Acclimation of Arabidopsis leaves developing at low temperatures. Increasing cytoplasmic volume accompanies increased activities of enzymes in the Calvin cycle and in the sucrose-biosynthesis pathway

Photosynthetic and metabolic acclimation to low growth temperatures were st udied in Arabidopsis (Heynh.). Plants were grown at 23 degrees C and then s hifted to 5 degrees C. We compared the leaves shifted to 5 degrees C for 10 d and the new leaves developed at 5 degrees C with the control leaves on p lants that had been left at 23 degrees C. Leaf development at 5 degrees C r esulted in the recovery of photosynthesis to rates comparable with those ac hieved by control leaves at 23 degrees C. There was a shift in the partitio ning of carbon from starch and toward sucrose (Suc) in leaves that develope d at 5 degrees C. The recovery of photosynthetic capacity and the redirecti on of carbon to Suc in these leaves were associated with coordinated increa ses in the activity of several Calvin-cycle enzymes, even larger increases in the activity of key enzymes for Suc biosynthesis, and an increase in the phosphate available for metabolism. Development of leaves at 5 degrees C a lso led to an increase in cytoplasmic volume and a decrease in vacuolar vol ume, which may provide an important mechanism for increasing the enzymes an d metabolites in cold-acclimated leaves. Understanding the mechanisms under lying such structural changes during leaf development in the cold could res ult in novel approaches to increasing plant yield.