REVERSIBLE INHIBITION OF TOMATO FRUIT GENE-EXPRESSION AT HIGH-TEMPERATURE - EFFECTS ON TOMATO FRUIT RIPENING

The reversible inhibition of three ripening-related processes by high- temperature treatment (38 degrees C) was examined in tomato (Lycopersi con esculentum L. cv Daniella) fruit. Ethylene production, color devel opment, and softening were inhibited during heating and recovered afte rward, whether recovery took place at 20 degrees C or fruit were first held at chilling temperature (2 degrees C) after heating and then pla ced at 20 degrees C. Ethylene production and color development proceed ed normally in heated fruit after 14 d of chilling, whereas the unheat ed fruit had delayed ethylene production and uneven color development. Levels of mRNA for 1-aminocyclopropane-1-carboxylic acid oxidase, phy toene synthase, and polygalacturonase decreased dramatically during th e heat treatment but recovered afterward, whereas the mRNA for HSP17 i ncreased during the high-temperature treatment and then decreased when fruit were removed from heat. As monitored by western blots, the HSP1 7 protein disappeared from fruit tissue after 3 d at 20 degrees C but remained when fruit were held at 2 degrees C. The persistence of heat- shock proteins at low temperature may be relevant to the protection ag ainst chilling injury provided by the heat treatment. Protein levels o f 1-aminocyclopropane-1-carboxylic acid oxidase and polygalacturonase also did not closely follow the changes in their respective mRNAs. Thi s implied both differences in relative stability and turnover rates of mRNA compared to protein and nontranslation of the message that accum ulated in low temperature. The results suggest that high temperature i nhibits ripening by inhibiting the accumulation of ripening-related mR NAs. Ripening processes that depend on continuous protein synthesis in cluding ethylene production, lycopene accumulation, and cell-wall diss olution are thereby diminished.