms of carbon assimilation in photosynthetic organs in Cleome (Cleomaceae)

Photosynthesis in different organs of Cleome was analysed in four species known to have differences in leaf photosynthesis: Cleome africana Botsch. (C-3), Cleome paradoxa R.Br. (C-3-C-4 intermediate), Cleome angustifolia Forssk. and Cleome gvnandra L. (C-4). The chlorophyll content, carbon isotope composition, stomatal densities, anatomy, levels and compartmentation of some key photosynthetic enzymes, and the form and function of photosynthesis were determined in different organs of these species. In the three xerophytes, C. africana, C. paradoxa, and C. angustifolia, multiple organs contribute to photosynthesis (cotyledons, leaves, petioles, stems and pods) which is considered important for their survival under arid conditions. In C. africana, all photosynthetic organs have C-3 photosynthesis. In C. paradoxa, cotyledons, leaves, stems and petioles have C-3-C-4 type features. In C. angustifolia, the pods have C-3 photosynthesis, whereas all other organs have C-4 photosynthesis with Kranz anatomy formed by a continuous, dual layer ofchlorenchyma cells. In the subtropical C-4 species C. gynandra, cotyledons, leaves, and pods develop C-4 photosynthesis, with Kranz anatomy around individual veins; but not in stems and petioles which have limited function of photosynthesis. The diversity in forms and the capacity of photosynthesis in organs of these species to contribute to their carbon economy is discussed.