What is the fate of xylem-transported CO 2 in Kranz-type C 4 plants?

• Published in: The New phytologist 2019-08, Vol.223 (3), p.1241-1252
• Main Authors: Stutz, Samantha S, Hanson, David T
• Format: Article
• Language: English
• Subjects: Biological Transport - radiation effects; Carbon - metabolism; Carbon Cycle - radiation effects; Carbon Dioxide - metabolism; Cell Respiration - radiation effects; Darkness; Light; Photosynthesis - radiation effects; Plant Leaves - physiology; Plant Leaves - radiation effects; Plant Transpiration - physiology; Plant Transpiration - radiation effects; Xylem - metabolism; Xylem - radiation effects
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.15908

High concentrations of dissolved inorganic carbon in stems of herbaceous and woody C plants exit leaves in the dark. In the light, C species use a small portion of xylem-transported CO for leaf photosynthesis. However, it is not known if xylem-transported CO will exit leaves in the dark or be used for photosynthesis in the light in Kranz-type C plants. Cut leaves of Amaranthus hypochondriacus were placed in one of three solutions of [NaH CO ] dissolved in KCl water to measure the efflux of xylem-transported CO exiting the leaf in the dark or rates of assimilation of xylem-transported CO * in the light, in real-time, using a tunable diode laser absorption spectroscope. In the dark, the efflux of xylem-transported CO increased with increasing rates of transpiration and [ CO *]; however, rates of C in A. hypochondriacus were lower compared to C species. In the light, A. hypochondriacus fixed nearly 75% of the xylem-transported CO supplied to the leaf. Kranz anatomy and biochemistry likely influence the efflux of xylem-transported CO out of cut leaves of A. hypochondriacus in the dark, as well as the use of xylem-transported CO * for photosynthesis in the light. Thus increasing the carbon use efficiency of Kranz-type C species over C species.