Polyamine content and chilling susceptibility are affected by seasonal changes in temperature and by conditioning temperature in cold-stored 'Fortune' mandarin fruit

'Fortune' mandarins are prone to develop pitting and necrosis upon exposure to low temperatures. We have examined the effect of field temperature duri ng fruit maturation and the effect of conditioning temperatures (from 2 to 37 degrees C) prior to cold storage on the content of polyamines (PAs) and on chilling susceptibility in order to understand the role of PAs in matura tion and chilling tolerance of this citrus cultivar. Chilling susceptibilit y and the content of PAs mere more affected by seasonal changes in field te mperature than by the stage of fruit maturity. The highest putrescine (Put) and spermidine (Spd) content was found in fruits exposed to the lowest fie ld temperatures. These fruits mere in turn more susceptible to develop chil ling injury (CI) after storage at 2 degrees C. Spermine (Spm), however, dec reased in attached fruit with time of exposure to temperatures below 12 deg rees C. Temperature pretreatments for 3 days above 20 degrees C of fruits d etached from the tree reduced CI, the more so the higher the conditioning t emperature. Put and Spd increased,vith temperature conditioning in detached fruits, differing from the response of fruits attached to the tree. No dir ect relationship between induced levels of these PAs and the tolerance to C I was found. Levels of Put and Spd increased at temperatures (22, 30 and 37 degrees C) which increased the tolerance and also at temperatures (6 and 1 2 degrees C) which accelerated the appearance of chilling symptoms. In cont rast, a significant increase in Spm levels,vas only found after conditionin g at 30 or 37 degrees C. After cold storage a general decline in PA levels occurred in all temperature-conditioned mandarins. In mast cases no signifi cant differences among fruit exposed to effective and non-effective pretrea tments mere observed. PA content increased again after transferring cold-st ored fruits to 20 degrees C, whereas the CI index was barely affected. In c onclusion, PA changes in the flavedo of 'Fortune' mandarins appear to be re lated to variations in temperature rather than to stage of maturity or tole rance to chilling.