Photorespiratory Characteristics of Isolated Bundle Sheath Strands of C₄ Monocotyledons

Abstract

Bundle sheath strands (free of mesophyll tissue) were isolated from leaves of Zea mays L., Panicum miliaceum L. and Chloris gayana L. The response of oxygen exchange to CO₂ and O₂ concentration in these strands was examined using ¹⁸O₂ and mass spectrometry. Bundle sheath strands from all these species showed considerable O₂ uptake at low CO₂, 40-80 µmol (mg Chl)-1 h^-1. This O₂ uptake was stimulated by O₂ in the range 60-300 µM and was suppressed 60-70% by 5 mM NaHCO₃. The remaining light-dependent O₂ uptake was similarly sensitive to increasing O₂ concentration. These results are interpreted in terns of the CO₂ concentrating function of C₄ photosynthesis and the low apparent rates of photorespiration observed in C₄ plants in vivo.