Coordinate and non-coordinate expression of the stress 70 family and othermolecular chaperones at high and low temperature in spinach and tomato

Stress 79 molecular chaperones are found in all the major subcellular compa rtments of plant cells, and they are encoded by a multigene family. Twelve members of this family have been identified in spinach. The expression of t he stress 70 molecular chaperones in response to heat shock is well-known a nd it appears that low temperature exposure can also stimulate their expres sion. However, it has been difficult to determine which member(s) of the fa mily are specifically responsive to low temperature. This study was initiat ed to determine the levels of expression of the stress 70 family members an d other selected chaperones in response to high and low temperature exposur e. During heat shock of spinach, of the 10 stress 70 family members that we re examined, all 10 showed increased RNA levels after one hour, and all sho wed down-regulation at longer durations of high temperature exposure. Howev er, the response to low temperature was quite variable and complex. Some me mbers were induced, some were transiently up-regulated, while others showed sustained up-regulation at a low non-freezing temperature. In comparison, the entirety of the molecular chaperone expression response of cold-sensiti ve tomato at the same low non-freezing temperature was even more dramatic w ith 11 of 15 molecular chaperones tested exhibiting elevated expression. Th e increased chaperone expression is consistent with the hypothesis that the biogenesis or stability of some proteins is compromised at low non-freezin g temperatures. In contrast, mild freezing sufficient to cause injury of sp inach did not materially activate chaperone expression.