Induction of chilling tolerance in grapefruit: Physiological and molecular aspects

Many tropical and subtropical fruits and vegetables, such as citrus, are sensitive to low chilling temperatures and, thus, must be stored after harvest at relatively high temperatures that enhance their deterioration. In previous studies, we found that a short pre-storage hot water rinsing treatment (at 62 degrees C for 20 s) markedly increased chilling tolerance in grapefruit and reduced the development of chilling injuries following 6 weeks of cold storage at 2 degrees C. Molecular analysis studies using PCR cDNA differential display and PCR cDNA subtraction techniques revealed that the hot water treatment increased the expression of several stressrelated cDNAs in the fruit peel tissue, including heat shock proteins (HSPs), dehydrins, and a sodium proton antiport gene known to be involved in plant salt tolerance. Evaluation of gene expression patterns showed that many of these stress genes were only temporarily induced by the heat treatment alone when the fruit were kept at ambient temperatures, but markedly and continually expressed by the combination of heat followed by cold storage.