Plant Molecular Biology 39: 21–34, 1999.
© 1999 Kluwer Academic Publishers. Printed in the Netherlands.
Coordinate and non-coordinate expression of the stress 70 family and
other molecular chaperones at high and low temperature in spinach and
Qin-Bao Li, Dale W. Haskell and Charles L. Guy
Plant Molecular and Cellular Biology Program, Department of Environmental Horticulture, University of Florida,
Gainesville, FL 32611-0670, USA (
author for correspondence)
Received 30 December 1997; accepted in revised form 14 July 1998
Key words: chilling injury, cold stress, HSC70, HSP70, protein biogenesis, stress proteins
Stress 70 molecular chaperones are found in all the major subcellular compartments of plant cells, and they are
encoded by a multigene family. Twelve members of this family have been identiﬁed in spinach. The expression of
the stress 70 molecular chaperones in response to heat shock is well-known and it appears that low temperature
exposure can also stimulate their expression. However, it has been difﬁcult to determine which member(s) of the
family are speciﬁcally responsive to low temperature. This study was initiated to determine the levels of expression
of the stress 70 family members and other selected chaperones in response to high and low temperature exposure.
During heat shock of spinach, of the 10 stress 70 family members that were examined, all 10 showed increased
RNA levels after one hour, and all showed down-regulation at longer durations of high temperature exposure.
However, the response to low temperature was quite variable and complex. Some members 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-sensitive tomato at the same low
non-freezing temperature was even more dramatic with 11 of 15 molecular chaperones tested exhibiting elevated
expression. The increased chaperone expression is consistent with the hypothesis that the biogenesis or stability
of some proteins is compromised at low non-freezing temperatures. In contrast, mild freezing sufﬁcient to cause
injury of spinach did not materially activate chaperone expression.
The heat shock response of protein synthesis in plants
was ﬁrst recognized less than 20 years ago [5, 34],
only a few years after the phenomenon was ﬁrst de-
scribed in the salivary gland of fruit ﬂy . Heat
shock protein (HSP) synthesis is induced by a rapid
rise in temperature of ca. 10
C or more from an
optimal growth temperature. Presently 11 HSP fami-
lies, consisting of functionally and structurally distinct
members, are known in plants . Overall, heat
shock proteins and the heat shock responses of plants,
animals and prokaryotes are highly conserved ,
suggesting that they perform a universally basic and
essential function during high temperature stress. Pre-
vailing thought holds that heat shock proteins play
a major role in mitigating the deleterious effects of
heat-induced protein denaturation .
Important functions, for most of the families of
the HSPs, are now reasonably well understood .
Not surprisingly, many of the known functions relate
to some aspect of protein metabolism such as stabi-
lizing native proteins , preventing aggregation of
denatured proteins [16, 68], refolding stress-denatured
proteins [19, 38], participating in the folding and as-
sembly of nascent polypeptides into functional forms
[8, 18], facilitating translocation across membranes
[33, 68]; assisting in the deposition/assembly of seed
storage protein bodies , and targeting nonnative
and folding incompetent polypeptides for degradation