168 ±16

64 ± 1

99± 12

50 ±6

however, solely due to an acceleration of the normal housekeeping reactions.

The so-called heat shock reaction of the cell is quite a different matter. For plants with a temperature optimum between 15 and 25 °C, this reaction takes place at temperatures above +35 °C and consists of:

• the slowing down of housekeeping reactions, particularly of the expression of the housekeeping genes;

• an almost exclusive synthesis of so-called heat shock proteins (HSPs);

• cessation of the production of the HSPs after 6-8 h; and

• a gradual resumption of the expression of the housekeeping genes.


| Table 3. Enzyme activities in the potato tuber tissue after 2 weeks of exposure to the day/night conditions quoted in column 2. The increased temperature treatment began 10 days after the initiation of tuber formation. (Lafta and Lorenzen 1995)


Temp, m Sucrose synthase

AG Pase



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