PHOTOSYNTHETICA

Photosynthetica 2009, 47(2):163-183 | DOI: 10.1007/s11099-009-0030-7

Pioneering research on C₄ leaf anatomical, physiological, and agronomic characteristics of tropical monocot and dicot plant species: Implications for crop water relations and productivity in comparison to C₃ cropping systems

M. A. El-Sharkawy^1,*

¹ Centro Internacional de Agricultura Tropical (CIAT), Cali, Colombia

The review is done to summarise the history of the discoveries of the many anatomical, agronomical, and physiological aspects of C₄ photosynthesis (where the first chemical products of CO₂ fixation in illuminated leaves are four-carbon dicarboxylic acids) and to document correctly the scientists at the University of Arizona and the University of California, Davis, who made these early discoveries. The findings were milestones in plant science that occurred shortly after the biochemical pathway of C₃ photosynthesis in green algae (where the first chemical product is a three-carbon compound) was elucidated at the University of California, Berkeley, and earned a Nobel Prize in chemistry. These remarkable achievements were the result of ground-breaking pioneering research efforts carried out by many agronomists, plant physiologists and biochemists in several laboratories, particularly in the USA. Numerous reviews and books written in the past four decades on the history of C₄ photosynthesis have focused on the biochemical aspects and give an unbalanced history of the multidisciplinary/multinstitutional nature of the achievements made by agronomists, who published much of their work in Crop Science. Most notable among the characteristics of the C₄ species that differentiated them from the C₃ ones are: (I) high optimum temperature and high irradiance saturation for maximum leaf photosynthetic rates; (II) apparent lack of CO₂ release in a rapid stream of CO₂-free air in illuminated leaves in varying temperatures and high irradiances; (III) a very low CO₂ compensation point; (IV) lower mesophyll resistances to CO₂ diffusion coupled with higher stomatal resistances, and, hence, higher instantaneous leaf water use efficiency; (V) the existence of the so-called "Kranz leaf anatomy" and the higher internal exposed mesophyll surface area per cell volume; and (VI) the ability to recycle respiratory CO₂ by illuminated leaves.

Additional key words: agriculture; biochemistry; breeding; carbon assimilation; crops; drought; enzymes; gas exchange; photorespiration; photosynthesis; water use efficiency

Received: September 2, 2008; Accepted: April 29, 2009; Published: June 1, 2009  Show citation