EFFECTS OF LONG-TERM CHILLING UNDER LOW IRRADIANCE ON PHOTOSYNTHESIS PARAMETERS OF 4 FABACEAE SPECIES OF DIFFERENT CHILLING TOLERANCE

The four Fabaceae species of different chilling tolerance (Pisum sativ um L., Glycine max. Merr., Phaseolus vulgaris L. and Vigna unguiculata L.) were subjected to simulated bad weather periods at the beginning of the growth season. The treatment parameters were 14 d at constant 1 0-degrees-C, 100 mumol m-2 s-1, 80 % relative humidity within a 12 h p hotoperiod. During chilling and subsequent recovery, photosynthesis, c hlorophyll fluorescence and assimilate concentrations, as well as ribu lose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity were fol lowed. Despite the observation that no significant photoinhibition had been induced by the treatment, French bean and cowpea showed a strong decrease of photosynthetic capacity within the first week. During chi lling soybean, French bean and cowpea virtually did not grow further, but accumulated large amounts of starch, in contrast to pea. Specific activity of RuBPCO (Mg2+- and HCO3--activated) was not altered signifi cantly by the chilling treatment. Yet in French bean a general protein breakdown occurred in the second week. At the same time, a very stron g decrease of q(P) was obtained in this species, indicating a breakdow n of the electron transport. Pea and soybean were not negatively affec ted by the long-term chilling.