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 during 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 maturation and chilling tolerance of this citrus cultivar. Chilling susceptibility and the content of PAs mere more affected by seasonal changes in field temperature than by the stage of fruit maturity. The highest putrescine (Put) and spermidine (Spd) content was found in fruits exposed to the lowest field temperatures. These fruits mere in turn more susceptible to develop chilling injury (CI) after storage at 2 degrees C. Spermine (Spm), however, decreased in attached fruit with time of exposure to temperatures below 12 degrees C. Temperature pretreatments for 3 days above 20 degrees C of fruits detached from the tree reduced CI, the more so the higher the conditioning temperature. Put and Spd increased,vith temperature conditioning in detached fruits, differing from the response of fruits attached to the tree. No direct relationship between induced levels of these PAs and the tolerance to CI 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 12 degrees C) which accelerated the appearance of chilling symptoms. In contrast, a significant increase in Spm levels,vas only found after conditioning 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 significant differences among fruit exposed to effective and non-effective pretreatments mere observed. PA content increased again after transferring cold-stored fruits to 20 degrees C, whereas the CI index was barely affected. In conclusion, PA changes in the flavedo of 'Fortune' mandarins appear to be related to variations in temperature rather than to stage of maturity or tolerance to chilling.