LOW NIGHT TEMPERATURES HAVE A DIFFERENTIAL EFFECT ON THE DIURNAL CYCLING OF GENE-EXPRESSION IN COLD-SENSITIVE AND TOLERANT TOMATOES

Comparisons were made between the changes in mRNA levels induced by low night temperatures in the cold-sensitive tomato and two altitudinal ecotypes of the wild species L. hirsutum. Changes in mRNA levels were detected by resolving in vitro translation products of poly(A)+ RNA by 2-D PAGE. The treatment was applied by first growing plants in a thermoperiod of 25/18-degrees-C and then switching to 25/6-degrees-C. All tomatoes displayed a diurnal cycling in which a set of mRNAs accumulated at the end of the 18-degrees-C nights, whereas another accumulated at the end of the 25-degrees-C days. The accumulation of night specific mRNAs was inhibited by 6-degrees-C nights in the cold sensitive tomatoes while that of the tolerant one was only marginally affected. All tomatoes showed a similar reduction in the apparent turnover rate of the day specific mRNAs during the 6-degrees-C nights. Finally, low night temperatures induced the accumulation of six to eight mRNAs in all genotypes. This number increased by 15 in L. esculentum after the seventh night and are likely involved in stress response rather than acclimation/tolerance. The tomato is proposed as a genetic model to discriminate genes involved in acclimation/tolerance from those involved in stress response.