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. (C3), Cleome paradoxa R.Br. (C3-C4 intermediate), Cleome angustifolia Forssk. and Cleome gynandra L. (C4). 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 C3 photosynthesis. In C. paradoxa , cotyledons, leaves, stems and petioles have C3-C4 type features. In C. angustifolia , the pods have C3 photosynthesis, whereas all other organs have C4 photosynthesis with Kranz anatomy formed by a continuous, dual layer of chlorenchyma cells. In the subtropical C4 species C. gynandra , cotyledons, leaves, and pods develop C4 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. There is great interest in plants that capture CO2 from the atmosphere and concentrate it in leaves to support photosynthesis. The present study shows the diversity in expression and function of this and other forms of photosynthesis in cotyledons, leaves, stems, petioles and pods during the life cycle of Cleome species. Further investigation into the genetic regulation of development of these forms within and between species is needed. [ABSTRACT FROM AUTHOR]