PLANT PHYSIOLOGY , Vol 104, Issue 4 1429-1437, Copyright © 1994 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Protein Synthesis and Breakdown during Heat Shock of Cultured Pear (Pyrus communis L.) Cells
I. B. Ferguson, S. Lurie and J. H. Bowen
Horticulture and Food Research Institute of New Zealand, Private Bag 92 169, Auckland, New Zealand (I.B.F., J.H.B)
Cultured pear (Pyrus communis L. cv Passe Crassane) cells were subjected to
temperatures of 39, 42, and 45[deg]C. Heat-shock protein (hsp) synthesis
was greater at 30[deg]C than at temperatures above 40[deg]C and continued
for up to 8 h. Both cellular uptake of radiolabeled methionine and total
protein synthesis were progressively lower as the temperature was
increased. Polysome levels decreased immediately when cells were placed at
39 or 42[deg]C, although at 39[deg]C the levels began to recover after 1 h.
In cells from both temperatures, reassembly occurred after transfer of
cells to 25[deg]C Four heat-shock-related mRNAs[mdash]hsp17, hsp70, and
those of two ubiquitin genes[mdash]all showed greatest abundance at
39[deg]C and decreased at higher temperatures. Protein degradation
increased with time at 42 and 45[deg]C, but at 39[deg]C it increased for
the first 2 h and then decreased. In the presence of cycloheximide, which
prevented hsp synthesis, protein degradation at 39[deg]C was as great as
that at 45[deg]C in the absence of cycloheximide. The data suggest that
hsps may have a role in protecting proteins from degradation at the
permissive temperature of 39[deg]C. At temperatures high enough to inhibit
hsp synthesis, protein degradation was enhanced. Although ubiquitin may
play a role in specific protein degradation, it does not appear to be
involved in increased protein degradation occurring above 40[deg]C.
