Figure 4.

Effects of low and freezing temperatures on the expression response of Arabidopsis CBF3 and LTI78 genes. A, Expression response of CBF3 and LTI78 genes to freezing temperature in Arabidopsis. Three-week-old soil-grown (23°C, 12-h day; lights were on from 6 am to 6 pm) Arabidopsis plants were exposed to freezing temperatures by placing them directly in −2.6°C for 0.5 h, after which the temperature was decreased to −6°C at 1°C h⁻¹. Temperature was kept at −6°C for 1 h, after which it was allowed to increase to 8°C during the next 3 h. Plants were kept at low positive temperature overnight. The experiment started at 8:30 am, and after 1 h at freezing temperature plants were sprayed with tap water to initiate extracellular freezing. The 1-h time sample was collected just before spraying. All of the leaves in the rosette were collected for RNA analysis. B, Expression response of CBF3 and LTI78 genes in Arabidopsis in response to LT. The experimental design was the same as in the freezing experiment, except that plants were exposed to LT (2°C, 12-h day) for the indicated times. LT treatment started at 9 am. The samples were analyzed with RNA gel-blot hybridization using a ³²P-labeled cDNA probe for LTI78 and a gene-specific probe for CBF3. The histograms show normalized values for each gene after standardization to ribosomal signal intensities, presented as percentages of the highest value.