Postharvest heat treatments

Heating tomato fruit (Lycoperiscon esculentum) for 48 h at 38 degrees C prevented chilling injury from developing after 21 d at 2 degrees C, whereas unheated fruit developed high levels of injury. Although the overall protein pattern as seen by Coomassie blue staining was similar from heated and unheated fruit, some high- and many low-molecular-mass proteins were observed in the heated fruit that were absent or present in reduced amounts in unheated fruit. When fruit wer injected with [35S]methionine at harvest and then heated, they accumulated high levels of specific radiolabeled proteins that could still be detected after 21 d at 2 degrees C. If the fruit were held at 20 degrees C after heating, the label in the proteins declined rapidly and these fruit were also sensitive to chilling injury. Hsp70 antibody reacted more strongly with proteins from heated and chilled fruit than with proteins from chilled fruit. Hsp18.1 antibody reacted strongly with proteins from heated fruit but not with those from unheated fruit. A 23-kD protein, highly labeled in heated fruit but not in unheated fruit, had its amino terminus sequenced. To our knowledge, this is the first report showing a relationship between the persistence of heat-shock proteins and chilling tolerance in a plant tissue.