Regulation of mesophyll photosynthesis in intact wheat leaves by cytoplasmic phosphate concentrations

摘要

The effect ofD-(+)-mannose, inorganic phosphate (Pi) and mannose-6-phosphate on net mesophyll CO2assimilation rate (A) and stomatal conductance (gs) of wheat (Triticum aestivumL.) leaves was studied. The compounds were supplied through the transpiration stream of detached leaves from plants grown in sand in growth cabinets or glasshouses, with different concentrations of Pi (0.25, 1.0 and 4.0 mM) supplied during growth. In all cases, 10 mMD-(+)mannose caused 40–60 reduction of A within 30 min, though the time courses differed for flag leaves and the sixth leaf on the mainstem of glasshouse- and cabinet-grown plants.D-(+)Mannose had a similar effect on A in leaves having a fourfold range in total phosphate content. Effects ofD-(+)mannose in reducing gswere always slower than on A. When the CO2concentration in the leaf chamber was adjusted to maintain intercellular CO2concentration (Ci) constant as A declined after mannose supply, gsstill declined indicating that stomatal closure was not caused by changing Ci. Supplying mannose-6-phosphate at 10 and 1 mM and Pi at 5 and 10 mM concentrations caused rapid reductions in gsand also direct reductions in A. The observed effects of mannose and Pi on assimilation are consistent with the proposed regulatory role of cytoplasmic Pi in determining mesophyll carbon assimilation that has been derived previously using leaf discs, protoplasts and chloroplast