Contrasting responses of photosynthesis at low temperatures in different annual legume species

Growth, net photosynthetic rate (P-N), chlorophyll fluorescence induction kinetics, and stromal fructose-1,6-bisphosphatase (sFBPase) in annual legumes native to the Mediterranean region, two clovers (Trifolium subterraneum L. ssp. oxaloides Nyman cv. Clare and T michelianum Savi cv. Giorgia) and two Medicago species (M polymorpha L. cv. Anglona and M truncatula Gaertn. cv. Paraggio), shifted from 20 to 10 degrees C for 1 d or developed at 10 degrees C were compared with controls kept at 20 degrees C. Cold development produced a larger stimulation of growth in the clover cv. Giorgia and the Medicago cv. Paraggio. Transferring plants to low temperatures affected PN relatively less in clovers than in Medicago plants. Development at 10 degrees C relieved the inhibition of photosynthesis in Giorgia and Paraggio, but not in Clare and Anglona, which correlated with increases in the maximum rate of carboxylation by ribulose-1,5-bisphosphate carboxylase/oxygenase, RuBPCO (V-emax), and the photon-saturated rate of electron transport (J(max)). In Medicago, transfer from high to low temperature inhibited photosynthesis in a lesser extent in Anglona than in Paraggio, which showed severe limitations at level of V-emax and J(max). Development at 10 degrees C in Paraggio produced an efficient photosynthetic cold acclimation, this being associated with a two-fold increase of quantum yield of photosystem 2 electron transport (Delta F/F'(m)) and with the activity of sFBPase. By contrast, Anglona showed an irreversible inhibition of PN coupled with the reduction of carbon metabolism by impairment of Calvin cycle enzyme activities such as RuBPCO and sFBPase, resulting in a poor cold acclimation of photosynthesis in this cultivar.