Low night temperature effect on photosynthate translocation of two C4 grasses

Translocation of assimilates in plants of Echinochloa crus-galli, from Quebec and Mississippi, and of Eleusine indica from Mississippi was monitored, before and after night chilling, using radioactive tracing with the short-life isotope ¹¹C. Plants were grown at 28°/22°C (day/night temperatures) under either 350 or 675 µl·l^-1 CO₂. Low night temperature reduced translocation mainly by increasing the turn-over times of the export pool. E. crus-galli plants from Mississippi were the most susceptible to chilling; translocation being completely inhibited by exposure for one night to 7°C at 350 µl·l^-1 CO₂. Overall, plants from Quebec were the most tolerant to chilling-stress. For plants of all three populations, growth under CO₂ enrichment resulted in higher ¹¹C activity in the leaf phloem. High CO₂ concentrations also seemed to buffer the transport system against chilling injuries.